SATHYABAMA UNIVERSITY should maintain silence while doing the experiment and any doubts should ... 1 Determination of Total Hardness of Water Sample by ... EBT indicator

SATHYABAMA UNIVERSITY(Established Under Section 3 of UGC Act, 1956)

Jeppiaar Nagar, Rajiv Gandhi road, Chennai – 600 119

DEPARTMENT OF CHEMISTRY

I SEMESTER / II SEMESTER

Subject Name: Engineering Chemistry LabSubject code: SCY4051

LAB MANUAL(Common to ALL Branches)

Name :

Year : Branch and Section

Roll No. :

Sathyabama University Faculty of S & H, Department of Chemistry

Engineering Chemistry lab manual (SCY4051) 1 Regulations 2015

GENERAL INSTRUCTIONS

Students will not be allowed for the practical classes without lab coat, shoes, lab manual,observation book and record note book.

Students should maintain their observation note book and record note book neatly.

Both the record and observation note book should be covered with brown sheet.

Students should write the date, name of the expt., diagram, tabulation, procedure, etc. intheir observation note book before entering the lab.

Students should write the completed experiment in the record note book, only after getting itcorrected in the observation note.

Students will not be allowed to enter into the lab without getting the previous experimentcorrected in the record.

In the record, LHS should be used for diagrams, tabular column, calculation and modelgraph (if any) and RHS should be used for writing aim, formula, apparatus required,procedure and the result.

Diagrams, tabular column and graph should be drawn with pencil and procedure in blue inkand students should paste the graph along with the corresponding experiments neatly.

Titles and subtitles should be in capital letters and it should be underlined only with black penor pencil.

Students who are late for the practical class will not be allowed to do their experiment.

100% attendance is compulsory for all the laboratory classes.

Absentees will not be allowed to do their experiments in their subsequent classes.

A place and number will be allotted to each student. Students have to follow this number forregular practical classes for the whole semester.

Students should maintain silence while doing the experiment and any doubts should beclarified only with the staff members.

There will be a plastic tray on each working table. All glass ware (except burette) will be keptin the tray.

Do not place any glass apparatus on the working table. They should be kept only in theplastic tray. Do not keep the glass ware at the edge or corner of the table so that breakageof glass ware can be avoided. Always keep your place neat, clean and dry.

There will be a white colour plastic bottle available in the tray. It should be used to fill distilledwater and not the tap water. Distilled water will be kept at a particular place in the chemistrylab. Make sure for the distilled water before filling it in the bottle.



All glass wares should be washed first with tap water and then should be rinsed with distilledwater.

Numbered solution bottles are kept on the side tables in the lab. Students should take thebottles according to their seat number (for some solutions need not follow the seat number,consult with staff for more information). After the completion of experiment, these bottlesshould be replaced in the same place.

The reagents for the experiments will also be on the side tables. Students should not bringthem to their place as these reagents are common for all the students.

Each concordant reading should be attested by the staff members before proceeding to thenext part of the experiment. Without getting the readings attested, students should notproceed with the experiment.

Students should wash all the glass ware after completing the experiment and should bereplaced in the plastic tray.

The instruments kept in the lab are already calibrated. These instruments should not bedisturbed or tampered. All the instruments and electrodes should be handled carefully.

Any breakage or damage to glass ware or equipment should be informed to the staffmembers (do not touch or clean the broken glass wares) immediately. Students should signin the breakage register and the breakage amount will be collected.

Materials like filter paper, glass beads etc. should not be thrown in the sink after their usage.

Students are requested not to leave the lab without the permission of the staff in-charge.

Your place will be checked by the assistants for cleanliness and for the replacement of theglass ware. Students have to leave the lab only after the period gets over.

How to fill a burette?Wash the burette and funnel with tap water. Check for any leakages. Inform the staff

member, in case of leakage. Take small volume of distilled water, rinse the burette and funnelthoroughly. Keep the funnel in the burette and add small portion of the solution which should betaken in the burette. Rinse the burette and funnel thoroughly with that solution. Drain this solution inthe sink and then fill the burette till the zero level. Open the stopper at the base and release the airbubbles from the bottom of the burette. Add more of the solution to adjust for the zero level till thelower meniscus coincides with the zero mark for colourless solutions (if the lower meniscus is notvisible, as in the case of coloured solutions, upper meniscus can be used for zero adjustment). Now

Concentrated acids, particularly sulphuric acid, should be addedvery carefully. More care has to be taken while adding any acid or

while heating the glass wares. If any injury arises due to acid orheat, wash the area immediately with sufficient water and seek the

medical assistance.



the burette solution is ready for titration. The burette should be filled up to zero level every timebefore starting a new titration.

How to use the pipette?Wash the pipette with tap water and check for any breakage, particularly at the tip. Insert the

pipette into the wash bottle containing distilled water to draw water for rinsing. Take the pipette out byclosing it with the index finger (finger should be dry) and rinse the pipette thoroughly by inverting thepipette. Drain the distilled water completely. After cleaning with distilled water, the pipette should berinsed with the respective solution the same way as before. Always insert the pipette well into thesolution to prevent sucking of solution into the mouth. When the solution reach the safety bulb, closethe top of the pipette with the index finger and adjust the solution level to the mark present near thebulb and then drain the solution into the conical flask. After draining the solution, touch the bottom ofthe conical flask for complete draining of the solution. The last drop of the solution present in thepipette after complete draining of the solution should not be blown out. Now the solution is ready fortitration.

How to make up a solution?You will be provided with a small volume of a solution in a small bottle. This solution has to

be transferred into the standard flask without spilling even a drop. Follow the instructions givenbelow:

Check for any breakage and wash the glass rod, funnel, volumetric standard flask andstopper thoroughly with tap water and rinse with distilled water. Keep the funnel on the volumetricstandard flask. Carefully transfer the solution given in the small bottle into the volumetric standardflask through a glass rod and the funnel. While transferring, the solution bottle should touch the glassrod and the glass rod should be well inside the funnel. This is followed to avoid the spillage of thesolution. After transferring the solution, use small volume of distilled water for rinsing the solutionbottle and transfer the rinsing to the volumetric standard flask. The glass rod should not be takenaway from the funnel. Again rinse the bottle with little distilled water and transfer the rinsing into thevolumetric standard flask through the glass rod and the funnel. Repeat this procedure for 3 or 4times. After ensuring the complete transfer of the solution, wash the glass rod with distilled water.Wash the funnel with distilled water. (Every time a small quantity of distilled water has to be addedso that after all this process the total liquid volume in the standard flask will be less than the mark)Now add distilled water slowly up to the mark using a pipette. The lower meniscus should coincidewith the mark (if the lower meniscus is not visible then upper meniscus can be considered). Closethe stopper tightly and invert the standard flask and gently shake the solution by turning the standardflask up and down several times to get a solution of uniform concentration.

Burette Funnel Standard flask Pipette Conical flask Glass rod

Wash bottle



S. No. Name of the Experiment Page No.

1 Determination of Total Hardness of Water Sample by EDTAmethod 5

2 Estimation of Mixture of Acids by Conductometric Titration 9

3 Estimation of Fe2+ by Potentiometric Titration 14

4 Determination of Molecular Weight of a Polymer by ViscosityMeasurement Method 19

5 Determination of pKa Value of Glycine Using pH Meter 24

6 Estimation of Iron by Using Photocolorimeter 29

LIST OF EXPERIMENTS



Expt. No. 1 Date_________________

1. DETERMINATION OF TOTAL HARDNESS OF WATER SAMPLE BY EDTA METHOD

AIM:To estimate the total hardness of the given sample of water by EDTA method.

PRINCIPLE:Hardness of water is due to the presence of dissolved salts of calcium and magnesium.

Hardness of water is determined by titrating a known volume of water sample with EDTA, usingEriochrome Black T (EBT) as the indicator, in the presence of ammonium hydroxide – ammoniumchloride buffer to maintain the pH at 10.

APPARATUS & REAGENTS:Burette, pipette, conical flask, EDTA, Standard hard water, NH4OH-NH4Cl buffer solution,

EBT indicator.

PROCEDURE:

TITRATION I - STANDARDIZATION OF EDTA SOLUTION:Pipette out 20 ml of the standard hard water into a clean conical flask. Add about 5ml of (NH4Cl +NH4OH) buffer solution and a small quantity of Eriochrome Black T indicator. The solution turns towine red in colour. Titrate against EDTA solution taken in the burette until the solution turns to steelblue colour. Repeat the titration for concordant values. Let V1 be the volume of EDTA consumed bystandard hard water.

TITRATION II - ESTIMATION OF TOTAL HARDNESS OF GIVEN WATER SAMPLE:Pipette out 20 ml of sample hard water into a clean conical flask. Add about 5 ml of (NH4Cl + NH4OH)buffer solution and a small quantity of Eriochrome Black T indicator. The solution turns to wine red incolour. Titrate against EDTA solution taken in the burette until the solution turns to steel blue colour.Repeat the titration for concordant values. Let V2 be the volume of EDTA consumed by the samplehard water.

RESULT: Total hardness of the given sample of water = ………… ppm (parts of CaCO3 per millionparts of water).



OBSERVATIONS AND CALCULATION:

Titration I - Standardization of EDTA solution:

Burette : EDTA solutionPipette solution : 20 ml of std. hard water + 5ml buffer solutionIndicator : Eriochrome Black TEnd point : Wine red to steel blue

Sl. No. Volume of Std.hard water

Burette Reading Volume ofEDTA

ConcordantValueInitial Final

1 ml of standard hard water = 1 mg of CaCO3 equivalent hardness …..(1)20 ml of standard hard water = 20 mg of CaCO3 equivalent hardness …..(2)20 ml of standard hard water consumes = V1 ml of EDTA …..(3)

From equation (1) and (2):

V1 ml of EDTA = 20 mg of CaCO3 equivalent hardness

1 ml of EDTA =1

20

Vmg of CaCO3 equivalent hardness

Titration II - Estimation of Total Hardness of Water:

Burette : Standardised EDTA solutionPipette solution : 20ml water sample + 5ml buffer solutionIndicator : Eriochrome Black TEnd point : Wine red to steel blue

S. No. Volume of GivenWater Sample

Burette Reading Volume ofEDTA

ConcordantValueInitial Final

20 ml of sample hard water consumes = V2 ml of EDTA20 ml of sample hard water = V2 x 1 ml of EDTA

20 ml of sample hard water =1

220

VV mg of CaCO3 equivalent hardness

1000 ml of sample hard water =20

100020

12

VV mg of CaCO3 equivalent hardness

Total hardness of given water sample =1

21000V

V ppm.



SHORT PROCEDUREDETERMINATION OF TOTAL HARDNESS OF WATER SAMPLE BY EDTA METHOD

Titration I - Standardization of EDTA solution:

Burette : EDTA solutionPipette solution : 20 ml of std. hard water + 5ml buffer solutionIndicator : Eriochrome Black TEnd point : Wine red to steel blue

1 ml of EDTA =1

20

Vmg of CaCO3 equivalent hardness

Titration II - Estimation of Total Hardness of Water:

Burette : Standardised EDTA solutionPipette solution : 20ml water sample + 5ml buffer solutionIndicator : Eriochrome Black TEnd point : Wine red to steel blue

Total hardness of given water sample =1

21000V

V ppm.

Result: Total hardness of the given sample of water = ………… ppm (parts of CaCO3 per millionparts of water).



VIVA-VOCE QUESTIONS:1. Define hard water and soft water.2. Define hardness of water.3. What are the hardness causing constituents?4. Distinguish between carbonate hardness and non-carbonate hardness.5. How is hardness of water expressed? (or) Bring out the significance of calcium carbonate

equivalents?6. Bring out the relationship between ppm and mg/lit.7. How does eriochorme black-T function as an indicator in EDTA titration?8. In EDTA titration NH4Cl-NH4OH buffer is used. Why?9. Every soft water is not demineralized water whereas every demineralized water is soft water.

Justify10. Differentiate between soft water and demineralized water.11. Name any two of the important disadvantages of using hard water for domestic purposes.



Expt. No. 2 Date_________________

2. ESTIMATION OF MIXTURE OF ACIDS BY CONDUCTOMETRIC TITRATION

AIM:To estimate the amount of acids present in the whole of the given solution. You are provided

with standard 0.2 N sodium hydroxide solution.

PRINCIPLE:During the titration of mixture of acids (strong acid HCl and weak acid CH3COOH) vs strong

base (NaOH), initially the conductance is very high due to the presence of fast moving H+ ions ofstrong acid. Upon titration, the fast moving H+ ions are replaced by slow moving Na+ ions. Thereforethe conductance of the solution decreases. During the titration of NaOH vs HCl the following reactiontakes place in the vessel.

Na+ OH− + H+ Cl− → Na+ Cl− + H2O

After the end point there will be slow rise in the conductance of the solution due to the slightdissociation of weak acetic acid. As sodium hydroxide is added, the hydroxide reacts with the acid toform water and acetate.

Na+ OH− + H+ CH3COO− → Na+ CH3COO− + H2O

A plot between volume of NaOH added versus the conductance of the solution, will give twointersection points. The first point corresponds to the first titre value between strong acid vs strongbase. The second point corresponds to the second titre value between weak acid vs strong base.

APPARATUS & REAGENTS:Conductivity meter, beaker, burette, pipette, glass rod, sodium hydroxide, hydrochloric acid

etc.

PROCEDURE:Makeup the given acid solution into a clean 100 ml standard flask with distilled water. Pipette

out 20 ml of the made up acid solution into a clean 100 ml beaker. Pipette out 20ml of distilled waterinto the beaker. Rinse the conductivity cell thoroughly with distilled water and immerse into thebeaker. Stir the solution gently and carefully with a glass rod. Measure the initial conductance of acidsolution. Now add 1 ml of NaOH from the burette. Stir the solution carefully with the glass rod andnote the conductance.



Continue the titration by adding NaOH (in an aliquot of 1 ml) from the burette. When we addNaOH the conductance initially decreases up to certain volume of NaOH. After that, the conductancestarts increasing slightly for the addition of NaOH. After a particular volume the conductanceincreases rapidly. Plot a graph between the conductance values and volume of NaOH added asshown in the model graph. The first point of intersection of the two lines in the graph gives the firstend point of the titration. Consider this value as V1. Consider the second point of intersection of thetwo lines in the graph as V3. V3―V1 gives the second end point of the titration.

RESULT:The amount of hydrochloric acid present in the whole of the given solution = ______ g.The amount of acetic acid present in the whole of the given solution = ______ g.

OBSERVATIONS. No. Volume of NaOH added (ml) Conductance (m Mho)

1 12 23 34 45 56 67 78 89 910 1011 1112 1213 1314 1415 1516 1617 1718 1819 1920 2021 2122 2223 2324 2425 2526 2627 2728 2829 2930 30



CALCULATIONSEstimation of HCl:

Volume of NaOH (V1) = ml (obtained from graph)

Normality of NaOH (N1) = 0.2 N

Volume of Mixture of acids (V2) = 20 ml

Normality of strong acid-HCl (N2) =

Equivalent weight of HCl = 36.5

Amount of HCl present in 1000ml(x) = N2 × 36.5

The amount of HCl present in thewhole of the given solution =

Estimation of CH3COOH:

Volume of NaOH (V4) = (V3-V1) ml (obtained from graph)

Normality of NaOH (N1) = 0.2 N

Volume of mixture of acids (V2) = 20 ml

Normality of weak acid-CH3COOH (N3) =

Equivalent weight of acetic acid = 60

Amount of acetic acid present in 1000ml (y) = N3 × 60

The amount of acetic acid present in the wholeof the given solution =

Model graph:

g1000

100x

200.2graph)from(obtainedV1

g1000

100y

200.2graph)from(obtainedV4



SHORT PROCEDUREESTIMATION OF MIXTURE OF ACIDS BY CONDUCTOMETRIC TITRATION

Aim: To estimate the amount of hydrochloric acid and acetic acid present in the whole of the givenusing 0.2N standard sodium hydroxide (NaOH).

Principle: Initially the conductance is high due to the presence of fast moving H+ ions. Upontitration the fast moving H+ ions are replaced by slow moving Na+ ions. Therefore, the conductancedecreases on addition of NaOH solution. After the first equivalence point, the conductance increasesslightly and rapidly after the second equivalence point.

H+ Cl¯ + Na+ OH¯ Na+ Cl¯ + H2ONa+ OH− + H+ CH3COO− Na+ CH3COO− + H2O

Procedure:Calibrate the conductivity meter with 0.1N KCl solution.

Conductance = 13.6milli mhosTitrate Standard NaOH against HCl solutionBurette Solution : Standard NaOHPipette Solution : 20ml of made up acid solution + 20ml of distilled waterEnd point : Obtained from graph

Model Table: Model Graph:

Volume ofNaOH (ml)

Conductance(mMhos)

V × 0.2Normality of acid =

20Equivalent weight of HCl = 36.5, Equivalent weight of CH3COOH = 60

Result:The amount of HCl present in the whole of the given solution

Normality of HCl x 36.5 x 100= = ________g.

1000The amount of CH3COOH present in the whole of the given solution

Normality of CH3COOH × 60 × 100= = ________g.

1000



VIVA-VOCE QUESTIONS:

1. What is conductance?2. What are the different types of conductors?3. Define Ohm’s law.4. What is the advantage of conductometric titration?5. Why the conductance is decreasing initially?6. What is the difference between specific conductance and equivalent conductance?7. What is cell constant?8. How will you calibrate a conductivity meter?9. What is the unit of conductance?10. What is the relation between conductance and temperature?11. What is the relation between conductance and concentration of the solution?12. What are the differences between anode and cathode?13. What is ionic mobility?



Expt. No. 3 Date_________________

3. ESTIMATION OF Fe2+ BY POTENTIOMETRIC TITRATION

AIM:To estimate the amount of ferrous ions present in the whole of the given solution. You are

provided with s standard 0.1 N potassium dichromate solution.

PRINCIPLE:The electrode potential of any redox system can be obtained by coupling it with a reference

electrode (like saturated calomel electrode) of known potential (0.2422V). By connecting a cell withthe calomel electrode, the potential of ferrous-ferric redox system can be determined. The redox cellcan be represented as

Hg/Hg2Cl2, KCl(saturated)// Fe3+ - Fe2+ / Ptfor which

Ecell = ER.H.S _ EL.H.S

by applying the Nernst equation,

2422.0log0591.0

2

3

/ 23

Fe

Fe

nEE o

FeFecell

Where E is the emf of the electrode, o

FeFeE 23 /

is the standard electrode potential for ferrous-ferric

system, n is the number of electrons involved in the reaction, F is the Faraday’s constant, R is thegas constant and T is the temperature.

Ferrous ions are oxidized to ferric ions by adding potassium dichromate whichsimultaneously increases the e.m.f of the cell. A sharp increase in the e.m.f. at the end point which isdue to complete conversion of ferrous to ferric ions.

APPARATUS & REAGENTS:Potentiometer, standard calomel electrode, platinum electrode (indicator electrode), beaker,

burette, pipette, glass rod, standard flask, potassium dichromate, ferrous solution and sulphuric acid.

PROCEDURE

TITRATION:Transfer the given ferrous ion solution into a clean 100 ml standard flask. Make up the

solution with distilled water. Pipette out 20 ml of the made up solution into a 100 ml beaker and add20 ml of dil. H2SO4. Immerse the platinum and calomel electrodes in the solution and connect themto the potentiometer. Stir the solution and note the initial constant e.m.f. of the solution. Then add 0.5



ml aliquots of K2Cr2O7 solution from the burette and note the e.m.f. Initially, the difference in e.m.f.will be small followed by a large difference in the e.m.f. values near the end point. After the end pointagain the difference in e.m.f values will be small. By calculating ∆E, ∆V and ∆E / ∆V, a graph isplotted by taking volume of K2Cr2O7 solution (V) on the X-axis and ∆E / ∆V on the Y-axis. From thegraph, the volume of K2Cr2O7 solution consumed is determined.

RESULT:Amount of Fe2+ ions present in the whole of the given solution = ________ g.

TITRATION:

S. No. Volume ofK2Cr2O7, V (ml)

Observed e.m.f,E (milli volts) ∆E ∆V ∆E / ∆V

(millivolts/ml)1 02 0.53 14 1.55 26 2.57 38 3.59 410 4.511 512 5.513 614 6.515 716 7.517 818 8.519 920 9.521 1022 10.523 1124 11.525 1226 12.527 1328 13.529 1430 14.531 15



CALCULATION:

Volume of K2Cr2O7 solution (V1) = mlStrength of K2Cr2O7 solution (N1) = 0.1 NVolume of Fe2+ solution (V2) = 20 mlStrength of Fe2+ solution (N2) =

20

1.0)(1 graphfromObtainedV

Amount of Fe2+ ions present in 1000 ml (Y) = Normality of Fe2+ × Equivalent weight of Fe2+

= N2 × 55.85Amount of Fe2+ ions present in 100 ml of the solution =

10

Y

= _________ g

Model graph



VIVA-VOCE QUESTIONS:1. What is a redox reaction?2. Define oxidizing and reducing agents. Give egs.3. Define e.m.f, standard electrode potential Eo.4. What is a reference electrode? Give examples.5. What is an indicator electrode? Give examples.6. Construct a calomel electrode and give its types.7. Give the cell representation for redox reaction.8. Write the Nernst equation for the ferrous-ferric system.9. What happens to the e.m.f. of the cell when the [Fe3+] ion concentration increases?10. What are the advantages of potentiometric titration?11. What will be the colour change of the working solution after the end point?12. Why Platinum electrode is used as an anode?13. Write the redox reaction for the experiment.14. How the e.m.f. of the cell vary at the end point?15. Represent a first derivative graph for the redox titration.



Volume of K2Cr2O7

ΔE

/ΔV

SHORT PROCEDUREESTIMATION OF Fe2+ BY POTENTIOMETRIC TITRATION

Aim: To determine the amount of ferrous ions present in the whole of the given solution using 0.1Nstandard potassium dichromate (K2Cr2O7).Principle: For a ferrous – ferric system the electrode potential is determined by combining withsaturated calomel electrode to form a cell represented as

Hg / Hg2Cl2, KCl (Sat) // Fe3+, Fe2+/PtProcedure:Titration : Standard dichromate Vs Ferrous ion SolutionBurette Solution : Standard K2Cr2O7

Pipette Solution : 20ml of made up ferrous solution + 20ml dil. H2SO4

End Point : Obtained from the graphEquivalent weight of Fe2+ = 55.85

Model Table: Model Graph:

Sl.No

Volume ofK2Cr2O7,

V (ml)Observed

emf, E(milli volts)

∆E(mV)

∆V(ml)

∆E / ∆V(mV/ml)

Strength of Fe2+ solution (N2) =20

1.0)(1 graphfromObtainedV

Amount of Fe2+ ions present in 1000 ml of thesolution (Y)

= Normality of Fe2+ solution × Equivalentweight

= N2 × 55.85Amount of Fe2+ ions present in 100 ml of the solution =

10

Y

= _________ g

Result: Amount of Fe2+ present in the whole of the given solution = _________g.



Expt. No. 4 Date_________________

4. DETERMINATION OF MOLECULAR WEIGHT OF A POLYMER BY VISCOSITYMEASUREMENTS

AIM:To determine the molecular weight of the given polymer by viscosity method using Ostwald

viscometer.

PRINCIPLE:The viscosity of a polymer solution is high compared to that of the pure solvent. The molecular

weight of a polymer is proportional to the intrinsic viscosity of its solution (ηi) when the polymermolecular chain is extended to its full contour length. The value of intrinsic viscosity is proportional tothe square root of the molecular weight M, when the polymer is in a solvent. The relationshipbetween intrinsic viscosity and molecular weight is given by Mark-Kuhn-Hownik’s empirical equationas,

KMi

where α is a measure of the shape of the polymer molecular chain (coiled or extended form) and thevalue is usually from 0.5 to 0.8. The value of the constant K depends on the polymer and the solventinvolved.

For a liquid flowing through a capillary tube, the time required to pass through the capillary tube isrelated to the absolute viscosity according to the equation:

Vl

t

8

Pr4

where V is the volume of the liquid which pass through the capillary, r is the radius of the capillary, l isthe length of the capillary and P is the pressure head under which the liquid flow takes place. If ηand ηo are the absolute viscosities of the polymer solution and the pure solvent respectively and tand t0 are their corresponding flow times and if the same capillary tube is used then, the relativeviscosity is:

oot

t

Hence for each concentration calculate the values of η/η0 and ηsp (specific viscosity)

1

osp t

t



From the plot of ηsp/C vs concentration of the polymer, intrinsic viscosity can be calculated.

APPARATUS & REAGENTS:Viscometer (Ubblehodeor Ostwald), stop watch, beaker (50 ml, 100 ml), standard flasks(

100ml, 25ml), pipette 10 ml and burette 50 ml.

PROCEDURE:2.5 g of the given polymer is exactly weighed and transferred into a 100 ml beaker. It is

dissolved with minimum amount of solvent (water or benzene) with constant stirring using a glassrod. The polymer solution is transferred into a 100 ml standard flask and made upto the mark usingdistilled water. It is shaken for uniform concentration. The resulting solution is 2.5% polymer solution.

25 ml of 0.25%, 0.5%, 0.75%, 1%, and 1.25% polymer solutions are prepared as follows.Pipette out 2.5, 5, 7.5, 10, and 12.5 ml of 2.5% polymer solution in a 25 ml standard flask. Thenmake up the polymer solution with distilled water and shake the solution thoroughly. Pipette out 10 mlof each solution into a viscometer. The flow time of the solvent (t0) and the polymer solution (t) inseconds is noted. The flow time can be determined as follows.

Wash the viscometer and 10 ml pipette with distilled water and dry it. Fix the viscometervertically in a stand. Pipette out 10 ml of the solvent into the lower bulb of the viscometer and suckthe liquid carefully into the upper bulb, so that the liquid level is above the mark. Allow the liquid toflow freely. When the liquid level crosses the upper mark, start a stopwatch. When the liquid levelcrosses the lower mark, stop the stopwatch. Repeat it for two times. The average value is the flowtime of water.

Similarly determine the flow time of given polymer solutions at different concentrations.Tabulate the results. From the flow time we can calculate the specific viscosity.

1

osp

1

osp t

t

From the plot of ηsp/C versus concentration, the intrinsic viscosity (Y - intercept) ηi can be determined.Using ηi, α and K values, the molecular weight of the polymer can be determined.

RESULT: The molecular weight of the given polymer sample =



Flow time of pure solent, t0 = -------- sec.Sl.No.

Conc. of the polymersolution, C

Time of flow(sec) η/ η0 = t/t0 ηsp = (t/t0) - 1 ηsp/C

1. 0.25%2. 0.5%3. 0.75%4. 1%5. 1.25%

ηi = KMα

log ηi = log K + α logM

log ηi - log klog M =

α

log M = X

M = antilog of X

Polymer solution α KPolyvinyl pyrolidone – Water system 0.59 39.3 x 10 -5 dl/gPolyvinyl alcohol – Water system 0.64 45.3 x 10 -5 dl/g

MODEL GRAPH:



VIVA-VOCE QUESTIONS:1. Define Viscosity.2. What is Viscosity Coefficient of a liquid?3. Define density of a liquid.4. What is Specific gravity?5. How is Specific gravity and density related?6. What is the S.I unit of Viscosity Coefficient?7. What are the factors that influence the viscosity of a liquid?8. How does the viscosity vary with temperature?9. Why should the viscometer to be dried before the measurements are done?10. Why is acetone used for cleaning viscometer?11. Why is viscometer not rinsed with given liquid or water?12. Why do you require laboratory temperature for viscosity determination?13. How is the viscosity of a liquid related to its mobility?14. What is fluidity of a liquid?15. What is effect of molecular weight on viscosity?16. Explain another method used for determination of viscosity of liquid?



SHORT PROCEDUREDETERMINATION OF MOLECULAR WEIGHT OF A POLYMER BY VISCOSITY METHOD

Aim: To determine the molecular weight of a polymer by viscosity method.Principle: The molecular weight of a polymer is proportional to the intrinsic viscosity of its solution(ηi). The relationship between intrinsic viscosity and molecular weight is given by η i = KMα. Where ‘α’is a measure of the shape of polymer molecular chain. The value ‘K’ depends on the polymer and thesolvent used.Procedure: 2.5% of a polymer solution is prepared by dissolving 2.5gm of the polymer in 100ml of

the solvent. From this 2.5% solution, 0.25%, 0.5%, 0.75%, 1% and 1.25% solutions are prepared.10ml of this solution is pipetted out into a viscometer and the flow time is noted. The flow time for thesolvent(t0) and all these solutions (t) are noted.The specific viscosity is given by:

ηsp = (t/t0) – 1ηsp/C is plotted against C. The Y – intercept is intrinsic viscosity (ηi) . Using ‘α’ and ‘K’ values the

molecular weight is calculated using the formula:ηi = KM α

Model Graph:

Model Table:Sl.No.

Concentration ofthe polymer solution Time of flow η/η0 = t/t0 ηsp =

(t/t0)– 1 ηsp / C

1 Distilled water2 0.25%3 0.5%4 0.75%5 1.0%6 1.25%

Result: The molecular weight of the given polymer sample =

SYSTEM K(dl/gm) αPoly vinylalcohol - water 45.3x10-5 0.64



Expt. No. 5 Date_________________

5. DETERMINATION OF pKa VALUES OF GLYCINE BY pH TITRATION METHOD

AIM:To determine the pKa value of the given amino acid, glycine using pH titration method

PRINCIPLE:Amino acids have the general formula NH2-CHR-COOH. They can act as both acids and

bases. In water, most amino acids exist as zwitter ions, i.e., a dipolar ion. Thus, they are amphotericmolecules that can be titrated with both acid and alkali. Glycine, the simplest amino acid, has oneacid and one amine group and is diprotic in nature. Isoelectric point, pI, is the pH of an amino acid atwhich the net charge on the molecule is zero. When such an amino acid is titrated against a base, itacts as an acid, and with an acid, it acts as a base.

The pH of such a weak acid or base can be calculated from the Henderson-Hasselbalch equation

][

][log

speciesacidic

speciesbasicpKpH a

APPARATUS AND REAGENTS:0.1 N glycine, 0.1 N HNO3, 0.5 N NaOH, pH meter, pH glass electrode, burettes, beaker and

buffer solutions (4, 7 and 9) for calibrating pH meter.

PROCEDURE:10 ml of the given 0.1 N amino acid, glycine is pipetted out into a clean 100 mL beaker

followed by the addition of 10 mL of 0.1 HNO3 and 20 mL of distilled water. A pH glass electrode isrinsed in deionized water and immersed in the glycine solution. The pH of the mixture is recordedusing a calibrated pH meter is in the range of 1.5-1.6 . A clean burette is taken and filled with 0.4 NNaOH. Add increments of 0.5mL of NaOH from the burette. The solution is stirred well using a glassrod and the change in pH is recorded. Initially, the pH of the solution increases steadily and thendrastically at the isoelectric point and then increases steadily. The alkali is added in increments tillthe pH reaches to 12.5.. The readings are recorded in a tabular column as shown in Table 1.



The titration curve is plotted with Volume of NaOH on the x axis and pH on the y axis. The twoplateaus on the curve obtained is noted which represents the pKa values of glycine. These valuesare then compared with that reported in literature.

RESULT: The two pKa values of glycine are ________ and __________.



TITRATION CURVE OF GLYCINE

Sl.No.

Volume ofNaOH Observed pH

1 02 0.53 14 1.55 2.06 2.57 3.08 3.59 4.010 4.511 5.012 5.513 6.014 6.515 7.016 7.517 8.018 8.519 9.020 9.521 10.0



VIVA-VOCE QUESTIONS:

1. Define pKa.2. What is dissociation constant?3. What are monoprotic and polyprotic compounds?4. Give examples of monoprotic and diprotic acids.5. Glycine is an example of monoprotic or polyprotic. Justify.6. Define pI or Isoelectric point.7. How can the pI of a polyprotic compound be calculated?8. What happens when water is added to glycine?9. How does an aqueous solution of glycine exist?10. What happens when an acid is added to a zwitter ion of glycine?11. What happens when a base is added to a zwitter ion of glycine?12. What is zwitter ion or dipolar ion?13. How many pKa values does glycine have and what are they?14. How do you prepare 0.1M solution of glycine, HCl and NaOH?15. What are the titrants used to determine the pKa values of glycine?16. How is pKa value determined from graph?17. How are pH and pKa value related?18. Define Molarity and Normality.19. How do you prepare 0.1N solution of glycine, HCl and NaOH?20. How does the protonated form of zwitter ion of glycine exist?21. How does the deprotonated form of zwitter ion of glycine exist?22. Explain the migration of glycine at acidic and alkaline pH towards electrodes in an electric

field.23. Give the expression of Henderson-Hassellbalch equation.



SHORT PROCEDUREDETERMINATION OF pKa VALUES OF GLYCINE BY pH TITRATION METHOD

Aim: To determine pKa value of the given amino acid, glycine using pH titration methodPrinciple: Amino acids have the general formula NH2-CHR-COOH. They can act as both acids andbases. In water (neutral pH), most amino acids exist as zwitter ions, i.e., a dipolar ion. When anamino acid is titrated against a base, it acts as an acid, and with an acid, it acts as a base.

The pH of such a weak acid or base can be calculated from the Henderson-Hasselbalch equation

][

][log

speciesacidic

speciesbasicpKpH a

Procedure:Glycine vs. NaOHBurette solution: 0.1N HClPipette solution: 10 mL of 0.1 N glycine +10 mL of 0.1N HNO3+ 20 mL distilled waterpKa value obtained from the graph.

Model Table:Glycine Vs NaOH

Sl.No.

Volume ofNaOH

ObservedpH

1 02 0.53 1

Model Graph:

Result: The two pKa values of glycine are ________ and __________.



Expt. No. 6 Date_________________

ESTIMATION OF IRON BY PHOTOCOLORIMETRIC METHODAIM

To estimate the amount of Fe3+ ion present in the given water sample usingspectrophotometer.

PRINCIPLEWhen a monochromatic light passes through a homogeneous coloured solution, a portion of

incident light is reflected, a portion is absorbed and the remaining is transmitted.I0 = Ir + Ia + It

WhereI0 = Intensity of light incident on the solutionIr = Intensity of incident light reflectedIa = Intensity of incident light absorbedIt = Intensity of incident light transmitted

Ir is usually eliminated and hence I0 = Ia + It. The mathematical statement of

Beer- Lambert’s Law is given by

T = I/I0 = 10– kcl

WhereT = transmittance of solutionI = intensity of light leaving the solutionI0 = intensity of light incident on the solutionK = molar absorption coefficientC = concentration of the solution in moles/ litrel = length of absorbing layer

(OR) A = log I0/I = k c l

where A is the absorbance or optical density of solutioni.e when a ray of monochromatic light passes through an absorbing medium, its absorbancedecreases exponentially as the concentration of absorbing substance and the width or thicknessincreases independently. Keeping the path length constant (say l = 1 cm), the variation is only due toconcentration, c.

Fe3+ ion alone does not give any colour in water solution. However, it develops a red colourwhen it reacts with potassium thiocyanate solution.



Fe3+ + 6KSCN → [Fe(SCN)6]3-+ 6K+

Red colour complexFurther, this colour is in the blue region, (λ=480 nm). Spectrophotometer has a wide range of

adaptability that allows selection of monochromatic light of any wavelength in the visible spectrum.

INSTRUMENTATION

The light source is an ordinary light bulb and monochromatic light is obtained by using either aglass prism or a diffraction grating. The monochromatic light then passes through the filter and isdirected through a cell containing the sample. The incident light passes through the solution and hitsthe photoelectric cell and the output of this can be seen in the display.

APPARATUS AND REAGENTSPhotocolorimeter, 100 mL standard flasks, 10% potassium thiocyanate, 1:1 hydrochloric acid

solution, standard ferric ion solution (100 ppm).

PROCEDURE

Prepare a series of standard solution containing 2-10 ppm of iron by adding 1 ml of 1:1 HCl and 1 ml of 10% potassium thiocyanate solution. The red solution is made up to 100 mL in astandard flask. Switch on the photocolorimeter and warm it up for about 10 minutes. Adjust themonochromator at the wavelength λ = 480 nm.The blank is distilled water with the reagents used forthe experiment. Keep the blank solution in the cuvette and adjust the instrument to transmittancecorresponding to 100 or absorbance is zero. Similarly, place the various standard concentrations ofiron solutions in the cuvette one by one and measure the corresponding absorbance. Also, measurethe absorbance of the unknown solution. Draw the calibration graph between the absorbance of thestandard solution and concentration. The concentration of the unknown solution is determined fromthe calibration graph.

RESULT:

Amount of iron present in the given solution = ______________ ppm.



λ = 480 nm Distilled water Blank = zero absorbance.

Sl. No. Concentration Absorbance

1 Blank 0

2 2ppm

3 4ppm

4 6ppm

5 8ppm

6 10ppm

7 Unknown

Spectrophotometer

Model graph



Viva-voce questions1. What is meant by ppm?2. State Beer-Lambert's law.3. What is absorbance?4. What is colorimeter?5. Mention the significance of colorimeter?6. What is the principle of colorimeter?7. What is the reaction condition for estimation of iron?8. Write the chemical reaction for the experiment.9. What is the colour of the ferric-thiocyanate during complex formation?10. What is the diagrammatic representation of principle of photocolorimeter?11. What are the steps to operate the photocolorimeter?12. What is the blank solution of the estimation of iron by photocolrimeter?13. What is meant by unknown solution?



SHORT PROCEDUREESTIMATION OF IRON BY USING PHOTOCOLORIMETRIC METHOD

Aim: To estimate the amount of Fe3+ ions present in the whole of the given solution usingphotocolorimetric method.

Principle: According to Beer-Lambert’s law, when a monochromatic light is passed through atransparent homogeneous solution, the intensity of transmitted light decreases exponentially with theconcentration and thickness of the solution.

It/Io = e-kCl

Where,

It = intensity of transmitted lightIo = intensity of incident lighte = base of neutral logarithmk = a constantC = concentrationl = thickness of the solution

Fe3+ ion alone does not give any colour in water solution. However, it develops a redcolour when it reacts with potassium thiocyanate solution in acid medium.

Fe3+ + 6KSCN → [Fe(SCN)6]3-+ 6K+

Red colour complex

Procedure:Standard iron solutions – 2 ppm, 4 ppm, 6 ppm, 8 ppm and 10 ppm

Standard iron solution + 1 ml of 1:1 HCl + 1 ml of potassium thiocyanate made upto 100 ml.

Model Table:λ= 480 nm.Distilled water Blank = zero absorbanceS.No Concentration Absorbance

1 2 ppm2 4 ppm3 6 ppm4 8 ppm5 10 ppm6 Unknown

Result: Amount of iron present in the given solution = ________ ppm.

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