+2 Chemistry - Most Important Questions and Answers
1. SOLUTIONS
1. State Henry’s law. Give its mathematical form.
Ans: Henry’s law states that at constant temperature, the solubility of a gas in a liquid is directly
proportional to the pressure of the gas.
Mathematically, p = KH.χ (where p is the partial pressure, χ is the mole fraction and KH is the Henry’s law
constant).
2. Write any two applications of Henry’s law.
Ans: (i) In the preparation of soda water and soft drinks.
(ii) A medical condition known as Bends in Scuba divers.
3. State Raoult’s law.
Ans: The law states that for a solution of volatile liquids, the partial vapour pressure of each component in
the solution is directly proportional to its mole fraction in the solution.
Mathematically, p1 = p0χ1, p2 = p0χ2
1 2
4. What are ideal solutions? Write any two properties of ideal solutions. Give one example for such solution.
Ans: These are solutions which obey Raoult’s law at all concentrations.
For an ideal solution, p1 = p0χ1, p2 = p0χ2, ∆mixH = 0 and ∆mixV = 0.
1 2
E.g.: a mixture of benzene and toluene.
5. What are non-ideal solutions?
Ans: These are solutions which do not obey Raoult’s law at all concentrations. For such solutions, p1 ≠ p01χ1,
p2 ≠ p02χ2, ∆mixH ≠ 0 and ∆mixV ≠ 0.
6. What type of deviation is shown by a mixture of chloroform and acetone? Give reason.
Ans: Negative deviation. Chloroform can form hydrogen bond with acetone. So, the solute – solvent
interaction increases and hence the vapour pressure decreases.
7. Draw a vapour pressure curve, by plotting vapour pressure against mole fraction for: (i) an ideal solution (ii)
a solution that show positive deviation from Raoult’s law (iii) A solution that show negative deviation from
Raoult’s law.
Ans:
(i) Ideal solution (ii) Positive deviation from (iii) Negative deviation from
Raoult’s law Raoult’s law
8. What are azeotropes?
Ans: They are constant boiling mixtures and have the same composition in liquid and vapour phases.
9. Explain the different types of azeotropes?
There are 2 types of azeotropes:
Minimum boiling azeotropes: Formed by solutions which show large positive deviation from Raoult’s law.
E.g. 95% aqueous solution of ethanol by volume.
Maximum boiling azeotrope: Formed by solutions which show large negative deviation from Raoult’s law.
E.g. 68% aqueous solution of HNO3 by mass.
10. What are colligative properties? Name the four types of colligative properties.
Ans: These are properties which depend only on the number of solute particles and not on their nature.
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 1
, The important colligative properties are (i) Relative lowering of vapour pressure (ii) Elevation of boiling
point (iii) Depression of freezing point (iv) Osmotic pressure.
11. What is osmotic pressure?
Ans: It is the excess pressure that must be applied on the solution side to prevent osmosis.
12. What is reverse osmosis? Write any one of its applications.
Ans: It is the process of flow of solvent molecules from solution side to solvent side through a semi-
permeable membrane (SPM), when a pressure greater than osmotic pressure is applied on the solution
side. [OR, If a pressure larger than the osmotic pressure is applied to the solution side, the direction of
osmosis gets reversed]. It is used in desalination of sea water OR in water purification.
13. For determining the molecular mass of polymers, osmotic pressure is preferred. Why?
Ans: This is because the magnitude of osmotic pressure is large even for very dilute solutions.
14. Write any 2 advantages of osmotic pressure measurement over other colligative property measurements?
Ans: (i) Osmotic pressure can be measured at room temperature.
(ii) Here molarity of the solution is used instead of molality, which can be determined easily.
15. What are isotonic solutions? Give an example.
Ans: Two solutions having the same osmotic pressure are called isotonic solutions. E.g. 0.9% (mass/volume)
NaCl solution and our blood cells.
16. For intravenous injections only solutions with osmotic pressure equal to that of 0.9% NaCl solution is used.
Why?
Ans: This is because the fluid inside our blood cell is isotonic with 0.9% (mass/volume) NaCl solution. So,
osmosis does not occur
17. Define van’t Hoff factor. What is its value for KCl solution, if there is 100% dissociation.
Normal molar mass
Ans: van’t Hoff factor (i) = 𝐴𝑏𝑛𝑜𝑟𝑚𝑎𝑙 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
For KCl, i = 2
18. What happens to the colligative properties when ethanoic acid is treated with benzene? Give reason.
Ans: Colligative properties decrease. This is because ethanoic acid (acetic acid) dimerises in benzene, due to
hydrogen bonding. So the number of particles and hence colligative properties decrease.
19. Calculate the osmotic pressure exerted by a solution prepared by dissolving 1.5 g of a polymer of molar
mass 185000 in 500ml of water at 370C. (R = 0.083 L bar K-1mol-1)
Ans: Here w2 = 1.5 g, R = 0.083 L barK-1mol-1, M2 = 185000, T = 37 + 273 = 310 K and V= 500 mL = 0.5 L
w RT 1.5 x 0.083 x 310
We Know that, osmotic pressure, π = 2 = = 4.17 x 10-4 bar
M2V 185000 x 0.5
20. 18g of glucose, C6H12O6, is dissolved in 1 kg of water in a sauce pan. At what temperature will water boil at
1.013 bar? (Kb for water is 0.52 K kg mol–1, boiling point of water = 373.15 K)
1000 𝐾𝑏𝑤2
Ans: We know that, ΔTb =
𝑤1𝑀2
Here w2 = 18 g, w1 = 1 kg = 1000g, Kb = 0.52 K kg mol-1, M2 = 180 g mol-1, T0b = 373.15 K, ΔTb = ?, Tb = ?
On substituting in the above equation, we get
1000 x 0.52 x 18
ΔTb = = 0.052 K
1000 x 180
Also ΔTb = Tb – Tb0
i.e. 0.052 = Tb – 373.15
So, Tb = 0.052 + 373.15 = 373.202 K
2. ELECTROCHEMISTRY
21. What is a Galvanic cell?
Ans: It is a device that converts chemical energy of some redox reactions to electrical energy.
E.g. Daniel cell, Dry cell etc.
22. Write the representation of a Daniel cell. Also write its anode reaction, cathode reaction and net reaction?
Ans: Representation of Daniel cell: Zn|Zn2+||Cu2+|Cu
Anode reaction: Zn → Zn2+ + 2 e–
Cathode reaction: Cu2+ + 2 e- → Cu
Net reaction: Zn + Cu2+ → Zn2+ + Cu
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 2
, 23. Write the Nernst equation for a Daniel cell.
Ans: E = E0 + 0.0591 log [𝐶𝑢2+]
cell cell 2 [𝑍𝑛2+]
24. Define molar conductivity. What is its unit?
Ans: It is the conductivity of V volume of electrolytic solution containing 1 mol of electrolyte, placed in a
conductivity cell having unit distance between the electrodes and unit area of cross-section.
1000
OR, Molar conductivity (Λm) = where is the conductivity and M is the molarity of the solution.
M
Its unit is S cm2 mol-1 OR ohm-1 cm2 mol-1.
25. How does molar conductivity of a solution vary with concentration or dilution? Explain.
Ans: The molar conductivity increases with dilution (decrease in concentration) for both strong and weak
electrolytes. This is due to the increase in ionic mobility, for strong electrolytes and increase in degree of
dissociation, for weak electrolytes.
OR, the graph:
26. State Kohlrausch’s law of independent migration of ions. State any one of its applications.
Ans: It states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions
of the anion and the cation of the electrolyte.
Application: It is used to calculate the limiting molar conductivity of any electrolytes.
27. What is meant by limiting molar conductivity (𝚲0m )?
Ans: It is the molar conductivity of an electrolytic solution at zero concentration.
28. 𝚲0 for NaCl, HCl and NaAc are 126.4, 425.9 and 91.0 S cm2 mol–1 respectively. Calculate 𝚲0 for HAc.
m m
Ans: Given 𝚲0 (NaCl) = 126.4 Scm2mol–1, 𝚲0 (HCl) = 425.9 Scm2mol–1 and 𝚲0 (NaAc) = 91.0 Scm2mol–1
m m m
On applying Kohlrausch’s law,
𝚲0 (HAc) = 𝚲0 (NaAc) + 𝚲0 (HCl) – 𝚲0 (NaCl)
m m m m
= 91.0 + 425.9 – 126.4 = 390.5 Scm2mol-1
29. Write any two differences between primary cell and secondary cell.
Ans:
Primary cell Secondary cell
Cannot be recharged or reused. Can be recharged and reused.
The cell reaction cannot be reversed. The cell reaction can be reversed.
E.g. Dry cell, Mercury cell E.g.: Lead storage cell, Ni-Cd cell
30. What is the electrode potential of the Standard Hydrogen Electrode (SHE), which is used as a reference
electrode, to determine the electrode potential of an unknown electrode.
Ans: Zero volt (0 V)
31. Write the anode and cathode reactions occur in the operation of a lead storage battery. Mention the
electrolyte used in the battery.
–
Ans: Anode reaction: Pb + SO2−4 → PbSO4 + 2e
+ –
Cathode reaction: PbO2 + SO2− 4 + 4H + 2e → PbSO4 + 2H2O
Net reaction: Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
Electrolyte used is 38% H2SO4 .
32. The cell potential of a mercury cell is 1.35 V, and remains constant during its life. Give reason.
Ans: Because the cell reaction does not involve any ion in solution.
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 3
1. SOLUTIONS
1. State Henry’s law. Give its mathematical form.
Ans: Henry’s law states that at constant temperature, the solubility of a gas in a liquid is directly
proportional to the pressure of the gas.
Mathematically, p = KH.χ (where p is the partial pressure, χ is the mole fraction and KH is the Henry’s law
constant).
2. Write any two applications of Henry’s law.
Ans: (i) In the preparation of soda water and soft drinks.
(ii) A medical condition known as Bends in Scuba divers.
3. State Raoult’s law.
Ans: The law states that for a solution of volatile liquids, the partial vapour pressure of each component in
the solution is directly proportional to its mole fraction in the solution.
Mathematically, p1 = p0χ1, p2 = p0χ2
1 2
4. What are ideal solutions? Write any two properties of ideal solutions. Give one example for such solution.
Ans: These are solutions which obey Raoult’s law at all concentrations.
For an ideal solution, p1 = p0χ1, p2 = p0χ2, ∆mixH = 0 and ∆mixV = 0.
1 2
E.g.: a mixture of benzene and toluene.
5. What are non-ideal solutions?
Ans: These are solutions which do not obey Raoult’s law at all concentrations. For such solutions, p1 ≠ p01χ1,
p2 ≠ p02χ2, ∆mixH ≠ 0 and ∆mixV ≠ 0.
6. What type of deviation is shown by a mixture of chloroform and acetone? Give reason.
Ans: Negative deviation. Chloroform can form hydrogen bond with acetone. So, the solute – solvent
interaction increases and hence the vapour pressure decreases.
7. Draw a vapour pressure curve, by plotting vapour pressure against mole fraction for: (i) an ideal solution (ii)
a solution that show positive deviation from Raoult’s law (iii) A solution that show negative deviation from
Raoult’s law.
Ans:
(i) Ideal solution (ii) Positive deviation from (iii) Negative deviation from
Raoult’s law Raoult’s law
8. What are azeotropes?
Ans: They are constant boiling mixtures and have the same composition in liquid and vapour phases.
9. Explain the different types of azeotropes?
There are 2 types of azeotropes:
Minimum boiling azeotropes: Formed by solutions which show large positive deviation from Raoult’s law.
E.g. 95% aqueous solution of ethanol by volume.
Maximum boiling azeotrope: Formed by solutions which show large negative deviation from Raoult’s law.
E.g. 68% aqueous solution of HNO3 by mass.
10. What are colligative properties? Name the four types of colligative properties.
Ans: These are properties which depend only on the number of solute particles and not on their nature.
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 1
, The important colligative properties are (i) Relative lowering of vapour pressure (ii) Elevation of boiling
point (iii) Depression of freezing point (iv) Osmotic pressure.
11. What is osmotic pressure?
Ans: It is the excess pressure that must be applied on the solution side to prevent osmosis.
12. What is reverse osmosis? Write any one of its applications.
Ans: It is the process of flow of solvent molecules from solution side to solvent side through a semi-
permeable membrane (SPM), when a pressure greater than osmotic pressure is applied on the solution
side. [OR, If a pressure larger than the osmotic pressure is applied to the solution side, the direction of
osmosis gets reversed]. It is used in desalination of sea water OR in water purification.
13. For determining the molecular mass of polymers, osmotic pressure is preferred. Why?
Ans: This is because the magnitude of osmotic pressure is large even for very dilute solutions.
14. Write any 2 advantages of osmotic pressure measurement over other colligative property measurements?
Ans: (i) Osmotic pressure can be measured at room temperature.
(ii) Here molarity of the solution is used instead of molality, which can be determined easily.
15. What are isotonic solutions? Give an example.
Ans: Two solutions having the same osmotic pressure are called isotonic solutions. E.g. 0.9% (mass/volume)
NaCl solution and our blood cells.
16. For intravenous injections only solutions with osmotic pressure equal to that of 0.9% NaCl solution is used.
Why?
Ans: This is because the fluid inside our blood cell is isotonic with 0.9% (mass/volume) NaCl solution. So,
osmosis does not occur
17. Define van’t Hoff factor. What is its value for KCl solution, if there is 100% dissociation.
Normal molar mass
Ans: van’t Hoff factor (i) = 𝐴𝑏𝑛𝑜𝑟𝑚𝑎𝑙 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
For KCl, i = 2
18. What happens to the colligative properties when ethanoic acid is treated with benzene? Give reason.
Ans: Colligative properties decrease. This is because ethanoic acid (acetic acid) dimerises in benzene, due to
hydrogen bonding. So the number of particles and hence colligative properties decrease.
19. Calculate the osmotic pressure exerted by a solution prepared by dissolving 1.5 g of a polymer of molar
mass 185000 in 500ml of water at 370C. (R = 0.083 L bar K-1mol-1)
Ans: Here w2 = 1.5 g, R = 0.083 L barK-1mol-1, M2 = 185000, T = 37 + 273 = 310 K and V= 500 mL = 0.5 L
w RT 1.5 x 0.083 x 310
We Know that, osmotic pressure, π = 2 = = 4.17 x 10-4 bar
M2V 185000 x 0.5
20. 18g of glucose, C6H12O6, is dissolved in 1 kg of water in a sauce pan. At what temperature will water boil at
1.013 bar? (Kb for water is 0.52 K kg mol–1, boiling point of water = 373.15 K)
1000 𝐾𝑏𝑤2
Ans: We know that, ΔTb =
𝑤1𝑀2
Here w2 = 18 g, w1 = 1 kg = 1000g, Kb = 0.52 K kg mol-1, M2 = 180 g mol-1, T0b = 373.15 K, ΔTb = ?, Tb = ?
On substituting in the above equation, we get
1000 x 0.52 x 18
ΔTb = = 0.052 K
1000 x 180
Also ΔTb = Tb – Tb0
i.e. 0.052 = Tb – 373.15
So, Tb = 0.052 + 373.15 = 373.202 K
2. ELECTROCHEMISTRY
21. What is a Galvanic cell?
Ans: It is a device that converts chemical energy of some redox reactions to electrical energy.
E.g. Daniel cell, Dry cell etc.
22. Write the representation of a Daniel cell. Also write its anode reaction, cathode reaction and net reaction?
Ans: Representation of Daniel cell: Zn|Zn2+||Cu2+|Cu
Anode reaction: Zn → Zn2+ + 2 e–
Cathode reaction: Cu2+ + 2 e- → Cu
Net reaction: Zn + Cu2+ → Zn2+ + Cu
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 2
, 23. Write the Nernst equation for a Daniel cell.
Ans: E = E0 + 0.0591 log [𝐶𝑢2+]
cell cell 2 [𝑍𝑛2+]
24. Define molar conductivity. What is its unit?
Ans: It is the conductivity of V volume of electrolytic solution containing 1 mol of electrolyte, placed in a
conductivity cell having unit distance between the electrodes and unit area of cross-section.
1000
OR, Molar conductivity (Λm) = where is the conductivity and M is the molarity of the solution.
M
Its unit is S cm2 mol-1 OR ohm-1 cm2 mol-1.
25. How does molar conductivity of a solution vary with concentration or dilution? Explain.
Ans: The molar conductivity increases with dilution (decrease in concentration) for both strong and weak
electrolytes. This is due to the increase in ionic mobility, for strong electrolytes and increase in degree of
dissociation, for weak electrolytes.
OR, the graph:
26. State Kohlrausch’s law of independent migration of ions. State any one of its applications.
Ans: It states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions
of the anion and the cation of the electrolyte.
Application: It is used to calculate the limiting molar conductivity of any electrolytes.
27. What is meant by limiting molar conductivity (𝚲0m )?
Ans: It is the molar conductivity of an electrolytic solution at zero concentration.
28. 𝚲0 for NaCl, HCl and NaAc are 126.4, 425.9 and 91.0 S cm2 mol–1 respectively. Calculate 𝚲0 for HAc.
m m
Ans: Given 𝚲0 (NaCl) = 126.4 Scm2mol–1, 𝚲0 (HCl) = 425.9 Scm2mol–1 and 𝚲0 (NaAc) = 91.0 Scm2mol–1
m m m
On applying Kohlrausch’s law,
𝚲0 (HAc) = 𝚲0 (NaAc) + 𝚲0 (HCl) – 𝚲0 (NaCl)
m m m m
= 91.0 + 425.9 – 126.4 = 390.5 Scm2mol-1
29. Write any two differences between primary cell and secondary cell.
Ans:
Primary cell Secondary cell
Cannot be recharged or reused. Can be recharged and reused.
The cell reaction cannot be reversed. The cell reaction can be reversed.
E.g. Dry cell, Mercury cell E.g.: Lead storage cell, Ni-Cd cell
30. What is the electrode potential of the Standard Hydrogen Electrode (SHE), which is used as a reference
electrode, to determine the electrode potential of an unknown electrode.
Ans: Zero volt (0 V)
31. Write the anode and cathode reactions occur in the operation of a lead storage battery. Mention the
electrolyte used in the battery.
–
Ans: Anode reaction: Pb + SO2−4 → PbSO4 + 2e
+ –
Cathode reaction: PbO2 + SO2− 4 + 4H + 2e → PbSO4 + 2H2O
Net reaction: Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
Electrolyte used is 38% H2SO4 .
32. The cell potential of a mercury cell is 1.35 V, and remains constant during its life. Give reason.
Ans: Because the cell reaction does not involve any ion in solution.
+2 CHEMISTRY – MOST IMPORTANT QUESTIONS AND ANSWERS 3
