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NCERT Solutions for Class 11 Chemistry Chapter 7 Equilibrium

NCERT Solutions for Class 11 Chemistry Chapter 7 Equilibrium

Edited By Sumit Saini | Updated on Aug 22, 2022 08:40 AM IST

NCERT Solutions for Class 11 Chemistry Chapter 7 Equilibrium- In this chapter, you will get the NCERT solutions for class 11 chemistry chapter 7 Equilibrium of chemical and physical processes and details about equilibrium's dynamic nature. There are some insights about the equilibrium constant, the law of mass action and what are the factors affecting the equilibrium state. It is a lengthy and also an important chapter of NCERT syllabus class 11 chemistry.

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In NCERT solutions for class 11 chemistry chapter 7 Equilibrium, there are 73 questions in the exercise. The NCERT solutions for class 11 chemistry chapter 7 Equilibrium are prepared and solved by chemistry experts. These NCERT solutions will help you in the preparation of your class 11 final examination as well as in the various competitive exams like JEE Mains, NEET, BITSAT, etc. By referring to the NCERT solutions for class 11 , students can understand all the important concepts and practice questions well enough before their examination

What is the Equilibrium?

Equilibrium is the state of a process in which the properties like the concentration of the system, pressure, and temperature do not change with the passage of time. It can be established for both chemical and physical processes. At the stage of equilibrium, the rate of forwarding and reverse reactions are equal. The state of equilibrium can only be achieved if the reversible reaction is taking place in a closed system.

Important formulas of NCERT class 11 chemistry chapter 7 Equilibrium
1.Equilibrium constant, K
K=KfKb
2. Concentration quotient, Q
Q=[C]c[D]d[A]a[B]b
3. ΔGo=2.303RTlogK
4. Kw=[H+][OH]
5. pH=log[H+]

NCERT Solutions for Class 11 Chemistry Chapter 7 Equilibrium

Question 7.1(a) A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.

What is the initial effect of the change on vapour pressure?

Answer :

By increasing the volume of the container suddenly, initially, the vapour pressure would decrease. It is due to, the amount of vapour has remained the same but it is distributed in a larger volume.

Question 7.1(b) A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.

How do rates of evaporation and condensation change initially?

Answer :

Here the temperature is constant so that the rate of evaporation is also the same as before. On increasing the volume of the container, the density of vapour decreases due to which the rate of collision between vapour particles decreases. Hence the condensation rate also decreases initially.

Question 7.1(c) A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased .

What happens when equilibrium is restored finally and what will be the final vapour pressure?

Answer :

When equilibrium is restored, the rate of evaporation is equal to the rate of condensation. The temperature is constant and the volume is changed. The vapour pressure is temperature-dependent, not volumes. So, that final vapour pressure is equal to the initial vapour pressure.

Question 7.2 What is K c for the following equilibrium when the equilibrium concentration of each substance is: [SO 2 ]= 0.60M, [O 2 ] = 0.82M and [SO 3 ] = 1.90M ?

2SO_2_(g)+O_2_(g )\rightleftharpoons 2SO_3_(g)

Answer :

Followings are the given information values to solve the above problems-
[SO2]=0.60M[O2]=0.82M[SO3]=1.90M
The given chemical equation is -

2SO_2_(g)+O_2_(g )\rightleftharpoons 2SO_3_(g)

The equilibrium constant for this reaction is expressed as;
Kc=[SO3]2[SO2]2[O2]

=[1.90]2[0.60]2[0.82]=12.22M1 (approx)


Question 7.3 At a certain temperature and total pressure of 10 5 Pa, iodine vapour contains 40% by volume of I atoms

I(g)2I(g)

Calculate Kp for the equilibrium.

Answer :

It is given that total pressure (P T )is 105 Pa and partial pressure of I atom = 40 % of P T
So, the partial pressure of I atom = 40100×105=4×104 Pascal

The partial pressure of I2 = 60% of P T

So, the partial pressure of I2 = 60100×105=6×104 Pascal

Now, for the reaction I(g)2I(g)
Kp=(pI)2pI2=(4×104)26×104 Pa
=2.67\times 10^4\ Pa

Question 7.4 Write the expression for the equilibrium constant, K c for each of the following reactions:

(i) 2NOCl_{(g)}\rightleftharpoons 2NO_{(g)}+Cl{2}_{(g)}

(ii) \\2Cu(NO_3)_2_(s)\rightleftharpoons 2CuO_{(s)}+4NO_2_{(g)}+O_2_{(g)}

(iii) CH_3COOC_2H_5_{(aq)}+H_{2}O_{(l)}\rightleftharpoons CH_{3}COOH_{(aq)}+C_{2}H_{5}OH_{(aq)}

(iv) CH_3COOC_2H_5_{(aq)}+H_{2}O_{(l)}\rightleftharpoons CH_{3}COOH_{(aq)}+C_{2}H_{5}OH_{(aq)}

(v) I_{2}_{(s)}+5F_{2}\rightleftharpoons 2IF_{5}

Answer :

The equilibrium constant for any reaction can be written as (concentration of products) / (concentration of reactants). And we considered constant values for the solids and liquids because their density per unit volume or mass per unit volume does not change.
Thus,
(i)
K_c = \frac{[NO]^2[Cl_2]}{[NOCl]^2} (ii)
Kc=[CuO]2[NO2]4[O2][Cu(NO3)2]2
(iii)

Kc=[CH3COOH][C2H5OH][CH3COOC2H5]

(iv)
Kc=1[Fe3+][OH]

(v)
Kc=[IF5]2[F2]5

Question 7.5 Find out the value of K c for each of the following equilibria from the value of K p :

(i) 2NOCl _{(g)}\rightleftharpoons 2NO_{(g)}+Cl_{2}_{(g)};K_{p}=1.8 \times 10^{-2} at 500K

(ii)CaCO_{3}_{(s)}\rightleftharpoons CaO_{(s)}+CO_{2}_{(g)};K_{p}=167 at 1073K

Answer :

We know that the relation between Kp and Kc is expressed as;

Kp=Kc(RT)Δn ............................(i)
here Δn = (no. of moles of product) - (no. of moles of reactants)

R = 0.0831 bar L /mol/K, and

For (i)
Kp = 1.8×102 and Temp (T) = 500K

Δn = 3 - 2 = 1
By putting the all values in eq (i) we get

Kc=1.8×1020.0831×500=4.33×104

For (ii)
Kp = 167 and temp(T) = 1073 K
Δn = 2 - 1 = 1
Now, by putting all values in eq (i) we get,

Kc=1670.0831×1073=1.87

Question 7.6 For the following equilibrium, K c = 6.3 × 10 14 at 1000 K

NO_{(g)}+O_{3}_{(g)}\rightleftharpoons NO_{2}_{(g)}+O_{2}_{(g)}

Both the forward and reverse reactions in the equilibrium are elementary bimolecular reactions. What is K c , for the reverse reaction?

Answer :

It is given that,
Kc=6.3×1014
we know that Kc for the reverse reaction is the inverse of the forward equilibrium constant. Thus it can be calculated as:

Kc=1Kc
=16.3×1014
=1.58×1015

Question 7.7 Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

Answer :

For the pure liquids and solids, the molecular mass and the density at a particular temperature is always fixed and it is considered as a constant. Thus they can be ignored while writing the equilibrium constant expression

Question 7.8 Reaction between N 2 and O 2- takes place as follows:

2N_{2}_{(g)}+O_{2}_{(g)}\rightleftharpoons 2N_{2}O_{(g)}

If a mixture of 0.482 mol N 2 and 0.933 mol of O 2 is placed in a 10 L reaction vessel and allowed to form N 2 O at a temperature for which K c = 2.0 ×10 -37 , determine the composition of equilibrium mixture.

Answer :

It is given that,
Kc=2.0×1037
Let the concentration of N2O at equilibrium be x . So,

2N_{2}_{(g)}+O_{2}_{(g)}\rightleftharpoons 2N_{2}O_{(g)}

initial conc 0.482 0.933 0 (in moles)
at equilibrium 0.482- x 0.933 - x x (in moles)

The equilibrium constant is very small. So, we can assume 0.482- x = 0.482 and 0.933 - x = 0.933

We know that,

Kc=[N2O]2[N2]2[O2]
2×1037=(x/10)2(0.0482)2(0.0933) {dividing the moles by 10 to get concentration of ions)

x2100=2×1037×(0.0482)2×(0.0933)x2=43.35×1040x=43.35×1040x=6.6×1020

So, the concentration of [N2O]=x10=6.6×1020

Question 7.9 Nitric oxide reacts with Br 2 and gives nitrosyl bromide as per reaction given below:

2NO_{(g)}+Br_{2}_{(g)}\rightleftharpoons 2NOBr_{(g)}

When 0.087 mol of NO and 0.0437 mol of Br 2 are mixed in a closed container at a constant temperature, 0.0518 mol of NOBr is obtained at equilibrium. Calculate the equilibrium amount of NO and Br 2 .

Answer :

The initial concentration of NO and Br2 is 0.087 mol and 0.0437 mol resp.

The given chemical reaction is-
2NO_{(g)}+Br_{2}_{(g)}\rightleftharpoons 2NOBr_{(g)}

Here, 2 mol of NOBr produces from 2 mol of NO . So, 0.0518 mol of NOBr is obtained from 0.518 mol of NO .

Again, From 1 mol of Br2 two mol of NOBr produced. So, to produce 0.518 mol of NOBr we need 0.5182=0.0259 mol of Br2 .

Thus, the amount of NO present at equilibrium = 0.087 - 0.0518 = 0.0352 mol

and the amount of Br2 present at the equilibrium = 0.0437-0.0259 = 0.0178 mol

Question 7.10 At 450K, K p = 2.0 × 10 10 /bar for the given reaction at equilibrium.

2SO_{2}_{(g)}+O_{2}_{(g)}\rightleftharpoons 2SO_{3}_{(g)}

What is K c at this temperature?

Answer :

We have,
Kp=2×1010/bar
We know that the relation between Kp and Kc ;

Kp=Kc(RT)Δn
Here Δn = ( moles of product) - (moles of reactants)

2SO_{2}_{(g)}+O_{2}_{(g)}\rightleftharpoons 2SO_{3}_{(g)}

So. here Δn = 2-3 = -1

By applying the formula we get;

2×1010=Kc(0.0831L bar/K/mol)×450K
Kc=2×1010(0.0831L bar/K/mol)×450K

=74.79×1010Lmol1
= 7.48 ×1010Lmol1

Question 7.11 A sample of HI(g) is placed in flask at a pressure of 0.2 atm. At equilibrium the partial pressure of HI(g) is 0.04 atm. What is K p for the given equilibrium?

2HI_{(g)}\rightleftharpoons H_{2}_{(g)}+I_{2}_{(g)}

Answer :

The initial pressure of HI is 0.2 atm . At equilibrium, it has a partial pressure of 0.04 atm. Therefore, a decrease in the pressure of HI is 0.2 - 0.04 = 0.16 .

The given reaction is:

2HI_{(g)}\rightleftharpoons H_{2}_{(g)}+I_{2}_{(g)}

HI_{(g)}\rightleftharpoons 1/2H_{2}_{(g)}+1/2I_{2}_{(g)}

At equilibrium,
pHI=0.04pH2=0.162=0.08pI2=0.162=0.08

Therefore,
Kp=pH2×pI2p2HI
=0.08×0.08(0.04)2=4

Question 7.12 A mixture of 1.57 mol of N 2 , 1.92 mol of H 2 and 8.13 mol of NH 3 is introduced into a 20 L reaction vessel at 500 K. At this temperature, the equilibrium constant, K c for the reaction N_{2}_{(g)}+3H_{2}_{(g)}\rightleftharpoons 2NH_{3}_{(g)} is 1.7 × 10 2 . Is the reaction mixture at equilibrium? If not, what is the direction of the net reaction?

Answer :

We have,
N_{2}_{(g)}+3H_{2}_{(g)}\rightleftharpoons 2NH_{3}_{(g)}

Kc=1.7×102

The concentration of species are-
[N2]=1.57/20molL1[H2]=1.92/20molL1[NH3]=8.13/20molL1

We know the formula of

Qc=[NH3]2[N2][H2]3
=(8.13/20)2(1.57/20)(1.92/20)3=2.4×103
The reaction is not in equilibrium. Since Qc>Kc , the equilibrium proceeds in reverse direction.

Question 7.13 The equilibrium constant expression for a gas reaction is,

Kc=[NH3]4[O2]5[NO]4[H2O]5

Write the balanced chemical equation corresponding to this expression.

Answer :

The balanced chemical equation corresponding to the given expression can be written as:

4NO+6H2O4NH3+5O2

Question 7.14 One mole of H 2 O and one mole of CO are taken in 10 L vessel and heated to 725 K. At equilibrium 40% of water (by mass) reacts with CO according to the equation,

H_{2}O_{(g)}+CO_{(g)}\rightleftharpoons H_{2}_{(g)}+CO_{2}_{(g)}

Calculate the equilibrium constant for the reaction.

Answer :

The given reaction is-

H_{2}O_{(g)}+CO_{(g)}\rightleftharpoons H_{2}_{(g)}+CO_{2}_{(g)}

initial conc 1/10 1/10 0 0
At equilibrium 0.6/10 0.6/10 0.04 0.04

Now, the equilibrium constant for the reaction can be calculated as;

Kc=[H2][CO2][H2O][CO]
=.04×.04(.06)2

= 0.44 (approx)

Question 7.15 At 700 K, equilibrium constant for the reaction:

H_{2}_{(g)}+I_{2}_{(g)}\rightleftharpoons 2HI_{(g)}

is 54.8. If 0.5 mol L -1 of HI(g) is present at equilibrium at 700 K, what are the concentration of H 2 (g) and I 2 (g) assuming that we initially started with HI(g) and allowed it to reach equilibrium at 700K?

Answer :

We have,

The equilibrium constant of the reaction = 54.8

moles of HI = 0.5 mol/L

The given reaction is-

H_{2}_{(g)}+I_{2}_{(g)}\rightleftharpoons 2HI_{(g)}

So, the reverse equilibrium constant is Kc=1/Kc

Suppose the concentration of hydrogen and iodine at equilibrium be x

[I2]=[H2]=x

Therefore,

Kc=[H2][I2][HI]=x2(.5)2
So, the value of x = 0.2554.8=0.0675(approx) mol/L

Question 7.16 What is the equilibrium concentration of each of the substances in the equilibrium when the initial concentration of ICl was 0.78 M ?

2ICl _{(g)}\rightleftharpoons I_{2}_{(g)}+Cl_{2}_{(g)}; K_{c}=0.14

Answer :

The given reaction is:
2ICl(g)I2(g)+Cl2(g)
Initial conc. 0.78 M 0 0
At equilibrium (0.78 - 2 x ) M x M x M

The value of Kc=0.14

Now we can write,
Kc=[I2][Cl2][ICl]2
0.14=x2(.78x)20.374=x(.78x)

By solving this we can get the value of x = 0.167

Question 7.17 K p = 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of C 2 H 6 when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium?

C_{2}H_{6}_{(g)}\rightleftharpoons C_{2}H_{4}_{(g)}+H_{2}_{(g)}

Answer :

Suppose the pressure exerted by the hydrogen and ethene gas be p at equilibrium.

the given reaction is-

C_{2}H_{6}_{(g)}\rightleftharpoons C_{2}H_{4}_{(g)}+H_{2}_{(g)}

initial pressure 4 atm 0 0
At equilibrium 4 - p p p

Now,
Kp=pC2H4×pH2/pC2H6
0.04=p24p

By solving the quadratic equation we can get the value of p = 0.38

Hence,at equilibrium,

pC2H6 = 4 - p = 4 -.038

= 3.62 atm

Question 7.18(i) Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

CH_{3}COOH _{(l)}+C_{2}H_{5}OH\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)}

(i) Write the concentration ratio (reaction quotient), Q c , for this reaction (note: water is not in excess and is not a solvent in this reactio n)

Answer :

The given reaction is-
CH_{3}COOH _{(l)}+C_{2}H_{5}OH\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)} the concentration ratio (reaction quotient) of the given chemical reaction is-

Qc=[CH3COOC2H5][H2O][CH3COOH][C2H5OH]

Question 7.18(ii) Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

CH_{3}COOH _{(l)}+C_{2}H_{5}OH_{(l)}\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)}

(ii) At 293 K, if one starts with 1.00 mol of acetic acid and 0.18 mol of ethanol, there is 0.171 mol of ethyl acetate in the final equilibrium mixture. Calculate the equilibrium constant.

Answer :

Let the volume of the mixture will be V.
CH_{3}COOH _{(l)}+C_{2}H_{5}OH_{(l)}\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)}

initial conc. 1/V 0.18/V 0 0

At equilibrium 1.171V (= 0.829/V) 1.171V 0.171 0.171

So the equilibrium constant for the reaction can be calculated as;

Kc=(0.171)2(0.829)(0.009)

=3.92 (approx)

Question 7.18(iii) Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

CH_{3}COOH_{(l)}+C_{2}H_{5}OH_{(l)}\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)}

(iii) Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and maintaining it at 293 K, 0.214 mol of ethyl acetate is found after sometime. Has equilibrium been reached?

Answer :

Let the volume of the mixture will be V.
CH_{3}COOH_{(l)}+C_{2}H_{5}OH_{(l)}\rightleftharpoons CH_{3}COOC_{2}H_{5}_{(l)}+H_{2}O_{(l)}

initial conc. 1/V 0.5/V 0 0

At equilibrium 1.214V (= 0.786/V) 1.214V 0.214 0.214

Therefore the reaction quotient of the reaction-

Qc=(0.214)2(0.786)(0.286)

=0.2037(approx)

Since Qc<Kc equilibrium has not been reached.

Question 7.19 A sample of pure PCl 5 was introduced into an evacuated vessel at 473 K. After equilibrium was attained, concentration of PCl 5 was found to be 0.5 × 10 -1 mol L -1 . If value of K c is 8.3 × 10 -3 , what are the concentrations of PCl 3 and Cl 2 at equilibrium?

PCl_{5}_{(g)}\rightleftharpoons PCl_{3}_{(g)}+Cl_{2}_{(g)}

Answer :

We have,

concentration of PCl5 = 0.05 mol/L
and Kc=8.3×103

Suppose the concentrations of both PCl3 and Cl2 at equilibrium be x mol/L. The given reaction is:

PCl5(g)PCl3(g)+Cl2(g)

at equilibrium 0.05 x x

it is given that the value of the equilibrium constant, Kc=8.3×103

Now we can write the expression for equilibrium as:

Kc=x20.05=8.3×103
x=4.15×104
=0.0204 (approx)

Hence the concentration of PCl3 and Cl2 is 0.0204 mol / L

Question 7.20 One of the reaction that takes place in producing steel from iron ore is the reduction of iron(II) oxide by carbon monoxide to give iron metal and CO 2 . FeO_{(s)}+CO_{(g)}\rightleftharpoons Fe_{(s)}+CO_{2}_{(g)} ; K p = 0.265 atm at 1050K What are the equilibrium partial pressures of CO and CO 2 at 1050 K if the initial partial pressures are: pCO = 1.4 atm and pCO2 = 0.80 atm?

Answer :

We have,

Kp=0.265
the initial pressure of CO and CO2 are 1.4 atm and 0.80atm resp.

The given reaction is-

FeO_{(s)}+CO_{(g)}\rightleftharpoons Fe_{(s)}+CO_{2}_{(g)}

initially, 1.4 atm 0.80 atm

Qp=pCO2pCO=0.801.4=0.571
Since Qp>Kc the reaction will proceed in the backward direction to attain equilibrium. The partial pressure of CO2 will increase = decrease in the partial pressure of CO2 = p

Kp=pCO2pCO=0.80p1.4+p=0.265
=0.371+.265p=0.80p

By solving the above equation we get the value of p = 0.339 atm

Question 7.21 Equilibrium constant, K c for the reaction

N_{2}_{(g)}+3H_{2}_{(g)}\rightleftharpoons 2NH_{3}_{(g)}

At 500 K is 0.061 At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L -1 N 2 , 2.0 mol L -1 H 2 and 0.5 mol L -1 NH 3 . Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?

Answer :

The given reaction is:

N_{2}_{(g)}+3H_{2}_{(g)}\rightleftharpoons 2NH_{3}_{(g)}

at a particular time: 3.0molL -1 2.0 molL -1 0.5molL -1

Now, we know that,

Qc=[NH3]2/[N2][H2]3
=(0.5)2/(3.0)(2.0)3=0.0104

It is given that K c = 0.061

Since, Qc Kc, the reaction mixture is not at equilibrium.

Again, Qc<Kc , the reaction will proceed in the forward direction to attain the equilibrium.

Question 7.22 Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:

2BrCl_{(g)}\rightleftharpoons Br_{2}_{(g)}+Cl_{2}_{(g)}

For which K c = 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10 -3 mol L -1 , what is its molar concentration in the mixture at equilibrium?

Answer :

Suppose the x amount of bromine and chlorine formed at equilibrium. The given reaction is:

2BrCl_{(g)}\rightleftharpoons Br_{2}_{(g)}+Cl_{2}_{(g)}

Initial Conc. 3.3×103 0 0

at equilibrium 3.3×103 - 2 x x x

Now, we can write,

Kc=[BR2][Cl2][BrCl2]2
32=x2(3.3×1032x)2
5.66=x(3.3×1032x)
x+11.32x=18.678×103

By solving the above equation we get,

x = 1.51×103

Hence, at equilibrium [BrCl2]=3.3×103(2×1.51×103)
=0.3×103 M

Question 7.23 At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO 2 in equilibrium with soild carbon has 90.55% CO by mass

C_{(s)}+CO_{2}_{(g)}\rightleftharpoons 2CO_{(g)}

Calculate K c for this reaction at the above temperature .

Answer :

Suppose the total mass of the gaseous mixture is 100 g.
Total pressure is 1 atm

Mass of CO = 90.55 g
And, mass of CO2 = (100 - 90.55) = 9.45 g

Now, number of moles of CO = 90.55/28 = 3.234 mol (mol. wt of CO = 28)
Number of moles of CO2 = 9.45/44 = 0.215 mol (mol. wt of CO2 = 44)

Partial pressure of CO ,

pCO=nCOnCO+nCO2pT

=3.2343.234+0.215×1
= 0.938 atm

Similarly partial pressure of CO2 ,

pCO2=nCO2nCO+nCO2pT
= 0.062 atm

Thus, Kp=(0.938)2(0.062)14.19

By using the relation Kp=Kc(RT)Δn
Kc=14.19(0.083×1127)1
= 0.159 (approx)

Question 7.24 Calculate a) ΔG0 for the formation of NO2 from NO and O2 at 298K

NO(g)+12O2(g)NO2(g)

where

ΔfG+[NO2]=52.0kJ/mol

ΔfG+[NO]=87.0kJ/mol

ΔfG+[O2]=0kJ/mol

Answer :

Given data,

ΔfG+[NO2]=52.0kJ/mol
ΔfG+[NO]=87.0kJ/mol

ΔfG+[O2]=0kJ/mol

given chemical reaction-
NO(g)+12O2(g)NO2(g)

for the reaction,
ΔG0 = ΔG0 (products) - ΔG0 (reactants)
= (52-87-0)
= -35 kJ/mol

Question 7.25 Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?

(a) PCl_{5}_{(g)}\rightleftharpoons PCl_{3}_{(g)}+Cl_{2}_{(g)}

(b) CaO(s)+CO2(s)CaCO3(s)

(c) 3Fe(s)+4H2O(g)Fe3O4(s)+H2(g)

Answer :

According to Le Chatellier's principle, if the pressure is decreased, then the equilibrium will shift in the direction in which more number of moles of gases is present.

So,

  • (a)The number of moles of reaction products will increase.
  • (b)The number of moles of reaction products will decrease
  • (c)The number of moles of reaction products remains the same.

Question 7.26 Which of the following reactions will get affected by increasing the pressure? Also, mention whether the change will cause the reaction to go into forward or backward direction.

(i) COCl2(g)CO(g)+Cl2(g)

(ii) CH4(g)+2S2(g)CS2(g)+2H2S(g)

(iii) CO2(g)+C(s)2CO(g)

(iv) 2H2(g)+CO(g)CH3OH(g)

(v) $CaCO_{3}(s)\rightleftharpoons CaO(s)+CO_{2(g)$

(vi) 4NH3(g)+5O2(g)4NO(g)+6H2O(g)

Answer :

According to Le Chatellier's principle , if the pressure is increased, then the equilibrium will shift in the direction in which less number of moles of gases is present. So, as per this rule following given reactions are affected by the increasing pressure-

The reaction (i), (iii), and (vi)- all proceeds in the backward direction

Reaction(iv) will shift in the forward direction because the number of moles of gaseous reactants is more than that of products.

Question 7.27 The equilibrium constant for the following reaction is 1.6 ×10 5 at 1024K

H2(g)+Br2(g)2HBr(g)

Find the equilibrium pressure of all gases if 10.0 bar of HBr is introduced into a sealed container at 1024K .

Answer :

Given that,
Kp for the reaction = 1.6×105

Kp=1/Kp=11.6×105=6.25×106

Let the pressure of both H2 and Br2 at equilibrium be p .

2HBrH2(g)+Br2(g)
initial conc. 10 0 0
at eq 10-2p p p

Now,
Kp=pBr2.pH2pHBr2
6.25×106=p2(102p)2
5×103=p(5p)
By solving the above equation we get,

p = 0.00248 bar

Hence the pressure of H2 and Br2 is 0.00248 bar and pressure of HBr is 0.00496 bar

Question 7.28(a) Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:

CH4(g)+H2O(g)CO(g)+3H2(g)

Write an expression for Kp for the above reaction.

Answer :

CH4(g)+H2O(g)CO(g)+3H2(g)
the expression of ionisation constant ( Kp) for the reaction can be defined as the ratio of the product of concentration to the product of reactants.
Kp=pCO.pH23pCH4.pH2O

Question 7.28(b) Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:

CH4(g)+H2O(g)CO(g)+3H2(g)

How will the values of Kp and composition of equilibrium mixture be affected by

(i) increasing the pressure

(ii) increasing the temperature

(iii) using a catalyst?

Answer :

(i) According to Le Chatellier's principle, if pressure is increased, then the reaction will shift towards the less number of moles of gases. So, here the direction of equilibrium is backward and the value of Kp decreases.

(ii) According to Le Chatellier's principle, as the reaction is endothermic, the equilibrium will shift in the forward direction. The value of Kp is increases.

(iii) The equilibrium of the reaction is not affected by the presence of the catalyst. It only increases the rate of reaction.

Question 7.29(a) Describe the effect of :

(a) addition of H 2

2H2(g)+CO(g)CH3OH(g)

Answer :

2H2(g)+CO(g)CH3OH(g)
(a)According to Le Chatelliers principle, on the addition of dihydrogen, the number of mole of H2 increases on the reactant side. Thus to attain the equilibrium again the reaction will move in the forward direction.

(b) According to Le Chatellier's principle, on the addition of methyl alcohol, the number of moles of methyl alcohol increases on the product sides. So, to attain the equilibrium, the reaction will proceed in a backward direction.

(c) If we remove the CO from the reactant side, the concentration on the reactant side will decrease and to attain an equilibrium, the reaction will shift backward direction

(d) On removal of CH3OH the equilibrium will shift in the forward direction.

Question 7.29(b) Describe the effect of :

addition of CH 3 OH

2H2(g)+CO(g)CH3OH(g)

Answer :

2H2(g)+CO(g)CH3OH(g)
According to Le Chatellier's principle, on the addition of methyl alcohol, the number of moles of methyl alcohol increases on the product sides. So, to attain the equilibrium, the reaction will proceed in a backward direction.

Question 7.29(c) Describe the effect of :

removal of CO

2H2(g)+CO(g)CH3OH(g)

Answer :

2H2(g)+CO(g)CH3OH(g)
If we remove the CO from the reactant side, the concentration on the reactant side will decrease and to attain an equilibrium, the reaction will shift backward direction

Question 7.30 At 473 K, equilibrium constant K c for decomposition of phosphorus pentachloride, PCl 5 is 8.3 ×10 -3 . If decomposition is depicted as,

PCl5(g)PCl3(g)+Cl2(g),ΔrH+=124.0kJmol1

(a) write an expression for Kc for the reaction.
(b) what is the value of K c for the reverse reaction at the same temperature ?
(c) what would be the effect on K c if

(i) more PCl 5 is added
(ii) pressure is increased
(iii) the temperature is increased ?

Answer :

We have,
PCl5(g)PCl3(g)+Cl2(g),ΔrH+=124.0kJmol1
Equilibrium constant for the above reaction = 8.3×103

(a) Expression of Kc for this reaction-
Kc=[PCl3][Cl2]PCl5

(b) The value of reverse equilibrium constant can be calculated as;

Kc=1Kc
=18.3×103=1.20×102

(c).i Kc would remain the same because the temperature is constant in this case.

(c). ii If we increase the pressure, there is no change in Kc because the temperature is constant in this case also.

(c). iii In an endothermic reaction, the value of Kc increases with increase in temperature.

Question 7.31 Dihydrogen gas used in Haber’s process is produced by reacting methane from natural gas with high temperature steam. The first stage of two stage reaction involves the formation of CO and H 2 . In second stage, CO formed in first stage is reacted with more steam in water gas shift reaction,

CO(g)+H2O(g)CO2+H2(g)

If a reaction vessel at 400 °C is charged with an equimolar mixture of CO and steam such that pCO=pH2O = 4.0 bar, what will be the partial pressure of H 2 at equilibrium? Kp= 10.1 at 400°C

Answer :

We have,
The partial pressure of CO and H2O is 4 bar and the Kp=10.1
Let p be the partial pressure of CO2 and H2 at equilibrium. The given reaction is-

CO(g)+H2O(g)CO2+H2(g)
Initial concentration 4 bar 4 bar 0 0
At equilibrium 4 - p 4 - p p p

Therefore, we can write,
10.1=pCO2.pH2pCO.pH2O
10.1=p2(4p)23.178=p(4p)p=(4p)×3.178
By solving the above equation we get, p = 3.04

Hence, the partial pressure of dihydrogen at equilibrium is 3.04 bar

Question 7.32 Predict which of the following reaction will have an appreciable concentration of reactants and products:

(a) Cl2(g)2Cl(g);Kc=5×1039
(b) Cl2(g)+2NO(g)2NOCl(g);Kc=3.7×108
(c) Cl2(g)+2NO2(g)2NO2Cl(g);Kc=1.8

Answer :

If the value of Kc is in the range of 103 to 103 , then the reaction has appreciable concentrations of both reactants and products.

Therefore, the third reaction (c) (Kc=1.8) will have an appreciable concentration of reactants and products.

Question 7.33 The value of K c for the reaction 3O2(g)2O3(g) is 2.0 ×10 -50 at 25°C. If the equilibrium concentration of O 2 in air at 25°C is 1.6 ×10 -2 , what is the concentration of O 3 ?

Answer :

We have,

equilibrium constant of the reaction = 2×1050
the concentration of dioxygen [O2] = 1.6×102

the given reaction is-

3O2(g)2O3(g)
Then we have,
(equilibrium constant)
Kc=[O3(g)]2/[O2(g)]3

2×1050=[O3]2/(1.6×102)3[O3]2=2×1050×(1.6×102)3

=8.192×1056

[O3]=8.192×1056=2.86×1028

Thus the concentration of dioxygen is 2.86×1028

Question 7.34(a) The reaction,

CO(g)+3H2(g)CH4(g)+H2O(g)

is at equilibrium at 1300 K in a 1L flask. It also contain 0.30 mol of CO , 0.10 mol of H2 and 0.02 mol of H2O and an unknown amount of CH 4 in the flask. Determine the concentration of CH 4 in the mixture. The equilibrium constant, K c for the reaction at the given temperature is 3.90.

Answer :

Given that,
Total volume = 1L
0.3 mol of CO , 0.10 mol of dihydrogen( H2 )and the 0.02 mol of water( H2O )
the equilibrium constant = 3.90

Let x be the concentration of methane at equilibrium. The given reaction is-

CO(g)+3H2(g)CH4(g)+H2O(g)
At equilibrium, 0.3 mol/L 0.1 mol/L x 0.02 mol/L

Therefore,

Kc=0.02×x(0.3)(0.1)=3.90
x=(3.9)(0.3)(0.1)3(0.02)
=5.85×102

Thus the concentration of methane at equilibrium is =5.85×102

Question 7.34(b) What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species:

HNO2,CN,HClO4,F,OH,CO32andS2

Answer :

A conjugate acid-base pair means that the species are differed by only one proton. for example; HCl is an acid because it donates a proton to water. So HClCl , and H3O+H2O these pairs are called conjugate acid-base pair.

Species
Conjugate acid-base
HNO2
NO2 (Base)
CN
HCN (Acid)
HClO4
ClO4 (base)
F
HF (acid)
OH
H2O (acid)
CO32
HCO3 (acid)
S2
HS (acid)


Question 7.35 Which of the followings are Lewis acids? H2O,BF3,H+andNH4+

Answer :

Lewis acid-
Those species which can accept the pair of electrons are called Lewis acids. For example Boron trifluoride ( BF3 ), ammonium ion( NH4+ ) and the hydrogen ion( H+ ). Among them water molecule is a Lewis base, it can donate pair of electrons.

Question 7.36 What will be the conjugate bases for the Brönsted acids: HF,H2SO4andHCO3 ?

Answer :

When Brönsted acids lose their proton then they become a conjugate base of that corresponding acids.
Followings are the conjugate base of Brönsted acid-

  • HFF
  • H2SO4HSO4
  • HCO3CO32

Question 7.38 Write the conjugate acids for the following Brönsted bases: NH2,NH3andHCOO .

Answer :

When Brönsted base accepts a proton then they become a conjugate acid of that corresponding base.
Followings are the conjugate acid of Brönsted base-

NH2NH3
NH3NH4+

HCOOHCOOH

Question 7.39 The species: H2O,HCO3,HSO4andNH3 can act both as Brönsted acids and bases. For each case give the corresponding conjugate acid and base.

Answer :

When acid or base accept or lose a proton, they form conjugate acid or base of that corresponding species.

Lists of the conjugate acid and conjugate base of the given species-

Species
Conjugate acid
Conjugate base
H2O
H3O+
OH
HCO3
H2CO3
CO32
HSO4
H2SO4
SO42
NH3
NH4+
NH2


Question 7.40 Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base:
(a) OH
(b) F
(c) H+ .
(d) BCl3

Answer :

Species which donate pair of an electron are called Lewis base and which accepts pair of electrons are called acid.

(a) OH is a Lewis base since it can donate its lone pair of electrons.

(b) F is a Lewis base since it can donate a pair of electrons.

(c) H+ is a Lewis acid since it can accept a pair of electrons.

(d) BCl3 is a Lewis acid since it can accept a pair of electrons.

Question 7.41 The concentration of hydrogen ion in a sample of soft drink is 3.8 × 10 -3 M. what is its pH?

Answer :

We have,
the concentration of Hydrogen ion sample is 3.8×103 M
So, pH=log[H]+
=log(3.8×103)=3log3.8=2.42

Question 7.42 The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen ion in it.

Answer :

We have,
The pH of a sample of vinegar is 3.76
pH =?

Therefore,
pH=log[H+]log[H+]=pH
Taking antilog on both sides we get,
[H+] = antilog (-3.76)
[H+]=1.74×104

Hence the concentration of hydrogen ion [H+]=1.74×104

Question 7.43 The ionization constant of HF, HCOOH and HCN at 298K are 6.8 × 10 -4 , 1.8 × 10 -4 and 4.8 × 10 -9 respectively. Calculate the ionization constants of the corresponding conjugate base.

Answer :

We have,
IOnization constant of hydrogen fluoride, methanoic acid and hydrogen cyanide are 6.8×104, 1.8×104 and 4.8×109 respectively.

It is known that,
Kb=KwKa ...........................(i)

Kb of the conjugate base F
=10146.8×104

=1.5×1011

Similarly,
By using the equation (i)
Kb of the conjugate base HCOO
=10141.8×104

=5.6×1011

Again, with the help of eq (i)
Kb of the conjugate base CN
=10144.8×109
=2.8×106

Question 7.44 The ionization constant of phenol is 1.0 × 10 -10 . What is the concentration of phenolate ion in 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01M in sodium phenolate?

Answer :

We have,
The ionization constant of phenol is 1.0×1010 , and
the concentration of phenol is 0.05 M
degree of ionisation = ?

Ionization of phenol;
C6H5OH+H2OC6H5O+H3O+
At equilibrium,
the concentration of various species are-
[C6H5OH]=0.05x
[C6H5O]=[H3O+]=x
As we see, the value of ionisation is very less. Also x will be very small. Thus we can ignore x .

Ka=[C6H5O][H3O+][C6H5OH]1010=x20.05x=1010×0.05

x=2.2×106

Hence the concentration of phenolate ion is [C6H5O]=2.2×106

Let α be the degree of dissociation of phenol in the presence of 0.01 M of phenolate ion.

C6H5OHC6H5O+H+
Concentration (1 - α ) 0.05 0.05 α 0.05 α

So,
[C6H5OH]=0.05(1α)=0.05
[C6H5O]=0.05α+0.010.01M

[H3O+]=0.05α

therefore,

Ka=(0.01)(0.05α)0.051010=0.01αα=108
The degree of dissociation is 108

Question 7.45 The first ionization constant of H 2 S is 9.1 × 10 -8 . Calculate the concentration of HS - ion in its 0.1M solution. How will this concentration be affected if the solution is 0.1M in HCl also? If the second dissociation constant of H2S is 1.2 × 10 -13 , calculate the concentration of S 2- under both conditions.

Answer :

We have,
1st ionisation constant of hydrogen sulphide is 9.1×108 and the 2nd dissociation constant is 1.2×1013

Case 1st-(absence of hydrochloric acid)

To calculate the concentration of HS
Let x be the concentration of HS and the ionisation of hydrogen sulphide is;
H2SH++HS
0.1 M

At equilibrium, the concentration of various species are,
Since the dissociation constant is is very small. So, x can be neglected.
the concentration of H2S = 1- x M
the concentration of HS and H+ is x M
So,
Ka=x20.1=9.1×108
from here x can be calculated and we get, x=9.54×105M

Case 2nd (In presence of 0.1 M, HCl)
Suppose H2S is dissociated is x .Then at equilibrium,
[H2S]=0.1x0.1, [H+]=0.1+x0.1 and the [HS]=xM
So,
Ka=x(0.1)0.1=9.1×108
Thus the concentration of [ HS ] is 9.1×108

Question 7.46 The ionization constant of acetic acid is 1.74 × 10 -5 . Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its pH.

Answer :

It is given,
The ionisation constant of acetic acid is 1.74×105 and concentration is 0.05 M

The ionisation of acetic acid is;

CH3COOHCH3COO+H+
Therefore,
Ka=[CH3COO][H+][CH3COOH]=[H+]2[CH3COOH]
[H+]=(1.74×105)(5×102)=9.33×104 =[CH3COO]

So, the pH of the solution = log(9.33×104)
= 4log(9.33)
= 3.03

We know that,
α=KaC
α=1.74×1050.05=1.86×102

Question 7.47 It has been found that the pH of a 0.01M solution of an organic acid is 4.15. Calculate the concentration of the anion, the ionization constant of the acid and its pK a .

Answer :

We have,
pH of organic acid is 4.15 and its concentration is 0.01M

Suppose the organic acid be HA. The dissociation of organic acid can be written as;

HAH++A

pH=4.15
log[H+]=4.15[H+]=7.08×105 (By taking antilog of -4.15)

Now,
Ka=[H+][A]/[HA]

[H+]=[A]=7.08×105

[HA] = 0.01

Then,

Ka=(7.08×105)2/0.01Ka=5.01×107

Thus
pKa=log(5.01×107)=6.30

Question 7.48 Assuming complete dissociation, calculate the pH of the following solutions:

(a) 0.003 M HCl

(b) 0.005 M NaOH

(c) 0.002 M HBr

(d) 0.002 M KOH

Answer :

Assuming the complete dissociation. So, α=1

(a) The ionisation of hydrochloric acid is
HClH++Cl
Since it is fully ionised then [H+]=[Cl]=0.003M
Therefore,
pH of the solution = log(0.003)
= 3log(3)
= 2.52

(b) The ionisation of 0.005MNaOH
NaOHNa++OH
[Na+]=[OH]=0.005M
Therefore,
pOH of the solution =
=log(0.005)=3log5=2.301
pH of the solution is equal to (14 - 2.301 =11.70)

(c) The ionisation of 0.002MHBr
HBrH++Br
[Br]=[H+]=0.002M
Therefore,
pH of the solution =
=log(0.002)=3log2=2.69
pH of the solution is equal to (2.69)

(d) The ionisation of 0.002M KOH
KOHK++OH
[OH]=[K+]=0.002M
Therefore,
pOH of the solution =
=log(0.002)=3log2=2.69
pH of the solution is equal to (14 - 2.69 = 11.31)

Question 7.49(a) Calculate the pH of the following solutions:

2 g of TlOH dissolved in water to give 2 litre of solution.

Answer :

Here, 2 g of TlOH dissolves in water to give 2 litres of solution
So, the concentration of TlOH =
[TlOH(aq)]=22g/L=1221M (the molar mass of TlOH is 221)

TlOH can be dissociated as TlOH(aq)Tl++OH

OH(aq)=TlOH(aq)=1221M

Therefore, Kw=[H+][OH] (since K w = 1014 )

So, the concentration of [H+] = 221×1014

Thus PH=log[H+]=log(221×1014)
= 11.65(approx)

Question 7.49(b) Calculate the pH of the following solutions:

0.3 g of Ca(OH)2 dissolved in water to give 500 mL of solution.

Answer :

The calcium hydroxide ion dissociates into-
Ca(OH)2Ca2++2OH
Molecular weight of Ca(OH)2 = 74
the concentration of [Ca(OH)2] = 0.3×100074×500=0.0081M

[OH]=[Ca(OH)2]=0.0081M

We know that,
[H+]=Kw[OH]=10140.0162
= 61.7×1014

Thus PH=log[H+]=log(61.7×1014)
= 14 - 1.79 = 12.21

Question 7.49(c) Calculate the pH of the following solutions:

0.3 g of NaOH dissolved in water to give 200 mL of solution.

Answer :

NaOH dissociates into NaOHNa++OH
So, the concentration of [NaOH] = 0.3×1000200×40M=0.0375M

[OH]=[NaOH]=0.0375M

We know that ,
[H+]=Kw[OH]=10140.0375=2.66×1013

Now, PH = log[H+]
=log(2.66×1013)=12.57

Question 7.49(d) Calculate the pH of the following solutions:

1mL of 13.6 M HCl is diluted with water to give 1 litre of solution.

Answer :

We know that,
M 1 V 1 (before dilution) = M 2 V 2 (after dilution)

initially V 1 = 1mL and M 1 = 13.6 M
and V 2 = 1L and M 2 = ?

By putting all these values we get,

M2=13.6×1031=1.36×102
[H+]=1.36×102

Thus PH=log[H+]=log(1.36×102)
= 1.86 (approx)

Question 7.50 The degree of ionization of a 0.1M bromoacetic acid solution is 0.132. Calculate the pH of the solution and the pK a of bromoacetic acid.

Answer :

We have,

Degree of ionization(a) = 0.132
Concentration of bromoacetic acid (C) = 0.1 M

Thus the concentration of H3O+=C.a
= 0.0132

Therefore
pH=log[H+]=log(0.0132)
= 1.879

Now, we know that,
Ka=C.a2
So, pKa=log(C.a2)
=log(0.1×(0.0132)2)=log(0.0017)=2.76 (approx)

Question 7.51 The pH of 0.005M codeine (C18H21NO3) solution is 9.95. Calculate its ionization constant and pK b.

Answer :

We have,
C = 0.005 M
PH = 9.95 and POH = 14 - 9.95 = 4.05

we know that POH=log[OH]
4.05=log[OH]

By taking antilog on both sides we get.

concentration of [OH] = 8.91×105

C.a = 8.91×105
So, a = 1.782×102

We know that,
Kb=C.a2
=0.005×(1.782×102)2=0.0158×104

Thus
pKb=log(Kb)
=log(0.0158×104)=5.80

Question 7.52 What is the pH of 0.001M aniline solution? Calculate the degree of ionization of aniline in the solution. Also, calculate the ionization constant of the conjugate acid of aniline.(K b = 4.27×1010 )

Answer :

We have,
C = 0.001 M
Kb = 4.27×1010
Degree of inozation of aniline (a) = ?
Ionization constant of the conjugate acid ( Ka ) = ?

We know that
Kb = C.a2
4.27×1010 = (0.001) a2
Thus a=4270×1010
= 65.34×104

Then [Base] = C.a = ( 65.34×104 )( 0.001 )
= 0.653×105

Now, POH=log(0.65×105)=6.187
PH=14POH
= 14 - 6.187
= 7.813

It is known that,

Ka×Kb=Kw
So, Ka=10144.27×1010
=2.34×105 This is ionization constant.

Question 7.53(a) Calculate the degree of ionization of 0.05M acetic acid if its pK a value is 4.74. How is the degree of dissociation affected when its solution also contains

0.01M

Answer :

We have,
C = 0.05 M
pKa=4.74=log(Ka)
By taking antilog on both sides we get,
(Ka)=1.82×105=C.(α)2
from here we get the value of α=1.82×1055×102
=1.908×102

After adding hydrochloric acid, the concentration of H+ ions increases and due to that the equilibrium shifts towards the backward direction. It means dissociation will decrease.

(i) when 0.01 HCl is taken
CH3COOHCH3COO+H+
Initial conc. 0.05 0 0
after dissociation 0.05 - x 0.001+ x x

As the dissociation is very small.
So we can write 0.001+ x 0.001 and 0.05 - x 0.05

Now, Ka=[CH3COO][H+][CH3COOH]
=(0.001)(x)(0.05)=x50

So, the value of x = (1.82×105)(0.05)0.01

Now degree of dissociation = (amount dissociated) / (amount taken)

= 1.82×103(0.05)0.05
= 1.82×103

Question 7.53(b) Calculate the degree of ionization of 0.05M acetic acid if its pK a value is 4.74. How is the degree of dissociation affected when its solution also contains

0.1M in HCl ?

Answer :

Let the x amount of acetic acid is dissociated in this case

CH3COOHCH3COO+H+

Initial conc. 0.05 0 0
after dissociation 0.05 - x 0.1+ x x

As the dissociation is very small.
So we can write 0.1+ x 0.1 and 0.05 - x 0.05

Ka=[CH3COO][H+][CH3COOH]
=(0.1)(x)(0.05)=2x

So, the value of x = (1.82×104)(0.05)0.1

Now the degree of dissociation = (amount dissociated) / (amount is taken)

= 1.82×104(0.05)0.05
= 1.82×104

Question 7.54 The ionization constant of dimethylamine is 5.4 × 10 -4 . Calculate its degree of ionization in its 0.02M solution. What percentage of dimethylamine is ionized if the solution is also 0.1M in NaOH?

Answer :

We have,

(Degree of ionization) Kb=5.4×104
Concentration of dimethylamine = 0.02 M

α=KbC=5.4×1040.02
α=0.1643

If we add 0.1 M of sodium hydroxide. It is a strong base so, it goes complete ionization

NaOHNa++OH
(0.1 M) (0.1 M)

and also,

(CH3)2NH+H2O(CH3)2NH2++OH
0.02- x x x

[OH]=x+0.10.1 (since the dissociation is very small)

Therefore,

Kb=x(0.1)0.02
x=5.4×104(0.020.1)
=0.0054

Hence in the presece of 0.1 M of sodium hydroxide , 0.54% of dimethylamine get dissociated.

Question 7.55(a) Calculate the hydrogen ion concentration in the following biological fluids whose pH are given below:

Human muscle-fluid, 6.83

Answer :

We have PH= 6.83

It is known that PH=log[H+]

Therefore,
6.83=log[H+]
By taking antilog on both sides we get,
[H+]=1.48×107M

Question 7.55(b) Calculate the hydrogen ion concentration in the following biological fluids whose pH are given below:

Human stomach fluid, 1.2

Answer :

We have PH= 1.2

It is known that PH=log[H+]

Therefore,
1.2=log[H+]
By taking antilog on both sides we get,
[H+]=0.063 M

Question 7.55(c) Calculate the hydrogen ion concentration in the following biological fluids whose pH are given below:

Human blood, 7.38

Answer :

we have PH= 7.38

It is known that PH=log[H+]

Therefore,
7.38=log[H+]
By taking antilog on both sides we get,
[H+]=4.17×108 M

Question 7.55(d) Calculate the hydrogen ion concentration in the following biological fluids whose pH are given below:

Human saliva, 6.4.

Answer :

we have PH= 6.4

It is known that PH=log[H+]

Therefore,
6.4=log[H+]
By taking antilog on both sides we get,
[H+]=3.98×107 M

Question 7.56 The pH of milk, black coffee, tomato juice, lemon juice and egg white are 6.8, 5.0, 4.2, 2.2 and 7.8 respectively. Calculate corresponding hydrogen ion concentration in each

Answer :

We already know that pH can be calculated as- log[H+]
to calculate the concentration of [H+] = antilog (- pH )

Thus, the hydrogen ion concentration of followings pH values are-

(i) pH of milk = 6.8
Since, pH=log[H+]
6.8 = log[H+]
log[H+] = -6.8

[H+] = anitlog(-6.8)

= 1.5×107M


(ii) pH of black coffee = 5.0

Since, pH=log[H+]

5.0 = log[H+]

log[H+] = -5.0

[H+] = anitlog(-5.0)

= 105M


(iii) pH of tomato juice = 4.2

Since, pH=log[H+]

4.2 = log[H+]

log[H+] = -4.2

[H+] = anitlog(-4.2)

= 6.31×105M


(iv) pH of lemon juice = 2.2

Since, pH=log[H+]

2.2 = log[H+]

log[H+] = -2.2

[H+] = anitlog(-2.2)

= 6.31×103M

(v) pH of egg white = 7.8

Since, pH=log[H+]

7.8 = log[H+]

log[H+] = -7.8

[H+] = anitlog(-7.8)

= 1.58×108M

Question 7.57 If 0.561 g of KOH is dissolved in water to give 200 mL of solution at 298 K. Calculate the concentrations of potassium, hydrogen and hydroxyl ions.What is its pH?

Answer :

We have 0.562 g of potassium hydroxide ( KOH ). On dissolving in water gives 200 mL of solution.
Therefore, concentration of [KOH(aq)] = 0.561×1000200g/L

= 2.805 g/L

=2.805×156.11M=0.05M
KOH(aq)K+(aq)+OH(aq)
It is a strong base. So, that it goes complete dissociation.

[OH]=0.05M=[K+]

It is known that,

Kw=[H+][OH][H+]=Kw[OH]
=10140.05=2×1013M

Therefore,
pH=log(2×1013)=12.69

Question 7.58 The solubility of Sr(OH)2 at 298 K is 19.23 g/L of solution. Calculate the concentrations of strontium and hydroxyl ions and the pH of the solution.

Answer :

By given abova data, we know the solubility of Sr(OH)2 at 298 K = 19.23 g/L

So, concentration of [Sr(OH)2]

= 19.23/121.63M (Molecular weight of Sr(OH)2 = 121.63 u)

= 0.1581 M

Sr(OH)2(aq)Sr2+(aq)+2(OH)(aq)

Sr2+=0.1581M
and the concentration of [OH] =2×0.1581M=0.3162M
Now

It is known that,
Kw=[OH][H+]

[H+]=10140.3162
= 3.16×1014

Therefore pH=log(3.16×1014)=13.5

Question 7.59 The ionization constant of propanoic acid is 1.32×105 . Calculate the degree of ionization of the acid in its 0.05M solution and also its pH. What will be its degree of ionization if the solution is 0.01M in HCl also?

Answer :

Let the degree of ionization of propanoic acid be α . Then Let suppose we can write propanoic acid to be HA,

It is known that,

We have
ionization constant of propanoic acid ( Ka )= 1.32×105 and the concentration is 0.005 M

α=KaC
By putting the values in above formula we get,

α=1.32×1050.05=1.62×102
[Acid] = [H3O]+ = C. α = 8.15×104

Therefore, pH=log[H3O+]
=log[8.15×104]
=3.08


If we add 0.01M hydrochloric acid then,

AH+H2OH3O++A
initial con C 0 0
at equi. C - x C 0.01 + x x

Now, by using the formula of Ka=(x)(0.01)Cx
=(x)(0.01)C

The value of x is calculated as ;
1.32×105×0.010.01=1.32×105 (Degree of ionisation)

Question 7.60 The pH of 0.1M solution of cyanic acid (HCNO) is 2.34. Calculate the ionization constant of the acid and its degree of ionization in the solution.

Answer :

We have,
Concentration of cyanic acid = 0.1 M
pH=log[H+] =2.34

Therefore, the concentration of [H+] = antilog (-2.34)
= 4.5×103

It is known that,
[H+] =C.α = 4.5×103
α=4.5×1030.1=4.5×102

Then Ionization constant ( Ka ) =C.α2 =
=(0.1)(4.5×102)2
=2.02×104

Question 7.61 The ionization constant of nitrous acid is 4.5 × 10 -4 . Calculate the pH of 0.04 M sodium nitrite solution and also its degree of hydrolysis.

Answer :

We have,
Ionization constant of nitrous acid =4.5×105
Concentration of sodium nitrite ( NaNO2 ) = 0.04 M
Degree of hydrolysis can be calculated as;
Kh=KwKa=10144.5×104=0.22×1010
Sodium nitrite is a salt of sodium hydroxide (strong base) and the weak acid ( HNO2 )
NO2+H2OHNO2+OH
Suppose x moles of salt undergoes hydrolysis, then the concentration of-
[NO2]=0.04x0.04
[HNO2]=x , and
[OH]=x

Therefore
kh=x20.04=0.22×1010
from here we can calculate the value of x ;
x=0.0088×1010=0.093×105=[OH]

[H3O+]=Kw[OH]=10140.093×105
=10.75×109M

Now pH=log(10.75×109M)=7.96

Therefore the degree of hydrolysis

Question 7.62 A 0.02M solution of pyridinium hydrochloride has pH = 3.44. Calculate the ionization constant of pyridine.

Answer :

Given,
pH = 3.44

We know that

pH=log[H+]
By taking antilog on both sides we get,
[H+] = antilog (- 3.44)

[H+]=3.63×104

pyridinium hydrochloride completely ionised.

Then Kh = (conc. of products)/ (conc, of reactants)
= (3.63×102)20.02 (? Concentration is 0.02M)

Kh=6.58×106

Now,
Kh=Kw/Ka

Ka=Kw/Kh


=1014/6.58×106=1.51×109 (approx)

Question 7.63 Predict if the solutions of the following salts are neutral, acidic or basic: NaCl,KBr,NaCN,NH4NO3,NaNO2andKF

Answer :

Salts of strong acid and strong base are neutral in nature for example-

  • NaCl(NaOH+HCl)
  • KBr(KOH+HBr)

Salts of a strong base and weak acid are basic in nature for example-

  • NaCN(HCN+NaOH)
  • NaNO2(HNO2+NaOH)
  • KF(KOH+HF)

Salts of strong acid and a weak base are acidic in nature for example-

  • NH4NO3(NH4OH+HNO2)

Question 7.64 The ionization constant of chloroacetic acid is 1.35 × 10 -3 . What will be the pH of 0.1M acid and its 0.1M sodium salt solution?

Answer :

We have,
Ionisation constant of chloroacetic acid( Ka ) is 1.35×103
The concentration of acid = 0.1 M
Ionisation if acid, =
ClCH2COOHClCH2COO+H+

We know that,
Ka=[ClCH2COO][H+][ClCH2COOH] ....................(i)
As it completely ionised
[ClCH2COO]=[H+]

Putting the values in eq (i)
1.35×103=[H+]20.02
[H+]=1.35×103×0.02=1.16×102
Therefore, pH of the solution = log(1.16×102)
= 2log(1.16)
= 1.94

Now,

0.1 M ClCH2COONa (sod. chloroacetate) is basic due to hydrolysis-

ClCH2COO+H2OCH2ClCOOH+OH

For a salt of strong base+strong acid

pH=7+pKa+logC2=7+2.87+log0.12pH=7.94

Question 7.65 Ionic product of water at 310 K is 2.7 × 10 -14 . What is the pH of neutral water at this temperature?

Answer :

We have the ionic product of water at 310 K is 2.7×1014
It is known that,
ionic product Kw=[H+][OH]

SInce [H+]=[OH] , therefore Kw=[H+]2

Kw at 310 K is 2.7×1014
Kw=2.7×1014=[H+]2
here we can calculate the value of [H+] concentration.

[H+]=2.7×1014=1.64×107

Thus, pH=log[H+]
=log(1.64×107)
=6.78

Hence the pH of neutral water is 6.78

Question 7.66(a) Calculate the pH of the resultant mixtures:

10 mL of 0.2M Ca(OH) 2 + 25 mL of 0.1M HCl

Answer :

Given that,
Vol. of 0.2 M Ca(OH)2 = 10 mL
Vol. of 0.1 M HCl = 25 mL

therefore, by using the formula,

M(OH)=M1V1(base)M2V2(acid)V1+V2
By substituting the value in these equations, we get;

(0.2×2)(0.1×2)10+25=1.525=0.06

Now, pOH=log[OH]
=log(0.06)=1.221

since pH+pOH=14
pH=14pOH
= 14-1.221
= 12.78

Question 7.66(b) Calculate the pH of the resultant mixtures:

10 mL of 0.01M H 2 SO 4 + 10 mL of 0.01M Ca(OH) 2

Answer :

In this case, both the solutions have the same number of moles of H+ and OH , therefore they both can get completely neutralised. Hence the pH = 7.0

Question 7.66(c) Calculate the pH of the resultant mixtures:

c) 10 mL of 0.1M H 2 SO 4 + 10 mL of 0.1M KOH

Answer :

Given that,

Volume of 0.1 M KOH = 10 mL, and

Volume of 0.1 M H2SO4 = 10 mL

So, by using the formula of,

M(H+)=M1V1(acid)M2V2(base)V1+V2
By putting the values we get,

2(0.1×10)0.1×1010+10=120=5×102

Hence, pH=log[H+]=log(5×102)=1.30

Question 7.67 Determine the solubilities of silver chromate, barium chromate, ferric hydroxide, lead chloride and mercurous iodide at 298K from their solubility product constants given in Table. Determine also the molarities of individual ions.

Answer :

Solubility product is the product of ionic concentrations in a saturated solution.
Ksp=[A+][B]
(i) silver chromate ( Ag2CrO4 )
Ionization of silver chromate

Ag2CrO42Ag++CrO42
Let " s " be the solubility of Ag2CrO4
[Ag+]=2s
[CrO42]=s
According to the table Ksp of Ag2CrO4 = 1.1×1012

1.1×1012=(2s)2.s=1.1×1012=2s3

s=1.1×101243
=0.65×104

(ii) Barium chromate ( BaCrO4 )
Ionization of silver chromate

BaCrO4Ba2++CrO42
Let " s " be the solubility of BaCrO4
[Ba2+]=s
[CrO42]=s
According to the table Ksp of BaCrO4 = 1.2×1012

1.2×1010=s.s=1.1×1010=s2

s=1.2×10101
=1.09×105

(iii) Ferric hydroxide ( Fe(OH)3 )
Ionization of Ferric hydroxide

Fe(OH)3Fe3++3OH
Let " s " be the solubility of Fe(OH)3
[Fe3+]=s
[OH]=3s
According to the table Ksp of Fe(OH)3 = 1.0×1038

1.0×1038=s.(3s)3=1.0×1038=27s4

s=1.0×1038274
=1.39×1010

(iv)

Lead chloride ( PbCl2 )
Ionization of Lead chloride

PbCl2Pb2++2Cl
Let " s " be the solubility of PbCl2
[Pb2+]=s
[Cl]=2s
According to the table Ksp of PbCl2 = 1.6×105

1.6×105=s.(2s)2=1.6×105=4s3

s=1.6×10543
=1.58×102

So molarity of Pb2+=1.58×102M and molarity of Cl=3.16×102M

Question 7.68 The solubility product constant of Ag 2 CrO 4 and AgBr is 1.1 × 10 -12 and 5.0 × 10 -13 respectively. Calculate the ratio of the molarities of their saturated solutions.

Answer :

silver chromate ( Ag2CrO4 )
Ionization of silver chromate

Ag2CrO42Ag++CrO42
Let " s " be the solubility of Ag2CrO4
[Ag+]=2s
[CrO42]=s
Ksp of Ag2CrO4 = 1.1×1012

1.1×1012=(2s)2.s=1.1×1012=2s3

s=1.1×101243
=0.65×104

Ionization of Silver bromide ( AgBr )
AgBrAg++Br

Ksp of AgBr = 5×1013

[Ag+]=s
[Br]=s

5×1013=s.s=5×1013=s2

s=5×10131=0.5×1012
=7.07×107

Now, the ratio of solubilities
ss=6.5×1051.1×1012
=9.91

Question 7.69 Equal volumes of 0.002 M solutions of sodium iodate and cupric chlorate are mixed together. Will it lead to precipitation of copper iodate? (For cupric iodate K sp = 7.4 × 10 -8 ).

Answer :

We have,
solubility product ( Ksp ) of cupric iodate = 7.4×108

When equal volumes of sodium iodate and cupric chlorate are mixed together the molar concentration of both the solution becomes half (= 0.001)

Ionization of cupric iodate is;

Cu(IO3)2Cu2++2IO3
0.001 M 0.001 M

So, Ksp can be calculated as;

Ksp=[Cu2+][IO3]2
=(0.001)3=109

Sinc eionic product is less than the Ksp so no precipitation occurs.

Question 7.70 The ionization constant of benzoic acid is 6.46 × 10 -5 and Ksp for silver benzoate is 2.5 × 10 -13 . How many times is silver benzoate more soluble in a buffer of pH 3.19 compared to its solubility in pure water?

Answer :

It is given that,
pH of buffer solution is 3.19. So, the concentration of H+ ion can be calculated as;
[H+]=antilog(pH)
= antilog (-3.19)
= 6.46×104M

Ionization of benzoic acid;

C6H5COOHC6H5COO+H3O+
It is given that Ka=6.46×105
Therefore,
Double subscripts: use braces to clarify
Double subscripts: use braces to clarify

Question 7.71 What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, K sp = 6.3 × 10 -18 ).

Answer :

We have,
The solubility product of the FeS=6.3×1018

Equals number of moles of ferrous sulphate and sodium sulphide are mixed in an equal volume.

Let s be the concentration of ferrous sulphate and sodium sulphide. On mixing the equimolar solution, the volume of the concentration becomes half.
So, [FeSO4]=[Na2S]=s2M

The ionisation of ferrous sulphide;
FeSFe2++S2
Therefore, for no precipitation, ionic product = solubility product
Ksp=(s2)(s2)6.3×1018=s24
By solving the above equation, we get
s=5.02×109

The maximum concentration of both the solution is s=5.02×109 M

Question 7.72 What is the minimum volume of water required to dissolve 1g of calcium sulphate at 298 K? (For calcium sulphate, K sp is 9.1 × 10 -6 )

Answer :

We have,
The solubility product of calcium sulphate is 9.1×106 .
given mass of calcium sulphate = 1g

Ionization of calcium sulphate;

CaSO4Ca2++SO42
Therefore,
Double subscripts: use braces to clarify

Let the solubility of calcium sulphate be s .
Then,
Ksp=s29.1×106=s2s=9.1×106
=3.02×103 mol/L

Thus,
mass/ (mol. wt) × volume =3.02×103 Molarity
mass = 3.02×136×103=0.41g

So, that to dissolve 1 g of calcium sulphate we need = 1/0.41L=2.44L of water.

Question 7.73 The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is 1.0 × 10 -19 M. If 10 mL of this is added to 5 mL of 0.04 M solution of the following: FeSO4,MnCl2,ZnCl2andCdCl2. in which of these solutions precipitation will take place?

Answer :

We have,
the concentration of [S2]=1×1019 and the volume of the solution containing sulphur ion = 10 mL.
Volume of metal salts solution added = 5mL
Before mixing,

[S2]=1×1019 M
[M2+]=0.04M

After mixing,

Volume = 15 mL

So, the concentration of [S2]=1×1019×1015
=6.67×1020M

concentration of [M2+]=0.04M×515
=1.33×102

So, the ionic product = [M2+][S2]
= (6.67×1020)(1.33×102)
= 8.87×1022

For the precipitation of the solution, the ionic product should be greater than the corresponding Double subscripts: use braces to clarify values.
Double subscripts: use braces to clarify of FeS, MnS, ZnS, CdS are 6.3×1018,\2.5×1013, 1.6×1024 and 8×1027 respectively.

Hence precipitation will take place in CdCl2 and ZnCl2 metal salts.

More About Equilibrium Class 11 NCERT Chemistry Chapter 7 Solutions

After studying NCERT solutions for class 11 chemistry chapter 7 Equilibrium, you will be able to identify equilibrium's dynamic nature involved in chemical and physical processes; explain the law of equilibrium; explain characteristics of equilibria involved in chemical and physical processes; write expressions for equilibrium constants; explain factors affecting the equilibrium state of a reaction; classify substances as bases or acids according to Bronsted-Lowry, Arrhenius and Lewis concepts; also able to classify bases and acids as weak or strong in terms of their ionization constants and calculate solubility product constant.

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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