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
Calculate the freezing point of the solution when 31 g of ethylene glycol (C2H6O2) is dissolved in 500 g of water.
(Kf for water = 1.86 K kg mol–1)
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.
Cryoscopic constant of a liquid is ____________.
A solution containing 1.8 g of a compound (empirical formula CH2O) in 40 g of water is observed to freeze at –0.465° C. The molecular formula of the compound is (Kf of water = 1.86 kg K 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.
Of the following four aqueous solutions, total number of those solutions whose freezing points is lower than that of 0.10 M C2H5OH is ______. (Integer answer)
- 0.10 M Ba3 (PO4)2
- 0.10 M Na2 SO4
- 0.10 M KCl
- 0.10 M Li3 PO4
Out of the following 1.0 M aqueous solution, which one will show the largest freezing point depression?
The 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.
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.
