Talk to Our counsellor: Give a missed call 07019243492

NCERT Solutions For Class 12 Chemistry chapter 2-Solutions

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for class-12 Chemistry Chapter 2 Solutions is prepared by our senior and renowned teachers of Physics Wallah primary focus while solving these questions of class-12 in NCERT textbook, also do read theory of this Chapter-2 Solutions while going before solving the NCERT questions. Our Physics Wallah team Prepared Other Subjects NCERT Solutions for class 12.

Chapter 2 Solutions

Answer the following Questions.

Question1. Calculate the mass percentage of benzene (C6H6) and carbon tetrachloride (CCl4) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.

Solution :
Mass percentage of C6H6 chapter 2-Solutions

chapter 2-Solutions

Mass percentage of CCl4chapter 2-Solutions

chapter 2-Solutions

Alternatively,

Mass percentage of CCl4 = (100 − 15.28)%

= 84.72%

Question2. Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.

Solution :
Let the total mass of the solution be 100 g and the mass of benzene be 30 g.

∴Mass of carbon tetrachloride = (100 − 30)g

= 70 g

Molar mass of benzene (C6H6) = (6 × 12 + 6 × 1) g mol−1

= 78 g mol−1

∴Number of moles of chapter 2-Solutions

= 0.3846 mol

Molar mass of carbon tetrachloride (CCl4) = 1 × 12 + 4 × 35.5

= 154 g mol−1

∴Number of moles of CCl4 = 70 / 154

= 0.4545 mol

Thus, the mole fraction of C6H6 is given as:

chapter 2-Solutions

chapter 2-Solutions

= 0.458

Question3. Calculate the molarity of each of the following solutions: (a) 30 g of Co(NO3)2. 6H2O in 4.3 L of solution (b) 30 mL of 0.5 M H2SO4 diluted to 500 mL.

Solution :
Molarity is given by:

chapter 2-Solutions

(a) Molar mass of Co (NO3)2.6H2O = 59 + 2 (14 + 3 × 16) + 6 × 18

= 291 g mol−1

∴Moles of Co (NO3)2.6H2Ochapter 2-Solutions

= 0.103 mol

Therefore, molarity chapter 2-Solutions

= 0.023 M

(b) Number of moles present in 1000 mL of 0.5 M H2SO4 = 0.5 mol

∴Number of moles present in 30 mL of 0.5 M H2SO4 m17f204c0.gif

= 0.015 mol

Therefore, molaritychapter 2-Solutions

= 0.03 M

Question4. Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.

Solution :
Molar mass of urea (NH2CONH2) = 2(1 × 14 + 2 × 1) + 1 × 12 + 1 × 16

= 60 g mol−1

0.25 molar aqueous solution of urea means:

1000 g of water contains 0.25 mol = (0.25 × 60)g of urea

= 15 g of urea

That is,

(1000 + 15) g of solution contains 15 g of urea

Therefore, 2.5 kg (2500 g) of solution contains chapter 2-Solutions

= 36.95 g

= 37 g of urea (approximately)

Hence, mass of urea required = 37 g

Question5. Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g mL-1.

Solution :
(a) Molar mass of KI = 39 + 127 = 166 g mol−1

20% (mass/mass) aqueous solution of KI means 20 g of KI is present in 100 g of solution.

That is, 

20 g of KI is present in (100 − 20) g of water = 80 g of water

Therefore, molality of the solutionchapter 2-Solutions

chapter 2-Solutions

= 1.506 m

= 1.51 m (approximately)

(b) It is given that the density of the solution = 1.202 g mL−1

∴Volume of 100 g solution chapter 2-Solutions

chapter 2-Solutions

= 83.19 mL

= 83.19 × 10−3 L

Therefore, molarity of the solution chapter 2-Solutions

= 1.45 M

(c) Moles of KI chapter 2-Solutions

Moles of water NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, mole fraction of KI chapter 2-Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.0263

Question6.  H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

Solution :
It is given that the solubility of H2S in water at STP is 0.195 m, i.e., 0.195 mol of H2S is dissolved in 1000 g of water.

Moles of water NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 55.56 mol

∴Mole fraction of H2S, xNCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.0035

At STP, pressure (p) = 0.987 bar

According to Henry’s law:

p = KHx

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 282 bar

Question7. Henry’s law constant for CO2 in water is 1.67 × 108 Pa at 298 K. Calculate the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm CO2 pressure at 298 K.

Solution :
It is given that: 

KH = 1.67 × 108 Pa

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 2.5 atm = 2.5 × 1.01325 × 105 Pa

= 2.533125 × 105 Pa

According to Henry’s law:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.00152

We can write, chapter 2-Solutions

[Since, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutionsis negligible as compared toNCERT Solutions for Class 12 Chemistry]

In 500 mL of soda water, the volume of water = 500 mL

[Neglecting the amount of soda present]

We can write:

500 mL of water = 500 g of water

nH20= 27.78 mol of water

Now, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, quantity of CO2 in 500 mL of soda water = (0.042 × 44)g

= 1.848 g

Question8. The vapour pressure of pure liquids A and B are 450 and 700 mm Hg respectively, at 350 K. Find out the composition of the liquid mixture if total vapour pressure is 600 mm Hg. Also find the composition of the vapour phase.

Solution :
It is given that:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 450 mm of Hg

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 700 mm of Hg

ptotal = 600 mm of Hg

From Raoult’s law, we have:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, total pressure, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1 − 0.4

= 0.6

Now, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 450 × 0.4

= 180 mm of Hg

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 700 × 0.6

= 420 mm of Hg

Now, in the vapour phase:

Mole fraction of liquid ANCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.30

And, mole fraction of liquid B = 1 − 0.30

= 0.70

Question9. Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.

Solution :
It is given that vapour pressure of water, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 23.8 mm of Hg

Weight of water taken, w1 = 850 g

Weight of urea taken, w2 = 50 g

Molecular weight of water, M1 = 18 g mol−1

Molecular weight of urea, M2 = 60 g mol−1

Now, we have to calculate vapour pressure of water in the solution. We take vapour pressure as p1.

Now, from Raoult’s law, we have:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, the vapour pressure of water in the given solution is 23.4 mm of Hg and its relative lowering is 0.0173.

Question10. Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C. Molal elevation constant for water is 0.52 K kg mol−1.

Solution :
Here, elevation of boiling point ΔTb = (100 + 273) − (99.63 + 273)

= 0.37 K

Mass of water, wl = 500 g

Molar mass of sucrose (C12H22O11), M2 = 11 × 12 + 22 × 1 + 11 × 16

= 342 g mol−1

Molal elevation constant, Kb = 0.52 K kg mol−1

We know that:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 121.67 g (approximately)

Hence, 121.67 g of sucrose is to be added.

Question11. Calculate the mass of ascorbic acid (Vitamin C, C6H8O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. Kf = 3.9 K kg mol−1.

Solution :
Mass of acetic acid, w1 = 75 g

Molar mass of ascorbic acid (C6H8O6), M2 = 6 × 12 + 8 × 1 + 6 × 16

= 176 g mol−1

Lowering of melting point, ΔTf = 1.5 K

We know that:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 5.08 g (approx)

Hence, 5.08 g of ascorbic acid is needed to be dissolved.

Question12. Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL of water at 37°C.

Solution :
It is given that:

Volume of water, V = 450 mL = 0.45 L

Temperature, T = (37 + 273)K = 310 K

Number of moles of the polymer, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

We know that: 

Osmotic pressure, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 30.98 Pa

= 31 Pa (approximately)

Question13. Define the term solution. How many types of solutions are formed? Write briefly about each type with an example.

Solution :
Homogeneous mixtures of two or more than two components are known as solutions.

There are three types of solutions.

(i) Gaseous solution:

The solution in which the solvent is a gas is called a gaseous solution. In these solutions, the solute may be liquid, solid, or gas. For example, a mixture of oxygen and nitrogen gas is a gaseous solution.

(ii) Liquid solution:

The solution in which the solvent is a liquid is known as a liquid solution. The solute in these solutions may be gas, liquid, or solid.

For example, a solution of ethanol in water is a liquid solution.

(iii) Solid solution:

The solution in which the solvent is a solid is known as a solid solution. The solute may be gas, liquid or solid. For example, a solution of copper in gold is a solid solution.

Question14. Give an example of solid solution in which the solute is a gas.

Solution :
In case a solid solution is formed between two substances (one having very large particles and the other having very small particles), an interstitial solid solution will be formed. For example, a solution of hydrogen in palladium is a solid solution in which the solute is a gas.

Question15. Define the following terms:

(i) Mole fraction 

(ii) Molality 

(iii) Molarity 

(iv) Mass percentage.

Solution :
(i) Mole fraction:

The mole fraction of a component in a mixture is defined as the ratio of the number of moles of the component to the total number of moles of all the components in the mixture.

i.e.,

Mole fraction of a component NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Mole fraction is denoted by ‘x’.

If in a binary solution, the number of moles of the solute and the solvent are nA and nB respectively, then the mole fraction of the solute in the solution is given by,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Similarly, the mole fraction of the solvent in the solution is given as:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

(ii) Molality

Molality (m) is defined as the number of moles of the solute per kilogram of the solvent. It is expressed as:

Molality (m)NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

(iii) Molarity

Molarity (M) is defined as the number of moles of the solute dissolved in one Litre of the solution.

It is expressed as:

Molarity (M)NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

(iv) Mass percentage:

The mass percentage of a component of a solution is defined as the mass of the solute in grams present in 100 g of the solution. It is expressed as:

Mass % of a component NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Question15. Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of the solution is 1.504 g mL−1?

Solution :
Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in an aqueous solution. This means that 68 g of nitric acid is dissolved in 100 g of the solution.

Molar mass of nitric acid (HNO3) = 1 × 1 + 1 × 14 + 3 × 16 = 63 g mol−1

Then, number of moles of HNO3 NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1.079 mol

Given, 

Density of solution = 1.504 g mL−1

(Mass / Density) = Volume of 100 g solution = NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Molarity of solution NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Question16. A solution of glucose in water is labelled as 10% w/w, what would be the molality and mole fraction of each component in the solution? If the density of solution is 1.2 g mL−1, then what shall be the molarity of the solution?

Solution :
10% w/w solution of glucose in water means that 10 g of glucose in present in 100 g of the solution i.e., 10 g of glucose is present in (100 − 10) g = 90 g of water.

Molar mass of glucose (C6H12O6) = 6 × 12 + 12 × 1 + 6 × 16 = 180 g mol−1

Then, number of moles of glucose NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.056 mol

Molality of solution NCERT Solutions for Class 12 Chemistry= 0.62 m

Number of moles of water NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 5 mol

Mole fraction of glucoseNCERT Solutions for Class 12 Chemistry

And, mole fraction of water NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1 − 0.011

= 0.989

If the density of the solution is 1.2 g mL−1, then the volume of the 100 g solution can be given as: 

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Molarity of the solution NCERT Solutions for Class 12 Chemistry

= 0.67 M

Question17. How many mL of 0.1 M HCl are required to react completely with 1 g mixture of Na2CO3 and NaHCO3 containing equimolar amounts of both?

Solution :
Let the amount of Na2CO3 in the mixture be x g.

Then, the amount of NaHCO3 in the mixture is (1 − x) g.

Molar mass of Na2CO3 = 2 × 23 + 1 × 12 + 3 × 16

= 106 g mol−1

Number of moles Na2CO3 NCERT Solutions for Class 12 Chemistry

Molar mass of NaHCO3 = 1 × 23 + 1 × 1 × 12 + 3 × 16

= 84 g mol−1

Number of moles of NaHCO3 NCERT Solutions for Class 12 Chemistry

According to the question,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

⇒ 84x = 106 − 106x

⇒ 190x = 106

⇒ x = 0.5579

Therefore, number of moles of Na2CO3 NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.0053 mol

And, number of moles of NaHCO3 NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.0053 mol

HCl reacts with Na2CO3 and NaHCO3 according to the following equation.

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

1 mol of Na2CO3 reacts with 2 mol of HCl.

Therefore, 0.0053 mol of Na2CO3 reacts with 2 × 0.0053 mol = 0.0106 mol.

Similarly, 1 mol of NaHCO3 reacts with 1 mol of HCl.

Therefore, 0.0053 mol of NaHCO3 reacts with 0.0053 mol of HCl.

Total moles of HCl required = (0.0106 + 0.0053) mol

= 0.0159 mol

In 0.1 M of HCl,

0.1 mol of HCl is preset in 1000 mL of the solution.

Therefore, 0.0159 mol of HCl is present in NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 159 mL of the solution

Hence, 159 mL of 0.1 M of HCl is required to react completely with 1 g mixture of Na2CO3 and NaHCO3, containing equimolar amounts of both.

Question18. A solution is obtained by mixing 300 g of 25% solution and 400 g of 40% solution by mass. Calculate the mass percentage of the resulting solution.

Solution :
Total amount of solute present in the mixture is given by,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 75 + 160

= 235 g

Total amount of solution = 300 + 400 = 700 g

Therefore, mass percentage (w/w) of the solute in the resulting solution, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 33.57%

And, mass percentage (w/w) of the solvent in the resulting solution,

= (100 − 33.57)%

= 66.43%

Question19. An antifreeze solution is prepared from 222.6 g of ethylene glycol (C2H6O2) and 200 g of water. Calculate the molality of the solution. If the density of the solution is 1.072 g mL−1, then what shall be the molarity of the solution?

Solution :
Molar mass of ethylene glycolNCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 2 × 12 + 6 × 1 + 2 ×16

= 62 gmol−1

Number of moles of ethylene glycol NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 3.59 mol

Therefore, molality of the solution NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 17.95 m

Total mass of the solution = (222.6 + 200) g

= 422.6 g

Given, 

Density of the solution = 1.072 g mL−1

Volume of the solution NCERT Solutions for Class 12 Chemistry

= 394.22 mL

= 0.3942 × 10−3 L

∴ Molarity of the solution NCERT Solutions for Class 12 Chemistry

= 9.11 M

Question20. A sample of drinking water was found to be severely contaminated with chloroform (CHCl3) supposed to be a carcinogen. The level of contamination was 15 ppm (by mass):

(i) express this in percent by mass

(ii) determine the molality of chloroform in the water sample.

Solution :
(i) 15 ppm (by mass) means 15 parts per million (106) of the solution.

Therefore, percent by mass NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1.5 × 10−3 %

(ii) Molar mass of chloroform (CHCl3) = 1 × 12 + 1 × 1 + 3 × 35.5

= 119.5 g mol−1

Now, according to the question,

15 g of chloroform is present in 106 g of the solution.

i.e., 15 g of chloroform is present in (106 − 15) ≈ 106 g of water.

∴ Molality of the solutionNCERT Solutions for Class 12 Chemistry

= 1.26 × 10−4 m

Question21. What role does the molecular interaction play in a solution of alcohol and water?

Solution :
In pure alcohol and water, the molecules are held tightly by a strong hydrogen bonding. The interaction between the molecules of alcohol and water is weaker than alcohol−alcohol and water−water interactions. As a result, when alcohol and water are mixed, the intermolecular interactions become weaker and the molecules can easily escape. This increases the vapour pressure of the solution, which in turn lowers the boiling point of the resulting solution.

Question22. Why do gases always tend to be less soluble in liquids as the temperature is raised?

Solution :
Solubility of gases in liquids decreases with an increase in temperature. This is because dissolution of gases in liquids is an exothermic process. 

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, when the temperature is increased, heat is supplied and the equilibrium shifts backwards, thereby decreasing the solubility of gases.

Question23. State Henry’s law and mention some important applications?

Solution :
Henry’s law states that partial pressure of a gas in the vapour phase is proportional to the mole fraction of the gas in the solution. If p is the partial pressure of the gas in the vapour phase and x is the mole fraction of the gas, then Henry’s law can be expressed as:

p = KH x

Where, 

KH is Henry’s law constant

Some important applications of Henry’s law are mentioned below.

(i) Bottles are sealed under high pressure to increase the solubility of CO2 in soft drinks and soda water.

(ii) Henry’s law states that the solubility of gases increases with an increase in pressure. Therefore, when a scuba diver dives deep into the sea, the increased sea pressure causes the nitrogen present in air to dissolve in his blood in great amounts. As a result, when he comes back to the surface, the solubility of nitrogen again decreases and the dissolved gas is released, leading to the formation of nitrogen bubbles in the blood. This results in the blockage of capillaries and leads to a medical condition known as ‘bends’ or ‘decompression sickness’. 

Hence, the oxygen tanks used by scuba divers are filled with air and diluted with helium to avoid bends. 

(iii) The concentration of oxygen is low in the blood and tissues of people living at high altitudes such as climbers. This is because at high altitudes, partial pressure of oxygen is less than that at ground level. Low-blood oxygen causes climbers to become weak and disables them from thinking clearly. These are symptoms of anoxia.

Question24. The partial pressure of ethane over a solution containing 6.56 × 10−3 g of ethane is 1 bar. If the solution contains 5.00 × 10−2 g of ethane, then what shall be the partial pressure of the gas?

Solution :
Molar mass of ethane (C2H6) = 2 × 12 + 6 × 1

= 30 g mol−1

∴Number of moles present in 6.56 × 10−3 g of ethaneNCERT Solutions for Class 12 Chemistry

= 2.187 × 10−4 mol

Let the number of moles of the solvent be x.

According to Henry’s law,

p = KHx

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Number of moles present in 5.00 × 10−2 g of ethane NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1.67 × 10−3 mol

According to Henry’s law,

p = KHx

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 7.636 bar

Hence, partial pressure of the gas shall be 7.636 bar.

Question25. What is meant by positive and negative deviations from Raoult's law and how is the sign of ΔsolH related to positive and negative deviations from Raoult's law?

Solution :
According to Raoult’s law, the partial vapour pressure of each volatile component in any solution is directly proportional to its mole fraction. The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions. The solutions that do not obey Raoult’s law (non-ideal solutions) have vapour pressures either higher or lower than that predicted by Raoult’s law. If the vapour pressure is higher, then the solution is said to exhibit positive deviation, and if it is lower, then the solution is said to exhibit negative deviation from Raoult’s law.

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Vapour pressure of a two-component solution showing positive deviation from Raoult’s law

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Vapour pressure of a two-component solution showing negative deviation from Raoult’s law

In the case of an ideal solution, the enthalpy of the mixing of the pure components for forming the solution is zero.

ΔsolH = 0

In the case of solutions showing positive deviations, absorption of heat takes place.

∴ΔsolH = Positive

In the case of solutions showing negative deviations, evolution of heat takes place.

∴ΔsolH = Negative

Question26. An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?

Solution :
Here,

Vapour pressure of the solution at normal boiling point (p1) = 1.004 bar

Vapour pressure of pure water at normal boiling point NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Mass of solute, (w2) = 2 g

Mass of solvent (water), (w1) = 98 g

Molar mass of solvent (water), (M1) = 18 g mol−1

According to Raoult’s law,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 41.35 g mol−1

Hence, the molar mass of the solute is 41.35 g mol−1.

Question27. Heptane and octane form an ideal solution. At 373 K, the vapour pressures of the two liquid components are 105.2 kPa and 46.8 kPa respectively. What will be the vapour pressure of a mixture of 26.0 g of heptane and 35 g of octane?

Solution :
Vapour pressure of heptane NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Vapour pressure of octane NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 46.8 kPa

We know that, 

Molar mass of heptane (C7H16) = 7 × 12 + 16 × 1

= 100 g mol−1

∴ Number of moles of heptane NCERT Solutions for Class 12 Chemistry

= 0.26 mol

Molar mass of octane (C8H18) = 8 × 12 + 18 × 1

= 114 g mol−1

Number of moles of octane = 35 /114 mol

= 0.31 mol

Mole fraction of heptane,NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.456

And, mole fraction of octane, x2 = 1 − 0.456

= 0.544

Now, partial pressure of heptane, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.456 × 105.2

= 47.97 kPa

Partial pressure of octane, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.544 × 46.8

= 25.46 kPa

Hence, vapour pressure of solution, ptotal = p1 + p2

= 47.97 + 25.46

= 73.43 kPa

Question28. The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.

Solution :
1 molal solution means 1 mol of the solute is present in 1000 g of the solvent (water).

Molar mass of water = 18 g mol−1

= Number of moles present in 1000 g of water NCERT Solutions for Class 12 Chemistry

= 55.56 mol

Therefore, mole fraction of the solute in the solution is

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions.

It is given that,

Vapour pressure of water, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 12.3 kPa

Applying the relation, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

⇒ 12.3 − p1 = 0.2177

⇒ p1 = 12.0823

= 12.08 kPa (approximately)

Hence, the vapour pressure of the solution is 12.08 kPa.

Question29. Calculate the mass of a non-volatile solute (molar mass 40 g mol−1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.

Solution :
Let the vapour pressure of pure octane beNCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Then, the vapour pressure of the octane after dissolving the non-volatile solute is NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Molar mass of solute, M2 = 40 g mol−1

Mass of octane, w1 = 114 g

Molar mass of octane, (C8H18), M1 = 8 × 12 + 18 × 1

= 114 g mol−1

Applying the relation,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, the required mass of the solute is 8 g.

Question30. A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate: molar mass of the solute  vapour pressure of water at 298 K.

Solution :
(i) Let, the molar mass of the solute be M g mol−1

Now, the no. of moles of solvent (water), NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

And, the no. of moles of solute, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Applying the relation:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

 

After the addition of 18 g of water:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Again, applying the relation:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

 

Dividing equation (i) by (ii), we have:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, the molar mass of the solute is 23 g mol−1.

(ii) Putting the value of ‘M’ in equation (i), we have:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, the vapour pressure of water at 298 K is 3.53 kPa.

Page No 60:

Question31. A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K.

Solution :
Here, ΔTf = (273.15 − 271) K

= 2.15 K

Molar mass of sugar (C12H22O11) = 12 × 12 + 22 × 1 + 11 × 16

= 342 g mol−1

5% solution (by mass) of cane sugar in water means 5 g of cane sugar is present in (100 − 5)g = 95 g of water.

Now, number of moles of cane sugarNCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.0146 mol

Therefore, molality of the solution, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.1537 mol kg−1

Applying the relation,

ΔTf = Kf × m

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 13.99 K kg mol−1

Molar of glucose (C6H12O6) = 6 × 12 + 12 × 1 + 6 × 16

= 180 g mol−1

5% glucose in water means 5 g of glucose is present in (100 − 5) g = 95 g of water.

∴ Number of moles of glucose NCERT Solutions for Class 12 Chemistry

= 0.0278 mol

Therefore, molality of the solution, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.2926 mol kg−1

Applying the relation,

ΔTf = Kf × m

= 13.99 K kg mol−1 × 0.2926 mol kg−1

= 4.09 K (approximately)

Hence, the freezing point of 5% glucose solution is (273.15 − 4.09) K= 269.06 K.

Question32. Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 Kwhereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 Kkg mol−1. Calculate atomic masses of A and B.

Solution :
We know that,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Then, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 110.87 g mol−1

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 196.15 g mol−1

Now, we have the molar masses of AB2 and AB4 as 110.87 g mol−1 and 196.15 g mol−1 respectively.

Let the atomic masses of A and B be x and y respectively.

Now, we can write:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Subtracting equation (i) from (ii), we have

2y = 85.28

⇒ y = 42.64

Putting the value of ‘y’ in equation (1), we have

x + 2 × 42.64 = 110.87

⇒ x = 25.59

Hence, the atomic masses of A and B are 25.59 u and 42.64 u respectively.

Question33. At 300 K, 36 g of glucose present in a litre of its solution has an osmotic pressure of 4.98 bar. If the osmotic pressure of the solution is 1.52 bars at the same temperature, what would be its concentration?

Solution :
Here, 

T = 300 K

π = 1.52 bar

R = 0.083 bar L K−1 mol−1

Applying the relation,

π = CRT

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.061 mol

Since the volume of the solution is 1 L, the concentration of the solution would be 0.061 M.

Question34. Suggest the most important type of intermolecular attractive interaction in the following pairs.

(i) n-hexane and n-octane

(ii) I2 and CCl4

(iii) NaClO4 and water

(iv) methanol and acetone

(v) acetonitrile (CH3CN) and acetone (C3H6O).

Solution :
(i) Van der Wall’s forces of attraction.

(ii) Van der Wall’s forces of attraction.

(iii) Ion-diople interaction.

(iv) Dipole-dipole interaction.

(v) Dipole-dipole interaction.

Question35. Based on solute-solvent interactions, arrange the following in order of increasing solubility in n-octane and explain. Cyclohexane, KCl, CH3OH, CH3CN.

Solution :
n-octane is a non-polar solvent. Therefore, the solubility of a non-polar solute is more than that of a polar solute in the n-octane.

The order of increasing polarity is: 

Cyclohexane < CH3CN < CH3OH < KCl

Therefore, the order of increasing solubility is: 

KCl < CH3OH < CH3CN < Cyclohexane

Question36. Amongst the following compounds, identify which are insoluble, partially soluble and highly soluble in water?

(i) phenol (ii) toluene (iii) formic acid

(iv) ethylene glycol (v) chloroform (vi) pentanol.

Solution :
(i) Phenol (C6H5OH) has the polar group −OH and non-polar group −C6H5. Thus, phenol is partially soluble in water.

(ii) Toluene (C6H5−CH3) has no polar groups. Thus, toluene is insoluble in water.

(iii) Formic acid (HCOOH) has the polar group −OH and can form H-bond with water. Thus, formic acid is highly soluble in water.

(iv) Ethylene glycol NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutionshas polar −OH group and can form H−bond. Thus, it is highly soluble in water.

(v) Chloroform is insoluble in water.

(vi) Pentanol (C5H11OH) has polar −OH group, but it also contains a very bulky non-polar −C5H11 group. Thus, pentanol is partially soluble in water.

Question37. If the density of some lake water is 1.25 g mL−1 and contains 92 g of Na+ ions per kg of water, calculate the molality of Na+ ions in the lake.

Solution :
Number of moles present in 92 g of Na+ ions =NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions/15a811d2.gif

= 4 mol

Therefore, molality of Na+ ions in the lake NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions/70b51c55.gif

= 4 m

Question38. If the solubility product of CuS is 6 × 10−16, calculate the maximum molarity of CuS in aqueous solution.

Solution :
Solubility product of CuS, Ksp = 6 × 10−16

Let s be the solubility of CuS in mol L−1.

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Now, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= s × s

= s2

Then, we have, Ksp = NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 2.45 × 10−8 mol L−1

Hence, the maximum molarity of CuS in an aqueous solution is 2.45 × 10−8 mol L−1.

Question39. Calculate the mass percentage of aspirin (C9H8O4) in acetonitrile (CH3CN) when 6.5 g of C9H8O4 is dissolved in 450 g of CH3CN.

Solution :
6.5 g of C9H8O4 is dissolved in 450 g of CH3CN.

Then, total mass of the solution = (6.5 + 450) g

= 456.5 g

Therefore, mass percentage ofC9H8O4 NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions/45acb878.gif

= 1.424%

Question40. Nalorphene (C19H21NO3), similar to morphine, is used to combat withdrawal symptoms in narcotic users. Dose of nalorphene generally given is 1.5 mg. Calculate the mass of 1.5 × 10−3 m aqueous solution required for the above dose.

Solution :
The molar mass of nalorphene NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutionsis given as:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

In 1.5 × 10−3m aqueous solution of nalorphene,

1 kg (1000 g) of water contains 1.5 × 10−3 mol35b0e89a.gif

= 0.4665 g

Therefore, total mass of the solution NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

This implies that the mass of the solution containing 0.4665 g of nalorphene is 1000.4665 g.

Therefore, mass of the solution containing 1.5 mg of nalorphene is:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, the mass of aqueous solution required is 3.22 g.

Question41. Calculate the amount of benzoic acid (C6H5COOH) required for preparing 250 mL of 0.15 M solution in methanol.

Solution :
0.15 M solution of benzoic acid in methanol means,

1000 mL of solution contains 0.15 mol of benzoic acid

Therefore, 250 mL of solution contains = NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutionsmol of benzoic acid

= 0.0375 mol of benzoic acid

Molar mass of benzoic acid (C6H5COOH) = 7 × 12 + 6 × 1 + 2 × 16

= 122 g mol−1

Hence, required benzoic acid = 0.0375 mol × 122 g mol−1

= 4.575 g

Question42. The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.

Solution :
NCERT Solutions for Class 12 Chemistry Chapter 2 - SolutionsNCERT Solutions for Class 12 Chemistrym23e1cd65.jpg

Among H, Cl, and F, H is least electronegative while F is most electronegative. Then, F can withdraw electrons towards itself more than Cl and H. Thus, trifluoroacetic acid can easily lose H+ ions i.e., trifluoroacetic acid ionizes to the largest extent. Now, the more ions produced, the greater is the depression of the freezing point. Hence, the depression in the freezing point increases in the order:

Acetic acid < trichloroacetic acid < trifluoroacetic acid

Question43. Calculate the depression in the freezing point of water when 10 g of CH3CH2CHClCOOH is added to 250 g of water. Ka = 1.4 × 10−3, Kf = 1.86 K kg mol−1.

Solution :
Molar mass of NCERT Solutions for Class 12 ChemistryNCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

∴No. of moles present in 10 g of NCERT Solutions for Class 12 Chemistry

=  0.0816 mol

It is given that 10 g of NCERT Solutions for Class 12 Chemistry is added to 250 g of water.

∴Molality of the solution, NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Let α be the degree of dissociation of NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistryundergoes dissociation according to the following equation:

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Since α is very small with respect to 1, 1 − α ≈ 1

Now, NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Again,

NCERT Solutions for Class 12 Chemistry

Total moles of equilibrium = 1 − α + α + α

= 1 + α

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Hence, the depression in the freezing point of water is given as:

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Question44. 19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water observed is 1.0°C. Calculate the van’t Hoff factor and dissociation constant of fluoroacetic acid.

Solution :
It is given that:

NCERT Solutions for Class 12 Chemistry

We know that:

NCERT Solutions for Class 12 Chemistry

Therefore, observed molar mass of NCERT Solutions for Class 12 Chemistry

The calculated molar mass of NCERT Solutions for Class 12 Chemistryis:

NCERT Solutions for Class 12 Chemistry

Therefore, van’t Hoff factor, NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Let α be the degree of dissociation of NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Now, the value of Ka is given as:

NCERT Solutions for Class 12 Chemistry

NCERT Solutions for Class 12 Chemistry

Taking the volume of the solution as 500 mL, we have the concentration:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry

 

Therefore,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

 

Question45. Vapour pressure of water at 293 Kis 17.535 mm Hg. Calculate the vapour pressure of water at 293 Kwhen 25 g of glucose is dissolved in 450 g of water.

Solution :
Vapour pressure of water, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 17.535 mm of Hg

Mass of glucose, w2 = 25 g

Mass of water, w1 = 450 g

We know that,

Molar mass of glucose (C6H12O6), M2 = 6 × 12 + 12 × 1 + 6 × 16

= 180 g mol−1

Molar mass of water, M1 = 18 g mol−1

Then, number of moles of glucose,   NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.139 mol

And, number of moles of water, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 25 mol

We know that,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

⇒ 17.535 − p1 = 0.097

⇒ p1 = 17.44 mm of Hg

Hence, the vapour pressure of water is 17.44 mm of Hg.

Question46. Henry’s law constant for the molality of methane in benzene at 298 Kis 4.27 × 105 mm Hg. Calculate the solubility of methane in benzene at 298 Kunder 760 mm Hg.

Solution :
Here, 

p = 760 mm Hg

kH = 4.27 × 105 mm Hg

According to Henry’s law,

p = kHx

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 177.99 × 10−5

= 178 × 10−5 (approximately)

Hence, the mole fraction of methane in benzene is 178 × 10−5.

Question47. 100 g of liquid A (molar mass 140 g mol−1) was dissolved in 1000 g of liquid B (molar mass 180 g mol−1). The vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid A and its vapour pressure in the solution if the total vapour pressure of the solution is 475 Torr.

Solution :
Number of moles of liquid A, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.714 mol

Number of moles of liquid B, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 5.556 mol

Then, mole fraction of A, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 0.114

And, mole fraction of B, xB = 1 − 0.114

= 0.886

Vapour pressure of pure liquid B, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 500 torr

Therefore, vapour pressure of liquid B in the solution,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 500 × 0.886

= 443 torr

Total vapour pressure of the solution, ptotal = 475 torr

∵ Vapour pressure of liquid A in the solution,

pA = ptotal − pB

= 475 − 443

= 32 torr

Now, 

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 280.7 torr

Hence, the vapour pressure of pure liquid A is 280.7 torr.

Question48. Vapour pressure of pure acetone and chloroform at 328 K are 741.8 mm Hg and 632.8 mm Hg respectively. Assuming that they form ideal solution over the entire range of composition, plot ptotal’ pchloroform’ and pacetone as a function of xacetone. The experimental data observed for different compositions of mixture is.

100 ×xacetone 

0

11.8

23.4

36.0

50.8

58.2

64.5

72.1

pacetone /mm Hg

0

54.9

110.1

202.4

322.7

405.9

454.1

521.1

pchloroform/mm Hg

632.8

548.1

469.4

359.7

257.7

193.6

161.2

120.7

Solution :
From the question, we have the following data

100 ×xacetone 

0

11.8

23.4

36.0

50.8

58.2

64.5

72.1

pacetone /mm Hg

0

54.9

110.1

202.4

322.7

405.9

454.1

521.1

pchloroform/mm Hg

632.8

548.1

469.4

359.7

257.7

193.6

161.2

120.7

ptota(mm Hg)

632.8

603.0

579.5

562.1

580.4

599.5

615.3

641.8

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

It can be observed from the graph that the plot for the ptotal of the solution curves downwards. Therefore, the solution shows negative deviation from the ideal behaviour.

Question49. Benzene and toluene form ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.

Solution :
Molar mass of benzene NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Molar mass of toluene NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Now, no. of moles present in 80 g of benzene NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions= 1.026

And, no. of moles present in 100 g of toluene  = 100/92 = 1.087 mol

∴Mole fraction of benzene, xb NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

And, mole fraction of toluene, 40d13744.gif

It is given that vapour pressure of pure benzene, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

And, vapour pressure of pure toluene, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Therefore, partial vapour pressure of benzene,NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

And, partial vapour pressure of toluene,1eb10835.gif

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, mole fraction of benzene in vapour phase is given by:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Question50. The air is a mixture of a number of gases. The major components are oxygen and nitrogen with approximate proportion of 20% is to 79% by volume at 298 K. The water is in equilibrium with air at a pressure of 10 atm. At 298 Kif the Henry’s law constants for oxygen and nitrogen are 3.30 × 107 mm and 6.51 × 107 mm respectively, calculate the composition of these gases in water.

Solution :
Percentage of oxygen (O2) in air = 20 %

Percentage of nitrogen (N2) in air = 79%

Also, it is given that water is in equilibrium with air at a total pressure of 10 atm, that is, (10 × 760) mm Hg = 7600 mm Hg

Therefore, 

Partial pressure of oxygen, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 1520 mm Hg

Partial pressure of nitrogen, NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 6004 mmHg

Now, according to Henry’s law:

p = KH.x

For oxygen:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

For nitrogen:

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Hence, the mole fractions of oxygen and nitrogen in water are 4.61 ×10−5and 9.22 × 10−5 respectively.

Question51. Determine the amount of CaCl2 (i = 2.47) dissolved in 2.5 litre of water such that its osmotic pressure is 0.75 atm at 27°C.

Solution :
We know that,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

Here, 

R = 0.0821 L atm K-1mol-1

M = 1 × 40 + 2 × 35.5

= 111g mol-1

Therefore, w NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

= 3.42 g

Hence, the required amount of CaCl2 is 3.42 g.

Question52. Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K2SO4 in 2 liter of water at 25° C, assuming that it is completely dissociated.

Solution :
When K2SO4 is dissolved in water,NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutionsions are produced.

 ⇒ Total number of ions produced = 3

⇒ i =3

Given, 

w = 25 mg = 0.025 g

V = 2 L

T = 250C = (25 + 273) K = 298 K

Also, we know that: 

R = 0.0821 L atm K-1mol-1

M = (2 × 39) + (1 × 32) + (4 × 16) = 174 g mol-1

Appling the following relation,

NCERT Solutions for Class 12 Chemistry Chapter 2 - Solutions

NCERT Solutions For Class 12 Chemistry Chapter Wise.

  1. Chapter 1 The Solid States

  2. Chapter 2 Solutions

  3. Chapter 3 Electrochemistry

  4. Chapter 4 Chemical Kinetics

  5. Chapter 5 Surface Chemistry

  6. Chapter 6 General Priciples and Processes of Isolation of Elements

  7. Chapter 7 The P Block Elements

  8. Chapter 8 The D and F Elements

  9. Chapter 9 Coordination Compounds

  10. Chapter 10 Haloalkanes and Haloarenes

  11. Chapter 11 Alcohols, Phenols and Ethers

  12. Chapter 12 Aldehydes, ketones and Carboxylics Acids

  13. Chapter 13 Amines

  14. Chapter 14 Biomolecules

  15. Chapter 15 Polymers

  16. Chapter 16 Chemistry In Everyday Life

Talk to Our counsellor