30gram urea is diss in sufficient water to produce 2litre of solution. Calculate molality of solution.
Answers
Answer:
Ideal Solution Non-ideal Solution
Obey Raoult's law at every range of concentration. Do not obey Raoult's law.
Neither heat is evolved nor absorbed during dissolution. Endothermic dissolution; heat is absorbed.
Explanation:
(a) Vapour pressure of water, p1 = 23.8 mm of Hg
Weight of water = 846 g
Weight of urea = 30 g
Molecular weight of water (H2O) = 1 × 2 + 16 = 18 g mol−1
Molecular weight of urea (NH2CONH2) = 2N + 4H + C + O
= 2 × 14 + 4 × 1 + 12 + 16
= 60 g mol−1
Number of moles of water n1 = 846 / 18 = 47
Number of mole of urea n2 = 30 / 60 = 0.5
Now, we have to calculate vapour pressure of water in the solution. We take vapour pressure as p1.
Use the formula of Raoult’s law
(P10 - P1) / P10 = n2 / (n1-n2)
Plug the values we get
(23.8 - p1) / 23.8 = 0.5 / (47+0.5)
(23.8 - p1) / 23.8 = 0.5106
after cross multiply
23.8 – p1 = 23.8 × 0.5106
Solve it we get p1 = 11.6 mm Hg
So, Vapour pressure of water in the given solution = 11.6 mm of Hg