CollegePractical Chemistry

[FOR F.Y. B.Sc.](As per the Revised Syllabus 2016)

H.N. PATEL, M.Sc., D.H.E. S.P. TURAKHIA, M.Sc., D.H.E.

Ex Principal & Head of Ex-Professor of Chemistry,Department of Chemistry, K.J. Somaiya College of

Sheth L.U.J. & Sir M.V. College of Science & Commerce,Arts, Science & Commerce, Vidyavihar (E), Mumbai - 77.Andheri (E), Mumbai - 69.

DR. S.S. KELKAR, M.Sc., Ph.D. DR. S.R. PUNIYANI, M.Sc., Ph.D.

Ex-Principal & Head of Head of Department of Chemistry,Department of Chemistry, K.C. College of Arts,

Vartak College of Arts, Science & Commerce, Science & Commerce,Vasai (W), Dist. Thane. Churchgate, Mumbai - 20.

DR. K.P. JAIN, M.Sc., Ph.D.

Head of Department of Chemistry,BNN College of Arts, Science and Commerce,

Bhiwandi, Dist. Thane.

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PREFACE TO THE TWENTY-NINTHREVISED EDITION

We are extremely pleased to place the twenty-ninth revised edition of F.Y. B.Sc. Chemistry PracticalsBook in the hands of the students of University of Mumbai from this academic year 2016-17.

It is a completely revised edition, keeping the objectives essentially the same as before. The principlesof each and every experiment have been explained clearly and in simple terms.

This syllabus is revised as per the Guidelines provided by University Grants Commission (UGC)and all the experiments are written accordingly. UGC has abolished Anlaytical Chemistry Section, hence,all the experiments are accomodated in conventional Physical, Inorganic and Organic Chemistry Sectionsfrom the academic year 2016-17.

As per the revised syllabus, analysis of semimicro qualitative mixture is to be carried out withoutusing H2S. Authors are of the opinion that classical method of qualitative analysis is of great importancefrom the learning point, as it gives the best correlation between theory and analytical practice. Once thebasic concepts are known to the students, then only the alternative method without using H2S can be tried.Hence, both the methods, i.e., original conventional and the revised as suggested by the syllabus committeeof Chemistry are given for the students for better and thorough understanding of semimicro qualitativeanalysis.

Characterisation of Organic Compounds is set in Semester II.

All the experiments in this edition are written as per the instructions given by Board of Studies inChemistry at the time of conducting workshops. We have tried our best to keep the tract while writingprocedure of all the experiments without deviating from the instructions of BOS.

However, Professors of a few colleges find it difficult to follow the procedure as prescribed in manyof the experiments on account of shortage of apparatus or the equipments available.

The model analysis of inorganic mixture has been retained to guide the students while writing theirjournals. Theory and experiment will help them to prepare themselves for viva voce.

We record our gratefulness to our colleagues in particular and all concerned in general, whoseconstructive criticism and suggestions have been very helpful.

Mumbai,June, 2016 — AUTHORS

SEMESTER-IPaper I

I. PHYSICAL CHEMISTRY

(l) To prepare 0.1 N succinic acid and standardise NaOH solution of two different concentrations.(2) To determine the rate constant for the hydrolysis of ester using HCl as a catalyst.(3) To determine enthalpy of dissolution of salt (like KNO3).

II. INORGANIC CHEMISTRY

(l) Commercial Analysis of (any two):(a) Mineral acid.(b) Organic acid.(c) Salt of weak acid and strong base.

(2) Titration using double indicators:Analysis of solution of Na2CO3 and NaHCO3.

Paper II

(3) Gravimetric Analysis:(a) To determine the percentage purity of sample of BaSO4 containing NH4Cl.(b) To determine the percentage purity of sample of ZnO containing ZnCO3.

III. ORGANIC CHEMISTRY

(1) Purification of any two organic compounds by recrystallisation, selecting suitable solvent.(provide 1 g). Learners are expected to report:(a) Solvent for recrystallisation.(b) Mass and the melting points of purified compound.Note:Learners should calibrate thermometer before determining melting point.

(2) Chromatography: (Any one):(a) Separation of a mixture of two sugars by ascending paper chromatography.(b) Separation of a mixture of o and p nitrophenols by thin layer chromatography (TLC).

SYLLABUS

SEMESTER-IIPaper I

I. PHYSICAL CHEMISTRY

(1) To determine the rate constant for the saponification reaction between ethyl acetate and NaOH.(2) To prepare various compositions of buffer solutions of different pH using sodium acetate and

acetic acid solutions and determine their pH values by using pH meter.(3) To determine concentration of given sample of KMnO4 by colorimetric method (learners are

expected to determine λmax) and plot calibration curve.(4) To standardise commercial sample of HCl using borax and to write material safety data (MSD)

of the chemicals involved.

II. INORGANIC CHEMISTRY

(1) Qualitative Analysis (at least 4 mixtures to be analysed):Semimicro Inorganic Qualitative Analysis of a sample containing two cations and two anions.Cations (from amongst):Pb2+, Ba2+, Ca2+, Sr2+, Cu2+, Cd2+, Fe2+, Ni2+, Mn2+, Mg2+, Al3+, Cr3+, K+, NH4

+.Anions (from amongst):CO3

2–, S2–, SO32–, SO4

2–, NO2–, NO3

–, PO43–, Cl–, Br–, I–.

Scheme of analysis should avoid use of sulphide ion in any form for precipitation/separation ofcations.

Paper II

(2) Redox Titration:To determine the percentage of copper (II) present in a given sample by titration against astandard aqueous solution of sodium thiosulphate (iodometry titration).

III. ORGANIC CHEMISTRY

(a) Characterisation of organic compound containing C, H, (O), N, S, X elements. (Minimum6 compounds).

CONTENTS

Semester-I(01) Chemical Kinetics 3 – 11

(1) To prepare 0.1 N succinic acid and standardise the NaOH solution, of two differentconcentrations.

(2) To determine the rate constant for the hydrolysis of an ester using HCl as acatalyst.

(3) To determine enthalpy of dissolution of salt (like KNO3).(02) Analysis of Commercial Samples 12 – 17

(1) To determine the strength of commercial sample of hydrochloric acid.(2) To determine the strength of acetic acid – an organic acid by titrimetric method.(3) To determine the strength of salt of weak acid and strong base.

(03) Titrimetry/Volumetric Analysis 18 – 23(1) To analyse the solution of Na2CO3 and NaHCO3 using double indicators.

(04) Gravimetric Analysis 24 – 27(1) To determine the percentage purity of sample of BaSO4 containing NH4Cl.(2) To determine the percentage purity of sample of ZnO containing ZnCO3.

(05) Purification of Organic Compounds by Recrystallisation 28 – 34(1) To crystallise the given organic compound. Find the weight and purity of crystals

by mixed melting point technique.(2) Find the purity of given compound by mixed melting point technique.(3) Calibration of a thermometer.

(06) Chromatography 35 – 39(1) Separation of a mixture of two sugars by ascending paper chromatography.(2) Separation of a mixture of o and p nitrophenols by thin layer chromatography

(TLC).

Semester-II(01) Chemical Kinetics 43 – 45

(1) To determine the rate constant for the saponification reaction between ethyl acetateand NaOH.

(02) pH metry 46 – 47

(1) To prepare various compositions of buffer solutions of different pH using sodiumacetate and acetic acid solutions and determine their pH values by using pH meter.

(03) Colorimetry 48 – 50(1) To determine the concentration of given sample of KMnO4 by colorimetric method.

(04) Analysis of Commercial Samples 51 – 55(1) To standardise commercial sample of HCl using borax and to write material safety

data (MSD) of the chemicals involved.(05) Semimicro Qualitative Analysis 56 – 82

(1) Semimicro Inorganic Qualitative Analysis of a sample containing two cations andtwo anions.

(06) Volumetric Analysis/Redox Titrations 83 – 88(1) To determine the percentage of copper (II) present in the given copper sulphate

solution by iodometric titration.(07) Characterisation of Organic Compound Containing

C, H, (O), N, S, X Elements 89 – 108(08) Aquaintance with Safety Measures in a Laboratory 109 – 111

APPENDICES 112 – 124(A) Standard Acids, Alkalies, Solvents and Indicators.

(B) Reagents and Chemicals required for Experiments and Estimations.

(C) Organic Reagents used in Semimicro Qualitative Analysis.

(D) Preparation of Important Reagents.

(E) Equivalent Weights of Important Compounds.

(F) Physical Constants of Different Liquids at Room Temperature.

(G) Chemical Reactions.

(H) Enthalphy of Solution of Electrolytes.

(I) Atomic Weights of Elements.

(J) Logarithmic Tables.

SEMESTER - I

3

1CHEMICAL KINETICS

Every chemical reaction takes place at a definite rate at the given experimental conditions. The mostimportant conditions are the concentrations (or pressures) of the reacting substances, temperature and thepresence of a catalyst.

Some chemical reactions are extremely fast whereas some are extremely slow. Between these twoextremes, there are many reactions which proceed at intermediate speed. It is possible to study the rates ofthese reactions at the different experimental conditions in the laboratory. A study of these reactions haslaid the foundation of chemical kinetics.

The rate of reaction:The rate of a chemical reaction is defined as the change in concentration of a reactant or a product

in an unit interval of time.

Experimental measurement of the reaction rates:(1) An increase in temperature increases the velocity of the reaction. Hence, kinetic studies of reactions

are carried out at constant temperature. In the laboratory, the temperature is maintained constant duringthe period of experiment by keeping the reaction mixture in a thermostat or a waterbath.

(2) If reaction can be stopped after a known interval by cooling, diluting or by addition of somereagent, then the change in concentration due to the reaction up to that time interval can be determined byany suitable method. The actual method used in finding the concentration changes with time dependsupon the nature of the reactants and the products.

A commonly used technique is to remove samples of reaction mixture at definite intervals, stop thereaction by cooling with the addition of ice and to analyse the sample by titration.

Order of reaction:The way in which the rate of a reaction varies with the concentration of reacting substances, is

generally indicated by the order of reaction. The number of molecules (or atoms) whose concentrations(or pressures) determine the rate of the reaction is called the order of reaction.

4 College Practical Chemistry (F.Y. B.Sc.)

Molecularity of the reaction:Another way of classification of chemical reactions is according to their molecularities. The

molecularity is the number of atoms or molecules taking part in each step leading to chemical reaction.Thus, the distinction is clear that the order of reaction applies to the experimental rate equation and

molecularity applies to the theoretical mechanism. In many cases, the order and molecularity of a reactionis same.

First order reactions:(1) In a first order reaction, the rate of reaction is directly proportional to the concentration of one

reactant.(2) The integrated rate equation for a first order reaction is given by:

102.303= aK log

t a x−

Where, K = specific reaction ratea = initial molar concentration of the reacting substance

a – x = amount of reactant remaining after time t(3) The specific reaction rate (K) has the dimensions of reciprocal time, i.e., time–1.(4) The half time, i.e., the time taken for the initial concentration of the reactant to be reduced to half

its value, is given by:

1/20.693

tK

=

Thus, the half time for a first order reaction is independent of the initial concentration.(5) Graphical determination of K:The graph of log10 (a – x) against t is a straight line.

Fig. 1.1

Second order reactions:The rate equation for second order reaction with equal initial concentration of the reactants is:

xK =

t a a x1

( ) × −

log 10

(a

– x)

t

Slope2 303

2 303 Slope

K.

K .

−=

∴ = ×

Chemical Kinetics 5

Determination of Order of Reaction:

Equifraction method (Half time method):(1) The reaction is carried out at different initial concentrations. Then, the time required for a definite

fraction of the reaction to take place is found out. It is usually the time required to complete half of thereaction. (However, any suitable fraction can be taken).

(2) For the first order reaction, it is given by:

1/ 20.693t

K=

Thus, it is independent of the initial concentration. It will take the same time to reduce the amount ofreactant from 1 mole to 0.5 mole as it will require to decrease the amount from 0.001 to 0.0005 mole in thesame volume. This is one of the most striking properties of the first order reaction.

(3) In the second order reaction in which a = b, (equal concentration of both reactants) the half timeis given by:

1/21

at

K=

i.e., half time is inversely proportional to the initial concentration.(4) In general, for an nth order reaction,

1/ 2 –11nt a

a

Starting with two different initial concentrations a1 and a2, if t1 and t2 are the corresponding halftimes or time for equal fraction for corresponding reactions, the order n of the reaction is given by:

10 1 10 2

10 2 10 1

log log1

log logt t

na a−

= +−

Graphical determination of order of reaction:(i) Starting with different initial concentrations a1 and a2, plot a graph of x (titre reading) against t

(time), for both the Sets on the same graph paper. (Fig. 1.2)(ii) Divide a1 (Set I) and a2 (Set II) by any convenient number. This gives two fractions say x1 and

x2 respectively. (See that x1 and x2 are chosen from the middle portion of the curves.)(iii) Determine the order of the reaction using the following equation:

( )( )

10 1 10 2

10 2 10 1

log log1

log logt t

nx x−

= +−

where, t1 and t2 are the time periods corresponding to the fractions x1 and x2 respectively.

6 College Practical Chemistry (F.Y. B.Sc.)

Fig. 1.2

Important points regarding kinetic experiments:

(1) Reaction mixture is prepared in the glass stoppered bottle. It should be kept in thewater bath till the completion of the experiment.

(2) Glass stopper should be placed back immediately after removing the required quantityof the reaction mixture with the help of the pipette.

(3) The conical flask should be shaken constantly throughout the titration.(4) Precautions should be taken to maintain specific time intervals as time factor is very

important.(5) Plot the graph with suitable scale. Show all the calculations systematically.

Experiment No. 1Aim: To prepare 0.1 N succinic acid and standardise the NaOH solution, of two different concentrations.Theory: A chemical readily available in pure form is a primary standard. It should not be either hygroscopicor efflorescent. It’s solution should be stable for a considerable period of time.

Succinic acid satisfies all these parameters, hence, can be used as a primary standard.Sodium hydroxide is hygroscopic and exact weighing is not possible. Hence, it is treated as a secondary

standard and is used in liquid/solution form. It is standardised against primary standard. Standardisationinvolves acid base reaction, where H+ ions of succinic acid react with OH– ions of NaOH.

2 2

2

2 2

CH COOH CH COONa| 2 NaOH | 2H OCH COOH CH COONa

+ → +

(2H+ + 2OH– → 2H2O)Requirements: 0.08 N and 0.1 N NaOH solutions, succinic acid solid (A.R.), 1% phenolphthalein indicator,100 cm3 standard measuring flask, burette, 10 cm3 and 25 cm3 pipettes, 100 cm3 beaker, 150 cm3 conicalflask etc.Procedure:

Preparation of standard succinic acid solution: Prepare 100 cm3 of 0.1 N succinic acid (0.590 gof succinic acid dissolved in 100 cm3 of distilled water) in a standard measuring flask.

a1

a2

t1 t2

Set I

Set II

x1 x2

Chemical Kinetics 7

(I) Standardisation of 0.08 N NaOH Solution:(1) Fill the burette with the supplied 0.08 N NaOH solution.(2) Pipette out 10 cm3 of 0.1 N succinic acid solution in a 150 cm3 conical flask. Add 2-3 drops of

1% phenolphthalein indicator to it. Shake well.(3) Titrate it gently against the supplied NaOH solution from the burette. End point will be from

colourless to pink colour. (x cm3)

(II) Standardisation of 0.1 N NaOH Solution:(1) Rinse the burette thoroughly with distilled water and then fill it up with the supplied 0.1 N

NaOH solution.(2) Pipette out 10 cm3 of 0.1 N succinic acid solution in a 150 cm3 conical flask. Add 2-3 drops of

1% phenolphthalein indicator to it. Shake well.(3) Titrate it gently against the supplied NaOH solution from the burette. End point will be from

colourless to pink colour. (y cm3).

Reaction:

(1) 2 2

2

2 2

CH COOH CH COONa| 2 NaOH | 2H OCH COOH CH COONa

+ → +

Observations and Calculations:

(I) Standardisation of the supplied 0.08 N NaOH solution:Succinic acid → NaOH

N1V1 = N2V2

0.1 × 10 = N2 × x

∴ N2 =0.1 10

x×

= A N.

(II) Standardisation of the supplied 0.1 N NaOH solution:Succinic acid → NaOH

N1V1 = N3V3

0.1 × 10 = N3 × y

∴ N3 =0.1 10

y×

= B N.

Results:(1) Normality of the supplied (0.08 N) NaOH solution = (A) = ___________ N.(2) Normality of the supplied (0.1 N) NaOH solution = (B) = ___________ N.

8 College Practical Chemistry (F.Y. B.Sc.)

Experiment No. 2

Aim: To determine the rate constant for the hydrolysis of an ester using HCl as a catalyst.Theory: The rate of hydrolysis of an ester (i.e., methyl acetate) is found to be directly proportional to theconcentration of H+ ions of the acid used as a catalyst.

Hydrolysis of methyl acetate takes place according to following reaction in the presence of H+ ion:

3 3 2 3 3(H )CH COOCH H O CH COOH CH OH

++ → +

Even though the reaction is bimolecular, due to large excess of water which also acts as a solvent,the kinetics of the reaction depends only on the concentration of methyl acetate. Hence, the reaction is offirst order. Such a reaction is called, pseudo unimolecular reaction.

The rate of reaction for such reaction can be calculated using the equation:

2.303= log aKa x−( )t where, a = initial concentration

x = amount reacted in given time t.In this reaction, the amount of acetic acid produced can easily be obtained by titrating the reaction

mixture with NaOH solution.The infinity reading: The titre reading [when hydrolysis is complete (T∝)] is obtained by taking the

reaction mixture (5 cm3 of methyl acetate + 100 cm3 of 0.1N HCl solution in a conical flask. The flask islightly corked and kept for 24 hours. Then 5 cm3 of the reaction mixture is titrated against standard 0.1NNaOH solution from the burette, using 2-3 drops of 1% phenolphthalein indicator. The titre reading iscalled T∝.Requirements: Glass stoppered bottles, water bath, burette, conical flask, pipette, 0.5N HCl solution,0.1N NaOH solution, methyl acetate, ice, 1% phenolphthalein indicator etc.

Procedure:(1) Take 100 cm3 of 0.5N HCl solution in one dry glass stoppered bottle.(2) Pipette out 5 cm3 of methyl acetate in another dry glass stoppered bottle.(3) Keep both the bottles in a water bath to attain room temperature.(4) Wash, rinse and fill the burette with 0.1N NaOH solution.(5) Keep one conical flask with a few ice pieces and 1 or 2 drops of 1% phenolphthalein indicator

in it ready.(6) At desired time, pour all the contents of the first bottle (i.e., HCl) in the second bottle (i.e.,

methyl acetate).(7) Shake the bottle for swift mixing and immediately pipette out 5 cm3 of the reaction mixture

and transfer it into the conical flask containing ice pieces and phenolphthalein indicator.(8) Carry out the titration rapidly with constant shaking till light pink colour is obtained. Record

this reading as zero reading (Tο).(9) Repeat the procedure at the time intervals of 10, 20, 30, 40 and 50 minutes. Record the readings

(Tt).

Chemical Kinetics 9

(10) Using the supplied value of T∝, calculate the values of a and (a – x).(11) With the supplied equation, calculate the values of specific reaction rate, K.(12) Plot the graph of log10 (a – x) against t and using the value of slope, find the value of K.

Observations and Calculations:a = (T∝ – To) = cm3 T∝ = cm3 (Given)

Time Titre reading x = (Tt – To ) (a – x) log (a – x) Kt Tt cm3 cm3 = (T∝ – Tt ) cm3 min–1

minutes

00 T0 zero1020

30

4050

∞ T∝ (Supplied)

Mean K = min–1

where, a = initial concentration of esterx = amount of ester reacted at time t (All in terms of 0.1N NaOH solution)(a – x) = amount of ester unreacted at time tTo = titration reading at zero time, i.e., when hydrolysis has not startedTt = titration reading at time tT∝ = titration reading when hydrolysis is completed.

K =2.303 log

( )a

t a – x

= [ ]2.303. log log( )a a xt

− −

= min–1.

Graph:Plot a graph of log (a – x) against t.

log

(a –

x)

t

b

a

c

Slope = abbc

Fig. 1.3

10 College Practical Chemistry (F.Y. B.Sc.)

The value of K is obtained from graph as:K = – 2.303 × Slope(Note: Slope has –ve value)

Results:(1) Value of rate constant:

(i) By calculation = min–1.(ii) By graph = min–1.

(2) The graph of log (a – x) against t is a straight line (with –ve slope) indicates that the reactionis of the first order.

Experiment No. 3

Aim: To determine enthalpy of dissolution of salt (like KNO3).Theory: The dissolution of certain salt in water takes place with the absorbance of energy, i.e., they areendothermic processes. Hence, there is the decrease in temperature during dissolution.

To measure the heat of solution ∆H(solution) for the solution of potassium nitrate in water, the reactioninvolved is:

KNO3(s) + H2O(aq) → K+(aq) + NO3

–(aq)

Requirements: Sensitive thermometer, 50 cm3 of 1M NaOH solution, 50 cm3 of 1M HCl solution, stirrer,calorimeter, solid KNO3 etc.

Procedure:(1) Take 100 cm3 of distilled water in a polythene bottle fitted with a sensitive thermometer in a

rubber cork.(2) Note down its constant temperature by taking 3 readings at an inteval of one minute (To).(3) Add exactly 10 g of KNO3 into it and immediately cork the polythene bottle.(4) Shake the bottle gently to dissolve KNO3 salt.(5) Measure the temperature of the solution.(6) Take readings at an interval of one minute (t1).(7) Note down the lowest temperature.

Observation Table:

Sr. Nos. Readings

Initial Final Minimum Temperature Difference in TemperatureTemperature after dissolution of KNO3 ∆ t = (T0 – Ts )of water (t0 ) (ts )

1

23

Mean Temperature t0 = _____ ºC ts = ______ ºC ∆t = ___ ºC.

Chemical Kinetics 11

Calculations:(1) Mass of distilled water = m = 100 g (density of water = 1 g/cm3)(2) Fall in temperature = ∆t = _____ ºC.(3) Specified heat of water = Cp = 4.18 Joules/g.(4) Heat of solution = Q = m × ∆t × Cp.(5) Molecular weight of KNO3 = 101.

∴ 10 g of KNO3 = 0.1 mole.

(6) Molar heat of solution = Heat of solution

moles of saltQ

moles

=

(Expected value of enthalpy of dissolution of KNO3 at 25ºC = 34.8 KJ/mole.)

Results:Enthalpy of dissolution of KNO3 = _____ KJ/mole.