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CIE 1

Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring RoadNew Delhi 110 018, Ph. : 9312629035, 8527112111

IONIC EQUILIBRIUM

C1A Ionic equilibrium is the study of equilibrium among ions in the aqueous solution. The process ofsplitting of a molecules into its ions is known as ionization.

C1B There are two types of electrolytes :

(i) strong electrolyte : are converted into ions element completely.

(ii) weak electrolyte : dissociation is incomplete. In aqueous solution of these compounds onlyslight amount of electrolyte ionises and there exist an equilibrium between ionizedmolecules and unionized molecules. for e.g.

(a) weak acids : CH3COOH, HCN etc.

(b) weak bases : NH4OH, C

5H

5N etc.

(c) weak salts : AgCl, PbCl2, AgCrO

4, MnS, H

2S etc.

C1C STRENGTH OF ACIDS AND BASES AND pH SCALE

Concept of Acids and Bases

(a) According to Arrhenius an acid is a substance that dissociates in water to give hydrogen ions, andbase is a substance that dissociates in water to give hydroxyl ion.

(b) According to Bronsted-Lowry Concept, acid is a substance that is capable of donating a hydrogenion (H+) and bases are substances capable of accepting a hydrogen ion (H+). In short, acids areproton donors and bases are proton acceptors.

(c) According to Lewis, acid is defined as a species which accepts electron pair and base which donatesan electron pair.

Acidic strength means the tendency of an acid to give H+ ions in water and basic strength means thetendency of a base to give OH ions in water. So more the tendency to give H+ or OH ions more willbe the acidic or basic strength of acid or base. In 1909 S.P.L. Sorrenson introduced a scale called pHscale or pOH scale to measure the acidic or basic strength of acids and bases

pH = log[H]

pOH = log[OH]

When [H+] of a solution is more than [OH+] the solution is called to be acidic. When [H+] of a solutionis less than [OH+] the solution is called to be basic. If [H+] and [OH] of a solution are equal thesolution is called neutral.

Practice Problems :

1. Water has pKw = 13.26 at 500C. Its pH will be

(a) 6.0 (b) 7.0 (c) 6.63 (d) 13.26

[Answers : (1) c]

C2A SELF IONISATION OF WATER

Pure water act as a very weak electrolyte i.e. it gets ionised very weakly to give H+ and OH ions, that

is H2O H+ + OH. Now, applying law of chemical equilibrium.

]OH[

]OH[]H[K

2

where K is equilibrium constant

K[H2O] = [H+] [OH]

Kw = [H+] [OH] where K

w is ionic product of water

Since the concentration of pure water is constant, so it multiplied by K will also be a constant (Kw)

called ionic product of water which is constant at constant temperature. The value of Kw is

approximately 1014 at 298 K.

Therefore, [H+] [OH] = 1014 at 298 K

As water gives equal amount of H+ and OH, we can say

[H+] [H+] = 1014 or [OH] [OH] = 1014

CIE 2


[H+] = 107 or [OH] = 107

pH = log 107 or pOH = log 107

pH = 7 or pOH = 7

For some other temperature

[H+]2 = [OH]2 = Kw

[H+] = [OH] = wK

pH = pOH = log wK

For pure water [H+] is always equal to [OH] so it is called neutral. For acidic or basic solution the[H+] and [OH] are not equal but their product is always equal to K

w at that temperature.

C2B COMMON ION EFFECT

If to an ionic equilibrium, we add any ion which appears in the equilibrium reaction, theequilibrium will shift in a direction opposite to that in which that ion appears.

So dissociation of weak acid and bases is suppressed in presence of strong acids and basesrespectively. Similarly the solubility of salts decreases in presence of any common ion of that salt.

C2C DETERMINATION OF pH OF ACIDS AND BASES

(i) Strong Acid : A strong acid is that which ionises completely to give maximum H+ ions. For e.g.

HCl H+ + Cl

Let the concentration of HCl is c. So the [H+] coming from acid is also c, but some [H+] is also comingdue to self ionisation of water (say x)

H2O H+ + OH

Now pH = log [H+]total

= log([H+]acid

+ [H+]water

)

But [H+]total

[OH]total

= Kw

(c + x) (x) = Kw

If we know c and Kw we can calculate x.

Now pH = log (c + x)

But in most of the cases if c is more than 106, the value of x will be negligible and we can take

pH = log c (as x

CIE 3


1

cK

2

a pH = log (c)

If < < 1 then 1 1 (i.e., if is less than 0.1)

Ka = c2 or

c

Ka

pH = log c = log cKlogc

Kc a

a

(iii) Strong acid + Weak acid

Suppose we want to calculate pH of a solution containing a strong acid (HX) and a weak acid (HY)whose concentrations are c

1 and c

2 respectively. Dissociation constant of weak acid is K

a.

HX H+ + A

c1

c1

HY H+ + YY

c2(1 ) c

2 c

2

)1(c

]c][cc[

]HY[

]Y[]H[K

2

221

total

totaltotala

1

]cc[K 21a

From above equation we can calculate

pH = log [H+]total

= log (c1 + c

2)

Note : In this case we have neglected H+ coming from water.

(iv) Two weak acids

Suppose we want to calculate pH of a mixture of two weak acids HX and HY whose concentrations

are c1 and c

2 and their dissociation constants are

21 aaKandK respectively..

HA H+ + A

c1(1

1) c

1

1 c

1

1

HB H+ + B

c2(1

2) c

2

2 c

2

2

)1(

)cc(

)1(c

)c)(cc(K

1

12211

11

112211a1

...(1)

)1(

)cc(

)1(c

)c)(cc(K

2

22211

21

222211a2

...(2)

For equation (1) and (2) we can calculate a1 and a

2

pH = log [H+]total

= log (c1

1 + c

2

2)

Note : In this case we have neglected [H+] coming from water.

(v) Dibasic (Dipotic) and Polyprotic weak acids

Dibasic acid is that acid which have the tendency to give two H+ ions per molecule of that acid e.g.H

2SO

4, H

2S etc. Let us calculate pH of a diprotic acid H

2A whose dissociation constants for first and

second proton are 1a

K and 2a

K respectively and concentration is c.

H2A H+ + HA

CIE 4


c(1 1) c

1+ c

1

HA H+ + A2

c1(1

2) c

1

2c

1

2

)1(c

)]1(c)[cc(

]AH[

]HA[]H[K

1

21211

total2

totaltotala1

)1(

)]1(c)[(

1

21211

)1(

)cc(

)1(c

)c)(cc(

]HA[

]A[]H[K

2

2211

21

21211

total

total2

totala2

From equation (1) and (2) we can calculate 1 and

2

pH = log[H+]total

= log (c1 + c

1

2)

Note : In this case we have neglected [H+] coming from water

pH OF BASES

The pH of bases can also be calculated as we have done for acids. In case of a base, instead of H+ wetake OH ions, instead of K

a we take K

b and instead of pH we calculate pOH. Then pH can be

calculated as pH = 14 pOH.

NOTE :

1. Strong acid [H+] = Normality

2. Strong Base [OH] = Normality

3. pH of mixture of strong acids / strong bases : We calculate the normality of final solution.

4. pH of mixture of strong acids and strong bases : we calculate normality of final solution.

i) If equivalents of acids > eq. of base. Final solution will be acidic and normality = [H+]

ii) If eq. of base > eq. of acid. Final solution will be alkaline and normality = [OH]

iii) If eq. of acid = eq. of base, final solution will be neutral and pH = 7 at 250C.

5. pH of weak monobasic acid or weak monoacidic base [H+] = CK]OH[CK ba

Here C/K a

Note : i) In above formula for , we have assumed is very small compared to one andhence neglected compared to one.

ii) In case when we use above formula and > 0.1, we do not apply aboveapproximation and if 0.1, approximation is valid.

6. pH of mixture of two weak acids : we must consider ionisation of two acid separtely in which

Total [H+] = [H+] produced from acid (1) and [H+] produced from acid (II) = C1

1 + C

2

2

Where C1, C

2 are concentration of two acids and

1 and

2 are degree of dissociation of acids in

presence of each other.

Practice Problems :

1. The pH of a solution obtained by dissolving 5 104 moles of Ca(OH)2 (strong electrolyte) to 100 ml

solution at 298 K will be

(a) 11 (b) 12 (c) 9.8 (d) 2

2. Consider the reaction A + H3O+ HA + H

2O. The K

a value for acid HA is 1.0 106. What is the

value of K for this reaction.

(a) 1.0 106 (b) 1.0 108 (c) 1.0 108 (d) 1.0 106

CIE 5


3. The ionisation constant of HCO2H is 1.8 104. What is the percent ionization of a 0.001 M

solution ?

(a) 66% (b) 42% (c) 34% (d) 58%

4. The pH of a 1010 M NaOH solution is nearest to

(a) 10 (b) 7 (c) 4 (d) 10

[Answers : (1) b (2) a (3) c (4) b]

C3 SALT HYDROLYSIS

Reaction in which cation or anion of the salt react with water to convert water acidic or basic innature, is known as salt hydrolysis.

1. Salt of a Strong Acid and Salt of Weak acid and Salt of Weak acid and

Weak Base e.g. NH4Cl Strong Base e.g. CH

3COONa Weak Base e.g. CH

3COONH

4

NH4+ + H

2O NH

4OH + H+ CH

3COO + H

2O NH

4+ + CH

3COO + H

2O

i) KH = K

W / K

bCH

3COOH + OH CH

3COOH + NH

4OH

ii)c

Kh H i) KH = Kw / Ka i) KH = Kw / Ka . Kb

iii) [H+] = Ch ii)c

Kh H ii) HKh

iv)b

w

K

cK]H[

iii)

c

KK]H[ aw

iii) [H+] = hKa, [OH] = hKb

v) pH = (1/2) iv) pH = 1/2 iv) b

aw

K

KK]H[

[pKw log c pK

b]. (pK

w + log c + pK

b)

vi) their solution is acidic v) their solution is basic v) pH = 1/2 [pKw + pK

a pK

b]

pH< 7 pH > 7

vi) solution is acidic if Ka > Kb

solution is basic ifKb > Ka.

solution is neutral ifKa = Kb

NOTE :

1. All the formulae for salt hydrolysis are for univalent salts. The term c in the above equationshowever represents the concentration of ion that undergoes hydrolysis.

2. In all the formulae mentioned above we have neglected h compared to one.

Practice Problems :

1. pH of 0.01 M HS will be :

(a)2

clog

2

pK7pH a (b)

2

clog

2

pK7pH b

(c)2

pKpKpH 21

(d)

2

pKpK7pH ba

CIE 6


2. The degree of hydrolysis of anilinium acetate is

(a) independent of initial concentration

(b) directly proportional to initial concentration

(c) inversely proportional to initial concentration

(d) inversely proportional to square root of initial concentration

3. The compound whose 0.1 M solution is basic is

(a) Ammonium acetate (b) Ammonium chloride

(c) Ammonium sulphate (d) Sodium acetate

4. Which of the following when mixed, will give a solution with pH greater than 7 ?

(a) 0.1 M HCl + 0.2 M NaCl

(b) 100 ml of 0.2 M H2SO

4 + 100 ml of 0.3 M NaOH

(c) 100 ml of 0.1 M CH3COOH + 100 ml of 0.1 M KOH

(d) 25 ml of 0.1 M HNO3 + 25 ml of 0.1 M NH

3

5. The correct order of increasing [H3O+] in the following aqueous solutions is

(a) 0.01 M H2S < 0.01 M H

2SO

4 < 0.01 M NaCl < 0.01 M NaNO

2

(b) 0.01 M NaCl < 0.01 M NaNO2 < 0.01 M H

2S < 0.01 M H

2SO

4

(c) 0.01 M NaNO2 < 0.01 M NaCl < 0.01 M H

2S < 0.01 M H

2SO

4

(d) 0.01 M H2S < 0.01 M NaNO

2 < 0.01 M NaCl < 0.01 M H

2SO

4

[Answers : (1) a (2) a (3) d (4) c (5) c]

C4 BUFFER SOLUTION

There are three types of buffers :

(i) Acidic buffer : This consists of solution of a weak acid and its conjugate base (i.e., its salt with weakor strong base). Let us consider an acid buffer containing acetic acid and sodium acetate (conjugatebase is CH

3COO).

CH3COOH CH

3COO + H+

CH3COONa CH

3COO + Na+

Now if we add any acid (H+) in this buffer it will shift the above equilibrium in backward directionand hence some H+ will be consumed to resist the change in pH. If we add base (OH) it will consumethe H+ from solution, but the above equilibrium will shift in forward direction and so the decrease inH+ are compensated by forward shift of equilibrium to some extent. If we add water (i.e., we dilutethe solution) the concentration of H+ will decrease which will shift the equilibrium in forwarddirection to give more H+ and so compensate the decrease in H+ concentration.

CH3COONa CH

3COO + Na+

CH3COOH CH

3COO + H+

Now due to the presence of CH3COO ions of salt the dissociation of CH

3COOH is suppressed due to

common ion effect of CH3COO ions. So we can assume that the total [CH

3COO] is almost equal to

(CH3COO) from salt.

]COOHCH[

]H[]COOCH[K

3

totaltotal3a

]COOCH[

]COOHCH[K]H[

3

3a

]COOCH[

]COOHCH[logKlogHlogpH

3

3a

CIE 7


]COOHCH[

]COOCH[logpKpH

3

3a

]Acid[

]Salt[logpKpH a

(ii) Basic buffer : It is a solution of a weak base and its conjugate acid (salt with weak or strong acid). Letus consider a buffer containing NH

4OH and NH

4Cl

NH4Cl NH

4+ + Cl

NH4OH NH

4+ + OH

The buffer action may be explained as in the case of acid buffer. The pH is given by

]Base[

]Salt[logpKpOH b

pH = 14 pOH

(iii) Salt buffer : A solution of a salt of weak acid with weak base (CH3COONH

4) also act as a buffer.

CH3COONH

4 CH

3COO + NH

4+

When an acid is added to it, the H+ combine with CH3COO to give CH

3COOH.

CH3COO + H+ CH

3COOH

When a base is added, the OH combine with NH4+ to give NH

4OH.

NH4+ + OH NH

4OH

The pH of this type of solution has been discussed already in the case of hydrolysis of such salts.

Practice Problems :

1. The pH of mixture of CH3COONa + CH

3COOH after adding water shows........value.

(a) Increased (b) Decreased (c) Constant (d) All

2. A certain buffer solution contains equal concentration of X and HX. The Kb for X is 1010. The pH

of the buffer is

(a) 4 (b) 7 (c) 10 (d) 14

3. One litre of a buffer solution containing 0.01 M NH4Cl and 0.1 M NH

4OH having pKb of 5 has pH of

(a) 9 (b) 10 (c) 4 (d) 6

[Answers : (1) c (2) a (3) b]

C5 SOLUBILITY PRODUCT

Insoluble substances like AgCl, BaSO4, PbCl

2, etc., are infact not completely insoluble when present

in an aqueous medium. A very small amout of these dissolves and is present as ions. Further, thereexists an equilibrium between the undissolved and the dissolved salt. For AgCl, the equilibriumequation may be written as,

AgCl(s) Ag+(aq) + Cl(aq)

Applying the law of mass action, ]AgCl[

]Cl][Ag[K

[AgCl] is assumed to be constant because of the fact that very little of this solid dissolved in aqueoussolution (by definition)

Ksp

= [Ag+][Cl]

NOTE :

1. Let the solubility of salt of weak acid and strong base is s1 in pure water, s

2 in basic buffer and s

3 in

acidic buffer then

s3 > s

1 > s

2

CIE 8


2. For Preciptitation, Ksp

< Kip

Mutual solubility of two springly soluble salts

Let Ksp

(AgCl) = x x and y are close

Ksp

(AgBr) = y

[Ag+] [Cl] = x ...(i)

[Ag+] [Br] = y ...(ii)

[Ag+] = [Cl] + [Br] ...(iii)

If salts were Ag2A and Ag

2B then ]B[]A[]Ag[

2

1

Divide equation (i) by (ii), we get,

y

x

]Br[

]Cl[

...(iv)

Divide equation (iii) by [Cl]

x

yx

x

y1

]Cl[

]Br[1

]Cl[

]Ag[

...(v)

From equation (i) and (v), we get

[Ag+]2 = x

)yx(x

[Ag+] = yx

Knowing [Ag+], we can calculate [Cl] and [Br] in the solution which will be the mutual solubility ofAgCl and AgBr respectively.

Practice Problems :

1. Ksp

of CaSO4 is 4 1012. CaSO

4 is precipitated on mixing equal volumes of the following solutions :

(a) 3 106 M CaCl2 and 3 106 M (NH

4)

2SO

4

(b) 4 106 M CaCl2 and 3 106 M (NH

4)

2SO

4

(c) 6 106 M CaCl2 and 3 106 M (NH

4)

2SO

4

(d) In all cases.

2. The precipitate of Ag2CrO

4 (K

sp = 1.9 1012) is obtained when equal volumes of the following are

mixed

(a) 104 M Ag+ + 104 M Cro42 (b) 102 M Ag+ + 103 M Cro

42

(c) 105 M Ag+ + 103 M Cro42 (d) 104 M Ag+ + 105 M Cro

42

3. M(OH)x has (K

SP 4 1012) and solubility 104 M. Then the value of x is

(a) 1 (b) 2 (c) 3 (d) 4

[Answers : (1) d (2) b (3) b]

CIE 9


SINGLE CORRECT CHOICE TYPE

1. A solution is a mixture of 0.05 M NaCl and 0.05 MNaI. The concentration of iodide ion in the solutionwhen AgCl just starts precipitating is equal to :

(Ksp

AgCl = 1 1010 M2 ; Ksp

AgI = 4 1016 M2)

(a) 4 106 M (b) 2 108 M

(c) 2 107 M (d) 8 1015 M

2. Silver iodide is used in cloud seeding to produce

rain AgI Ag+(aq) + I (aq); Ksp

= 8.5 107.

AgNO3 and KI are mixed to give [Ag+] 0.010 M;

[I] 0.015 M. Will AgI precipitate ?

(a) yes (b) no

(c) cant say

(d) this depends on [NO3] and [K+]

3. The conjugate acid of NH2 is

(a) NH3

(b) NH2OH

(c) NH4

+ (d) N2H

2

4. Which does not act as Bronsted acid

(a) NH4

+ (b) CH3COO

(c) HCO3

(d) HSO3

5. Conjugate base of hydrazoic acid is

(a) HN3

(b) N3

(c) N (d) N2

6. Which one is the strongest acid

(a) ClO3(OH) (b) ClO

2(OH)

(c) SO(OH)2

(d) HCOO

7. The solubility of A2X

3 is y mol dm3. Its solubility

product is

(a) 6y4 (b) 64y4

(c) 36y5 (d) 108y5

8. Which equilibrium can be described as Lewis acid-base reaction but not Bronsted acid-base reaction

(a) H2O + CH

3COOH H

3O+ +

CH3COO

(b) 2NH3 + H

2SO

4 2NH

4+ + SO

42

(c) NH3 + CH

3COOH NH

4+ +

CH3COO

(d) [Cu(H2O)

4]2+ + 4NH

3 [Cu(NH

3)

4]2+

+ 4H2O

9. A solution of pH 8 is.....basic than a solution of pH12

(a) Less (b) More

(c) Equally (d) None

10. pH of water is 7.0 at 250C. If water is heated to 700C,the

(a) pH will decrease and solution becomesacidic

(b) pH will increase and solution becomesbasic

(c) pH will remain constant as 7

(d) pH will decrease but solution will beneutral

11. Given, HF + H2O H

3O+ + F

F + H2O HF + OH

Which relation is correct

(a) Kb = K

w(b) K

b = 1/K

w

(c) Ka K

b = K

w(d) K

a/K

b = K

w

12. The heat liberated when one mole of water is formedby combining sulphuric acid and sodiumhydroxide is

(a) 34 kcal (b) 13.7 kcal

(c) 8.5 kcal (d) 25.5 kcal

13. The pH of solution A, B, C, D are 9.5, 2.5, 3.5 and5.5 respectively. The most acidic solution is

(a) A (b) B

(c) C (d) D

14. The solubility product of PbBr2 is 8 105. If the

salt is 80% dissociated in saturated solution, thesolubility of the salt is [Atomic weights of Pb andBr are 208 and 80 a.m.u. respectively]

(a) 12.486 g/lt (b) 6.25 103

(c) 5.25 (d) 9

15. The extent of ionisation increases

(a) with the increase in the concentration ofthe solute

(b) on addition of excess of water to thesolution

(c) on decreasing the temperature of thesolution

(d) on stirring the solution vigorously

16. The hydrogen ion concentration in weak acid ofdissociation constant K

a and concentration c is

nearly equal to

(a)c

Ka(b)

aK

c

(c) Kac (d) cKa

CIE 10


17. At 900C, pure water has [H3O+] = 106 mol litre1.

The value of Kw at 900C is

(a) 106 (b) 108

(c) 1012 (d) 1014

18. An acid solution of pH 6 is diluted hundred times.The pH of solution becomes approximately

(a) 6.95 (b) 6

(c) 4 (d) 9

19. About buffer solution which is correct ?

(a) It contains a weak acid and its conjugatebase

(b) It contains a weak base and its conjugateacid

(c) It shows little change in pH on addingsmall amount of acid or base

(d) None of the above

20. An acidic buffer solution can be prepared bymixing solution of

(a) Sodium acetate and acetic acid

(b) Ammonia and ammonium hydroxide

(c) Sulphuric acid and sodium sulphate

(d) Sodium chloride and sodium hydroxide

21. A mixture of weak acid (say acetic acid) and its saltwith a strong base (say sodium acetate) is a buffersolution. Which other pair of substances from thefollowing may have a similar property ?

(a) HCl and NaCl

(b) NaOH and NaNO3

(c) KOH and KCl

(d) NH4OH and NH

4Cl

22. When 1.0 ml of dilute HCl is added to 100 ml ofbuffer solution of pH 4, the pH of the solution

(a) Becomes 7.0

(b) Remain almost same

(c) Becomes 2.0

(d) Becomes 10.0

23. A precipitate is formed when

(a) the solution becomes saturated

(b) the ionic product is less than thesolubility product

(c) the ionic product is nearly equal to thesolubility product

(d) the ionic product exceeds the solubilityproduct

24. Solubility product of A2B is 4 109 (mol/lit)3. Its

solubility is

(a) 103 M (b) 41/3 103 M

(c) 104 M (d) 2 105 M

25. In which of the following solvents with AgBr havehighest solubility ?

(a) 103 M NaBr (b) 103 M NH4OH

(c) pure water (d) 103 M HBr

26. For pure water

(a) pH increases and pOH decreases withincrease in temperature

(b) pH decreases and pOH increases withincrease in temperature

(c) Both pH and pOH increases with increasein temperature

(d) Both pH and pOH decrease with increasein temperature

27. 1 M NH4OH and 1 M HCl are mixed to make total

volume of 300 mL. If pH of the mixture is 9.26 andpK

a (NH

4+) = 9.26 then volume ratio of NH

4OH and

HCl will be :

(a) 1 : 1 (b) 1 : 2

(c) 2 : 1 (d) 3 : 1

28. Kc for the reaction

[Ag(CN)2] Ag+ + 2CN, the equilibrium

constant at 250C is 4.0 1019, then the silver ironconcentration in a solutionwhich was originally 0.1molar in KCN and 0.03 molar in AgNO

3 is

(a) 7.5 1018 (b) 7.5 1018

(c) 7.5 1019 (d) 7.5 1019

29. The pKa of acetylsalicylic acid (aspirin) is 3.5. The

pH of gastric juice in human stomach is about 2 3and the pH in the small intestine is about 8. Aspirinwill be

(a) Unionized in the small intestine and inthe stomach

(b) Completely ionized in the small intensineand in the stomach

(c) Ionized in the stomach and almostunionized in the small intensine

(d) Ionized in the small intensine and almostunionized in the stomach

30. A certain weak acid has a dissociation constant of1.0 104. The equilibrium constant for its reactionwith a strong base is

(a) 1.0 104 (b) 1.0 1010

(c) 1.0 1010 (d) 1.0 1014

31. Solubility of BaF2 in a solution of Ba(NO

3)

2 will be

represented by the concentration term

(a) [Ba2+] (b) [F]

(c) [F] (d) 2[NO3]

CIE 11


32. Solubility products of Al(OH)3 and Zn(OH)

2 are

8.5 1023 and 1.8 104 respectively. If equal molesof Al3+ and Zn2+ ions are present in a solution, whichone will be precipitated first on addition ofNH

4OH ?

(a) Al(OH)3

(b) Zn(OH)2

(c) Both of them (d) None of them

33. At 500C, the self-ionization constant (ion

product) is 3024NH 10NHNHK 3 . How

many amide ions are present per mm3 of pureliquid ammonia ?

(a) 600 ions/mm3

(b) 6 106 ions/mm3

(c) 6 104 ions/mm3

(d) 60 ions/mm3

34. The pH of a solution is 5.0. To this solutionsufficient acid is added to decrease the pH to 2.0.The increase in hydrogen ion concentration is

(a) 100 times (b) 1000 times

(c) 2.5 times (d) 10 times

35. A solution contains 10 ml of 0.1 N NaOH and 10 mlof 0.05 N H

2SO

4, pH of this solution is

(a) 1 (b) Less than 7

(c) Greater than 7 (d) Zero

36. Which of the following solutions will have pH closeto 1.0 ?

(a) 100 ml of M/10 HCl + 100 ml of M/10NaOH

(b) 55 ml of M/10 HCl + 45 ml of M/10 NaOH

(c) 10 ml of M/10 HCl + 90 ml of M/10 NaOH

(d) 75 ml of M/5 HCl + 25 ml of M/5 NaOH

11. c

12. b

13. b

14. b

15. b

16. d

17. c

18. a

19. c

20. a

1. c

2. a

3. a

4. b

5. b

6. a

7. d

8. d

9. a

10. d

21. d

22. b

23. d

24. a

25. b

26. d

27. c

28. b

29. d

30. b

31. c

32. a

33. a

34. b

35. c

36. d

ANSWERS

(SINGLE CORRECT CHOICE TYPE)

EXCERCISE BASED ON NEWPATTERN

COMPREHENSION TYPE

Comprehension-1

Given that 2.0 104 mol each of Mn2+ and Cu2+

was contained in 1.0 L of a 0.0030 M HClO4 solu-

tion, and this solution was saturated with H2S. The

solubility if H2S, 0.10 mol/L, is assumed to be

independent of the presence of other materials inthe solution. (Given K

a(H

2S =1021 ),

Ksp

(MnS = 2.5 1010)

1. Determine whether or not each of the ions Mn2+ andCu2+ will precipitate as the sulfide.

(a) both MnS and CuS will be precipitated

(b) CuS is precipitated but MnS will notprecipitate

(c) MnS is precipitated but CuS will notprecipitate

(d) both will remain in the solution

2. How much percentage Cu2+ ions escapesprecipitations

(a) 1019 % (b) 4 1013 %

(c) 2 104 % (d) 9.8 1019 %

3. If the original solution is made neutral bybuffering the [H+] at 109 will MnS precipitate

(a) Precipitation takes place

(b) No precipitation takes place

(c) Ionic product is less than Ksp

(d) Ionic product is equal to the Ksp

Comprehension-2

A buffer solution was prepared by dissolving0.0200 mol propionic acid and 0.05 mol sodiumpropionate in enough water to make 1.00 L ofsolution. [Ka for propionic acid is 1.34 105].

4. The pH of buffer is

(a) 3.748 (b) 4.7

(c) 7.5 (d) 5.7

5. The pH change if 1.0 105 mol HCl was added to10 mL of the buffer is

(a) 0.051 (b) 0.051

(c) 0.0035 (d) 0.0035

6. The change in pH if 1.0 105 mol NaOH wereadded to 10 mL of the buffer is

(a) 0.051 (b) 0.051

(c) 0.0035 (d) 0.0035

CIE 12


MULTIPLE CORRECT CHOICE TYPE

1. Buffer solution can be prepared from a mixture of

(a) sodium acetate and acetic acid in water

(b) sodium acetate and hydrochloric acid inwater

(c) ammonia and ammonium chloride inwater

(d) ammonia and sodium hydroxide inwater

2. Which of the following sets represents theconjugate acid-base pair (s)

(a) H2O, H

3O+

(b) H2SO

4, SO

42

(b) CH3COOH, CH

3COO

(d) H3PO

4, PO

43

3. For which of the solution PH = pka

(a) 100 ml of 0.1 M CH3COOH + 100 ml of

0.1 M CH3COONa

(b) 100 ml of 0.1 M CH3COOH + 50 ml of

0.1 M NaOH

(c) 100 ml of 0.1 M CH3COOH + 100 ml of

0.1 M NaOH

(d) 100 ml of 0.1 M CH3COOH + 100 ml of

0.1 M NH3

4. Which of the following are Lewis bases ?

(a) Ag+ (b) CH4

(c) H2O (d) CN

5. PH of the following solution(s) is not affected bydilution

(a) 0.01 M CH3COONa

(b) 0.01 M NaHCO3

(c) 0.01 M CH3COONH

4

(d) buffer of 0.01 M CH3COONa and

0.01 M CH3COOH

6. Which of the following are conjugate acid-basepair(s)

(a) H3O+, OH (b) HS, S2

(c) H3O+, CH

3COO (d) HNO

2, NO

2

7. Which of the following reaction (s) represent selfionisation of water

(a) H2O H+ + OH

(b) 2H2O H

3O+ + OH

(c) 5H2O H

9O

4+ + OH

(d) none of these

MATRIX-MATCH TYPE

Matching-1

Column - A Column - B

(A) Ka(CH3COOH) = (p) [H+] = 1.1 107

1.8 105 normalityis N/100

(B) 250 cc N/10 HCl (q) [H+] = 2.3 109

solution is mixed with250 cc M/20 H

2SO

4

solution

(C) 250 cc N/10 HCl (r) [H+] = 0.1

solution is mixed with100 cc N/10 HClsolution

(D) 108 M HCl solution (s) [H+] = 23.33 1014

Matching-2


(A) 0.05 M of Na2SO

4(p) 1.8 108 mol/L

Ksp (BaSO4) = 1.5 109

(B) Ksp for PbBr2 is (q) 3 108 mol/L

8 105 salt is 80%dissociated

(C) 0.01 M of AgNO3

(r) 3.4 102 mol/LKsp (AgCl) = 1.8 1010

(D) 0.01 M of KCl (s) 1 105 mol/LKsp (AgCl) = 1.8 1010

Matching-3


(A) [(CH3)

3NH+] in an aq. (p) 8.0 103 M

solution that is 1.02 M(CH

3)

3 N is

(Kb = 6.02 105)

(B) For an 0.025 M solution (q) 1.025 104 Mof the weak diprotic acidH

2CO

3, the [H

3O+] conc. is

(given K1 = 4.2 107

K2 = 5.6 1011)

(C) The conc. of (r) 1.52 102 MCH

3CH

2COONa should

be added to 1 L of aq.solution containing 0.02 molof CH

3CH

2COOH to

obtain a buffer solution ofpH 4.75

(D) Conc. of HCN and NaCN (s) 1.39 105 Min a solution is 0.01 M each.Ka of HCN is 7.2 1010 theconc. of OH ion is

CIE 13


8. Which of the following will suppress the ionizationof phthalic acid in an aqueous solution ?

(a) KCl (b) H2SO

4

(c) HNO3

(d) NaOH

9. Which does not react with NaOH or which is notacid salt :

(a) NaH2PO

2(b) Na

2HPO

3

(c) Na2HPO

2(d) NaHCO

3

10. The dissociation constant of a weak acid HA is4.9 108. Then which are correct

(a) percentage ionisation is 7 104

(b) percentage ionisation is 7 102

(c) concentration of [OH] is1.43 1010 mole/litre

(d) concentration of [H+] is49 105 mole/litre

11. Given that the 0.01 M solution of KF andK

a(HF) = 6.6 154. Then which are correct

(a) The hydrolysis constant is 1.5 1011

(b) The degree of hydrolysis is 6.05 107

(c) Concentration of [H+] is 2.583 108

(d) The hydrolysis constant is 3 1011

12. The solubility of CaF2 in water at 180C is

2.04 104 mole/litre. Which are correct

(a) Ksp is 8.48 1012

(b) Ksp is 3.4 1011

(c) For precipitation ionic product > Ksp

(d) For precipitation ionic product < Ksp

13. Solid AgNO3 in added to a solution which is 0.1M

in Cl and 0.1 M in CrO42. If Ksp values for AgCl

and Ag2CrO

4 are 1.7 1012 respectively. Then

which are correct

(a) If AgCl precipitate then [Ag+] is1.7 109 M

(b) If Ag2CrO

4 precipitate then [Ag+] is

4.34 106 M

(c) If Ag2CrO

4 precipitate then [Cl] is

3.9 105 M

(d) If precipitate then [Cl] is 2.87 105M

14. 0.01 mole of AgNO3 is added to one litre of a

solution which is 0.1 M in Na2CrO

4 and 0.005 M in

NaIO3. Then which are correct.

Given that Ksp (Ag2CrO

4) = 108

Ksp (AgIO3) = 1013

(a) [Ag+] = 3.2 104 mol/L

(b) [CrO42] = 9.7 103 mol/L

(c) [Ag+] = 7.6 104 mol/L

(d) [IO3] = 3.125 1010 mol/L

15. A solution contains 0.10 M H2S and 0.3 M HCl.

Given that for H2S K

1 = 1 107 and

K2 = 1.3 1013. Which are correct

(a) [HS] = 3.33 108M

(b) [HS] = 3 108M

(c) [S2] = 1.44 1010M

(d) [S2] = 13 1013 M

16. A buffer solution is prepared by mixing 6g of aceticacid and 13.6 g of sodium acetage(CH

3COONa.3H

2O) and making the total volume

to 250ml. Which are correct.

Given that Ka = 1.8 105

log (1.8 105) = 4.74

log(0.9230) = 0.04

(a) pH of the solution is 4.74

(b) pH of the solution is 5.74

(c) pH change on addition of 1 ml of 1m-HClis 0.04

(d) pH change on addition of 1 ml of 1M-HClis zero

17. The dissociation constant for NH4OH is 4 105 and

that of CH3COOH is 1.8 105. Then which are

correct.

log(2) = 0.3010, log(3) = 0.4771

(a) Degree of hydrolysis is 63%

(b) Degree of hydrolysis is 37%

(c) pH is 11.57

(d) pH is 7.17

18. Freshly prepared Al(OH)3 and Mg(OH)

2 are stirred

vigorously in a buffer solution containing 0.25 mol/litre of NH

4Cl and 0.05 moles/litre of NH

4OH.

Which are correct

Given that, KbNH

4OH = 1.8 105

Al(OH)3 = 6.0 1023

KspMg(OH)2 = 6.0 1010

(a) [OH] = 3.6 105

(b) [OH] = 0.36 105

(c) [Mg2+] = 46.3

(d) [Mg2+] = 4.63

CIE 14


(Answers) EXCERCISE BASED ON NEW PATTERN

COMPREHENSION TYPE

1. b 2. b 3. a 4. b 5. a 6. b

MATRIX-MATCH TYPE

1. [A-q; B-s; C-r; D-p] 2. [A-q; B-p; C-r; D-p] 3. [A-p; B-q; C-r; D-s]

MULTIPLE CORRECT CHOICE TYPE

1. a, c 2. a, c 3. a, b 4. c, d 5. c, d 6. a, c

7. a, b, c 8. b, c 9. a, b, c 10. b, c 11. a, c 12. b, c

13. a, b, c 14. a, d 15. a, c 16. a, c 17. b, d 18. b, c

ASSERTION-REASON TYPE

1. B 2. D 3. B 4. D

Assertion-Reason Type

Each question contains STATEMENT-1 (Assertion)and STATEMENT-2 (Reason). Each question has4 choices (A), (B), (C) and (D) out of which ONLYONE is correct.

(A) Statement-1 is True, Statement-2 is True;Statement-2 is a correct explanationfor Statement-1

(B) Statement-1 is True, Statement-2 is True;Statement-2 is NOT a correctexplanation for Statement-1

(C) Statement-1 is True, Statement-2 is False

(D) Statement-1 is False, Statement-2 is True

1. STATEMENT-1 : 10 ml of 106 M HCl solution ismixed with 90 ml H

2O. pH will change nearly by

0.7 unit.

STATEMENT-2 : CH3COONH

4 and NH

4CN is

example of salt of weak acid and weak base inwater.

2. STATEMENT-1 : M(OH)X has K

sp 4 1012 and

solubility 1014M. The value of x may be 3.

STATEMENT-2 : Ksp as the product of ionicconcentrations with suitable powers of a sparinglysoluble in its saturated solution.

3. STATEMENT-1 : Ka for formic acid and acetic acidare 2.1 104 and 1.1 105 respectively. Therelative strength of acid is 4.36 : 1.

STATEMENT-2 : Relative strength of strong acidis K

1/K

2

4. STATEMENT-1 : Ka for butric acid is 2 105. The

pH of concentration of 0.2 M aqueous. Solution ofsodium butyrate is 9.5

STATEMENT-2 : pH in weak acid and strong base

is Clogpp2

1 kakw

CIE 15


INITIAL STEP EXERCISE

(SUBJECTIVE)

1. (a) Find the pH of 107 M solution of HCl at298 K

(b) Calculate the pH of 106 m CH3COOH.

ka(CH

3COOH) = 1.8 105.

2. Liquid ammonia ionizes to a slight extent. At 500C,

its ion product is 30

24NH 10]NH][NH[K 3 .

How many amide ions, NH2, are present per mm3

of pure liquid ammonia ?

3. When 0.100 mol of ammonia, NH3, is dissolved in

sufficient water to make 1.00 L of solution, thesolution is found to have a hydroxide ionconcentration of 1.34 103 M. Calculate K

b for

ammonia.

4. At 250C, a 0.0100 M ammonia solution is 4.1%ionized. Calculate (a) the concentration of the OH

and NH4+ ions (b) the concentration of molecular

ammonia (c) the ionisation constant of aqueousammonia (d) [OH] after 0.0090 mol of NH

4Cl is

added to 1.00 L of the above solution (e) [OH] of asolution prepared by dissolving 0.010 mol of NH

3

and 0.0050 mol of HCl per L.

5. Find the value of [OH] in a solution made bydissolving 0.0050 mol each of ammonia andpyridine (C

5H

5N) in enough water to make 200 cm3

of solution. What are the concentrations ofammonium and pyridinium ions ? K

b(NH

3) = 1.8

105, Kb (C

5H

5N) = 1.52 109.

6. Calculate [H+] in a solution that is 0.100 M HCOOHand 0.100 M HOCN. K

a(HCOOH) = 1.8 104,

Ka(HOCN) = 3.3 104.

7. What is the pH of a solution containing 0.010 molHCl/L ? Calculate the change in pH if 0.020 molNaC

2H

3O

2 is added to 1.0 L of this solution.

Ka(C

2H

4O

2) = 1.8 105.

8. Calculate the concentration of H3O+ ion in a

solution prepared by dissolving 0.20 mol ofHC

2H

3O

2 and 0.050 mol of Mg(C

2H

3O

2)

2 in enough

water to make 1.0 L of solution.K

aCH

3COOH = 1.8 105.

9. Calculate the pH of a solution made by mixing 50.0mL of 0.200 M NH

4Cl and 75.0 mL of 0.100 M

NaOH. Kb(NH

3) = 1.8 105.

10. Determine the pH of a solution after 0.10 mol ofNaOH is added to 1.00 L of a solution containing0.15 M HC

2H

3O

2 and 0.20 M NaC

2H

3O

2. Assume

no change in volume. Ka = 1.8 105.

11. How many moles of sodium hydroxide can be addedto 1.00 L of a solution 0.100 M in NH

3 and 0.100 M

in NH4Cl without changing the pOH by more than

1.00 unit ? Assume no change in volume.pKb

(NH3) = 4.75.

12. The acid ionization (hydrolysis) constant of Zn2+ is1.0 109. (a) Calculate the pH of a 0.0010 Msolution of ZnCl

2. (b) What is the basic dissociation

constant of Zn(OH)+ ?

13. Calculate the ammonia concentration of a solutionprepared by dissolving 0.150 mol of NH

4C

2H

3O

2 in

sufficient water to make 1.0 L of solution.K

a = K

b = 1.8 105.

14. K1 and K

2 for oxalic acid, H

2C

2O

4, are 5.6 102

and 5.4 105. What is [OH] in a 0.0050 Msolution of Na

2C

2O

4 ?

15. Bromphenol blue is an indicator with a Ka value of

5.84 105. What percentage of this indicator is inits basic form at a pH of 4.84 ? K

a(HBb) = 5.84

105 (HBb representing bromophenol blue).

16. 0.15 mole of pyridinium chloride has been addedinto 500 cm3 of 0.2 M pyridine solution. CalculatepH and hydroxyl ion concentration in the resultingsolution assuming no change in volume. (K

b for

pyridine = 1.5 109 M)

17. Calculate simultaneous solubility of AgCNS andAgBr in water. K

SP of AgBr = 5 1013 and K

SP of

AgCNS = 1 1012

18. Calculate the amount of (NH4)

2SO

4 in grams which

must be added to 500 ml of 0.200 M NH3 to yield a

solution with pH 9.35 (Kb for NH

3 = 1.78 105)

19. CH3COOH (50 mL, 0.1 M) is titrated against 0.1 m

NaOH solution. Calculate the pH at the addition of0 mL, 20 mL, 25 mL, 40 mL, 50 mL and 60 mL ofNaOH.

20. Calculate the percentage of hydrolysis of 0.003 Maqueous of NaOCN.

(Ka for HOCN = 3.33 104 M)

21. When 25 ml of 0.20 M acetic acid is neutralised with25 ml 0.20 M NaOH, the resulting solution is slightlyalkaline, calculate the pH of the resulting solution(K

a for acetic acid = 1.8 105).

22. What volume of 0.10 M sodium formate solutionshould be added to 50 ml of 0.05 M formic acid toproduce a buffer solution of pH 4.0 ? pK

a for

formic acid is 3.80.

23. Calculate the change in pH of one litre of buffersolution containing 0.10 mole each of NH

3 and

NH4Cl upon addition of

CIE 16


FINAL STEP EXERCISE

(SUBJECTIVE)

1. The self-ionization constant for pure formic acid,K = [HCOOH

2+][HCOO], has been estimated as

106 at room temperature. What percentage offormic acid molecules in pure formic acid, HCOOH,are converted to formate ion ? The density offormic acid is 1.22 g/cm3.

2. When 0.100 mol of NH3 is dissolved in sufficient

water to make 1.00 L of solution, the solution isfound to have a hydroxide ion concentration of 1.33 103 M. (a) What is the pH of the solution ? (b)What will be the pH of the solution after 0.100 molof NaOH is added to it ? (Assume no change involume). (c) Calculate K

b for ammonia. (d) How

will NaOH added to the solution affect the extentof dissociation of ammonia ?

3. Calculate the pH at which Mg(OH)2 begins to

precipitate from a solution containing 0.10 M Mg2+

ions. KSP

for Mg(OH)2 = 1.0 1011

4. A solution contains 0.10 M H2S and 0.3 M HCl.

Calculate the concentration of S2 and HS ins inthe solution. For H

2S

7a 100.1K 1

13a 103.1K 2

5. Calcium lactate is a salt of a weak organic acid andrepresented as Ca(Lac)

2. A saturated solution of

Ca(Lac)2 contains 0.13 mol of this salt in 0.50 litre

solution. The pOH of this solution is 5.60.Assuming a complete dissociation of the salt,calculate K

a of lactic acid.

(a) 0.02 mole of HCl

(b) 0.02 mole of NaOH

Given Kb of NH

3 = 1.8 105

24. The solubility product of PbBr2 is 8 105. If the

salt is 80% dissociated in saturated solution, findthe solubility of the salt. Atomic weights of Pb andBr are 208 and 80 a.m.u. respectively.

25. Given that Ksp

of CaF2 is 1.7 1010, how many

grams of it can be dissolved in (a) one litre 0.001 MNaF, (b) one litre 0.01 M CaCl

2.

26. The solubility products of BaSO4 and BaCrO

4 at

250C are 1 1010 and 2.4 1010 respectively.Calculate the simultaneous solubility of BaSO

4 and

BaCrO4.

27. One litre of a buffer solution has 0.13833 moles ofacetic acid and 0.1951 moles of sodium acetate.Calculate :

(a) pH of solution

(b) the change in pH on addition of 0.70 mlof 1 M HCl

(c) the change in pH on addition of 0.70 mlof 1 M NaOH

Neglect volume change, Ka = 1.8 105

28. (a) Determine the pH of a 0.10 M solution ofpyridine, C

5H

5N. (b) Predict the effect of addition

of pyridinium ion,C5H

5NH+, on the position of the

equilibrium. Will the pH be raised or lowered ? (c)Calculate the pH of 1.00 L of 0.10 M pyridinesolution to which 0.15 mol of pyridinium chloride,C

5H

5NH+Cl, has been added, assuming no change

in volume. Kb[C

5H

5N] = 1.52 109.

29. Calculate the pH of an aqueous solution of 1.0 Mammonium formate assuming completedissociation. (pk

a of formic acid = 3.8 and pk

b of

ammonia = 4.8)

30. What is the pH of a 1.0 M solution of acetic acid ?To what volume must one litre of this solution bediluted so that the pH of the resulting solution willbe twice the original value ?

Given : Ka = 1.8 105.

31. Calculate at 250C the hydrolysis constant and itsdegree of hydrolysis in 0.10 M solution of :(a) sodium acetate, and (b) sodium carbonate. Whatwill be the pH values ?

(Given : Ka(HAc) = 1.8 105 M and K

a(HCO

3) =

4.7 1011 M).

32. It is found that 0.1 M solution of three sodium saltsNaX, NaY and NaZ have pHs 7.0, 9.0 and 11.0,respectively. Arrange the acids HX, HY and HZ inorder of increasing strength. Where possible,calculate the ionization constants of the acids.

33. Calculate the hydrolysis constant and its degree ofhydrolysis in 102 M solution of NH

4Cl. What will

be its pH value ?

Given : Kb (NH

4OH) = 1.8 105 M.

34. Calculate the value of Kh,

h and pH of the

following solutions at 250C.

(i) 0.1 M ammonium acetate

Ka = K

b = 1.8 105 M

(ii) 0.1 M anilinium acetate

Ka = 1.8 105 M; K

b = 4.6 1010 M

(iii) 0.1 M ammonium carbonate

1aK = 4.5 107 M;

2aK = 4.7 10111 M

35. Calculate the pH of a solution made by adding 0.001mole of NaOH to 100 cm3 of a solution which is0.50 M in CH

3COOH and 0.50 M in CH

3COONa.

CIE 17


6. Calculate the amount of NH3 and NH

4Cl required

to prepare one litre buffer solution of pH 9.0, whentotal concentration of buffering reagents is 0.6 molL1. pK

b for NH

3 = 4.7.

7. Calculate the solubility of AgCN is a buffersolution of pH = 3.0 K

sp (AgCN) = 1.2 1016,

Ka(HCN) = 4.8 1010. There is no CN or Ag+ ion

in the buffer previously.

8. A solution of weak base BOH was titrated with HCl.The pH of the solution was found to be 10.04 and9.14 after the adding of 5 ml and 20 ml of the acidrespectively. Find the dissociation constant of thebase.

9. A sample of solid AgCl was treated with 5.00 ml of1.5 M Na

2CO

3 solution to give Ag

2CO

3. The

remaining solution contained 0.0026 g of Cl perlitre. Calculate the solubility product of AgCl(K

sp Ag

2CO

3 = 8.2 1012).

10. K for the reaction of Fe3+ to give Fe(OH)2+ and H+ is6.5 103. What is the maximum pH value whichcould be used so that at least 95% of the total iron(III) in a dilute solution exists as Fe3+ ?

11. At what minimum pH will 103 mol of Al(OH)3 go

into solution (V = 1L) as Al(OH)4 and at what

maximum pH it will dissolve as Al3+ ?

Given : Al(OH)4 Al3+ + 4OH

Keq

= 1.3 1034

Al(OH)3 Al3+ + 3OH

Ksp

= 5.0 1033

12. Calculate the [NH4+] ion concentration needed to

prevent Mg(OH)2 from precipitating in a litre of

solution which contains 0.01 mole NH3 and 0.001

mole of Mg2+, Kb(NH

3) = 1.8 105, K

sp

(Mg (OH)2) = 1.12 1011.

13. The pH of blood is maintained by a proper balanceof H

2CO

3 and NaHCO

3 concentrations. What

volume of 5M NaHCO3 solution should be mixed

with a 10 ml of sample of blood which is 2 M inH

2CO

3 in order to maintain a pH of 7.4 ?

Ka(H

2CO

3) = 7.8 107.

14. A certain acid base indicator is red in acidsolution and blue in basic solution. At pH = 5, 75%of the indicator is present in the solution in its blueform. Calculate K

a for the indicator and pH range

over which the indicator changes from 90%red 10% blue to 90% blue 10% red.

15. A weak base BOH was titrated against a strong acid.The pH at 1/4th equivalence point was 9.24. Enoghtstrong base (6 meq.) was now added to consumethe salt completely. The total volume was 50 ml.Find the pH at this point.

16. Solid AgNO3 is gradually added to a solution

containing equimolar concentration of Cl and I.If K

sp of AgCl and AgI are 1.7 1010 and 1.5 10

16 respectively, which one will precipitate first ? Alsofind the relative concentration of I and Cl justbefore the precipitation of AgCl.

17. An acid type indicator, HIn differs in colour fromits conjugate base (In). The human eye issensitive to colour differences only when the ratio(In)/(HIn) is greater than 10 or smaller than 0.1.What should be the minimum change in the pH ofthe solution to observe a complete colour change(K

a = 1.0 105).

18. A solution of weak acid HA was titrated with baseNaOH. The equivalence point was reached when36.12 ml of 0.1 M NaOH has been added. Now 18.06ml of 0.1 M HCl were added to titrated solution,the pH was found to be 4.92. What will be the pHof the solution obtained by mixing 10 ml of 0.2 MNaOH and 10 ml of 0.2 M HA.

19. A solution contains a mixture of Ag+ (0.10 M) andHg

2+2 (0.10 M) which are to be separated by selec-

tive precipitation. Calculate the maximum concen-tration of iodide ion at which one of them gets pre-cipitated almost completely. What % of that metalion is precipitated ? (K

sp of AgI = 8.5 1017 and K

sp

of Hg2I

2 = 2.5 1026)

20. The average concentrations of SO2 in the

atmosphere over a city on a certain day is10 ppm, when the average temperature is 298 K.Given that the solubility of SO

2 in water at 298 K is

1.3653 moles litre1 and the pKa of H

2SO

3 is 1.92,

estimate the pH of rain on that day.

21. The solubility of Pb(OH)2 in water is 6.7 106M.

Calculate the solubility of Pb (OH)2 in a buffer

solution of pH = 8.

22. For the reaction

[Ag (CN)2] Ag+ + 2CN,

the equilibrium constant at 250C is 4.0 1019.Calculate the silver ion concentration in a solutionwhich was originally 0.10 molar in KCN and 0.03molar in AgNO

3.

23. An aqueous solution of a metal bromide MBr2

(0.05M) is saturated with H2S. What is the

minimum pH which MS will precipitate ?

24. The solubility product (Ksp

) of Ca(OH)2 at 250C is

4.52 105. A 500 ml of saturated solution ofCa(OH)

2 is mixed with equal volume of 0.4 M

NaOH. How much Ca(OH)2 in milligrams is

precipitated ?

CIE 18


ANSWERS SUBJECTIVE (INITIAL STEP EXERCISE)

1. (a) 6.79 (b) 6.01 2. 600 ions/mm3

3. 1.81 105 4. (a) 0.00041 (b) 0.0096 (c)1.8 105 (d) 2.0 105 (e) 1.8 105

5. 5.7 108 6. 7.1 103 7. 2.748. 3.6 105 M 9. pH = 9.73 10. pH = 5.511. 0.082 mol of NaOH can be added 12. (a) 6.0 (b) 1.0 105

13. [NH3] = 8.3 104 14. 9.6 107 M

15. 80%16. 5 17. Solubility of AgCNS = 8.16 107 mol lt.1

18. 5.28 gm 19. (i) 2.85 (ii) 4.0969(iii) 4.5229 (iv) 4.699(v) 5.3011 (vi) 8.699(vii) 11.9586

20. 0.01 % 21. 8.3722. 39.625 ml 23. (a) pH decrease by 0.1761

(b) pH increase by 0.176124. 12.486 g l1

25. (a) 1.326 102 g, (b) 5.08 103 g26. 5.423 106, 1.3 105 M27. (a) 4.894 (b) 0.0038 less (c) 0.0038 more28. (a) 9.09 (b) 5.0131. (a) 0.55 109, 7.44 105, 8.9 (b) 2.127 104, 0.046, 11.6632. HX > HY > HZ, K

a(HY) = 105, K

a(HZ) = 109

33. 5.6 1010, 5.63 34. (i) 0.3086 104, 0.553 102, 7(ii) 1.208, 0.52, 4.71(iii) 11.82, 0.775, 9.79 35. 4.76

ANSWERS SUBJECTIVE (FINAL STEP EXERCISE)

1. 0.004 %

2. (a) 11.12 (b) 13 (c) 1.79 105 (d) The OH of the NaOH represses the dissociation ofNH

3

3. 9 4. [HS] = 3.33 108 M; [S2] = 1.44 1020 M

5. 9, 105 M

6. NH3 = 0.2 moles, NH

4Cl = 0.4 moles

7. 1.58 105 M each

8. 1.8 105 9. 1.71 1010 10. 0.908

11. 9.415, 4.233 12. 1.7 103 13. 78.37 ml

14. Ka = 3 105, 3.56 to 5.47 15. 11.22

16.

7108.8Cl

I;AgI

17. Minimum change in pH = 2 18. 8.96

19. 5 1013, 99.83% 20. 4.865

cie – 1 ionic equilibrium - einstein classeseinsteinclasses.com/ionic equilibrium.pdf · cie –...

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