Tablet-coating: not just a pretty colour - information and ... · CHEMICALS FOR HEALTHY LIFE TABLET AWCOATING: not just a pretty colour Information and Activities, related to the

CHEMICALS FOR HEALTHY LIFE

TABLET AWCOATING:not just a pretty colour

Information and Activities, related to the Health-care Industries, for Post-I 6 Science Courses

CHEMICALS FOR HEALTHY LIFE is a series of resources which use contexts fromthe health-care industries to introduce post-16 students to science concepts and tothe work of people within these industries. The resources are packaged in a formwhich enables teachers to select activities and supporting resources to suit theircourses. The student task sheets in the resources can be accessed on the internetso that they can be modified easily to suit particular students.

This resource has been prepared by John Lazonby and is based on research anddevelopment by Bill Sellicks, Luton Sixth Form College and Paul Newby, GlaxoWellcome Research and Development.

AcknowledgementsThe development of this resource was funded by Glaxo Wellcome and by theUniversity of York. The authors gratefully acknowledge the assistance and adviceprovided by the staff of Glaxo Wellcome and they wish to thank the technical staffand the students of Luton Sixth Form College for their contribution to thedevelopment of components of this resource.

We would like to thank the following people who gave valuable help and adviceduring the preparation of this resource:

Alida BurdettGavin CowleyTina FinchPeter HubertChristine J akeman,Anil KumarAnn LawrenceGill MillerJohn Ramsey

Rosemary SteerMiranda Stephenson

Debbie TantonGail Turner

David WaddingtonAlan Wingfield

Jean Woolley

Christ the King VI Form College, LewishamNorthallerton CollegeNorthallerton CollegeHighlands College, St Saviour, JerseyDrug Information Pharmacist, York District HospitalEducation Development Manager, Glaxo WellcomeQueen Margaret's School, Escrick, YorkCity of Stoke on Trent Sixth Form CollegeTICTACManager, Toxicology Unit,St George's Hospital Medical SchoolRoyal Forest of Dean College, ColefordChemical Industry Education Centre,University of YorkBungay High SchoolHealth Industry Information Officer,The Association of the British Pharmaceutical IndustryUniversity ofYorkChemical Industry Education Centre,University of YorkTICTACAdministrator, Toxicology Unit,St George's Hospital Medical School

Photograph acknowledgementsCover John Olivep13 St George's Hospital Medical Schoolp 15 T, B Paul Starrp16 T John Olivep 16 M,B Paul Starr

Barry Perks Graphi Des~~r~©LNl~IL ~~~l~~~(t~,[~lW2g~[gi[N)~~@ ~'.!~U\{CCL--:/~~~~

The copyright holders waive the copyright on the rna lal which follows to theextent that teachers may reproduce this material for us Ith students, but for allother purposes, permission to reproduce this material in an~ must be obt9,it:1eQ""from the Chemical Industry Education Centre. The material may iiOf15e-dupIicatedfor lending, hire or sale.

Art work

Design

Valmai FirthClare Wake

© Chemical Industry Education Centre

CHEMICALS FOR HEALTHY LIFE

TABLET-COATING:not just a pretty colour

Information and Activitiesfor Post-I6 Science Courses

Advanced GNVQ AS & A level BTECNational Project workScience Chemistry Diploma Health Chemistry

Science

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CHEMICALS FOR HEALTHY LIFETABLET-COATING:not just a pretty colour

About These Resources(pink paper)

Teacher's Notes(pink paper)

Technician's Notes(green paper)

Introducing Sheet (incorporating Tasks 1-4)(full-colour, 10 copies)

Task 5 Sheet(white paper)

Task 5 Support Sheet(white paper)

Task 5 Science Ideas and Techniques(white paper)



Task 6 Data Sheet 1(white paper)

Task 6 Data Sheet 2(white paper)


Task 7 Support Sheet(white paper)


Task 7 Data Sheet(white paper))

CONTENTS OFTHE RESOURCES

Page1

5

11

13

Microbiological contamination 17

18

Safe microbiological procedures 19

Chemical contamination 23

Infra-red spectroscopy 25

IR spectrum of the contaminant 29

IR spectrum of the tablet-coating 30

Developing new markets 31

32

Measuring the concentrations ofsolutions

Part 1- the ideas 33

Part 2- the techniques 35

Part 3- practising the calculations 39

Constant humidity solutions 41


ABOUT THESERESOURCES

This resource pack is one of a series published by the Chemicals for Healthy Lifeproject to support post-16 science courses, particularly Advanced GNVQScience.

Introducing Sheet

Each pack provides the following resources for students:

I '

Ten copies of this full-colour, folded A3 sheet are provided.It describes the 'place of work' context and so justifies thestudent tasks. It also aims to illustrate how the particularindustry and its products are important to the students'lives and the lives of others.

Where appropriate each task is supported by the followingphotocopiable resourcesprinted on white paper:

Task Sheet

Task Support Sheet

Data Sheets

Science Ideas andTechniques Sheets

This outlines the task and indicates which other resourcesthey may need to study. These sheets are available on theinternet, http://www.york.ac.uk/org/ciec/. so they can beedited easily to cater for the needs of your students and toclarify the specific evidence you wish them to produce.

This will be used at the teacher's discretion where studentslack the experience to undertake the more open-endedtask outlined on the Task Sheet.

These supply data required for the task.

These help students to research and develop a knowledgeof an experimental technique and/ or an understanding ofthe underlying science. For some students these could beused as the starting point for their own research, forothers they can be used as support for class teaching ofthe topics. Some of these sheets will help studentsprepare for particular items on the GNVQunit test.

These provide notes to help with curriculum planning, onsafety issues and on each task. Where appropriate,indications of possible outcomes of tasks and answers toproblems are given.

There are also resources for teachers and technicians:

Teacher's Notes(printed on pinkpaper)

Technician's Notes(printed on greenpaper)

Additional guidance is provided where significantpreparative work for tasks is needed.

How you could use these resources forAdvanced GNVQ

They are useful additions to the resources you have available to support yourprogramme of work for GNVQ. The complete package can be kept in a ring binderand you can select from the student resources those sheets which you wish them touse and so create separate student files. The followingpages identify each separatestudent resource and indicate how each task contributes to the GNVQcoverage andprovides opportunities for students to produce required evidence.

AS and A levelThe activities provide opportunities for students to relate the concepts andtechniques covered to industrial contexts. The contexts can also be used as thestarting points for investigations and project work.

Health ScienceThe Ititroducinq Sheet can be used as the starting point for a selection of theactivities for students followingcourses such as the BTECNational Diploma.

1

http://www.york.ac.uk/org/ciec/.

CHEMICALS FOR HEAL THY LIFETABLET-COATINGStudent resources- each box represents a separate resource sheet Task S

Science Ideasand Techniques

Safe,. microbiological

/' procedures

Task 6

Science Ideas••••••• and Techni:lues

••••••• Infra-re••••••• spectroscopyI-'

.• .•.•••...•.•••.. Task 6.•.•••..

DataSheets1 and 2

Task S

Microbiologicalcontamination

/L- ---'/

//

/

IntroducingSheet

Task 6

ChemicalcontaminationTasks 1- 4

\\\\\\\\

//

Task 7

/

Developingnew

markets

2

TaskS

SupportSheet

Task 7

Science Ideasand Techniques

Measuring/ concentrations

of solutions

Task 7

SupportSheet

Task 7

DataSheet

~

I

I

GNVQcoverageIn this pack teacher and student resources are provided for tasks related to the contextof the use of coatings on medicinal tablets. Some short tasks on the Introducing Sheethelp students to develop an appreciation of the function of the coating on tablets and tolearn about the processes involved in making and coating tablets. Some of these tasksprovide opportunities for students to practise some key skills. Students are then able toselect from the larger tasks which provide them with opportunities to research anddevelop an understanding of some science concepts and techniques, and to prepareevidence required for Advanced GNVQin Science.

Performance criteria covered by each task

TASK/Performance criteriaScience Elements 1 2 3 4 5 6 7

1.1 Investigate health and safety practices in laboratories 3-5

1.2 Select analytical strategies 1-5 1-5 1-5

1.3 Carry out analyses and evaluate results ~1,2J 1-43,4

8.1 Gather, process and evaluate scientific data 1-6

Key Skills ElementsN 3.1 Collect and record data 1-7

U 3.2 Tackle problems 1-9

M 3.3 Interpret and present data

C 3.1 Take part in discussions 1-5

0 3.2 Produce written material 1-5 1-5 1-5

M 3.3 Use images

3.4 Read and respond to written materials

3.1 Prepare information 1-5

I 3.2 Process information

T 3.3 Present information 1-6

3.4 Evaluate the use of information technology

Science ideas and techniquesThe table below summarises the main science ideas and techniques which students are eitherassumed to know or to develop an understanding of during the unit.

Assumed knowledge Knowledge developed or revised

• Acidity, alkalinity and pH • Safe microbiological techniques

• Electromagnetic radiation

• IR spectroscopy

• The use of molarities andtitrations in quantitativeanalysis

• Reactions of iron(II) including itsidentification and its quantitativeestimation

3

Science evidence indicators arising from each task

Elem

4

l.~.

Evidence indicators

1.1 CASE STUDYNOTES

safety in a student activity on range ofhazards

(bio, chern & phys)

PRESENTATION on safety in the lab

1.2 PRESENTATION 2 analyses from 4 categories(environment, living, lab or industry)each analysis to include 6 points1 qualitative analysis

1 quantitative analysis

1.3 2 qualitative analysesto include 4 points

1 inorganic

4 LAB.REPORfS

1 organic

2 quantitative analysesto include 5 points

1 inorganic

1 organic

8.1 data from 4 investigationsRECORD

biological context

chemical context

physical context

primary data checked againstpublished data

RECORD data

manually processed

electronically processed

using formulae

using graphs

STATEMENT conclusion consistent with data,related to purpose and sources of error

TASK/Opportunities to produceevidence indicators

III 2 I 3 I 4 I : I 6 I 7 I

I I I I I v I I I

v

v

v

v

CHEMICALS FOR HEALTHY LIFETABLET-COATING:not just a pretty colourSafetyAlthough GNVQScience courses require students to plan independently many of theiractivities. the responsibility for safety in their practical work still lies with the teacher/tutorwho is in change of the students. It is assumed that the followingapply.

TEACHER'SNOTES

1 A risk assessment will exist for all practical activities. This will have been prepared bythe teacher/tutor. or by the student and checked by the teacher/tutor.

2 Plans produced by students for practical activities will be checked by the teacher/tutor.3 Practical work is conducted in a properly equipped and maintained laboratory.4 Any mains operated equipment is properly maintained. Any appliances brought in from

outside the school or college are safety checked using the employer's Portable ApplianceTesting programme before use,

5 Any fume cupboard operates at least to the standard of DES Design Note 29. FumeCupboards in Schools. (1982), HMSO.

6 Rules for student behaviour are strictly enforced.7 Eye protection is worn whenever there is a recognised risk to the eyes.8 Care is taken with normal laboratory operations such as heating substances and

handling heavy objects.9 Good laboratory practice is observed when chemicals. living organisms and materials of

living origin are handled.10 Students are taught techniques that minimise risks for such activities as pouring

chemicals. heating or smelling chemicals. and for handling micro-organisms.11 Fieldwork takes account of any gutdellnes produced by the employer.

Risk AssessmentsRisk assessments should be prepared using the General Risk Assessments in publisheddocuments, modified as appropriate to suit local circumstances. The followingare importantsources of information:DfEE. (1996), Safety in Science Education. London: HMSOASE, (1996), Safeguards in the School Laboratory {lOth Edition). Hatfield: Association forScience EducationASE, (1988), Topics in Safety, Hatfield: Association for Science EducationCLEAPSSSchool Science Service, (1989), Hazcards, Uxbridge: Brunel UniversityCLEAPSSSchool Science Service, (1989), Laboratory Handbook, Uxbridge: BruneI UniversitySSERC, (1991), Preparing COSHH Risk Assessments for Project Work in Schools, Edinburgh:Scottish Schools Equipment Research CentreHMI, (1993), Microbiology: An HMI Guide for Schools and Further Education, London: HMSO

The DfEE (1996) publication provides guidance on safety and on the legal posttion, detailednotes on a wide range of specific hazards and an extensive bibliography. This publicationstresses the need for risk assessments to be part of the documentation in daily use ratherthan on forms which may "not be consulted regularly" and "are not likely to be modified whenan activity is changed".

GNVQstudents have to prepare risk assessments as part of the evidence indicators forElement 1.1 and this provides the opportunity to establish the practice of using riskassessments as working documents which are integral to each practical activity and whichneed to be modified as plans are modified. The student task sheets stress that they have toprepare risk assessments for their plans and have them checked by their teacher beforestarting practical work, and that if they modify their plan they should consider whether or notthe risk assessment needs modifying.

It seems likely that students will find this easier if they adopt a standard approach toassessing risk. One possibility, based on that used in the individual investigation in SaltersAdvanced Chemistry, Activities and Assessment Pack, Heinemann, is to work through thefollowingsteps.1 List all of the chemicals (approximate quantities and, when in solution, concentrations),

items of equipment and operations to be used.2 Identify and note the hazards associated with the chemicals, equipment and operations.3 Note the precautions which they plan to take when using hazardous substances and

equipment and when carrying out hazardous operations.

5

Introducing SheetIt would be useful if students could read and discuss the sheet and do tasks 1 - 4 in smallgroups. These activities should establish the importance of tablet-coatings and help studentsto appreciate a range of possible reasons for using them. (Tasks 3 and 4 also provideopportunities to cover some of the Key Skills performance criteria.) The main stages in theprocess of making and coating tablets are identified and so the sheet provides thebackground to ensure that the more major tasks (Tasks 5-7) are seen as problems which aretypical of those faced by people working in this industry.

Coating materialsSugar and gelatin coatings are still used but the major constituent of many coatings is nowhydroxypropylmethyl cellulose (HPMC)which is a soluble polymer.

Enteric (intestinal) coated tablets are designed so that they have a low solubility in an acidicenvironment by incorporating acidic groups into the polymer coating. This means that theytend to be absorbed in the intestine rather than in the stomach.

Task 1Which tablet is coated and how thick is the coating?This simple task will acquaint students some of the characteristics of coatings. Standarduncoated Aspirin tablets could be compared with the enteric coated version (Nuseals).However, the latter are quite expensive and for this investigation the uncoated Aspirins couldbe compared with iron tablets.

The coated tablet should be much harder to crush. Typical thickness of the coating is aboutO.Imm.

Task 2How soluble are the tablets?It is not intended that students should carry out a carefully designed investigation. Thepurpose of the task is to reveal that the coating does appear to influence the solubility,particularly in acidic solutions. This is a useful point for them to bear in mind when they doTask 3.

In this task, in order that the comparison is reasonable, enteric coated aspirin tablets oughtto be compared with uncoated aspirins, but even then the Validity of the comparison islimited by the doses of the tablets being different. Nevertheless, a rough comparison of thetimes taken for the tablets to dissolve is possible and they will find coated tablets dissolve lessreadily than uncoated. Enteric aspirins are used where patients have stomach conditionswhich will be exacerbated by aspirin.

Task 3Why are coatings important?The art work showing the different conditions in the gastro-intestinal tract should promptdiscussions about how coatings might influence the stage at which the tablets dissolve andare absorbed by the body and so this should give them a starting point for their discussionson the reasons why manufacturers might want to coat tablets.

Expected suggestions could include:• to prevent problems with unpleasant-tasting medicines,• to prevent chemical deterioration of the tablet due to attack by air/oxygen, water vapour

or brought about by the action of light,• to prevent physical damage to tablets which might be caused during the packaging

process and hence lead to inconsistency of dose,• to ensure that the medicine is released only in the part of the digestive system where it is

meant to be released,• to allow release of the medicine over a period of time, or to allow release of medicine after

a time interval,• to improve appearance,• to make the tablet easier to swallow by making it smoother,• to help in identification,• to respond to marketing requirements.

You may wish to ask groups to report back at this stage before they read about theproduction process and undertake Task 4.

6

Task 4The cost of a mistake?This task can be used to provide students with the opportunity to collect data from people(their local pharmacist) outside the school and so cover that part of the range of Key Skills.Number. Element 3.1. Otherwise they will need to be supplied with a table of current prices.Different groups could be encouraged to estimate the loss for different medicines and thenasked to report back to each other.

Task 5Microbiological contaminationTask Sheet 5 establishes the context for the investigation which requires the students toidentify the stage in the tablet-coating process at which a biological contaminant wasintroduced.

This task requires the students to use microbiological techniques. Task 5 Science Ideas andTechniques. Safe microbiological procedures will help students appreciate the need for specialprecautions but it is assumed that where students are unfamiliar with specific techniquesthey will be taught them.

Task 5 Support Sheet could be used if students have difficulty but if it is not used then thisassignment provides students with the opportunity to demonstrate achievement at the meritand distinction levels.

The method of preparing the contaminated sample is given in the Technician's notes.

Four samples should be supplied for testing:

Sample A-Sample B-Sample C-

Water used to hydrate the coating materialPowdered coating materialHydrated coating material - taken from storage vessel immediately afterhydrationHydrated coating material - taken from spray nozzlesSample D-

They should see evidence of microbial growth in both samples C and D indicating that thecontamination occurred at the stage of hydration of the tablet-coating material.

Task 6Chemical contaminationThis assignment provides an opportunity to introduce students to IR spectroscopy. Task 6Science Ideas and Techniques or other sources such as Royal Society of Chemtstry. (1992),Modem Chemical Techniques and the associated video could be used to support thisintroduction.

The chemical contaminant is propan- 2-01which is used for washing out the containers. Ithas been withdrawn with a syringe from the space above the tablets in a sealed container. Ithas then been dissolved in a solvent and its IR spectrum obtained. This is given on Task 6Data Sheet 1. The spectrum of the pure coating material is given for comparison on Task 6Data Sheet 2. Students should be able to suggest the type of bond responsible for thosepeaks marked with asterisks as absorptions caused by:

O-H in alcohols and phenols.C-H in alkanes. alkenes and arenes.

and from this deduce that it is probably an alcohol. The exact identity of the contaminantcould be confirmed by comparing the spectrum to the spectra from a range of authenticalcohols (Chemical Information System (CIS) Database, produced by IMPACTGroup.Department of Chemistry. University of Surrey is an interesting way to do this) but if this isnot possible. the use of the technique will have been introduced without going to this stage.

7

Task 7Developing new marketsTask Sheet 7 sets out the context for the task which asks students to devise a method ofmonitoring the resistance of the coating on iron tablets. Students are required to investigatethe chemical dissolution of the coating in an acidic environment as found in the stomach.

Students are then asked to use the method developed in an investigation of the effects ofdifferent climatic conditions on the coating on iron tablets. A team approach could be usedfor this task with different students or groups of students investigating the effects of differentclimatic conditions.

In this task students are encouraged to select a titration technique for estimating the timetaken for an acidic solution to breach the coating and dissolve some of the iron(II) sulphate.Students will need to research or revise the chemical properties of aqueous solutions ofiron(II) and sulphate ions. The most obvious method will be to titrate samples of solutionwith standard potassium manganate(VII) solution.

A complication with this method is that some students will find out that hydrochloric acid ispresent in the stomach and therefore wish to use it in their investigation, but chloride ionsas well as iron (II) ions will react with manganate(VII) ions. The simplest solution to theproblem is to use dilute sulphuric acid.

If a more open task is set, in which students research other methods rather than justtitrations, then some may develop methods using hexacyanoferrate(III) indicator and possiblycolorimetry. Some may attempt to develop a method based on increasing turbidity caused bythe precipttatlon of barium sulphate.

Task 7 Support Sheet will provide help with the titration method for those students who find itdifficult. The following graph was obtained by students at Luton Sixth Form College, usingthe technique given on the support sheet and a graph-plotting program.

Graph of volume of manganate{VII) solution against time

12

4

10

8

titre (cnf) 6

2

time (min)

8

II

Task 7 provides an opportunity for students to develop their understanding of titrations as amethod of quantitative analysis. Task 7 Science Ideas and Techniques can be used bystudents for this purpose. The sheet is in three parts:

Part 1 deals with the principles of using titrations in quantitative analysis.Part 2 provides a step by step gutde for preparing standard solutions and carrying outtitrations.Part 3 provides some problems which can be used by students to practise using datafrom titrations.

The answers to the problems on Part 3 are:

1. 10.6 g2. 5.3 g3. 0.08M4. 0.003 moles5. 0.08 mol dm-36. 1.18 g

94.4%7. 0.045M

1.53 g dm-3

For the investigation of the effects of different climatic conditions students are required toresearch the temperature and humidity conditions in a city in a hot dry region and another ina hot humid region (a World Atlas is likely to be the most convenient source of such data) andthen, with the help of Task 7 Data Sheet, simulate these conditions. Samples of tablets areexposed to the different conditions and then the effects on the coating are investigated usingthe method, previously developed, of monitoring the time for the coating to be breached.

Keeping tablets in a desiccator in the presence of vapour above saturated potassiumhydroxide solution will simulate low relative humidity and in the presence of saturatedpotassium sulphate solution it will simulate high relative humidity.

However, to avoid the dangers associated with concentrated potassium hydroxidesolution, the low humidity could be achieved with a drying agent such as anhydrouscalcium chloride.

If the Task 7 Support Sheet is not used, the assignment provides opportunities to produceevidence of achievement at merit or distinction levels.

9

10

---------


TECHNICIAN'SNOTES

Task 5MICROBIOLOGICAL CONTAMINATION

Equipment and materials for advanced preparationcalcium carbonate powder or powdered blackboard chalk (substitute tablet-coating)freeze-dried brewer's yeastnutrient agar1 cm-' syringes or graduated l cm-' pipettes100 cm-' malt extract broth or 5% glucose solution in 250 cm-' conical flask5 Petri dishes8 small screw-top bottlesspreaderglass rodincubatorrefrigerator500 cm-' beakerClingfilm/foil and non-absorbent cotton wool

In the procedures which follow, all glassware and other equipment must be sterile andshould have been autoclaved if possible.

Preparation of micro-organism sampleUse a freeze dried sample of brewer's yeast (Saccharomyces cerevisiae, readily availablefrom supermarkets) for this. This procedure should be followed so that the number ofcolony forming units (cfu's) of the organism used to contaminate the sample is controlled.

In the instructions which follow, use aseptic technique throughout. See Task 5 ScienceIdeas and Techniques.

1 Add 0.5 g of brewer's yeast to the 100 cm-' of malt extract broth or 5% glucose solutionin a conical flask. Plug the neck of the conical flask with cotton wool and cover withfoil. Incubate this for 42 to 72 hours at 20 - 25 "C, until the suspension is cloudy.

Serial dilution of the micro-organism suspension

1,.",,,,,,,,,,,,1 1",·,·,,·· """<""'%,,' I"""""";;"",,w., I 1""""""" "·"""""8%"""M;",,1 1""""'iiM;;'@'@iOF" ""iii",1

0.1 em3 0.1 em3 0.1 em3 0.1 em3 0.1 em3

2 Transfer 9 cm-' of sterile 5% glucose solution to each of 8 screw-top bottles. Label these1 to 8.

3 Take a 1 cm3 sample of the micro-organism suspension prepared in step 1 above usinga syringe or pipette. Add this to tube 1. Close lid securely and shake to mix contentsthoroughly. This now contains the neat sample diluted by a factor of 10.

11

4 Repeat step 3, by transferring 1 cm' from tube 1 into tube 2. Again, ensure thoroughmixing of contents.

Continue the dilution series until you have produced 8 tubes as shown in theillustration. Each tube will be a 1:10 dilution of the previous tube.

5 Using a syringe or pipette, remove separate 0.1 cm-' samples from tubes 4, 5, 6, 7 and8, and spread these using an alcohol-flamed spreader on separate sterile agar plates.

6 Allow the plates to incubate at 20-25 0C for 48-72 hours. In the meantime keep tubes 1to 8 in a refrigerator.

7 After incubation, examine plates for growth, and select the plate and correspondingtube which produces a count of between 100 and 1000 separate colonies of yeasts.The contents of this tube will be used to contaminate the tablet-coating sample.

Preparation of contaminated tablet-coating sample8 Add 19 of powdered tablet-coating to a 500 cm3 beaker, add 100 cm' sterile water and

stir vigorously.

9 Remove a 1 cm3 sample from the tube chosen in step 7 above and add to the beakercontaining the suspension of tablet-coating and stir vigorously.

This suspension of contaminated tablet-coating can now be supplied to students in 2sample tubes and should be labelled 'Sample C' and 'Sample D'. Each student or groupof students will need only 5 cm-' of these samples.

Other samples needed for microbiological examinationPer student group;10 5 cm-' of sterile water used to make up the contaminated tablet-coating sample. Label

this 'Sample A'

11 19 of the dry tablet-coating powder (labelled 'Sample B')

Other equipment and materialsIn addition to the four samples prepared as above, each student group will need:

4 sterile Petri dishessterile teat-pipettes150 em" of sterile nutrient agarwater bath to keep agar molten before pouring platessellotapeaccess to incubator

12

----- ------

INTRODUCING CHE.MICALS FOR HE.ALTHY LIFE.

This pack is eonceriied with the workof eeople wiio eve10p 'and monitor theguali~ of the coatings on medicinaltablets. This lntroducing Sheet willhelp you to appreciate the importanceof coatings on tablets and to see howthe tasks you do relate to thoseundertaken by people in thepharmaceutical industry.

13

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14

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All bulk ingredients are stored in bins which are moved by monorail.

Uncoated tablets are checked as they leave the tablet press. Workers atthis stage must wear protective clothing.

lR spectroscopy being used to monitor thepurity of ingredients.

Tablet coating machine - after coating a batch of tablets. The coating material,suspended in water, is pumped through the nozzles at a pressure of between 2

and 5 atmospheres depending on the desired droplet size.

© Chemical Industry Education Centre, University of York


TASK SHEET


A pilot plant has produced its firstbatch of tablets of a new medicinecalled Immitac. Your team hasalready established by testing thetablets that there has been somemicrobiological contaminationduring the part of the processduring which the tablets arecoated. The main stages in thispart of the process are shown in theFlow Chart.

Please prepare a written report.

Memo DdeTo BS (Analytical team manager)From PN (Project leader)

Type of analysis: microbiological

Samples: A - water used in hydrationB - powdered coating materialC - hydrated coating material,

taken from storage vesselimmediately after hydration

D - hydrated coating material,taken from spray nozzlesStorage of dry powdered coating

material from manufacturer.Notes:Check if microbiological contamination isoccurring during the preparation of thecoating material and if so at what stage.

Hydration - weighed powder isstirred with distilled water for 2hours to produce a suspension.

Spraying - suspension is sprayedonto tablets at 50°C

Your task

• Devise a method of tracing the stage in the process where thiscontamination has occurred. You will need to use standardmicrobiological techniques. Task 5 Science Ideas and Techniques,Safe microbiological techniques could be used as a starting point foryour research into relevant safety techniques and regulations.

• Prepare a report of the effects of safety regulations on your plan,including a risk assessment and the safety procedures to befollowed.

• Prepare a presentation in which you justify your proposed methodof tracing the stage at which the contamination occurred.

• After you have had your plan and risk assessment checked carryout the analysis. If you have to modify your plan, check if themodifications influence your risk assessment.

• Prepare a report of your analysis.

17

4 samples of material from tablet -coating process4 sterile Petri dishessterile teat-pipettessterile nutrient agarwater bathsellotapeincubator



Equipment and materials needed:

Use aseptic technique throughout.

1. Loosen the top of the nutrientagar bottle and stand it in aboiling water bath to melt theagar. Allowthe agar to cool to55°C.

2. QUickly,using a sterile pipette,place l cm" of the liquidsamples in the centre of each of4 separate Petri dishes (or O.lgin the case of the solid sample)and close the lids immediately.

3. Pour the agar onto each of the 4plates so that each isapproximately half filled withthe mixture. After pouring eachplate, replace the lid and swirlthe plate to ensure that thesample is evenly distributed.Allowto cool so that the agarsolidifies.

4. Tape the lids and place theplates, agar side uppermost, inan incubator for 7 days at 20-25°C.

5. After this time, examine theplates by eye for colonies. Donot remove the lids.Decide if you think any of thesamples are contaminated andif so, at what stage in theprocess this occurred.

18

TASKSUPPORT SHEET


SCIENCE IDEAS ANDTECHNIQUES

Task 5SAFE MICROBIOLOGICAL PROCEDURES

What is involved in microbiological investigations?Many investigations involve culturing (growing under controlledconditions) micro-organisms. This usually involves the following basicsteps:

1 Preparing a sterile (freefrom micro-organisms)substance (medium) forthe micro-organism togrow on. The mediummust provide thenutrients needed by themicro-organism.

2 Transferring the micro-organism to the mediumand putting a lid on thedish.

3 Leaving the dish at theappropriate temperature(incubating) so that themicro-organism will grow.

4 Observing and recordingwhat growth hasoccurred.

19

Why take precautions?Microbiologicalaerosols are the mainsource of risk. These are tiny droplets ofwater with micro-organisms, such asbacteria, in them. The droplets are releasedinto the air while you perform normallaboratory operations. Even if the water inthe droplets evaporates, the suspendedmaterial in them is so small that it willremain airborne for some time.

Pathogenic micro-organisms are harmfulmicro-organisms. Although micro-organisms that you use in your experimentsare considered safe for school use, youcannot be sure that pathogenic strains willnot develop or that there will not be anypathogenic contamination. It is safer toregard all micro-organisms as potentiallypathogenic and take necessary precautionsto protect yourself and your colleagues.

and your experiment.

Micro-organisms are present all around us - in the air, on our hands andon the surface of objects. If you are doing an experiment involvingparticular micro-organisms, then your experiment will become invalid ifthere is contamination by other micro-organisms. You have to usetechniques which avoid such contamination. These are called aseptictechniques. Aseptic means free from germs.

You have to take precautions to protect;

yourself

20

Protecting yourself and your colleaguesWhen culturing micro-organisms it is usually safer to do this on a solidmedium (agar) rather than in a liquid (broth). This avoids spills andaerosol formation, but whichever type of medium is used the followingprecautions should be taken.

1 Wear clean protective clothing and eye protection.

2 Wash your hands before and after practical work.

3 Make sure cuts and scratches are covered with plasters.

4 Wipe the top of your bench with disinfectant before and after eachpractical session.

5 Never put anything in your mouth. This means you should not licklabels, chew pens, pencils or fingers and always use teat-pipettes fortransferring material. Never pipette by mouth.

6 Report any spillages of microbiological material to your supervisorwho will know how to deal with it.

7 Make sure any instruments used for transferring micro-organismsare sterilised before and after use - see the next section on aseptictechniques.

8 When incubating cultures thelids of Petri dishes should besecured with self-adhesive tape,but not completely sealed. Theyshould not be opened forexamination.

9 All used cultures and glasswareshould be moved to anappropriate place after use priorto autoclaving by yourtechnician or teacher. Anautoclave is like a large pressurecooker into which the equipmentcan be placed and heated to ahigh temperature so that all themicro-organisms are destroyed.

10 Micro-organisms should never be isolated from potentially dangeroussources such as human fluids, body surfaces, drains or sinks.

21

Protecting your experiment by using aseptic techniquesThe purpose of these techniques is to avoid contamination by micro-organisms fromthe air or by putting sterile equipment in contact with non-sterile surfaces such asyour hands, clothes or the bench.

(Ifyou have not used a technique before, your teacher will demonstrate it to you)

1 The medium must be autoclaved after preparation. This will usuallybe done for you so that you will be provided with sterile medium.

2 Containers need to be openedwhen pouring the nutrientmedium from a bottle and whensamples of micro-organisms aretransferred from a container tothe medium.

Containers should be opened forthe minimum time and in thecase of Petri dishes by tilting thelid away from the body ratherthan by lifting it off.

The screw-cap of a containershould be unscrewed as shownin the diagram and kept in thehand - not put on the bench.

The neck of the container shouldthen be sterilised by flaming(turning briefly in the flame of aBunsen burner) this kills anymicro-organisms living aroundthe neck.

The sample can then beremoved. The neck should thenbe flamed again and the capreplaced, taking care not totouch the hot neck of thecontainer.

3 Instruments used for transferring micro-organisms should be sterilised before andafter use.

If it is a metal loop (inoculator) itshould be held in a Bunsen flame.

If it is a glass teat-pipette itshould be placed in disinfectantor autoclaved.

Other sources of informationHMI, (1993) Microbiology An HMI guide for schools and further education,London: HMSODfEE, (1996), Safety in Science Education, London: HMSOASE, (1996), Safeguards in the School Science Laboratory, Hatfield:Association for Science Education

22


Task 6CHEMICAL CONTAMINATION

Currently you are working on a projectwhich is developing the process forproducing tablets of a new medicinecalled Immitac.

By testing the vapour in the spaceabove some tablets stored in a sealedcontainer you have detected somechemical contamination. Your task is toidentity the type of compound causingthis contamination as a first stage intracking down the source of thecontamination.

An analytical technique called infra-redspectroscopy OR)has been used toinvestigate the vapour. Task 6 DataSheets 1 and 2 provide the IR spectra ofthe contaminant and of the pure coatingmaterial.

Your task

• Find out about the technique of IRspectroscopy. Use Task 6 ScienceIdeas and Techniques as yourstarting point for your research.

• Use the spectra on the data sheetsto help you respond to the memo.

• Prepare a presentation whichjustifies the choice of IR as theanalytical method for this stage ofthe investigation.

TASK SHEET

Project: Immitac - pilot

Memo Date _

To BS(Analytical team manager)From PN(Project leader)

Type of analysis: IR

Samples: 1 - contaminant2 - pure tablet coating

Notes:Please check the IR spectra provided.Identify the key peaks (marked withasterisks) in the spectrum of thecontaminant. Suggest which bond typeeach peak corresponds to and the typeof compound causing thecontamination.Please prepare a written report.

23

24

------ --- ---- -~


Task 6INFRA-RED SPECTROSCOPY


ColouredfiltersWhite light is a mixture of light ofdifferent colours. When white lightshines on a red filter only red light istransmitted. The blue and green partsof the light have been absorbed by thefilter. The filter contains substanceswhich absorb blue and green light.

~~~e __ """~ __ 1 •red filter

~eyeYsees red

IlrceSimilarly a filter which transmitsgreen light must contain substanceswhich absorb red and blue light.

whitelight . I·

green filter

~eyeYsees green

lent)

Different colours of light have differentwavelengths. So the substances in agreen filter absorb light of a differentwavelength than the substances in ared filter.

Visible light, which is the light our eyes are sensitive to, is only part ofthe electromagnetic spectrum. AE shown in the diagram there areelectromagnetic waves with longer and shorter wavelengths which wecannot see. The infra-red region of the electromagnetic spectrum isbetween the visible region and the microwave region. Its wavelength islonger than that of visible light but certain wavelengths of infra-redradiation can also be absorbed by certain substances.

radio waves microwaves infra-red

(!)

;§(JJ

os: ultra- X-raysviolet

y-rays

Wavelength (m)

Infra-red (IR) spectroscopy is one of a number of important analyticaltechniques which depend on the ability of certain molecules to absorbelectromagnetic radiation of particular wavelengths. The instrumentused for this analysis is called an IR spectrometer.

25

- -- -------___ ~o _

What happens in the IR spectrometer?In the spectrometer infra-red radiation is passed through the samplebeing analysed. If all the radiation passes through then this is recordedas 100% transmittance. If some radiation is absorbed then thetransmittance will be less than 100%. The instrument checks theradiation emerging from the sample to see if some wavelengths have beenabsorbed. The transmittance is recorded as an IR spectrum on a VDUoron a paper chart.

The lnfa-red spectrum of ethanol

800Wavenumber (crn')

Radio stations transmit radio waves of a particular frequency and youtune in by adjusting the receiver to that frequency. In the past stationswere located by tuning to particular wavelengths. The frequency andwavelength of electromagnetic radiation are related by the equation

C = AU which is:

speed = wavelength x frequency

Frequency is the number of waves per second and is measuredin hertz (Hz).

Wavelength is measured in metres (rn).

Speed is measured in metres per second (m S-I).

All electromagnetic radiation travels at the same speed, approximately3 x 108 m S-I. This means that a radiation with a high frequency musthave a lowwavelength and a radiation with a low frequency must have ahigh wavelength.

In IR spectroscopy, substances are exposed to radiation in the frequencyrange 1014 Hz - 1013 Hz which means it has wavelengths between2.5 x 10-6 and 1.5 x 10-7 metres. These are difficult numbers to deal withso the IR spectrometer records the transmittance for differentwavenumbers, which is l/wavelength. For IR radiation, wavenumbersmeasured in cm! are whole numbers and so are easy to remember anduse, which is why they are shown on the spectrum above.

26

What causes the absorption of infra-red radiation?The absorption occurs when the energy of the radiation is transferred to themolecule causing certain bonds to stretch or bend. Particular bonds requireparticular energies to do this.

For example, in an alcohol the O-H bondabsorbs a different quantity of energy whenit stretches than the c-o does when itstretches. But particular wavelengths ofradiation are associated with particularenergies and so radiation of differentwavelengths will cause theO-H bond and the c-o bond to stretch.

H H~ / C-O stretching

C-H stretching ~ C ~.H../Y- ,~~~\~ " H ~ 0- H stretching

~ ~H HWhen IR radiation is passed through a

substance whose molecules contain thesebonds, the IR spectrum will show that theseparticular wavelengths have been absorbedand so reveal the presence of these bonds.

Using IR spectraWhen you inspect the IR spectrum of a sample, absorbance [i.e. reducedtransmittance) at particular wavenumbers will correspond to particularbond types.

The table below gives the wavenumbers and the intensities of thereductions in transmittance which are caused by a selection of bondtypes. This information can be used when interpreting an IR spectrum.

You should not try to explain the whole spectrum. Try to link the mainreductions in transmittance to bond types and so find out what type ofcompound is present. Then try to match the whole spectrum to that of aknown sample so as to finally identify the compound.

Bond Location ~avenuDlber/cDll Intensity

C-H alkanes 2850-2950 M - Salkenes, arenes 3000-3100 M - Salkynes 3300 S

C=C alkenes 1610 to 1680 M

0> arenes several peaks in range variable1450 to 1650

C=C alkynes 2070 to 2250 M

c=o aldehydes, ketones, acids, 1680 to 1750 Sesters

c-o alcohols, ethers, esters 1000 to 1300 Saromatic esters and ethers 1300 to 1400 S

C=N nitrtles 2200 to 2280 M

C-CI chloralkanes 700 to 800 S

O-H alcohols, phenols 3580 to 3670 Scarboxylic acids 3230 to 3550 S (broad)

2500 to 3300 M (Broad)

N-H primary amines 3100 to 3500 SM = medium,S = strong

Use the data in the table to decide which of the absorbencies marked withasterisks on the ethanol spectrum are caused by C - H, C - 0 ando - H bonds in the ethanol.

If you are interested in how an infra-red spectrometer works, you couldread the next section.

27

Basic construction of an IR spectrometerInfra-red radiation from a heated filament is split into two parallelbeams. One passes through the sample and the other through areference cell. This ensures that the unwanted absorptions from waterand carbon dioxide in the air and from the solvent are cancelled outwhen they reach the detector.

The beams are analysed by passing them through a prism made ofsodium chloride. This is transparent to infra-red radiation and dispersesthe radiation into different wavelengths just as a glass prism will dispersewhite light into a spectrum of colours.

sample cell forsolution of sample

to chart recorderor computer infra-red

detector(thermo-couple)

reference cellfor solvent only

By rotating the prism, radiation of each wavelength can be directed to therecorder. This corresponds to the changing wavenumber along thehorizontal axis of the IR spectrum.

If the radiation of a particular wavenumber is completely transmittedthen this will appear as a line near to 100% transmittance. If radiationof a particular wavenumber causes a particular bond to vibrate in aparticular way then this radiation will be absorbed and this will show upas a downward movement on the chart recorder or the trace on the VOUwhich indicates a reduced transmittance.

Other sources of informationIf you would like to read a fuller account of infra-red spectroscopy then see SaltersAdvanced Chemistry, (1994), Chemical Ideas, Heinemann, pp 114-118, on whichthis sheet is based.A range of instrumental techniques, including IR, are described in ModemChemical Techniques, and the associated video, published by the Royal SOCietyofChemistry.

28

I

L


Task 6INFRA-RED SPECTRUM OF THE CONTAMINANT

DATA SHEET 1

~crvc"Erv~c0 Eu<l) ~..c

10...~ (!)I+- ..00 EE ::J::J C10...

(!)~ 0u 0 ~<l) 00. N 3\I)

u<l)10...

\

~..5

29


TASK 6INFRA-RED SPECTRUM OF THE TABLET-COATING

DATA SHEET 2

eoc:pt"V0U

\4-'Q)

:0 Et"V4-' ~Q)..c

"-4-' (1)1.4- ..00 EE :J:::::::l CI-. 0

(1)4-'

~U 0Q) 00.. NI.Il

"'0Q)I-.

\

~..5

30


Task 7DEVELOPING NEW MARKETS

TASK SHEET

The company wishes to develop its overseasmarket for iron tablets which, in particular,are taken during pregnancy. It isanticipated that some countries willwish tobuy in bulk and then store the tablets anddistribute them as needed within thecountry. It is therefore important that thecoating on the iron tablets will enable thetablets to have a long shelf-life in countrieswhich have very different climaticconditions. You have been asked to developa method of monitoring the effects ofdifferent climatic conditions on the coatingof the iron tablets.

UKsales

Annualsales Export

sales

Year

The coating protects the iron(II)sulphate in the tablet from atmosphericoxidation but it is also designed so that it will dissolve in the acidicconditions in the stomach so as to release the iron(II) sulphate. If thecoating on the tablet has deteriorated it will be breached more rapidlyunder acidic conditions.

Your task• If you are not familiar with titration as a technique for quantitative

analysis then work through the Task 7 Science Ideas andTechniques, Measuring concentrations oj solutions.

• Select a titration technique which will enable you to investigate thetime taken for the coating of tablets to be breached under diluteacidic conditions. When the coating is breached the tablet willbegin to dissolve. You therefore need to find a method of measuringthe concentration of a component of the tablet as it is released intosolution.

• Prepare a presentation describing and justifying your proposedanalytical strategy which will enable you to quantitatively analysefor a component of the tablets at regular time intervals and soestimate the time it takes to breach the coating. Your presentationmust include a risk assessment.

• When your plan has been approved, use it to estimate the timetaken for the coating to be breached on a sample of tablets straightfrom the bottle. Remember if you have to modify your plan, checkto see if the modifications influence your risk assessment.

• Use an atlas to find the mean temperature and relative humidity fora city in dry hot region and a city in a hot and humid region toensure that you have an idea of the range of conditions to whichtablets could be subjected. See Task 7 Data Sheet for details of howto simulate different climatic conditions.

• Expose a sample of tablets to one set of simulated climaticconditions before repeating the analysis to estimate the time forbreaching the tablet -coating. Prepare a written report of youranalysis.

31


Task 7DEVELOPING NEW MARKETSThe followingprocedure could be used to determine the time for thetablet-coating to be breached.

TASKSUPPORT SHEET

A large number of tablets and a large volume of acid are used so thatthe percentage change in total volume when portions are extractedfor analysis is relatively small.

acid

tablets

Procedure1. Place 1 drn' of O.05Msulphuric acid* in the large container with

a magnetic stirrer bar and place on a stirrer motor plate.

2. Place 20 iron tablets in a muslin bag, and gently lower thetablets into the acid. Start the clock.

3. QUicklyextract approximately 15 ern" of the mixture via the tapusing a numbered measuring cylinder or boiling tube. Recordthe time at which the tap is closed after extracting this portion.

4. Pipette 10 cm-' of this solution into a titration flask, and addapproximately 10 cm-' of dilute sulphuric acid. Titrate it with0.005M potassium manganate(VII) solution.

5 Repeat steps 3 and 4 at regular intervals - during the first 10minutes of the experiment, try to extract at least 4 samples - aslong as the titration portions are numbered, it should be possibleto titrate the portions at a stage in the procedure when theextraction of samples is less frequent. It should not be necessaryto extract portions so often after this - say every 10 minutes.Samples should be extracted until titration values are constant.

* A more accurate simulation of the conditions in the stomachwould use hydrochloric acid rather than sulphuric. However,hydrochloric acid reacts with potassium manganate(VII) and sowould interfere with the titration.

Processing resultsPlot a graph of titration results against time. Use the graph toestimate the time at which the coating was first breached.

32

CHEMICALS FOR HEALTHY LIFETABLET-COATING:not just a pretty colourTask 7MEASURING CONCENTRATIONS OF SOLTIONS (Part 1 - the ideas)The chemical reactions which occur in our bodies and help to keep usalive all occur in aqueous solution and so it is not surprising that theactive ingredients of most medicines are soluble in water. This meansthat in the pharmaceutical industries there is frequently a need tomeasure how much of a particular substance is dissolved in a certainvolume of solution (the concentration of a solution).

It is frequently more useful for chemists to measureconcentration in moles per dm-'. where a mole is oneformula mass (in grams) of the substance. The followingexample, shows the difference between these two types ofunits.

Units of concentrationConcentrations can be given as themass of dissolved substance per unitvolume of solution, for example, in theunits grams per litre (g I-I).

(1 litre is 1000 cm-' or 1 cubicdecimetre and so g I-I is usuallyexpressed as g dmP).

Different conventions are used underdifferent circumstances so it isimportant that the units being usedare given.


Each 5 mlcontains:Guaifenesin 100 mgL-Menthol 1.1 mg

On some medicine bottlesconcentrations of ingredients aregiven in mg per 5 ml spoonful..:

23161

graduation markIf 80 g of sodium hydroxide are dissolved in water,and the solution made up to 1 drn" with morewater, then the concentration of the solution is80 g dm:".

The formula of sodium hydroxide is NaOH.The relative atomic masses of the elementspresent are:

NaoH

Therefore the formula mass of NaOHTherefore the mass of 1 mole of NaOH

31 dm

23 + 16 + 1 = 4040 g

If a solution of sodium hydroxide contains 80 g drrr",then it contains 2 mol drn".

The number of moles per cubic decimetre of a solution is called themolarity of the solution.

This solution of sodium hydroxide is a 2 molar solution which isabbreviated to a 2M solution.

Check that you are able to calculate the concentrations of solutionsusing both systems of units by completing questions 1-5 in Part 3 of thissheet.

33

Using molarities to measure the concentrationsof solutions

If you want to find the concentration of a particularsolution of sodium hydroxide,

and you have a solution of sulphuric acid of knownmolarity available,

you can start by finding out how much of the sulphuricacid solution reacts with a known volume of the sodiumhydroxide solution.

This is done by measuring out a particular volume ofthe sodium hydroxide solution, say 25 ern", Then slowlyadd the sulphurtc acid solution and record how much ofyou have added when it has reacted with all of thesodium hydroxide.

You can tell when this point has been reached (called the end point) byhaving a few drops of an indicator present which changes colour whenthe reaction is complete. This process is called a titration.

If you found that you needed exactly 20 cm-' of the O.1M sulphuric acidto react with all of the sodium hydroxide, then you can use these data tocalculate the concentration of the sodium hydroxide solution. To do thisyou need to know the balanced chemical equation for the reaction, whichis:

From this you can see that 2 moles of NaOH react with 1 mole of H2S04.

You then need to calculate the number of moles of H2S04 used.1000 crn-' of O.lM H2S04 contains 0.1 moles of H2S04

20 em" of O.lM H2S04 contains 0.1 x 201000

0.002 moles of H2S04

From the balanced equation you knowthat this would react with 0.004 moles of NaOH

This number of moles of NaOH must have been present in the 25 cm-' ofsolution used.Therefore a litre of this solution would contain 0.004 x 1000

250.16 moles of NaOH

The number of moles in 1 litre is the molarity of the solution, so this is a0.16M solution.1 mole of NaOH is 40 g and so 0.16 moles 40 x 0.16

6.4 gThe concentration of the solution of sodium hydroxide is 6.4 g dm".

Questions 6 and 7 in Part 3 of this sheet provide other examples oftitration results. You can use them to practise using these type of data.

When should you use a titration?You can select titration as a suitable quantitative analytical techniqueto measure the concentration of a substance dissolved in water if thefollowing conditions are met:

• there is another soluble substance that it will react with• the reaction between the substances is rapid• there is some means of detecting when the reaction is complete• you know the balanced chemical equation which represents the

reaction34

ICHEMICALS FOR HEALTHY LIFETABLET-COATING:not just a pretty colour


Task 7MEASURING CONCENTRATIONS OF SOLUTIONS (Part 2 - thetechniques)Sometimes it will be necessary for you to make a solution of knownconcentration to use in a titration to find the concentration of anothersolution. A solution whose concentration is known accurately is called astandard solution. Sometimes you will be provided with a standardsolution which has been purchased from a supplieror made up for you. Ifyou make your own you haveto followa set procedure so that you do it asaccurately as possible.

graduation markA standard flask is used to allow the volume of thesolution to be measured accurately. Standard flasks aresometimes called volumetric flasks. When filled correctlyto the graduation mark on the neck of the flask, theycontain the stated volume when the solution is at thetemperature written on the flask.

Making a standard solutionThe followingstages are involved in making up astandard solution:

class B

• decide on the volume of solution you need and select a suitablevolumetric flask,

• work out the mass of solid you will have to dissolve in this volume togive a solution of the required concentration,

• weigh the solid accurately,

• dissolve the solid in a small volume of the solvent (usually distilledwater, but it can be an aqueous solution such as dilute sulphuricacid),

• transfer the solution to the volumetric flask and then add furthersolvent to make the solution up to the final volume.

Weighing out the solidAccurate weighing is carried out with the solid in a weighing bottle (noton a piece of paper). Weigh the bottle empty and then containing thesolid. Usually it is not necessary to weigh out the exact mass you havecalculated provided the mass is close and you record it accurately so thatyou can calculate the final concentration of the solution.

Making up the solution1 Take a clean beaker and rinse it with distilled water. Tip the solid

from the weighing bottle into the beaker. Rinse out the weighingbottle two or three times with distilled water, transferring thewashings to the beaker each time. It is important that all the solidgoes into the beaker.

2 Add enough distilled water to the beaker to dissolve the solidcompletely. Do not fill the beaker more than half full. The dissolvingmay take some time so be patient. It helps to stir but take care not tolose any of the solution by splashing. Remember to wash thesolution off the stirring rod into the beaker.

35

3 Wash out the volumetric flask a couple of times with distilled water.Pour the solution from the beaker into the flask through a glassfunnel. Wash down the walls of the beaker with a small quantity ofwater and pour the washings into the flask. Repeat this several timesand then rinse the funnel into the flask. Remove the funnel.

4 Using a measuring cylinder and then a wash bottle, carefully adddistilled water until the solution is 1 ern below the graduation mark.Nowadd water slowly from a clean dropping pipette until the bottomof the meniscus is just touching the graduation mark. When you aredoing this you must have your eye level with the graduation mark.

meniscus

5 Stopper the flask and invert it several times to mix the contentsthoroughly. Immediately label the flask with the name andconcentration of the solution.

36

Carrying out a titration

What is a titration?The process of adding one solution to a fixed volume of another solutionuntil the reaction is just complete is known as a titration. The volumeof solution added is measured accurately.

As explained in Part 1 if the concentration of one solution is knownaccurately, you can use the balanced equation for the reaction to workout the concentration of the other solution.

Titration apparatusYou must work carefully and measure volumes accurately to obtainreproducible and precise results in a titration. All glassware must beclean and you must use distilled water to make up the solutions. Belowis a list of the basic titration apparatus.

• burette and stand• small funnel for filling the burette• white tile• pipette• pipette filler• conical flasks (usually 250 crn-']• wash bottle and distilled water• small beaker for waste solution

25cm320°C

clasaD

A pipette is designed todeliver a fixed volume ofIlquid.

A burette is designed todeliver a measurable butvariable volume of Iiquid.

Preparing the burette1 Fill the burette with distilled water and check carefully for leaks. If

the burette leaks, check that the tap is clean and pushed well intothe socket. If the tap is the type which needs greasing, clean it andregrease. Discard the distilled water.

2 Using a small funnel, add 5-10 cm-' of the prepared solution to theburette. Remove the funnel. Take the burette from the stand and tipand rotate it to wash the inside surface with the solution. Run outthe solution into the waste beaker.

3 Clamp the burette vertically and, using the funnel, fill the burettewith the prepared solution so that the meniscus is above the zeromark. Place the waste beaker under the burette and open the tapuntil the solution fills the jet, making sure there are no air bubbles.Remove the funnel.

4 Carefully run out the solution until the bottom of the meniscus is onzero (or just below). The burette is now ready for use.

37

Pipetting out solution into the conical flasks5 Take a pipette of appropriate size (25 cm' is commonly used) and

rinse it with distilled water. Using a pipette filler, draw up a few cm'of the prepared solution. Remove the filler. Tip and rotate the pipetteto wash the inside surface with the solution. Then discard thesolution into the waste beaker.

7 Replace the filler and draw up the solution into the pipette until themeniscus is 1-2 ern above the graduation mark. Nowvery carefully,with your eye on level with the graduation mark and keeping thepipette vertical, allow the liquid level to fall slowly until the bottom ofthe meniscus is on the line.

8 Run the liquid into a clean conical flask keeping the pipette vertical.(The flask need not be dry; it may be wet with distilled water.) Whenthe movement of the meniscus stops, there will be a small quantity ofsolution left in the tip of the pipette. Dip the tip of the pipette belowthe surface of the liquid in the flask for 3 sec. Do not tap or blowout the remaining liquid.

9 Repeat the process to transfer equal portions of solution into twomore conical flasks. If an indicator is being used, add the requiredquantity.

Performing a rough titration10 Write down the burette reading to the nearest 0.05 cm-'. To do this

accurately your eye must be level with the meniscus. Place theconical flask containing the solution on a white tile under the buretteand run in the solution from the burette 1 em" at a time until, onshaking, the colour changes permanently. Your left hand shouldoperate the tap while your right hand shakes the flask. At the endpoint, note the new burette reading. Subtract your initial readingfrom this value to work out the volume of solution added. This isknown as the titre. This first value will only be approximate, so donot include it when you work out the average value.

Performing an accurate titration11 Refill the burette if necessary. Repeat the titration with a fresh

portion of solution in the second conical flask. As the rough endpoint is approached, add a drop at a time. shaking the flask aftereach addition, until one drop causes the colour to change. (Near theend point rinse down any splashes on the sides of the flask withdistilled water.)

12 Repeat the the titration two or three more times until you have twotttres within 0.1 em" of each other as shown in the sample results.

Use of a standard solution of sodium carbonate to determine theconcentration of a solution of hydrochloric acid

Titration resullts Rough 1 2 3

Pipette solution: 25 em" of0.0502 mol dm-' Na2C03Indicator: methyl orange(3 drops)Burette solution: hydrochloricacid of unkown concentration

Burette reading at 23.40 22.95 45.80 23.10finish /cm3Burette reading at 0.10 0.00 22.95 0.20start /cm3Volume added 23.30 22.95 22.85 22.90(titre) / cm-'

Average volume added from burette = 22.9 cm-' (average of titres 1, 2 and 3)

Use this average volume and the balanced equation for the reaction,

Na2C03 + 2HCl ~ 2NaCl + CO2 + H20

to calculate the concentration of the hydrochloric acid in mol dm", Usethe method given in Part 1 of this sheet.38

- - ------


Task 7MEASURING THE CONCENTRATONS OF SOLUTIONS (Part 3 - practisingthe calculations)


1. How much sodium carbonate, Na2C03, would you need to weigh out tomake 1 dm' of O.lM sodium carbonate solution?

2. How much sodium carbonate, Na2C03, would you need to weigh out tomake 250 crn-'of a solution with a concentration of 0.2 mol dm"?

3. If you had prepared a standard solution of sodium carbonate whichcontained 2.12 g of Na2C03 in 250 em" of solution, what would themolarity of this solution be?

4 If you transferred 25 cm' of iron(II) sulphate solution, with aconcentration of 0.12 mol dm", to a conical flask, how many moles ofiron(II) sulphate would the flask contain?

5. If you found that 25 ern" of a solution of sodium chloride contained0.002 moles, what would the concentration of this solution be in mol dm'?

6 A sample of sodium carbonate was known to be contaminated withsodium chloride. You are given the task of analysing the mixture tofind the percentage purity of the sample of sodium carbonate. Sodiumcarbonate solution can be titrated with hydrochloric acid, whereas thesodium chloride solution does not react with hydrochloric acid. Theequation for the reaction between sodium carbonate and hydrochloricacid is:

Na2C03 + 2HCI -7 2NaCI + H20 + CO2

You weighed out 1.25 g of the mixture and dissolved it in distilledwater to make 250 cm-' of solution.

You then titrated 25 cm-' portions of this solution with 0.105Mhydrochloric acid, using methyl orange as indicator. The averagevalue of your accurate titrations was 21.2 em". Calculate the mass ofsodium carbonate in 1.25 g of the mixture and hence the percentagepurity of the sample.

7. Dilute hydrogen peroxide solution can be used as an antiseptic,however, solutions of it gradually deteriorate as it decomposes towater and oxygen. The concentration of a hydrogen peroxide, H202,solution can be determined by titrating it with potassiummanganate(VII) , KMn04' solution. The hydrogen peroxide solution isacidifled. prior to titration, by adding dilute sulphuric acid. This iscalled a redox titration because the potassium manganate(VII) isreduced and the hydrogen peroxide is oxidised. The ionic equation forthe reaction is:

2Mn04- + 5H202 + 6H+ -7 2Mn2+ + 8H20 + 502

It is a complicated equation, but the only information you need from itis that 5 moles of hydrogen peroxide react with 2 moles of potassiummanganate(VII) .

You are given the task of finding the concentration of a particularhydrogen peroxide solution which you suspect has deteriorated.25 cm-' of hydrogen peroxide solution, after actdifytng with dilutesulphuric acid, reacted completely with 22.5 cm-' of 0.02M potassiummanganate(VII) solution. Calculate the concentration of the hydrogenperoxide solution in mol drrr ' and then in g dm".

39

40


Task 7CONSTANT HUMIDITY SOLUTIONSIn a closed container, the space above somewater will become saturated with water vapour.This means that at a constant temperature, thewater vapour pressure will be constant, whichmeans that the humidity in the space above thewater will be constant.

DATA SHEET

air spacesaturatedwith watervapour

water

If a solution of a salt in water is used instead of pure water, the humidity willdepend on the solute and the concentration of the solution as well as thetemperature. This provides the possibility of creating artificial climatic conditionswith particular temperatures and humidities.

In an enclosed space, such as a desiccator,a constant humidity can be maintained at agiven temperature by the presence of asaturated solution of a particular solute incontact with an excess of the solute.

saturatedsolution ofsalt

The table below shows the percentage relative humidity above saturatedsolutions of particular solutes at various temperatures. It is based on datataken from Pharmaceutical Handbook, 19th Edition, The Pharmaceutical Press.

Temperature jOeSaturated solution of: 0 5 10 15 20 25 30 35 40

potassium sulphate. K2S04 99 98 98 97 97 97 96 96 96potassium nitrate. KN03 97 96 95 94 93 92 91 89 88potassium chloride. KCI 89 88 88 87 86 85 84 83 82ammonium sulphate. (NH4bS04 83 82 82 81 81 80 80 80 79sodium chloride. NaCI 76 76 76 76 76 75 75 75 75amonium nitrate. NH4N03 77 74 72 69 65 62 59 55 53magnesium nitrate. Mg(N03)2.6H.z0 60 58 57 56 55 53 52 50 49potassium carbonate. K2C03 - - 47 44 44 43 43 43 42magnestum chloride. MgC12.6H20 35 34 34 34 33 33 33 32 32potassium ethanoate. KCH3C02 25 24 24 23 23 22 22 21 20lithium chloride. LiCI.H20 15 14 13 13 12 12 12 12 11

Anumber of these solutes are poisonous. Before planning to use anysolute carry out a risk assessment and have your plan checked by yourteacher before proceeding.

An almost 0% humidity could be obtained safely by the presence ofanhydrous calcium chloride in the desiccator.

41

CASH ANDCHEMICALS

PUBLICATIONS DESIGNED FORSCIENCE TEACHING

ON SITE

UNDERSTANDINGPLASTICS

A problem solvingpackage for post-16

chemistry and economicsstudents which explores

economic and engineeringdecisions made onchemical plants.

A book for post-16 studentsof chemistry and technology.Contains information on thechemistry, processing and

recycling of plastics and theirapplications in the areasof sport, construction,

automotive andpackaging.

THEESSENTIAL

CHEMICAL INDUSTRY

Reference book for post -16students and teachers

providing relevantinformation about

aspects of thechemical industry.

A GNVQ (Intermediate)teaching package containing

tutor's notes, student informationon metals, plastics, ceramics,

and composites.Suggestions for

assignment work

SPEAKERSFROM INDUSTRY

Provides practical guidanceon setting up and improving

visits from schools to industrialsites. The publication includeslists of research questions for

students to use at anindustrial site.

Practical guidance to teachersinviting industry speakersinto school. Includes some

suggested themes for post-16students and shows how

industrial experiencecan be linked

to the curriculum

POLYMERSPHYSICAL TESTING

Background informationon industrial standard testing

procedures, with practicaltests for students coveringstrength, hardness, tear,

impact resistance,flexure and wear

and abrasion.

ManagerMiranda Stephenson

Chemical Industry EducationCentre

Department of ChemistryUniversity of YorkYork YOlO SDD

Telephone (01904) 432523Fax (01904) 434078

email: [email protected]://www.york.ac.uk/org/ciec

The aim of theChemical Industry Education Centreis to improve mutual understanding betweenschools and the chemical industry so that teachers andindustrialists have a clearer insight into each others needs.

mailto:[email protected]

http://www.york.ac.uk/org/ciec

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