Advertisements
Advertisements
प्रश्न
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 .)
Advertisements
उत्तर
a) Freezing point: The freezing point of a liquid may be defined as the temperature at which the vapour pressure of solid is equal to the vapour pressure of liquid. A liquid freezes at a temperature at which the liquid and its solid coexist in equilibrium.
b) Solution:
Given:
Freezing point of pure solvent ( T° ) = 278.4 K
Mass of solute ( W2 ) = 2 g = 2 x 10-3 kg
Molar mass of solute ( M2 ) = 100 g mol-1 = 100 x 10-3 kg mol-1
Mass of solvent ( W1) = 100 g = 100 x 10-3 kg
Molal depression constant ( Kf )= 5.12 K kg mol-1.
To find: Freezing point of solution (T)
Formulae:
1. ΔTf = T° - T
2. ΔTf = `( "K"_"f" "W"_2 )/( "M"_2 "W"_1 )`
Calculation:
From formula (2),
ΔTf = `( "K"_"f" "W"_2 )/( "M"_2 "W"_1 )`
ΔTf = `( 5.12 xx 2 xx 10^-3 )/( 100 xx 10^-3 xx 100 xx 10^-3 )`
= `( 5.12 xx 2 )/10`
= 1.024 K
From formula (1),
ΔTf = T° - T
∴ T = T° - ΔTf
∴ T = 278.4 - 1.024 = 277.376 K
∴ Freezing point of the given benzene solution is 277.376 K.
APPEARS IN
संबंधित प्रश्न
1.0 x10-3Kg of urea when dissolved in 0.0985 Kg of a solvent, decreases freezing point of the solvent by 0.211 k. 1.6x10 Kg of another non-electrolyte solute when dissolved in 0.086 Kg of the same solvent depresses the freezing point by 0.34 K. Calculate the molar mass of the another solute. (Given molar mass of urea = 60)
Define Cryoscopic constant.
Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg mol−1. Calculate the atomic masses of A and B.
Calculate the depression in the freezing point of water when 10 g of CH3CH2CHClCOOH is added to 250 g of water. Ka = 1.4 × 10−3, Kf = 1.86 K kg mol−1.
Give reasons for the following:
Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.
Cryoscopic constant of a liquid is ____________.
0.01 M solution of KCl and BaCl2 are prepared in water. The freezing point of KCl is found to be – 2°C. What is the freezing point of BaCl2 to be completely ionised?
The freezing point of equimolal aqueous solution will be highest for ____________.
Which of the following 0.10 m aqueous solutions will have the lowest freezing point?
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):
In comparison to a 0.01 m solution of glucose, the depression in freezing point of a 0.01 m MgCl2 solution is ______.
If molality of dilute solution is doubled, the value of molal depression constant (Kf) will be ______.
Which has the highest freezing point?
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.
Latent heat of water (ice) is 1436.3 cal per mol. What will be molal freezing point depression constant of water (R = 2 cal/degree/mol)?
Calculate freezing point depression expected for 0.0711 m aqueous solution of Na2SO4. If this solution actually freezes at – 0.320°C, what will be the value of van't Hoff factor? (kg for water = 108b°C mol–1)
1000 g of 1 m sucrose solution in water is cooled to −3.534°C. What weight of ice would be separated out at this temperature 1 is ______ gm. Kf(H2O) = 1.86 K mol−1 Kg)
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.
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.
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.
