15 0 0
SELECTED

Problems in

Chemistry



15 0 0
SELECTED

Problems in

Chemistry
Ranjeet Shahi

ARIHANT PRAKASHAN (Series), MEERUT


Arihant Prakashan (Series), Meerut
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PREFACE
This work is the result of my teaching the JEE aspirants over the post
decade and a half. Often I have found that the students mess up with
the chemical reactions given in the problem and get themselves
entangled into them. The reason is that they are not able to
distinguish the relationships between the various chemical principles

and concepts. This book is an effort to make them master the
fundamentals of Chemistry through problems-solving, and apply
them intelligently to arrive at a correct solution.
The problems included in the book with their solutions, aim to give
you the mastery required for solving the intricate problems asked in
the exams such as JEE.
Critical analysis of the situation is required whatever be format of the
questions. This book just gives emphasis on this, and it is hoped that it
will give a boost to all the meritorious and hard-wroking students.
I shall like to thank Mr Yogesh Chand Jain, Chairman, Arihant Group,
for bringing the book in this nice form.

Suggestions for further improvement of the book are welcome.

Ranjeet Shahi


CONTENTS
1. Mole Concept

3

2. Acid-Base Titration

7

3. Redox Titration

12


4. Gaseous State

16

5. Thermochemistry

20

6. Thermodynamics

26

7. Atomic Structure

33

8. Chemical Bonding

36

9. Chemical Equilibrium

39

10. Ionic Equilibrium

47

11. Electrochemistry


57

12. Chemical Kinetics

67

13. Colligative Properties

75

14. Solid State

78

15. Surface Chemistry

80

16. Reaction Mechanism

81

17. Stereochemistry

95

18. Hydrocarbons

103


19. Alkyl Halides

120

20. Alcohols and Ethers

133

21. Aldehydes and Ketones

161

22. Carboxylic Acids and Its Derivatives

193

23. Amines

213

24. Aromatic Compounds

216

25. Carbohydrates, Amino Acids and Polymers

264

26. Miscellaneous


265

27. Qualitative Analysis

271

28. Co-odination Compounds

278

29. Representative Elements

285

30. Metallurgy

292

Solutions

295




Problems in Chemistry

3

MOLE CONCEPT

PROBLEM 1 A crystalline hydrated salt on being rendered anhydrous, loses 45.6% of its weight. The
percentage composition of anhydrous salt is: Al = 10.5%, K = 15.1%, S = 24.8% and O = 49.6%. Find
the empirical formula of the anhydrous and crystalline salt.
PROBLEM 2 How much quantity of zinc will have to be reacted with excess of dilute HCl solution to
produce sufficient hydrogen gas for completely reacting with the oxygen obtained by decomposing
5.104 g of potassium chlorate?
PROBLEM 3 A 1.85 g sample of mixture of CuCl 2 and CuBr 2 was dissolved in water and mixed
thoroughly with 1.8 g portion of AgCl. After reaction, the solid which now contain AgCl and AgBr was
filtered, dried and weighed to be 2.052 g. What was the % by weight of CuBr 2 in the mixture?
PROBLEM 4 1.0 g of a sample containing NaCl, KCl and some inert impurity is dissolved in excess of
water and treated with excess of AgNO 3 solution. A 2.0 g precipitate of AgCl separate out. Also sample
is 23% by mass in sodium. Determine mass percentage of KCl in the sample.
PROBLEM 5 A one gram sample containing CaBr 2 , NaCl and some inert impurity was dissolved in
enough water and treated with excess of aqueous silver nitrate solution where a mixed precipitate of
AgCl and AgBr weighing 1.94 g was obtained. Precipitate was washed, dried and shaken with an
aqueous solution of NaBr where all AgCl was converted into AgBr. The new precipitate which contain
only AgBr now weighed to be 2.4 g. Determine mass percentage of CaBr 2 and NaCl in the original
sample.
PROBLEM 6 Sulphur combines with oxygen to form two oxide SO 2 and SO 3 . If 10 g of S is mixed with
12 g of O 2 , what mass of SO 2 and SO 3 will be formed, so that neither S nor oxygen will be left at the end
of reaction?
PROBLEM 7 An aqueous solution of ethanol has density 1.025 g/mL and it is 8.0 M. Determine
molality m of this solution.
PROBLEM 8 An aqueous solution of acetic acid has density 1.12 g/mL and it is 5.0 m. Determine
molarity (M).
PROBLEM 9 Octane is a component of gasoline. Incomplete combustion of octane produces some CO
along with CO 2 and H 2O, which reduces efficiency of engine. In a certain test run, 1.0 gallon of octane is
burned and total mass of CO, CO 2 and H 2O produced was found to be 11.53 kg. Calculate efficiency of
the engine, density of octane is 2.65 kg/gallon.
PROBLEM 10 The formula of a hydrated salt of barium is BaCl 2 ⋅ xH 2O. If 1.936 g of this compound

gives 1.846 g of anhydrous BaSO 4 upon treatment with H 2SO 4 , calculate x.
PROBLEM 11 A mixture of CuSO 4 ⋅ 5H 2O and MgSO 4 ⋅ 7H 2O was heated until all the water was
driven-off. If 5.0 g of mixture gave 3 g of anhydrous salts, what was the percentage by mass of
CuSO 4 ⋅ 5H 2O in the original mixture?
PROBLEM 12 A sample of clay contain 15% moisture, and rest are CaCO 3 and non-volatile SiO 2 . This
on heating loses part of its moisture, but CaCO 3 is completely converted into CaO. The partially dried


4

Problems in Chemistry

sample now contain 7.35% moisture and 51.5% SiO 2 . Determine mass percentage of CaCO 3 in the
original sample.

PROBLEM 13 Chlorine dioxide (ClO 2 ), has been used as a disinfectant in air conditioning systems. It
reacts with water according to the reaction:
ClO 2 + H 2O → HClO 3 + HCl
In an experiment, a 10.0 L sealed flask containing ClO 2 and some inert gas at 300 K and 1.0
atmosphere pressure is opened in a bath containing excess of water and all ClO 2 is reacted quantitatively.
The resulting solution required 200 mL 0.9 M NaOH solution for neutralization. Determine mole
fraction of ClO 2 in the flask.

PROBLEM 14 Potassium salt of benzoic acid (C 6 H 5COOK) can be made by the action of potassium
permanganate on toluene as follows:
C 6 H 5CH 3 + KMnO 4 → C 6 H 5COOK + MnO 2 + KOH + H 2O
If the yield of potassium benzoate can’t realistically be expected to be more than 71%, what is the
minimum number of grams of toluene needed to achieve this yield while producing 11.5 g of
C 6 H 5COOK?


PROBLEM 15 Manganese trifluoride can be prepared by the following reaction:
MnI 2 ( s) + F2 ( g ) → MnF3 + IF5
What is minimum number of grams of F2 that must be used to react with 12.0 g of MnI 2 if overall
yield of MnF3 is no more than 75%.
PROBLEM 16 A compound containing Ca, C, N and S was subjected to quantitative analysis and
formula mass determination. A 0.25 g of this compound was mixed with Na 2CO 3 to convert all Ca into
0.16 g CaCO 3 . A 0.115 g sample of compound was carried through a series of reactions until all its S was
changed into SO 2–
4 and precipitated as 0.344 g of BaSO 4 . A 0.712 g sample was processed to liberate all
of its N as NH 3 and 0.155 g NH 3 was obtained. The formula mass was found to be 156. Determine the
empirical and molecular formula of the compound.
PROBLEM 17 A 0.2 g sample, which is mixture of NaCl, NaBr and NaI was dissolved in water and
excess of AgNO 3 was added. The precipitate containing AgCl, AgBr and AgI was filtered, dried and
weighed to be 0.412 g. The solid was placed in water and treated with excess of NaBr, which converted
all AgCl into AgBr. The precipitate was then weighed to be 0.4881 g. It was then placed into water and
treated with excess of NaI, which converted all AgBr into AgI. The precipitate was then weighed to be
0.5868 g. What was the percentage of NaCl, NaBr and NaI in the original mixture.
PROBLEM 18 A mixture of NaI and NaCl when heated with H 2SO 4 produced same weight of Na 2SO 4
as that of original mixture. Calculate mass percentage of NaI in the original mixture.
PROBLEM 19 Ammonia is manufactured by the reaction of N 2 and H 2 . An equilibrium mixture
contains 5.0 g of each N 2 , H 2 and NH 3 . Calculate mass of N 2 and H 2 present initially and maximum
amount of NH 3 that can be produced.
PROBLEM 20 Consider the following reactions:
XeF2 + F2 → XeF6
and
XeF6 + —( CH 2 —CH 2—
) n → —( CF2 —CF2 —
) n + HF + XeF4
Determine mass of F2 ( g ) required for preparation of 1.0 kg fluorinated polymer.



5

Problems in Chemistry

PROBLEM 21 2.5 g of a sample containing Na 2CO 3 ; NaHCO 3 and some non-volatile impurity on
gentle heating loses 12% of its weight. Residue is dissolved in 100 mL water and its 10 mL portion
required 15 mL 0.1 M aqueous solution of BaCl 2 for complete precipitation of carbonates. Determine
mass percentage of Na 2CO 3 in the original sample.
PROBLEM 22 2.0 g of a sample containing NaCl, NaBr and some inert impurity is dissolved in enough
water and treated with excess of AgNO 3 solution. A 3.0 g of precipitate was formed. Precipitate on
shaking with aqueous NaBr gain 0.76 g of weight. Determine mass percentage of NaCl in the original
sample.
PROBLEM 23 Based on the following information, determine value of x and y:
AgNO3

(CH 3 ) x AlCl y → xCH 4 ( g ) + yCl – + Al 3+ → AgCl( s)
0.643 g

0.222 g

0.996 g

PROBLEM 24 An organic compound containing C, H, O, N and Cl was analyzed and 0.15 g of sample
on combustion produced 0.138 g of CO 2 and 0.0566 g of H 2O. All the nitrogen in different 2.0 g sample
of compound was converted into NH 3 which was found to weigh 0.238 g. Finally the chlorine in a 0.125
g sample of compound was converted to Cl – and by reacting with AgNO 3 , 0.251 g AgCl was obtained.
Deduce the empirical formula of the starting organic compound.
PROBLEM 25 A 5.0 g sample of felspar containing Na 2O, K 2O and some inert impurity is dissolved in
dilute HCl solution and NaCl and KCl formed are separated by fractional crystallization. During

crystallization some less soluble impurities also comes out. Mass of NaCl, KCl and impurity
accompanying these salts was found to be 6.47 g. Solid crystal was then re-dissolved and required 300
mL of 0.3 M AgNO 3 for complete precipitation of chlorides. The precipitate thus, obtained was found to
contain 4.23% insoluble impurity. Determine mass percentage of Na 2O and K 2O in the original sample.
PROBLEM 26 Potassium chlorate (KClO 4 ) is made in the following sequence of reactions:
Cl 2 ( g ) + KOH → KCl + KClO + H 2O
KClO → KCl + KClO 3
KClO 3 → KClO 4 + KCl
What mass of Cl 2 is needed to produce 1.0 kg of KClO 4 ?
PROBLEM 27 Titanium oxide (TiO 2 ) is heated in stream of hydrogen to give water and a new oxide
Ti x O y . If 1.598 g TiO 2 produces 1.438 g Ti x O y , what is the formula of new oxide.
PROBLEM 28 A solution of copper sulphate that contain 15% CuSO 4 by weight has a density of 1.169
g/mL. 25 mL portion of this solution was reacted with excess of ammonia solution to form a dark blue
solution. When cooled, filtered and dried, 6.127 g of dark blue solid was obtained. A 0.195g solid was
analyzed for ammonia and required 30.63 mL of 0.1036 M HCl solution to reach the equivalence point.
In a separate analysis, 0.200 g was heated at 110°C to drive off water, producing 0.185 g of anhydrous
material. Deduce formula of the compound crystallized out from blue solution assuming that it contain
only one copper atom per formula unit. Also determine the percentage yield of crystallization process.
PROBLEM 29 0.1152 g of a compound containing carbon, hydrogen, nitrogen and oxygen are burned in
oxygen. The gases produced are treated further to convert nitrogen containing product into N 2 . The
resulting mixture of CO 2 , H 2O and N 2 is passed through a CaCl 2 drying tube, which gains 0.09912 g.
The gas stream was then bubbled through water where the CO 2 forms H 2CO 3 . Titration of this solution
required 28.8 ml 0.3283 M NaOH solution to reach the phenolphthalein end point. The excess O 2 was


6

Problems in Chemistry

removed by reaction with copper metal and the N 2 was collected in a 225 mL measuring bulb where it

exerted a pressure of 65.12 mm of Hg at 25°C. In a separate analysis, the molar mass of this compound
was found to be 146 g mol –1 . Deduce molecular formula of the starting compound.

PROBLEM 30 Pb(NO 3 ) 2 and KI reacts in aqueous solution to form an yellow precipitate of PbI 2 . In
one series of experiments, the masses of two reactants varied, but the total mass of the two was held
constant at 5.0 g. What maximum mass of PbI 2 can be produced in the above experiment ?
PROBLEM 31 An element X react with hydrogen leading to formation of a class of compounds that is
analogous to hydrocarbons. 5 g of X forms 5.628 g of a mixture of two compounds of X, XH 4 and X 2 H 6
in the molar ratio of 2 : 1. Determine molar mass of X.
PROBLEM 32 The mineral Argyrodite is a stoichiometric compound that contain silver, sulphur (– 2)
and an unknown element Y ( + 4). The mass-ratio of silver and Y in the compound is,
m( Ag) : m(Y ) = 11.88
Y forms a reddish brown lower sulphide on heating the mineral in stream of H 2 ( g ), in which Y is in
+ 2 state. The residue are Ag 2S and H 2S. To convert 10 g Argyrodite completely, 0.295 L of H 2 ( g )
measured at 400K and 1.0 atmosphere is required. Determine molar mass of Y and empirical formula of
mineral.

PROBLEM 33 Uranium is isolated from its ore by dissolving it as UO 2 (NO 3 ) 2 and separating it as
solid UO 2 (C 2O 4 ) ⋅xH 2O. A 1.0 g sample of ore on treatment with nitric acid yielded 1.48 g UO 2 (NO 3 ) 2
which on further treatment with 0.4 g Na 2C 2O 4 yielded 1.23 g UO 2 (C 2O 4 ) ⋅ xH 2O. Determine weight
percentage of uranium in the original sample and x.
PROBLEM 34 When iodine was added to liquid chlorine in cold condition, orange crystal of a
compound separate out. The amount of chlorine in a sample of crystal was determined by precipitating
AgCl. A 0.467 g sample of crystal gave 0.861 g of AgCl. Deduce empirical formula of the crystal.
PROBLEM 35 Urea is manufactured on large scale by passing CO 2 (g ) through ammonia solution
followed by crystallization. CO 2 for the above reaction is prepared by combustion of hydrocarbons. If
combustion of 236 kg of a saturated hydrocarbon produces as much CO 2 as required for production of
1000 kg of urea, deduce molecular formula of hydrocarbon.
PROBLEM 36 Sodium bicarbonate can be purified by dissolving it in hot water (at 60°C), filtering to
remove insoluble impurities, cooling to 0°C to precipitate solid NaHCO 3 and the filtering to remove the

solid leaving soluble impurities in solution. Some NaHCO 3 that remain in solution is not recovered. The
solubility of NaHCO 3 in water at 60°C is 164 g/L. Its solubility in cold water at 0ºC is 69 g/L. If a 250 g
impure sample of NaHCO 3 was purified by this method by dissolving first in 250 mL water at 60°C and
then crystallizing NaHCO 3 from 100 mL water at 0°C, 150 g NaHCO 3 was recovered. Determine
percentage purity of original sample.
PROBLEM 37 A 100 g solution was prepared by dissolving 46 g CuSO 4⋅xH 2O in 54 g of water and
mole fraction of CuSO 4 in solution was found to be 0.05. Determine x.
PROBLEM 38 An ore of iron contain FeS and non-volatile impurity. Roasting of this ore converts all
FeS into Fe 2 O3 and a 4% loss in weight was observed. Determine mass percentage of FeS in ore.
PROBLEM 39 Optical measurement is a very efficient method of determining molar mass of unknown
material. In one experiment, 3.0 g of an unknown polymeric material was dissolved in 100 mL of CCl 4
and transmittance of this solution was found to be 72%. Transmittance of a 0.001 M standard solution in


7

Problems in Chemistry

the same solvent, under identical experimental condition was 60%. Determine molar mass of unknown
polymer.

PROBLEM 40
shown below,

A crystalline polymer molecule is uniform prismatic in shape with dimensions as

300 Å
100Å

If density of this polymer is 1.2 g/cm 3 , determine molar mass.


PROBLEM 41 A mother cell disintegrate into sixty identical cells and each daughter cell further
disintegrate into 24 smaller cells. The smallest cells are uniform cylindrical in shape with diameter of
120 Å and each cell is 6000 Å long. Determine molar mass of the mother cell if density of the smallest
cell is 1.12 g/cm 3 .
PROBLEM 42 A sample of rock taken for analysis weigh 1.0 g on air dried basis. After drying for one
hour at 110°C, the sample weigh 0.9437 g. The calcium is precipitated as oxalate but weighed as CaSO 4 ;
that weigh 0.5g. The magnesium is precipitated as MgNH 4 PO4 which finally ignited to 0.5 g Mg 2 P2O 7 .
Find the percentage of CaO and MgO on oven dried basis and percentage of them and H 2O on air dried
basis.
PROBLEM 43 A sample is a mixture of Mohr’s salt and (NH 4 ) 2 SO 4 . A 0.5 g sample on treatment with
excess of BaCl 2 solution gave 0.75 g BaSO 4 . Determine percentage composition of the salt mixture.
What weight of Fe 2O 3 would be obtained if 0.2 g of the sample were ignited in air?
PROBLEM 44 A chloride mixture is prepared by grinding together pure BaCl 2⋅2H 2O, KCl and NaCl.
What is the smallest and largest volume of 0.15 M AgNO 3 solution that may be used for complete
precipitation of chloride from a 0.3g sample of the mixture which may contain any one or all of the
constituents?

ACID-BASE TITRATION
PROBLEM 45 A 1.5 g sample containing oxalic acid and some inert impurity was dissolved in enough
water and volume made up to 250 mL. A 20 mL portion of this solution was then mixed with 30 mL of an
alkali solution. The resulting solution was then treated with stoichiometric amount of CaCl 2 just needed
for precipitation of oxalate as CaC 2O 4 . Solution was filtered off and filtrate was finally titrated against
0.1 M HCl solution. 8.0 mL of acid was required to reach the equivalence point. At last, the above neutral
solution was treated with excess of AgNO 3 solution and AgCl obtained was washed, dried and weighed
to be 0.4305 g. Determine mass percentage of oxalic acid in the original sample.
PROBLEM 46 A 1.5 g sample containing P2O 3 and some inert impurity was dissolved in enough water
and boiled gently where P2O 3 disproportionated quantitatively into PH 3 and H 3 PO 4 . The solution was



8

Problems in Chemistry

further boiled for some time to let-off all PH 3 ( g ) and finally cooled to room temperature and diluted to
100 mL. A 10 mL portion of this solution was then mixed with 20 mL 0.3 M NaOH solution. Excess
alkali required 11.0 mL 0.05 M H 2SO 4 solution for back titration. Determine mass percentage of P2O 3 in
the original sample.

PROBLEM 47 2.5 g of a mixture containing CaCO 3 , Ca(HCO 3 ) 2 and NaCl was dissolved in 100 mL
water and its 10 mL portion required 10 mL 0.05 M H 2SO 4 solution to reach the phenolphthalein end
point. An another 10 mL portion of the same stock solution required 32.35 mL of the same acid solution
to reach the methyl orange end point. Determine mass percentage of CaCO 3 and Ca(HCO 3 ) 2 in the
original mixture.
PROBLEM 48 A solution contain both Na 2CO 3 and NaHCO 3 . 10 mL portion of this solution is mixed
with few drops of phenolphthalein indicator and titrated against 0.08 M H 2SO 4 solution. 7.0 mL of acid
was required to reach the end point A 5.0 mL portion of this solution was then taken for further analysis
and a few drops of methyl orange was added to it and finally titrated against same acid solution. 3.53 mL
of acid was required to reach the end point. Determine mass of Na 2CO 3 and NaHCO 3 per litre of
solution. Ignore volume change due to addition of indicator.
PROBLEM 49 A mixture was known to contain both KNO 3 and K 2SO 3 . To 0.486 g of the mixture,
dissolved in enough water to give 50 mL solution, was added 50 mL of 0.15 M HCl solution. The
reaction mixture was heated to expel all SO 2 and then 25 mL of the reaction mixture was titrated with 0.1
M KOH. The titration required 13.11 mL of the base. Calculate mass percentage of K 2SO 3 in the
mixture.
PROBLEM 50 An amino acid isolated from a piece of animal tissue was believed to be glycine. A 0.05 g
sample was treated in such a way that all nitrogen in it was converted into ammonia. This ammonia was
added to 50 mL of 0.05 M HCl solution. The excess acid remaining in the solution required 30.57 mL
0.06 M NaOH solution for complete neutralization. What was the percentage by mass of nitrogen? How
does this mass compare with percentage mass of nitrogen calculated from glycine (H 2 NCH 2COOH)?

PROBLEM 51 In a reaction, calcium orthophosphate on heating with magnesium produced calcium
phosphide, magnesium metaphosphate, calcium oxide and oxygen gas. Phosphide on hydrolysis
produces PH 3 gas. The PH 3 gas is burnt completely to P2O 5 using air, which contains 21%, by volume
of oxygen. Calculate the volume of air at STP required for combustion, if 2.4 g Mg was initially reacted
with calcium orthophosphate. All volumes are measured at STP.
PROBLEM 52 9.3 g of a mixture containing Li 2CO 3 , NaHCO 3 , Na 2CO 3 on strong heating produced
7.37 g of solid residue. The residue is dissolved in 200 mL water.
A 10 mL portion of this solution is mixed with 15 mL of a normal HCl solution. The excess acid
required 12 mL 0.5 N NaOH solution to reach the equivalence point. Determine the mass percentage of
NaHCO 3 and Na 2CO 3 in the original mixture. Li = 7, Na = 23.
PROBLEM 53 4.0 g of a monobasic, saturated carboxylic acid is dissolved in 100 mL water and its 10
mL portion required 8.0 mL 0.27 M NaOH to reach the equivalence point. In an another experiment, 5.0
g of the same acid is burnt completely and CO 2 produced is absorbed completely in 500 mL of a 2.0 N
NaOH solution. A 10 mL portion of the resulting solution is treated with excess of BaCl 2 to precipitate
all carbonate and finally titrated with 0.5 N H 2SO 4 solution. Determine the volume of the acid solution
that would be required to make this solution neutral.
PROBLEM 54 5.0 g of a mixture containing NaHCO 3 , NaCl and Na 2CO 3 is dissolved in 500 mL water
and its 10 mL portion required 12.4 mL 0.1 M HCl solution to reach the equivalence point. In an another


Problems in Chemistry

9

experiment, 10 mL portion of the same stock solution is mixed with 10 mL 0.15 M NaOH solution.
Excess NaOH required 12.6 mL 0.1 M HCl solution for back titration. Determine the mass percentage of
each component in the original mixture.

PROBLEM 55 6.4 g of a pure monobasic organic acid is burnt completely in excess of oxygen and CO 2
evolved is absorbed completely in one litre of an aqueous solution of NaOH. A 10 mL portion of this

solution required 14.5 mL of a normal HCl solution to reach the phenolphthalein end point. An another
10 mL portion of the same solution required 18 mL of the same HCl solution to reach the methyl orange
end point. If the organic acid contains 25% oxygen by weight, deduce the empirical formula of this acid
and strength of original NaOH solution.
PROBLEM 56 A complex of cobalt with ammonia is analyzed for determining its formula, by titrating it
against a standardized acid as follows:
Co(NH 3 ) x Cl 3 ( aq ) + HCl → NH +4 ( aq ) + Co 3+ ( aq ) + Cl – ( aq )
A 1.58 g complex required 23.63 mL 1.5 M HCl to reach the equivalence point. Determine formula.
If the reaction mixture at equivalence point is treated with excess of AgNO 3 solution, what mass of AgCl
will precipitate out?

PROBLEM 57 One litre solution of alkali is prepared by dissolving impure solid of alkali which contain
5% Na 2CO 3 and 8% CaCO 3 and 10% NaCl. A 10 mL portion of this solution required 9.8 mL of a 0.5 M
H 2SO 4 solution for neutralization. Calculate weight of alkali dissolved initially.
PROBLEM 58 40 g of a sample of caustic soda containing NaOH, Na 2CO 3 and inert impurity is
dissolved in water to prepare 1.0 litre solution. A 25 mL portion of this solution required 23.15 mL 1.022
N HCl for complete neutralization. To 25 mL another solution, excess of BaCl 2 is added, and resulting
solution required 22.55 mL HCl of same strength to reach the end point. Calculate mass percentage of
NaOH and Na 2CO 3 in the original sample.
PROBLEM 59 1.5 g of a sample containing Na 2CO 3 and NaHCO 3 is dissolved in 100 mL of water. A
25 mL portion of this solution required 22.45 mL 0.202 N HCl using methyl orange as indicator. In a
separate analysis, 25 mL portion of the same stock solution is mixed with 30 mL 0.204 N NaOH and then
excess of BaCl 2 is added resulting in precipitation of all carbonate as BaCO 3 . Filtrate required 9.98 mL
HCl of same strength. Calculate mass percentage of Na 2CO 3 and NaHCO 3 in the mixture.
PROBLEM 60 One gram sample of a saturated hydrocarbon is burned completely and liberated CO 2
was absorbed in a 1.0 L 0.2 N NaOH solution. To the resulting solution, excess of BaCl 2 crystals was
added and the solution was filtered off to free from BaCO 3 . A 10 mL portion of the extract required 12
mL 0.025 M H 2SO 4 solution for neutralization. Determine molecular formula of the hydrocarbon.
PROBLEM 61 2.0 g of a saturated, monobasic carboxylic acid was burned and liberated CO 2 was passed
through a concentrated solution of NaOH. The resulting solution was separated into two equal half and

analyzed. One half required 71.72 mL 1.0 N HCl to reach the end point in presence of phenolphthalein
indicator. The other half required 123.44 mL 1.0 N HCl to reach the end point in presence of methyl
orange indicator. Deduce formula of acid and determine mass of NaOH present initially.
PROBLEM 62 2.5 g of a mixture containing NaHCO 3 , Na 2CO 3 and NaCl is dissolved in 100 mL water
and its 50 mL portion required 13.33 mL 1.0 N HCl solution to reach the equivalence point. On the other
hand its other 50 mL portion required 19 mL 0.25 M NaOH solution to reach the equivalence point.
Determine mass percentage of each component.


10

Problems in Chemistry

PROBLEM 63 2.0 g of a crystal of CaCO 3 is dissolved in 50 mL water and then mixed with 50 mL of a
HCl solution. The resulting solution is boiled to remove all CO 2 and its 10 mL portion required 8.0 mL of
a NaOH solution to make the solution neutral. Also 20 mL of original HCl solution is equivalent to 96
mL of NaOH solution. Determine molarity of both NaOH and HCl solution.
PROBLEM 64 2.725 g of a mixture of K 2C 2O 4 , KHC 2O 4 and H 2C 2O 4 ⋅ 2H 2O is dissolved in 100 mL
H 2O and its 10 mL portion is titrated with 0.1 N HCl solution.
20 mL acid was required to reach the equivalence point. In another experiment, 10 mL portion of the
same stock solution is titrated with 0.1 N KOH solution. 20 mL of base was required to reach the
equivalence point. Determine mass percentage of each component in the mixture.
PROBLEM 65 A 1.0 g sample containing NH 4 NO 3 , (NH 4 ) 3 PO 4 and some inert impurity was
dissolved in 100 mL water its 10 mL portion required 15 mL 0.1 M NaOH solution to reach the
equivalence point. In a separate experiment, 10 mL of the same stock solution was treated with excess of
BaCl 2 solution and 0.077 g of barium phosphate precipitate was obtained. Determine mass percentage of
ammonium nitrate in the original sample.
PROBLEM 66 10.38 mg of a diprotic acid (containing (C, H and O) is burned completely and all CO 2
was absorbed in 100 mL of alkali solution. The resulting solution is separated into two-half and one-half
required 55 mL 0.005 M H 2SO 4 solution to reach the phenolphthalein end point. Other half was titrated

in presence of methyl orange indicator and 80 mL H 2SO 4 solution of same strength was required to
reach the end point. In a separate analysis, 0.168 g of the same acid required 16.18 mL 0.125 M NaOH
solution to reach the end point. Deduce formula of the acid and determine molarity of alkali solution used
initially.
PROBLEM 67 A 3.0 g sample containing Na 2CO 3 , NaHCO 3 , NaCl and some inert impurity was
dissolved in 100 mL of water and its 10 mL portion was titrated against 0.1 M HCl solution using
phenolphthalein indicator. 11.32 mL of acid solution was required to reach the end point. The resulting
solution was then mixed with excess of AgNO 3 solution resulting in formation of 0.306 g of AgCl
precipitate. The solution was filtered-off and filtrate was again titrated, but now against 0.05 M NaOH
solution. 42.64 mL of alkali was required to reach the end point. Determine mass percentage of Na 2CO 3 ,
NaHCO 3 and NaCl in the original sample.
PROBLEM 68 In neutralization titration of Na 3 PO 4 , if phenolphthalein is used as indicator, end point is
indicated only when Na 3 PO 4 is converted into Na 2 HPO 4 while, if methyl orange is used as indicator,
end point appear only when Na 3 PO 4 is converted into H 3 PO 4 . In an experiment a 4.0 g mixture
containing Na 3 PO 4 , Na 2 HPO 4 and NaH 2 PO 4 is dissolved in 50 mL water and its 10 mL portion
required 24.4 mL 0.1 M HCl solution to reach the end point using phenolphthalein indicator. In a
separate analysis, 10 mL portion of the same stock solution required 23.572 mL 0.5 M HCl solution to
reach the end point using methyl orange as indicator. Determine mass percentage of all components in
the mixture.
PROBLEM 69 A mixture containing LiHCO 3 , NaCl and Na 2CO 3 on gentle heating loses 26.5% of its
weight. 5.0 g of this mixture was heated gently and residue was dissolved in 100 mL water. A 10 mL
portion of this solution was then treated with 20 mL 0.2 M H 2SO 4 solution. A 10 mL portion of the
resulting solution required 3.86 mL 0.1 M NaOH solution to reach the end point. Determine mass
percentage of each component in the mixture.
PROBLEM 70 A mixture containing LiHCO 3 , NaHCO 3 and CaCO 3 on gentle heating loses 48.4% of
its weight. In an experiment, 5.0 g of this mixture was dissolved in 100 mL water and its 10 mL portion
was treated with 10 mL 0.5 M NaOH solution. The resulting solution was then treated with excess of


Problems in Chemistry


11

BaCl 2 solution resulting in precipitation of all carbonates as BaCO 3 . Precipitate was separated out by
filtration and filtrate required 15.3 mL 0.1 N HCl solution to reach the end point. Determine mass
percentage of all components present in the mixture.

PROBLEM 71 5.0 g of a mixture containing NaCl, NaHCO 3 , Na 2CO 3 and CaCO 3 on gentle heating
reduces to 4.25 g of solid residue. In a separate experiment, 1.0 g of the same mixture required 10 mL 0.2
M NaOH to reach the end point. In a 3rd experiment, 1.0 g of the same mixture was dissolved in 100 mL
water and required 10 mL 1.053 M HCl solution to reach the end point. Determine mass percentage of
each component in the mixture.
PROBLEM 72 2.0 g of a sample of CaCO 3 , NaHCO 3 and some volatile, inert impurity, was heated
strongly where CaCO 3 and NaHCO 3 , were decomposed into CaO and Na 2CO 3 respectively and all CO 2
gas produced in decomposition was absorbed in a 50 mL NaOH solution. NaOH was little less than the
stoichiometric requirement therefore, CO 2 during reaction with NaOH, produced Na 2CO 3 and some
NaHCO 3 . The resulting solution was titrated first in presence of phenolphthalein indicator and 5.0 mL
1.0 M HCl was required to reach the phenolphthalein end point. Methyl orange was then added and
titration continued with HCl of same strength where 15 mL HCl was required to reach the final end point.
On the other hand, the residue obtained after heating of the original sample was dissolved in water
and treated with excess of BaCl 2 , giving 0.985 g of BaCO 3 precipitate. Determine mass percentage of
CaCO 3 and NaHCO 3 in the original sample.
PROBLEM 73 A one gram sample containing NaOH as the only basic substance and some inert
impurity was left exposed to atmosphere for a very long time so that part of NaOH got converted into
Na 2CO 3 by absorbing CO 2 from atmosphere. The resulting sample was dissolved in water and volume
made upto 100 mL. A 100 mL portion of this solution required 16 mL 0.25 M HCl solution to reach the
equivalence point when methyl orange was used as indicator. In a separate analysis, 20 mL portion of the
same solution was taken alongwith phenolphthalein indicator and mixed with 50 mL of 0.1 M HCl
solution. An additional 9.00 mL 0.1 M Ba(OH) 2 solution was required to just restore the pink colour of
solution. Determine mass percentage of NaOH in the original sample and mass percentage of Na 2CO 3 in

the sample after exposure to atmosphere.
PROBLEM 74 The monochloroacetic acid (ClCH 2COOH) preservative in a 100 mL of carbonated
beverage was extracted by shaking with dimethyl ether and then returned to aqueous solution as
ClCH 2COO – by extraction with 1.0 M NaOH. This solution was acidified and treated with 50 mL
0.0452 M AgNO 3 solution where the following reaction occurred:
ClCH 2COOH + AgNO 3 + H 2O → HOCH 2COOH + H + + NO –3 + AgCl( s)
After filtering the AgCl, titration of filtrate required 10.43 mL of an NH 4SCN solution. Titration of a
blank taken through the entire procedure used 22.98 mL of same NH 4SCN solution. Calculate weight in
mg, of ClCH 2COOH in the beverage sample.
PROBLEM 75 2.0 g of a sample containing sodium oxalate, oxalic acid dihydrate and some inert
impurity was dissolved in 100 mL water and its 20 mL portion required 23.34 mL 0.04 M acidified
permanganate solution to reach the equivalence point. In a separate analysis, 20 mL portion of the same
stock solution required 26.67 mL 0.1 N NaOH solution to reach the end point. Determine mass
percentage of Na 2C 2O 4 and H 2C 2O 4⋅2H 2O in the original sample.
PROBLEM 76 A 1.5 g sample containing (NH 4 ) 2 SO 4 , NH 4 NO 3 and some inert impurity was
dissolved in water and volume made upto 100 mL. A 20 mL portion of this solution was mixed with 50
mL 0.1 M NaOH solution. A 30 mL aliquot of this resulting solution required 9.00 mL 1/28 M H 2SO 4
solution for complete neutralization. In a separate analysis, 32 mL of the original stock solution on


12

Problems in Chemistry

treatment with excess of BaCl 2 solution produced 0.466 g BaSO 4 precipitate. Determine mass
percentage of NH 4 NO 3 and (NH 4 ) 2 SO 4 in the original sample.

PROBLEM 77 A 1.0 g impure sample containing [Zn(NH 4 ) 4 ]Cl 2 and some inert impurity was treated
with 15 mL of 1 M NaOH solution where all complex is converted into Na 2 [Zn(OH) 4 ] . The excess base
1

required 10 mL M HCl solution for back titration.
6
(a) Determine percentage purity.
(b) If the last solution obtained after neutralization was treated with excess of AgNO 3 , what weight
of AgCl would have been produced?
PROBLEM 78 1.2 g of a salt with their empirical formula K x H y (C 2O 4 ) z was dissolved in 50 mL of
water and its 10 mL portion required 11.00 mL of a 0.1 M HCl solution to reach the equivalence point. In
a separate analysis, 15 mL of the stock solution required 20 mL 0.2475 M KOH to reach the equivalence
point. Determine empirical formula of the salt.
PROBLEM 79 Impure phosphoric acid for use in the manufacture of fertilizer is produced by the
reaction of sulphuric acid on phosphate rock of which a principal component is Ca 3 (PO 4 ) 2 and rest are
silica and other inert impurity. In an analysis, 2.0 g of a sample of rock salt was dissolved in 100 mL
H 2SO 4 solution. Excess sulphuric acid left in 20 mL of this solution required 40 mL 0.02 M NaOH for
back titration. In a separate analysis 20 mL of the above solution required 50 mL 0.04 M NaOH for
complete neutralization. Determine mass percentage of Ca 3 (PO 4 ) 2 in rock-sample.
PROBLEM 80 A 10 g sample of ammonium perchlorate containing some inert impurity was mixed
with 3 g Al powder where all perchlorate reacted to produce Al 2O 3 , N 2 , HCl and H 2O. All HCl was
absorbed in 100 mL 1 M NaOH solution. Determine percentage purity of perchlorate sample and volume
of 0.5 M HCl required to neutralize the above solution.
PROBLEM 81 Potassium superoxide (KO 2 ) is utilized in closed system breathing apparatus to remove
CO 2 and water from exhaled air. The removal of H 2O generate oxygen gas and KOH and this KOH in the
subsequent step remove CO 2 as KHCO 3 . 5.0 kg of an impure sample of KO 2 is just sufficient to remove
all CO 2 and H 2O from a closed room of dimension 10 m × 5 m × 3m. Determine mass of this KO 2
required to neutralize a 100 mL 0.1 M H 2SO 4 solution in a separate analysis. Assume room conditions to
be at 1.0 atmosphere and 300 K and mole fraction of CO 2 in that room is 0.01.
PROBLEM 82 3.25 g of a saturated, tribasic carboxylic acid required 68.4 mL of a 0.750 M NaOH
solution to reach the equivalence point. Determine molecular formula of acid.

REDOX TITRATION
PROBLEM 83


A sample of chrome-vanadium steel weighing 2.0 g was dissolved in a mixture of

sulphuric acid and just sufficient oxidant was added to raise the oxidation state of iron to Fe 3+ , the
chromium to Cr 2O 72– , vanadium to VO –3 and Mn to MnO –4 . The solution was then treated with HCl and
–
resulting solution still containing Fe 3+ , Cr 2O 2–
7 and VO 3 then treated with 25 mL of 0.101 M FeSO 4 .
This resulted in reduction of dichromate and VO –3 to Cr 3+ and VO 2+ in the solution respectively. Fe 2+
and VO 2+ in the solution was then titrated with 0.02236 M KMnO 4 and required 12.6 mL to reach the


13

Problems in Chemistry

equivalence point. A small amount of Fe 2+ was then added to again reduce the VO –3 produced by
KMnO 4 back to VO 2+ and this then titrated directly with 0.02236 M KMnO 4 , a process requiring 0.86
mL to reach the equivalence point. Calculate the following quantities:
(a) Moles of Fe 2+ in 25 mL sample of standard FeSO 4 solution.
(b) Moles of Fe 2+ titrated with 12.6 mL of standard KMnO 4 .
(c) Moles of Fe 2+ consumed by Cr 2O 2–
7 .
(d) Percentage of V and Cr in the steel
[Atomic weight of V = 51, Cr = 52]

PROBLEM 84 A sample of crude uranium oxide is known to be contaminated with iron. To determine
the extent of contamination, the crude oxide were dissolved and reduced with Zn to yield a solution
containing U 4+ and Fe 2+ . A 20 mL aliquot of this solution was treated with cupferron which precipitated
all uranium and the resulting precipitate on ignition yielded 423.3 mg of U 3O 8 . A further 20 mL sample

was treated with 0.024 M KMnO 4 solution and consumed 27.23 mL. Calculate mass percentage of
contamination if the iron were present as Fe 2O 3 in a sample of crude oxide containing 100 g of U 3O 8 .
KMnO 4 solution oxidised Fe 2+ to Fe 3+ and U 4+ to UO 2+
2 . Atomic mass of U = 238.
PROBLEM 85 A 5.0 g sample containing Pb 3O 4 , PbO 2 and some inert impurity is dissolved in 250 mL
dil. HNO 3 solution and 2.7 g of Na 2C 2O 4 was added so that all lead converted into Pb 2+ . A 10 mL
portion of this solution required 8.0 mL 0.02 M KMnO 4 for titration of excess of oxalate. In an another
experiment, 25 mL of solution was taken and excess oxalate was removed by extraction, this required 10
mL of a permanganate solution for oxidation of Pb 2+ to Pb 4+ . 10 mL this permanganate solution is
equivalent to 4.48 mL 5 V H 2O 2 solution. Calculate mass percentage of PbO 2 and Pb 3O 4 in the original
sample.
[Atomic mass of Pb = 207]
PROBLEM 86 An unknown cupric salt with formula Cu x (CO 3 ) y (OH) z is analyzed to determine the
exact formula. A 1.7225 g sample of salt was dissolved in 100 mL of pure water. A 50 mL portion of this
solution required 10 mL 1.0 N H 2SO 4 solution to reach the equivalence point if phenolphthalein was
used as indicator. Another 50 mL portion was titrated using methyl orange as indicator and 15 mL acid of
same strength was required. Deduce the formula of the salt.
PROBLEM 87 Both CaCl 2 and NaCl are used to melt ice and snow on roads in winter. A certain
company was marketing a mixture of these two compounds for this purpose. A chemist, wishing to
analyze the mixture, dissolved 1 g of it in water and precipitated the calcium by adding sodium oxalate.
The calcium oxalate was then carefully filtered, dissolved in dilute sulphuric acid, and titrated with 0.1
M KMnO 4 solution. The titration required 22 mL of the KMnO 4 solution. Calculate freezing point of an
aqueous solution which is 5% (w/V) of the above mixture. K f of water is 1.86 K kg mol –1 .
PROBLEM 88 A 4.25 g sample containing CaC 2O 4 , Na 2C 2O 4 and some inert impurity is heated gently
so that CaC 2O 4 decomposed as:
CaC 2O 4 → CaO + CO( g ) + CO 2 ( g )
All gaseous products were passed through a NaOH solution where following reaction occurred
quantitatively:
2NaOH + CO 2 ( g ) → Na 2CO 3



14

Problems in Chemistry

The resulting solution is separated into two equal part (by volume) and one part required 30 mL
0.5 M HCl to reach the phenolphthalein end point while the other half solution required 50 mL 0.5 M
HCl solution to reach the methyl orange end point. In a separate experiment same mass of the same
sample is dissolved into 100 mL dilute HCl solution and its 10 mL portion required 10 mL 0.1 M
K 2Cr 2O 7 solution. Determine the mass percentage of Na 2C 2O 4 in the original sample.

PROBLEM 89 In acidic solution, 45 mL KMnO 4 solution is required to react with 50 mL 0.25 N
Na 2C 2O 4 solution. How many mL of this same KMnO 4 solution would be required to oxidise 25 mL 0.1
N K 2C 2O 4 solution in alkaline medium where KMnO 4 is reduced to MnO 2 .
PROBLEM 90 A sample weighing 0.3 g containing K 3 [Fe(C 2O 4 ) 3 ] ⋅ 3H 2O,FeCl 3 ⋅ 6H 2O and inert
impurity is dissolved in dilute sulphuric acid and volume made up to 100 mL. A 20 mL portion of this
solution required 3.75 mL of 0.005 M acidified KMnO 4 solution to reach the equivalence point. In an
another experiment, 50 mL sample of the same stock solution is treated with Zn-amalgum and the
resulting solution required 17.5 mL of permanganate solution of same strength. Determine mass
percentage of FeCl 3 ⋅ 6H 2O in the original sample.
PROBLEM 91 A 6.1 g sample containing oxalic acid dihydrate, sodium oxalate and NaHC 2O 4 and is
dissolved in 100 mL of water and its 10.0 mL portion required 16 mL 0.25 M HCl to reach the
equivalence point. In another experiment 10.0 mL portion of the same stock solution required 24 mL
0.25 M NaOH to reach the equivalence point. Determine the mass percentage of all components in the
original mixture.
PROBLEM 92 A 0.127 g of an unsaturated oil was treated with 25 mL of 0.1 M ICl solution. The
unreacted ICl was then treated with excess of KI. Liberated iodine required 40 mL 0.1 M hypo solution.
Determine mass of I 2 that would have been required with 100.0 g oil if I 2 were used in place of ICl.
PROBLEM 93 Alkali metal nitrate on heating decomposes to metal nitrite and oxygen whereas alkaline
earth metal on heating decomposes into metal oxide, NO 2 and oxygen. In an experiment 15 g mixture of

NaNO 3 and Mg(NO 3 ) 2 was heated until no more gas were evolved. The water soluble part of residue
was used for analysis and dissolved in 1.0 litre water. 10 mL portion of this solution was reacted with 20
mL 0.02 M acidified KMnO 4 solution. The excess reagent required 10.00 mL 0.05 M oxalic acid
solution. Determine mass percentage of each nitrate in the mixture. Also determine the molar ratio of
oxygen to NO 2 in the gaseous products given off.
PROBLEM 94 The mass percentage of MnO 2 in a sample of mineral is determined by reacting with
As 2O 3 in acid solution. A 0.225 g sample of mineral is ground and boiled with 75 mL 0.0125 M As 2O 3
solution. After the reaction is complete, the solution is cooled and titrated with 2.28 ×10 –3 M acidified
KMnO 4 solution. 16.34 mL of the oxidizing agent solution was required to reach the end point.
Determine mass percentage of MnO 2 in the sample.
PROBLEM 95 A driver is arrested and asked to pass “breath analyzer” test. A sample consisting 56.5
mL of exhaled air is then bubbled into a spectrometer cell containing 3 mL 0.025% (w/V) K 2Cr 2O 7
solution. The transmittance of the solution was 41.5% initially and 43.4% after bubbling the sample
through the reaction cell. It is known that the alcohol content in blood stream is 2300 times higher than in
exhaled air and that the legal limit is 80 mg of alcohol per 100 mL of blood. Determine the concentration
of alcohol in the blood and state whether or not the driver should be charged with drunk driving.


Problems in Chemistry

15

PROBLEM 96 A sample of 0.3657 g powder containing only Ba(NO 3 ) 2 and Ca(NO 3 ) 2 are dissolved in
50 mL water. Ammonia is added to the solution to raise the pH than an excess of Na 2C 2O 4 is added to
precipitate the metals. The precipitate is then filtered, washed with 1.0 L of water and transferred to a
beaker containing 50 mL H 2O. The solution is acidified to solublise the precipitate and finally titrated
with 0.05 M KMnO 4 solution. A total of 13.94 mL of oxidizing agent solution was required to reach the
end point. Find the composition of the initial mixture. K sp. of BaC 2O 4 = 1.5 × 10 –8 and of
CaC 2O 4 = 2.34 × 10 –9 .


PROBLEM 97 1.0 g sample containing KO 2 and some inert impurity is dissolved in excess of aqueous
HI solution and finally diluted to 100 mL. The solution is filtered off and 20 mL of filtrate required 15
mL 0.4 M Na 2S 2O 3 solution to reduce the liberated iodine. Determine mass % of KO 2 in the original
sample.
PROBLEM 98 Cuprous ion is known to disproportionate quantitatively in acid medium. A 3.0 g sample
of Cu 2O is dissolved in dilute H 2SO 4 solution. The solution is filtered off and 8.3 g pure KI crystal is
added to filtrate. This caused precipitation of CuI with evolution of I 2 . The solution is filtered off and
filtrate is boiled till all I 2 is expelled off. Now, excess of an oxidizing agent is added to filtrate and
liberated iodine required 10 mL 1.0 N Na 2S 2O 3 solution. Calculate mass percentage of Cu 2O in the
original sample.
PROBLEM 99 To a 10 mL 1.0 M aqueous solution of Br 2 , excess of NaOH is added so that all Br 2
disproportionated to Br – and BrO –3 . The resulting solution is freed from bromide ion by extraction and
excess of OH – neutralized by acidifying the solution. The resulting solution is just sufficient to react
with 1.5 g of an impure CaC 2O 4 sample. Calculate percentage purity of oxalate sample.
PROBLEM 100 One gram of an impure sample of NaCl was dissolved in water and treated with excess
of AgNO 3 solution. The precipitate AgCl thus, formed undergo decomposition into Ag and Cl 2 ( g ) and
latter disproportionate into chlorate (V) and chloride ions and chloride is re-precipitated due to presence
of excess of AgNO 3 . If the original precipitate was 60% decomposed and final precipitate weigh 1.5
gram, determine mass percentage of NaCl in original sample.
PROBLEM 101 0.4 g of a sample containing CuCO 3 and some inert impurity was dissolved in diute
sulphuric acid and volume made up to 50 mL. To this solution was added 50 mL 0.04 M KI solution
where copper precipitate as CuI and iodide ion is oxidized into I –3 . A 10 mL portion of this solution is
taken for analysis, filtered, made free from I –3 and treated with excess of acidic permanganate solution.
Liberated iodine required 20 mL 2.5 m M sodium thiosulphate solution to reach the end point. Determine
mass percentage of CuCO 3 in the original sample.
PROBLEM 102 One gram of an unknown sample of NaCN is dissolved in 50 mL 0.33 M alkaline
solution of KMnO 4 and refluxed so that all cyanide is converted into cyanate (OCN – ). The reaction
mixture was cooled and its 5.0 mL portion was acidified by adding excess of sulphuric acid solution and
finally titrated with 19.0 mL 0.1 M FeSO 4 solution. Determine mass percentage of NaCN in the original
sample.

PROBLEM 103 5.0 mL of a pure liquid toluene is dissolved in 100 mL of dilute alkaline KMnO 4
solution and refluxed so that all toluene is oxidized into benzoic acid and a dark brown precipitate of
MnO 2 is formed. Solution is filtered off and filtrate and precipitate were analyzed separately. Precipitate


16

Problems in Chemistry

was re-dissolved into 100 mL 1.0 M acidified solution of Na 2C 2O 4 and excess of oxalate required 50.73
mL 0.1 M acidic dichromate solution for back titration. On the other hand 10.5 mL of filtrate was
acidified by adding excess of sulphuric acid and titrated with 0.1 M acidified solution of Na 2C 2O 4 . A 38
mL of oxalate solution was required to reach the end point. Determine density of liquid toluene and
molarity of original permanganate solution.

PROBLEM 104 A 2.0 g sample containing CaOCl 2 and NaOCl is dissolved in 100 mL water and its 10
mL portion was titrated against 0.15 M acidified solution of Na 2C 2O 4 . 10 mL of oxalate solution was
required to reach the end point. Titrated solution was then treated with excess of aqueous solution of
AgNO 3 where all chloride precipitates as AgCl and weighed to be 0.287 g. Determine mass percentage
of CaOCl 2 and NaOCl in original sample.

GASEOUS STATE
PROBLEM 105 6.0 g of He having average velocity 4 × 10 2 ms –1 is mixed with 12.0 g of Ne 20 having
the same average velocity. What is the average kinetic energy per mole in the mixture?
PROBLEM 106 The valve of a commercial cylinder of N 2 gas was left slightly open so that small
amount of gas leaked into the laboratory. The leak rate was proportional to the pressure difference
(internal pressure one atm). If the initial leak rate was found to be 1 g s –1 and initial pressure inside the
7.28 m 3 tank was 17180 kPa, what would be the pressure inside the tank after 10 days assuming
temperature of the lab to be 27°C.
PROBLEM 107 Calculate pressure exerted by 22.0 g of CO 2 in 0.5 L bulb at 300 K assuming it to be real

gas with a = 363 kPaL2 mol –2 and b = 42.67 cc/ mol.
PROBLEM 108 Molar volume of He at 10.1325 Mpa and 273 K is 0.011075 times its molar volume at
101.325 kPa. Calculate radius of He atom assuming negligible ‘a’.
PROBLEM 109 A gas mixture containing 5% by mass of butane and 95% by mass of Ar (40) is to be
prepared by allowing gaseous butane to fill an evacuated 40 L cylinder at 1.0 atm and 27°C. Calculate
mass of Ar that gives the desired composition and total pressure of the final mixture.
PROBLEM 110 Cl 2O 7 gas decomposes as:
Cl 2O 7 → Cl 2 + O 2
A partially decomposed gaseous mixture is allowed to effuse through a pin-hole and the gas coming
out initially was analyzed. The mole fraction of the O 2 was found to be 0.60, determine the degree of
dissociation.

PROBLEM 111 Proportion of a lighter isotope in a gaseous mixture containing both heavier and lighter
isotopes is increased by successive effusion of the gas mixture. A sample of neon gas has
22
Ne = 90% and 20 Ne = 10% by moles. In how many stages of successive effusion, 25% enrichment of
20

Ne would be achieved?


Problems in Chemistry

17

PROBLEM 112 The density of vapour of a substance at 1.0 atm and 500 K is 0.35 k/ m 3 . The vapour
effuses through a small hole at a rate of 1.33 times faster than oxygen under similar condition.
(a) Determine (i) Molecular weight (ii) Molar volume (iii) Compression factor (Z) of the
vapour (iv) Which forces among the gas molecules are dominating, the attractive or repulsive?
(b) If the vapour behaves ideally at 1000 K, determine the average translational kinetic energy

possessed by a molecule.
PROBLEM 113 Using van der Waals’ equation of state, calculate the pressure correction factor for two
moles of a gas confined in a four litre flask that exert a pressure of 11 atmosphere at 300 K.
b = 0.05 L mol –1 .
PROBLEM 114 For a van der Waals’ gas Z (compressibility factor) was found to be 1.5 at 273 K and one
atmosphere and TB of the gas is 107 K. Determine value of a and b.
PROBLEM 115 A flask containing 2.0 moles of He gas at 1.0 atm and 300K is connected to another
flask containing N 2 ( g ) at the same temperature and pressure by a narrow tube of negligible volume.
Volume of the nitrogen flask is three times volume of He-flask. Now the He-flask is placed in a
thermostat at 200 K and N 2 -flask in another thermostat at 400 K. Determine final pressure and final
number of moles in each flask.
PROBLEM 116 In a spherical glass flask A of radius 1.0 m, containing 300 g H 2 (g ), there was a rubber
balloon B containing some N 2 ( g ). Inside B, there was another rubber balloon C containing some oxygen
gas. At 27°C, it was found that the balloon B had radius 60 cm and of C was 30 cm. Calculate the total
weight of the gas inside the flask. Now 50 g H 2 ( g ) is further added to A, what would be the volume of B
and C.
PROBLEM 117 A partially decomposed PCl 5 (g ) along with its dissociation product is subjected to
diffusion study and the gases coming out initially collected in an another flask. The rate of effusion of
collected gaseous mixture was found to be 0.45 times rate of effusion of pure oxygen gas. Determine the
degree of dissociation of PCl 5 ( g ) in the original sample.
PROBLEM 118 One mole of a monoatomic gas confined in a 22.5 litre flask at 273 K exert a pressure of
0.98 atm, whereas expected pressure was 1.0 atm has the gas behaved ideally. Determine the van der
Waal’s constants ‘a’ and ‘b’ and Boyle’s temperature (TB ).
PROBLEM 119 One litre of a gas at 300 atm and 473 K is compressed to a pressure of 600 atm and 273
K. The compressibility factors found to be 1.072 and 1.375 respectively at the initial and final states.
Calculate the final volume.
PROBLEM 120 Calculate the van der Waal’s constants for ethylene. TC = 282 K,PC = 50 atm.
PROBLEM 121 The second Virial coefficient of an imperfect gas is 2 × 10 –2 (L/ mol) 2 . Calculate the
volume of a gm mole of the gas at 27°C and 5 atmosphere pressure.
PROBLEM 122 The van der Waal’s constant ‘b’ of a gas is 4.42 centilitre/mol. How near can the centres

of the two molecules approach each other?
PROBLEM 123 For carbon dioxide, critical density is 0.45 g/cc and its TC = 300 K. Determine its van
der Waal’s constants.


18

Problems in Chemistry

PROBLEM 124 The Virial equation for ethane gas is given by PV = RT + BP . At 0°C,
B = – 0.1814 L/ mol. Calculate volume of one mole of ethane at 10 atm, and ‘a’.
PROBLEM 125 An unknown gas (X) at 2.0 atmosphere and Ar (40) at 1.0 atmosphere were injected
simultaneously from the two ends of a 1.0 metre long glass tube and the first collision between X and Ar
occurred at a distance of 38 cm from Ar-end.Determine the molar mass of X assuming that gases were
injected at same temperature and through the pin-hole of identical geometry.
PROBLEM 126 Using van der Waals’ equation of state, calculate pressure developed by 100 g of CO 2
contained in a volume of 5.0 litre at 40°C. Also compare this value with that calculated using ideal gas
law and determine the percentage deviation from ideality. a = 3.6 atm L2 mol –2 , b = 44 cm 3 mol –1 .
PROBLEM 127 An equation of state for a non-ideal gas can be written as: PVm = A + BP + CP 2 ; where
Vm is the molar volume and P is the gas pressure in atmosphere. B = – 2.879 × 10 –2 and C = 14.98 × 10 –5
in litre atmosphere unit. Under the experimental condition, determine the pressure at which PV-P curve
will attain minimum.

PROBLEM 128 A modified form of van der Waal’s equation of state for 1.0 mole of gas is given as:
α 

P +
 (V – β) = RT

TV 2 

Deduce expression for the first Virial coefficient (B) and Boyle’s temperature in term of α and β if
Virial equation of state is:
PV
B C
= 1 + + 2 +…
RT
V V
PROBLEM 129 Assuming that dry air contain 79% N 2 and 21% O 2 by volume, calculate the density of
moist air at 25°C and 1.0 atmosphere when the relative humidity is 60%. The vapour pressure of water at
25°C is 23.76 mm of Hg.
PROBLEM 130 At what temperature, three moles of SO 2 will occupy 10 litre at a pressure of 15.0 atm if
it is a van der Waal’s gas with a = 6.71 atm L2 mol –2 and b = 56.4 cm 3 mol –1 .
PROBLEM 131 Pressure of He gas confined in a steel chamber drops from 4.0 to 1.0 atmosphere in 4.0
hours due to diffusion through a pin-hole in the steel chamber. If an equimolar mixture of He and
methane gas at 20 atmosphere and the same temperature are confined in the same chamber, what will be
the partial pressure of He and methane after 1.0 hour. Assume rate of diffusion to be linear function of
gas pressure and inverse function of square root of molar masses.
PROBLEM 132 One mole of a van der Waal’s gas at 0°C and 600 atmosphere occupies 0.075 L. If
b = 0.024 L mol –1 , determine compressibility factor (Z) and predict the type of force dominating among
the gas molecule.
PROBLEM 133 A one litre flask containing NH 3 (g ) at 2.0 atmosphere and 300 K is connected to
another 800 mL flask containing HCl(g) at 8.0 atmosphere and 300 K by means of a narrow tube of
negligible volume and gases were allowed to react quantitatively as:
NH 3 ( g ) + HCl( g ) → NH 4Cl( s); ∆H = – 43kJ/ mol