yo86 Km-').63. In winter, the normal temperature in a Himalayan's valley was found to be-10°C. Is a 30% by mass of aqueous solution of ethylene glycol (molarmass = 62) suitable for car radiator ? (K, for water = 1.86 K/m) (Pb.S.B. 2011)61. 34262. C,H63. It isfree
Answers
Given info : In winter, the normal temperature in a Himalayan's valley was found to be -10°C.
To find : Is a 30% by mass of aqueous solution of ethylene glycol (molar mass = 62) suitable for car radiator ?
solution : concentration of aqueous solution of ethylene glycol is 30% by mass.
it means, 30g of ethylene glycol is present in 100g of water.
mass of solute (ethylene glycol) = 30g
molar mass of ethylene glycol = 62g/mol
so no of moles of solute = mass of solute/molar mass of it
= 30g/62g/mol = 0.484 mol
mass of solvent (water) = mass of solution - mass of solvent = 100g - 30g = 70g
∴ molality of solution, m = no of moles of solute/mass of solvent in kg
= 0.484 mol/(70/1000 kg)
= 6.914 molal
now using formula, ∆Tf = kf × m
kf for water = 1.86 k kg/mol , m = 6.914 molal
so, ∆Tf = 1.86 × 6.914 = 12.86 ≈ 13°C
so here you see depression in freezing point is 13°C it means water doesn't free at -10°C when we add ethylene glycol.
Therefore, 30% by mass of aqueous solution of ethylene glycol is suitable for the car radiator.