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Chemistry HL Investigations - TEACHING NOTESChemistry HL Investigations - TEACHING NOTES 94I

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CHEMISTRY INVESTIGATIONS(For use with the IB Diploma programme)

THIRD EDITION

Volume 2 (relevant to the HL topics)

TEACHING NOTES

Author: Dr John Green

Series editor: David Greig

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Information for teachers

The process of skill assessment can be onerous. To make your work as simple and easy as possible, we have devised an Assessment Table which shows the relevant criteria with space for you to record the level achieved in that Investigation. This is also included in the Student Portfolio together with some advice for students. In each Investigation there is also provision for you to record the level awarded (‘completely’, ‘partially’ or ‘not at all’) for each aspect of the criterion. This also alerts students to what is being assessed in that Investigation, though of course this is advice only and in no way prescriptive. Teachers may wish to use the Investigations to assess other skills or may wish to keep a record of progress in other ways.

We know that many schools have sensors (for measuring pH pressure, temperature etc.) that can be linked to data logging software and if this technology is available then they are ideal for many of the Investigations, especially those where a continuous record of data is record is required. Some graphic display calculators can also be linked to sensors for data logging purposes (for example see http://education.ti.com/educationportal/sites/US/nonProductSingle/chemistry.html). Data which is collected in this way can be downloaded into computers running spreadsheets such as MS Excel. This software enables detailed analysis and display of data in graphical form which may also be imported into word processing packages such as MS Word that many students will use to present their laboratory reports. We encourage schools and student to use these tools to work in this way and would be pleased to pass on any advice you have for others.

Teaching Notes

In the pages that follow there are a collection of notes for the information of Heads of Department, Teachers and/or Laboratory Managers that will help in getting each practical to run smoothly. We realize that Health and Safety regulations vary from country to country and we strongly suggest that local regulations be checked and observed at all times. Although these Investigations and Teaching Notes have been prepared in good faith, absolutely no responsibility whatsoever will be accepted by the writer, editor or publisher for the safe and legal conduct of these activities.

They have been prepared in such a way that a teacher can photocopy them and complete the top section as an easy way to order materials as required.

Disclaimer

Please note that although every care has been taken in preparing and trialling these activities, absolutely no responsibility whatsoever can be accepted for any damage or accident which may occur for whatever reason during the conduct of any of these activities. Author and Editor

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Foreword

This collection of Investigations is part of a series which has been written specifi cally to support the teaching of the practical component of current International Baccalaureate Science courses (©IBO). These Investigations have been written by experienced IB teachers with very close reference to syllabuses and assessment guidelines which are current at the time of writing. It is vital that teachers consult syllabuses and assessment guidelines which are current at the time they use this material because these documents are subject to continual review and modifi cation. These Photocopy Masters and accompanying Teaching Notes may be used by anyone in the purchasing school but may not be passed on to another school. Additional collections of Investigations are currently being developed. The Investigations in this volume will fi t comfortably into a Practical Scheme of Work as required (see below), but they are not intended to be exclusive or exhaustive. A table is provided showing the relevant topics and suggested assessment focus for each Investigation. Each practical activity includes an Assessment table which is provided to assist teachers to record the level achieved with each Aspect using the scale of 0-2.

This collection of Investigations does not in any way form a proscribed Practical Scheme of Work, nor are all the experiments in the format given necessarily suitable as IA sample material. They are meant primarily to give teachers ideas of the sort of experimental work that is suitable for a PSOW and to assist teachers in designing their own PSOW. In order to help teachers choose appropriate IA samples, the Teaching Notes accompanying a particular experiment sometimes describe why this particular experiment could be considered suitable as an IA sample. Sample work submitted for IA moderation should follow the spirit of the IB Internal Assessment guidelines. If Data Collection and Processing is being assessed, then students must design and draw up their own data tables, decide the best way to analyse the data of a particular experiment. Similarly if Conclusion & Evaluation is being assessed, students should make their own unprompted evaluation of an experiment, as well as evaluating weaknesses in the method and ways in which it could be improved. It is hoped that this set of Investigations will help students achieve this.

If, for example, a “laboratory report” is submitted in which the data table has been given to the student (including units and uncertainties) then this cannot score any marks in respect of the “I” Aspect. Similarly, if the student has been told what variables to plot on a graph and how to calculate the value of a quantity from the gradient, then this would be inappropriate for assessment of the “Data Processing” Aspect. Again, if the student has been told on a worksheet to consider and comment on particular steps in the method, then this would not be suitable to use for assessment of the “Evaluation” Aspect.

It goes without saying that an experiment that is to be used to assess the Design criterion cannot be one that has been gives the student specifi c instructions about what to investigate it and the way in which this should be carried out. Perforce, Planning A and Planning B experiments must be open-ended in nature.

The author has trialled all of these activities and has suggested various safety precautions but will not accept any responsibility whatsoever for any accident that may arise during the conduct of these Investigations. We will however be pleased to receive any suggestions and comments from staff or students using this material.

Please refer to www.ibid.com.au for current information about other publications.

Dr John Green (Author) David Greig (Editor) Hong Kong 2008

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INVESTIGATION 1 - THE CHEMISTRY OF SOME TRANSITION METALS

Day/Date of lesson ________________ Period _______ Room ____

Teacher _____________________ No. of students/groups ________

Apparatus required

Per student:

6 x test tube 2 x boiling tube small beaker (~100 cm3) splints

Chemicals required

About 10 cm3 per student of aqueous solutions of the following. Th e concentration is not vital, from 1 mol dm-3 to 0.1 mol dm-3 will do unless stated otherwise: Chromium(III) sulfate Potassium chromate (VI) Hydrogen peroxide Manganese(II) sulfate Potassium manganate(VII) [0.01 mol dm-3 ] Iron(II) ammonium sulfate Iron(III) chloride Potassium thiocyanate Potassium iodide Cobalt(II) chloride Nickel(II) sulfate Copper(II) sulfate Sodium thiosulfate [0.2 mol dm-3 ]

Supplies of the following normal laboratory reagents (~50 cm3 per student)

Aqueous sodium hydroxide [2 mol dm-3] Aqueous ammonia [2 mol dm-3] Dilute sulfuric acid [1 mol dm-3 ] Concentrated hydrochloric acid

The following substances

Solid manganese(IV) oxide (~2 g per group) Solid glucose (~2 g per group)

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There are many parts to this Investigation and perhaps short comments on some of these are appropriate:

1 (a) Owing to the acidic nature of the solution, quite a large volume of aqueous alkali may be required to produce a permanent precipitate.

(b) Th e bubbles that are usually also observed are of course due to the thermal decomposition of the peroxide rather than being anything to do with the oxidation of the chromium.

2 (a) Th e initial pale buff precipitate should darken as oxygen from the air oxidises Mn(II) to Mn(III) – the basis of Winkler’s method for determining the concentration of dissolved oxygen.

(b) Strictly speaking to prove that the role of MnO2 is catalytic, it should be weighed before and aft er the reaction to show its mass remains constant.

(c) Th e colour change should vary with the pH:

pH Equation Initially Finally

Acidic MnO4- + 8 H+ + 5 e- ⇒ Mn2+ + 4 H2O Purple Colourless

Neutral MnO4- + 4 H+ + 3 e- ⇒ MnO2 + 2 H2O Purple Brown ppt

Alkaline MnO4- + e- ⇒ MnO4

2- Purple Green

3 (a) It should slowly turn brown as oxygen from the air oxidises Fe(II) to Fe(III) – this is much faster in alkaline solution than in acidic solution.

(c) Usually a faint reddish coloration appears owing to the presence of Fe(III) impurity in the Fe(II).

4. It actually takes quite a large excess of conc. HCl to get the solution to go a true blue colour.

5 (a) Th e colour of NiCl42- is not that diff erent to the hexaaqua ion – a direct comparison of the two may be

required.

(b) Whether a pale green precipitate of the hydroxide is seen depends on the concentrations of the solutions.

6 (a) To obtain the true yellow colour quoted in the text books it may be necessary to resort to reverse addition, i.e. adding a little of the aqueous copper salt to an excess of conc. HCl.

(b) Sometimes it is a bit tricky getting this to work well, I suspect owing to the low concentration of the alkali. Putting a pellet of solid NaOH into the boiling tube before heating it can oft en rescue the situation.

(c) Probably worth mentioning the volumetric use of this reaction to determine the concentration of copper(II) ions.

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INVESTIGATION 2 - TRANSITION METALS INVESTIGATION



As with any student designed practical, it is diffi cult to produce a precise list of equipment and reagents, and with the broad scope of this Investigation predicting these is even more diffi cult.

Th is is a good design practical giving a very broad scope for students to plan an Investigation. With some students this may be too broad and they may benefi t from having the range narrowed a little, by for example specifying a metal (such as “Investigating a reaction involving iron”) or a particular type of reaction (such as “Investigating the rate of a reaction involving a transition metal”) without making it so prescriptive as to make an assessment of Design invalid.

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INVESTIGATION 3 - PREDICTING ENTHALPY CHANGES



As with any student designed practical, it is diffi cult to produce a precise list of requirements, but below is the list of materials that the students are likely to request.

Apparatus required

Polystyrene cups with lidsTh ermometersWeighing bottlesBeakers (various sizes)Conical fl asks (various sizes)Measuring cylinders (various sizes)Volumetric fl asks (various sizes)Pipettes (various sizes)Test tubesBoiling tubesBalances

Chemicals required

Again it is diffi cult to predict, but experience shows that the following are likely to be requested:Dilute sulfuric/hydrochloric/nitric/ethanoic acidsAqueous ammoniaAqueous sodium hydroxideAqueous potassium manganate(VII)Aqueous hydrogen peroxideVarious metal carbonates and hydrogencarbonatesZinc powderMagnesium ribbon

Th is is a good design practical and the choice of reaction is always interesting to note. Students rarely realise that the loss of a gas can be a major source of heat loss, but the shortage of enthalpy data for ionic species in solution can oft en limit alternatives. It is perhaps worth having students calculate the loss in accuracy that comes from using a pipette as opposed to a measuring cylinder and comparing this to the uncertainty in the temperature rise (not to mention heat loss to the surroundings!).

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INVESTIGATION 4 - DETERMINING ENTROPY CHANGES



Apparatus required

Per group

Th ermometer (as accurate as possible, max temp. <50oC) 100 cm3 measuring cylinder 100 cm3 conical fl ask 20 cm3 pipette and fi ller 50 cm3 burette with fi lling funnel and white tile Polystyrene cup (~250 cm3 capacity) Steam generator (fl ask with a delivery tube and preferably a safety tube to guard against pressure build up)

Generally available

Balance capable of weighing to at least 0.01 g

Chemicals required

Solid calcium hydroxide (~5 g per group) Aqueous 0.1 M hydrochloric acid (~150 cm3 per group) Bromothymol blue indicator

Th e determination based on the latent heat of steam gives surprisingly good results, slightly dependent on how long and how well lagged the tube of the steam generator is.

Th e second part looks at an endothermic solubility equilibrium. Strictly speaking the equation

ΔG = -R.T.lnK

only applies for Kp, but we’ll gloss over that!

Th e fi nal part is quite complicated employing Hess’ Law to fi nd an enthalpy change and then using it to calculate a minimum value for ΔS given the limitations on the value of ΔG for a spontaneous reaction.

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INVESTIGATION 5 - DETERMINING THE RATE EXPRESSION FOR A REACTION



Apparatus required

Per group

2 x 100/150 cm3 conical fl ask 2 x boiling tube Stopwatch Th ermometer

Generally available:

6 x burettes for reagents

Chemicals required

About 50 cm3 per group of:

1 mol dm-3 hydrogen peroxide 0.1 mol dm-3 sulfuric acid 0.01 mol dm-3 aqueous potassium iodide 0.01 mol dm-3 aqueous sodium thiosulfate Fresh starch solution (~1%)

Th is is a fairly standard clock reaction adapted to allow students to elucidate a rate expression. Th e reaction gives fairly good fi rst order kinetics in iodide and peroxide. In the case of the hydrogen ion it is slightly more complex. Th ere appears to be a dependence on [H+], but not a simple fi rst order dependency. Probably there are two pathways, one acid catalysed the other not. At least it provides something more interesting for the students to discuss.

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INVESTIGATION 6 - MEASURING THE ACTIVATION ENERGY FOR A REACTION




Apparatus required

Th ermometersBeakers (various sizes)Conical fl asks (various sizes)Measuring cylinders (various sizes)Volumetric fl asks (various sizes)Pipettes (various sizes)Test tubesBoiling tubes Water baths at various temperatures (you may wish to fi x these for all the groups)RefrigeratorStop watches

Chemicals required

Th e students decide on suitable concentrations for the reagents, so quite large stocks of rather concentrated solutions is all that is required:

Dilute hydrochloric acid (2 M)Aqueous sodium thiosulfate (~1 M)

I fi nd it is best to allow students a short laboratory session to decide on suitable concentrations and then to hold the main laboratory session aft er giving them time to convert these preliminary fi ndings into a viable method.

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INVESTIGATION 7 - SOME CHARACTERISTICS OF VAPOUR PRESSURE



Apparatus required

Per group

Data logger with pressure sensor linked to fi t on to fl asks5 small Buchner fl asks (or multi-neck Quickfi t fl asks)1 large Buchner fl ask(or multi-neck Quickfi t fl asks)2 x 5 cm3 syringe with long tube attachedWater bath at ~40oC

Chemicals required

Propanone (~10 cm3)Propan-2-ol (~10 cm3)

Th is introduces students to the concept of vapour pressure and some of the factors that do, and perhaps more importantly do not, aff ect it. It is quite a fi ne balance choosing the correct temperature so as to get a reasonable vapour pressure that builds up at a fast enough rate. It is useful to discuss both the rate at which the vapour pressure increases as well as the fi nal saturated vapour pressure. Th e fi nal section gives students an opportunity to plan a more detailed quantitative Investigation.

INVESTIGATION 8 - A FURTHER INVESTIGATION INTO VAPOUR PRESSURE



Apparatus required

Th is provides an extension of Investigation 7. Students may choose to vary some variable such as temperature or the chain length of the alcohol but, maybe more interestingly, they will look at the vapour pressures of mixtures, so encountering Raoult’s Law and maybe deviations from it.

Students will order their own reagents and equipment, but the latter is likely to be similar to that required for Investigation 7.

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INVESTIGATION 9 - MEASURING THE FORMATION CONSTANT OF A COMPLEX ION



Apparatus required

Per group

5 test tubes Colorimeter/spectrophotometer Supply of cuvettes

To be shared

3 x burette (for the solutions below)

Chemicals required

0.001 M iron(III) nitrate (~50 cm3 per group) 0.1 M potassium thiocyanate (~50 cm3 per group) 0.01 M potassium thiocyanate (~30 cm3 per group)

(NB these need to be very clearly labelled)

Th is introduces students to the spectrophotometer/colorimeter as well as the idea of a calibration graph. Unfortunately the Investigation does not yield good results, even with good students. Th is is because other complex ions, such as [Fe(SCN)2(H2O)4]

+, are formed – see how many students come up with this explanation.

Maybe following up on this, could be an Extended Essay opportunity?

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INVESTIGATION 10 - INVESTIGATING THE EQUILIBRIUM CONSTANT FOR ESTER FORMATION



As with any student designed practical it is diffi cult to be precise about the exact requirements, but the following are probable.

Apparatus required

Per group Boiling tube with rubber bung (×5) Pipettes (various sizes) Pipette fi ller Measuring cylinders (various sizes) Volumetric fl asks (various sizes) Conical fl asks (various sizes) Burette

Chemicals required:

About 200 cm3 per student of Ethanol (clear methylated spirits) Ethanoic acid (glacial acetic acid) Ethyl ethanoate (ethyl acetate) 1 mol dm-3 aqueous sodium hydroxide

About 10 cm3 per student of Concentrated hydrochloric acid Phenolphthalein indicator

About 500 cm3 per student of Propanone (acetone)

Th is generally works well and if the students choose to try and evaluate the equilibrium constant under diff erent conditions it gives quite good results. Alternatively it gives plenty of scope to investigate Le Chatelier’s principle. Th e main problem is the time it takes and the fact that it can consume quite large quantities of expensive organic chemicals. To work well the mixtures of reagents really need to be left for 2-3 days for equilibrium to establish before doing the titration. Some students may require a little assistance in how to use their titration results to calculate a value for Kc.

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INVESTIGATION 11 - PH CHANGES DURING TITRATIONS



Apparatus required

Per group

Burette, stand & clamp 20 cm3 pipette & fi ller Small funnel 250 cm3 conical fl ask White tile pH meter

Chemicals required

Per group

~250 cm3 of 0.1 mol dm-3 solutions of: Sodium hydroxide (freshly made) Ammonia Ethanoic acid Hydrochloric acid Phenolphthalein indicator Methyl orange indicator

In this quite standard practical, rather than just getting students to plot pH against titre I have them plot all of the curves relative to the respective equivalence points. Th is avoids the problem of solutions (especially NH3) not being quite the correct concentration, as well as allowing students to display judgement in determining the equivalence point. Th e question about pH at the equivalence point is perhaps best answered by considering the nature of the salt formed. Th ough less familiar than the “half-neutralisation point”, a moments thought will show that in the ammonia titrations the “double neutralisation point” should give Ka for the ammonium ion. Th e requirement for fresh NaOH is that the presence of signifi cant amounts of carbonate/hydrogencarbonate leads to observable buff ering around the pH 8 region, spoiling the classic shapes of the curves.

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INVESTIGATION 12 - SOME MEASUREMENTS ON WEAK ACIDS AND BASES



Apparatus required

Per group

Test tubes with rubber bungs (x6) Boiling tubes with rubber bung (x5) Pipette (20 cm3) Burette Conical fl ask (250 cm3) Pipette fi ller

Generally available

As many pH meters as possible Wide and narrow range pH papers

Chemicals required

About 20 cm3 per group of

Aqueous ammonium sulfate (~1 mol dm-3) Aqueous sodium ethanoate (~1 mol dm-3) 0.05 mol dm-3 aqueous ammonia 0.002 mol dm-3 ethanoic acid 2 mol dm-3 hydrochloric acid 2 mol dm-3 aqueous sodium hydroxide


Methanoic acid (about 0.1 mol dm-3, but do not give concentration) 0.025 mol/dm-3 sodium dihydrogenphosphate


0.25 mol dm-3 sodium dihydrogenphosphate (also label ‘For Part 4’)


0.25 mol dm-3 disodium hydrogenphosphate 0.1 mol dm-3 aqueous sodium hydroxide Phenolphthalein indicator

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INVESTIGATION 12 (CONT.)

In part 4) I hope that students will decide to fi nd Ka by plotting [H+] against the ratio of salt concentrations as I feel this gives a far better feel for the reliability of the various results compared to just averaging the fi ve Ka values obtained. In the overall evaluation I think it is important that students realise that all of the methods share the inherent weakness that they rely on pH measurements, which being logarithmic produces a large uncertainty, especially as most school pH meters cannot be relied on to more than one decimal place. Another thing they should consider is to what extent an uncertainty in making up the solution is likely to lead to a signifi cant change in the pH, in other words are readings being taken in a buff ering region.

INVESTIGATION 13 - INVESTIGATING BUFFER SOLUTIONS




Apparatus required

Per group

Burettes Pipettes Measuring cylindersVolumetric fl asks Conical fl asks Beakers Weighing bottles

Generally available

pH meters Balances

Chemicals required:

1 mol dm-3 aqueous solutions of both strong and weak common acids & bases (students can then dilute these down to give the concentrations they require) Solid salts of both weak acids (sodium ethanoate) and weak bases (ammonium chloride) Solutions of common indicators

Students have a lot of scope in this Investigation. Determining “buff ering capacity” is oft en something they wish to test, but it is important for them to have a clear idea of what they mean by this.

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INVESTIGATION 14 - DETERMINING THE PKA OF AN INDICATOR BY COLORIMETRY



Apparatus required

Per group

~15 test tubes5 cm3 measuring cylinder Colorimeter/spectrophotometer Supply of cuvettes

To be shared

2 x burette (for the buffer solutions below)

Chemicals required

0.1 M hydrochloric acid (~5 cm3 per group) 0.1 M aqueous sodium hydroxide (~5 cm3 per group) 0.04% aqueous bromocresol purple indicator (~5 cm3 per group) pH 7 buff er (~25 cm3 per group, placed in a shared burette) pH 4 buff er (~25 cm3 per group, placed in a shared burette)

(NB these buffers need to be of the same concentration)

Apart from the fact that the colours are gorgeous, it is also a great Investigation! Th e colorimeter gives good results with an indigo fi lter (λmax 430 nm) and a yellow fi lter (λmax 580 nm), similarly with a spectrophotometer at similar wavelengths. Mixing the buff ers gives a range of pH values, but not enough in the pH 5-6 region, which gives the students an issue they ought to refer to in their evaluation.

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INVESTIGATION 15 - DETERMINING THE MOLAR MASS OF AN IRON(II) SALT



Apparatus required

Per group

Burette Small funnel 25 cm3 pipette Pipette fi ller 100 cm3 volumetric fl ask Weighing bottle 250 cm3 conical fl ask 100 cm3 conical fl ask

Generally available

Top pan balance reading to 0.01 g

Chemicals required:

Standardised 0.1 mol dm-3 aqueous sodium thiosulfate (~200 cm3 per group) Approximately 0.02 mol dm-3 aqueous potassium manganate(VII) (~300 cm3 per group) 1 mol dm-3 sulfuric acid (~200 cm3 per group) Solid potassium iodide (~5 g per group) Solid iron(II) ammonium sulfate (~5 g per group), labelled “Iron(II) salt” Freshly prepared starch indicator (~10 cm3 per group)

Th ough redox titrations are perhaps not overtly in the syllabus, including this in the AHL redox part of the syllabus aff ords an excellent opportunity to revise both half equations and students’ titration technique. Th e results should be good and hence aff ord an excellent opportunity to assess Manipulative Skills.

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INVESTIGATION 16 - UNDERSTANDING ELECTRODE POTENTIALS



Apparatus required

Per group

8 x 50 cm3 beakers 4 x test tubes 25 cm3 measuring cylinder 50 cm3 measuring cylinder Carbon electrode Filter paper Filter paper strips for salt bridges High resistance voltmeter/multimeter

Generally available

Filter paper Crocodile clips Wire Scissors Sandpaper

Chemicals required

Metal strips - magnesium, zinc, copper, lead (~1 cm x 3 cm)

~50 cm3 per group of each of the following:

Aqueous magnesium sulfate (~0.1 mol dm-3) Aqueous zinc sulfate (~0.1 mol dm-3) Aqueous copper sulfate (~0.1 mol dm-3) Aqueous lead nitrate (~0.1 mol dm-3) Aqueous sodium bromide (~0.1 mol dm-3) Saturated aqueous potassium nitrate Saturated aqueous lead chloride Aqueous 0.1 mol dm-3 iron(II) ammonium sulfate (freshly made) Aqueous 0.1 mol dm-3 iron(III) chloride Dilute sulfuric acid 0.1 mol dm-3 iodine in aqueous potassium iodide Aqueous 0.1 mol dm-3 potassium iodide Hydrogen peroxide (~10 volume)

Th e “set up” in part A is not the traditional one with separate beakers and salt bridges, (which can be substituted if preferred), but I fi nd this is a rapid way to measure a number of cell potentials quite quickly. (continued next page)

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Th e solutions are not the 1 mol dm-3 ones that should be used for standard conditions, but (especially as all the ions are of the same charge) I do not believe that this can explain the tremendous discrepancies with literature values, particularly for magnesium, that the results usually show. (If anybody has any suggestions (oxide layers?) I would like to hear from them.) In Part C the wording of the analysis is deliberately vague, in the hope that students will discover for themselves that they really need to plot log[concentration] to produce a useful calibration graph for the range of concentrations used. In Part D students should come to the conclusion that H2O2 (in the presence of acid) should oxidise I- to I2 and then fi nd a way of testing it.

INVESTIGATION 17 - INVESTIGATING ELECTRODE POTENTIALS



Apparatus required


Per group

Beakers Filter paper strips for salt bridges Carbon electrodes High resistance voltmeter/multimeter Sandpaper

Chemicals required

Metal strip electrodes (magnesium, zinc, copper, lead, iron etc.) Aqueous solutions of salts of these metals (~0.1 mol dm-3) Saturated aqueous potassium nitrate

Th is Investigation gives the students a great deal of scope to investigate how changing a particular variable aff ects electrode potentials. Th ey can either looks at a series of voltaic cells and then try to correlate the potentials obtained with other parameters (ionisation energy, ionic radius, hydration enthalpy, charge on ion etc.) or they can investigate the eff ect of a variable (temperature, concentration, solvent etc.) on one particular voltaic cell.

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INVESTIGATION 18 – A QUANTITATIVE INVESTIGATION INTO ELECTROLYSIS



Apparatus required


Power packs Wires & crocodile clips Electrode holders Multimeters Water baths Gas syringes Balances Sandpaper

Chemicals required

Carbon electrodes Dilute sulfuric/hydrochloric/nitric/ethanoic acidsCopper electrodes Aqueous copper sulfate/chloride/nitrateZinc electrodes Aqueous zinc sulfate/chloride/nitrateLead electrodes Aqueous lead nitrateMagnesium ribbon Aqueous magnesium sulfate/chloride/nitrateIron nails Aqueous iron(II) sulfate and iron(III) chlorideAqueous ammonia Aqueous sodium/potassium/calcium hydroxides

Students have met the basic ideas of electrolysis fairly early in the course (for example in Investigation 23 of the Core Portfolio), being a concept that students generally fi nd straightforward. I tend however, to leave this Investigation until very near the end, when they have had some practice at meeting the Design criterion. Th is then is one of my main investigations for fi nal assessment purposes. It probably makes for a far more interesting and varied Investigation if you veto time and current as independent variables.

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INVESTIGATION 19 – CARBOXYLIC ACIDS, AMINES AND RELATED COMPOUNDS



Apparatus required

Per group 6 x test tubes 2 x boiling tubes Boiling tube fi tted with a delivery tube to collect gas over water 250 cm3 beaker Th ermometer (0 - 110oC) Quickfi t apparatus for refl ux and distillation

Generally available Glass wool (plus plastic gloves to handle it with) Universal indicator and colour chart Narrow range indicator paper (pH 4 - 6)

Chemicals required: Ethanol Ethanoic acid (glacial)Ethyl ethanoate (ethyl acetate)Ethylamine (aqueous solution)Ethanamide (acetamide)Marble chips1 mol dm-3 ethanoic acid1 mol dm-3 hydrochloric acidMagnesium ribbonConcentrated sulfuric acidSolid sodium hydrogen carbonateMethanol2-hydroxybenzoic acid (salicylic acid)Ethanoyl chloride (acetyl chloride) Solution of decanedioyl chloride (sebacoyl chloride) in 1.1.1-trichloroethane (1.5 cm3 in 50 cm3) Aqueous 1.6-diaminohexane (hexamethylene diamine) (2.2 g in 50 cm3)

Th is is a collection of reactions that the students should be aware of and, working on the principle that you are more likely to remember something that you have done rather than just read about, I have put them all together into one practical session. When making ethyl ethanoate I add the hydrogencarbonate to neutralise any excess acid, so removing its smell and also the eff ervescence enhances the ester smell. My only defence of also making methyl salicylate is I like the smell!

Acyl chlorides are very reactive chemicals so I strongly recommend doing parts 6) and 7) as teacher demonstrations. Indeed in many parts of the world purchasing ethanoyl chloride and ethanoic anhydride is very diffi cult because of the importance of acetylation reactions in the manufacture of illegal drugs.

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INVESTIGATION 20 - SOME FACTORS AFFECTING THE REACTIONS OF HALOGENOALKANES



Apparatus required

Per group

6 x test tube 2 x boiling tube Bung with delivery tube to fi t boiling tubes

Chemicals required

Ethanol 1-chlorobutane 2-chlorobutane (iso-butyl chloride) 2-chloro-2-methylpropane (tert-butyl chloride) 1-bromobutane 1-iodobutane Aqueous sodium hydroxide (~1 mol dm-3) Aqueous silver nitrate (~0.01 mol dm-3) Dilute nitric acidBromine water Potassium hydroxide pellets

Th is works well, illustrating the anticipated eff ects of halogen and hydrocarbon chain structure on the relative rate of hydrolysis. In the case of the elimination reaction (CARE – hot concentrated alkali is very corrosive) I suspect it may be ethanol distilling over (and being oxidised by the bromine), rather than the formation of an alkene that leads to the decolourising of the bromine water!

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INVESTIGATION 21 – AN ORGANIC CHEMISTRY INVESTIGATION



Apparatus required

As with any student designed practical, it is diffi cult to produce a precise list of requirements and this is particularly true with regard to an Investigation as broad as this, which I would leave until very near the end of my Internal Assessment programme. It may be that you feel your students require a little more guidance, without being so prescriptive as to invalidate the exercise from a Design perspective. Th is could involve a focus like “Factors aff ecting the yield from esterifi cation reactions”, or “A study of the kinetics of the hydrolysis of halogenoalkanes”, or maybe “Investigations on the optical activity of chiral compounds”.

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