solutions

Question 1

What is the formula for molarity & molality?

Answer 1

M = W2/M2 x 1/V in litres
m = W2/M2 x 1/W1 in kg

Question 2

What are the factors that affect solubility of gas in liquid?

Answer 2

Temperature inversely prop.
Pressure directly prop.
Hydrogen bonds directly prop.

Question 3

State Henry’s law.

Answer 3

• Solubility of a gas in liquid is directly proportional to its partial pressure (and mole fraction).
  S or p = K(H) X
• K(H) is Henry’s constant viz. inversely prop. to solubility.
• X is chai.

Question 4

State Raoult’s law for volatile solute.

Answer 4

Partial pressure of each component is directly prop. to mole fraction of the component.
P(A) = P0(A)X(A)

Question 5

State Raoult’s law for non-volatile solute.

Answer 5

The relative lowering of vapour pressure is equal to the mole fraction of the non-volatile solute.

Question 6

Explain ideal solution.

Answer 6

• The solutions which obey Raoult’s law under all concentrations.
• A-B interactions = A-A & B-B
• ΔHmix and ΔVmix = 0
• Almost all dilute solutions
• Chlorobenzene & bromobenzene, n-hexane & n-heptane, benzene & toluene

Question 7

Explain negative deviation.

Answer 7

• A-B > A-A B-B
• vapour pressure decreases
• ΔHmix & ΔVmix = -ve
• acetone & chloroform, HCl & H2O
• occurs due to hydrogen bonds

Question 8

Explain positive deviation.

Answer 8

• A-B < A-A B-B
• vapour pressure increases
• ΔHmix & ΔVmix = +ve
• CS2 and acetone, ethanol and acetone

Question 9

What are azeotropes?

Answer 9

• Solutions which have same composition in liquid and vapour state.
• Minimum boiling azeotrope –> large +ve deviation; 95% alcohol in water
• Maximum boiling azeotrope –> large -ve deviation; 63% HCl in water

Question 10

What are colligative properties?

Answer 10

Properties of solution that depend only on number of solute particles and not on nature.

Question 11

Write formula for RLVP.

Answer 11

i.X(B) = P0(A) - P(A) / P0(A) = n(B) / n(A)

Question 12

Explain elevation in boiling point.

Answer 12

• If non-vol. solute is added to solvent, vapour pressure decreases –> boiling point increases
• ΔT(b) = K(b)m.i
• K(b) is ebullioscopic constant / molal elevation constant

Question 13

Write formula for depression in freezing point.

Answer 13

• ΔT(f) = K(f)m.i
• K(f) is cryoscopic constant / molal freezing point constant

Question 14

Discuss osmotic pressure.

Answer 14

• The excess hydrostatic pressure applied on the side of the solution to stop flow of solvent through semi-permeable membrane.
  π = CRT
• C is molarity

Question 15

Why is osmotic pressure method used to calculate molar masses of proteins?

Answer 15

• Osmotic pressure can be calculated at room temperature, which is necessary since proteins get denatured at very high or very low temperatures.
• The concentration term is molarity, which is easier to calculate than molality.
• The change in pressure is appreciable, even if quantity of sample is less. –> errors are avoided

Question 16

Write formulae for Vant Hoff’s factor.

Answer 16

α for dissociation = i - 1 / m - 1
α for association = i - 1 / 1/m - 1

Question 17

What is antifreeze?

Answer 17

• A mixture of ethylene glycol and water
• Strong H bonds –> high BP, low FP
• Used as coolant in hot countries & antifreeze in cold countries