Advertisements
Advertisements
Question
A 4% solution(w/w) of sucrose (M = 342 g mol−1) in water has a freezing point of 271.15 K. Calculate the freezing point of 5% glucose (M = 180 g mol−1) in water.
(Given: Freezing point of pure water = 273.15 K)
Advertisements
Solution
4% solution(w/w) of sucrose ⇒ 4 g sucrose in 96 g water
w2 (solute) = 4 g
w1 (solvent) = 96 g
M2 (solute) = 342 g mol−1
∆Tf = kf m
Tf = 271.15
T°f=273⋅15
ΔTf = Tf - T°f = (273. 15 - 271 . 15)K = 2.0K
`k_f = (Δ"T"_f)/(m)`
`m = (w^2)/("M" xx w_1) xx 1000 = (4 xx 1000)/(96 xx 342) = 0 .122"m"`
`k_f = (2)/(0.122) = 16.39"Km"^-1`
∆Tf = kf m.
* 5% solution(w/w) of glucose in water ⇒ 5 g glucose in 95 g H2O
w2 = 5 g
w1 = 95 g
M2 = 180 g
∆Tf = ` 16.39 xx (5 xx 100)/(95 xx 180) = 0.479`
∆Tf ≅ 0.48
T°f - Tf = 0.48
Tf = T°f - 0.48
= 273.15 - 0.48
= 272.67
APPEARS IN
RELATED QUESTIONS
Define Cryoscopic constant.
Define Freezing point.
What is the freezing point of a liquid? The freezing point of pure benzene is 278.4 K. Calculate the freezing point of the solution when 2.0 g of a solute having molecular weight 100 g mol-1
is added to 100 g of benzene.
( Kf of benzene = 5.12 K kg mol-1 .)
Which observation(s) reflect(s) colligative properties?
(i) A 0.5 m NaBr solution has a higher vapour pressure than a 0.5 m BaCl2 solution at the same temperature.
(ii) Pure water freezes at a higher temperature than pure methanol.
(iii) A 0.1 m NaOH solution freezes at a lower temperature than pure water.
Which of the following statement is false?
How does sprinkling of salt help in clearing the snow covered roads in hilly areas? Explain the phenomenon involved in the process.
Assertion: When NaCl is added to water a depression in freezing point is observed.
Reason: The lowering of vapour pressure of a solution causes depression in the freezing point.
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.
The depression in the 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.
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.
