20 gm of non electrolyte non volatile solute cxh2xox when dissolved in 100 gram water lower vapour pressure of solution by 1 by 100 th of the vapour pressure of pure water at this temprature what is the formula of compound
Answers
Vapour pressure of solution = Mole fraction of solvent × vapour pressure of pure solvent.
Mole fraction of solvent = Moles of solvent / Total moles of solvent and solute
Question A:
Let M be the molar mass of solute.
Mole ratio of solvent :
(100/18) / (100/8) + (20/M)
Substituting in the formula :
100 / 18 = 5.555
{5.555 / (5.555 + 20 / M)} × 23.76 = 22.41
131.99 = 22.41 [5.555 + 20 / M]
131.99 = 124.49 + 448.20/ M
131.99 M = 124.49 M + 448.20
131.99 M - 124.49 M = 448.20
7.5 M = 448.20
M = 59.76 grams / mol
Question B:
Given that the vapour pressure of the solution reduces to half the value of vapour pressure of pure water we have %
23.76/2 = 11.88
Let X be the mass of solute then
11.88 = [5.555 / 5.555 + X/59.76] × 23.76
65.99 + 11.88X / 59.76 = 131.99
3943.56 + 11.88X = 7887.72
11.88 X = 7887.72 - 3943.56
11.88 X = 3944.16
X = 3944.16 / 11.88
X = 332 g
The required weight is : 332 - 20 = 312 g
Answer is 312 g.
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Formula :
Vapour pressure of solution = Mole fraction of solvent × vapour pressure of pure solvent.
Mole fraction of solvent = Moles of solvent / Total moles of solvent and solute
Question A:
Let M be the molar mass of solute.
Mole ratio of solvent :
(100/18) / (100/8) + (20/M)
Substituting in the formula :
100 / 18 = 5.555
{5.555 / (5.555 + 20 / M)} × 23.76 = 22.41
131.99 = 22.41 [5.555 + 20 / M]
131.99 = 124.49 + 448.20/ M
131.99 M = 124.49 M + 448.20
131.99 M - 124.49 M = 448.20
7.5 M = 448.20
M = 59.76 grams / mol
Question B:
Given that the vapour pressure of the solution reduces to half the value of vapour pressure of pure water we have %
23.76/2 = 11.88
Let X be the mass of solute then
11.88 = [5.555 / 5.555 + X/59.76] × 23.76
65.99 + 11.88X / 59.76 = 131.99
3943.56 + 11.88X = 7887.72
11.88 X = 7887.72 - 3943.56
11.88 X = 3944.16
X = 3944.16 / 11.88
X = 332 g
The required weight is : 332 - 20 = 312 g
Answer is 312 g.