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Answer the following.
Answer the following: Arrange the following aqueous solutions in increasing order of osmotic…
Answer the following:
(a)[1.6666666666666667]
Arrange the following aqueous solutions in increasing order of osmotic pressure. Give reasons in support of your answer:
(1) $6\cdot0\text{g}$ per litre of urea solution (molecular weight of urea $= 60\text{g mol}^{-1}$)
(2) $72\cdot0\text{g}$ per litre of glucose solution (molecular weight of glucose $= 180\text{g mol}^{-1}$)
(3) $5\cdot85\text{g}$ per litre of sodium chloride solution (molecular weight of sodium chloride $= 58\cdot5\text{g mol}^{-1}$)
(b)[1.6666666666666667]
Calculate the mole fraction ($x$) of ethanol and water if $92\text{ g}$ of ethanol is dissolved in $540\text{ g}$ of water.
(Atomic mass of $\text{C} = 12$, $\text{O} = 16$ and $\text{H} = 1$)
(c)[1.6666666666666667]
What type of azeotropic mixture will be formed by a solution of chloroform and acetone? Justify your answer based on strength of intermolecular interactions that develops in the solution.
Answer
Answer (a)
Official answer keyOrder, first to last: urea, sodium chloride, glucose
Osmotic pressure is a colligative property proportional to the number of solute particles.
(1) Urea: $6/60 = 0.1$ mol, 0.1 mol of particles (non-electrolyte)
(2) Glucose: $72/180 = 0.4$ mol, 0.4 mol of particles
(3) NaCl: $5.85/58.5 = 0.1$ mol, which gives $2\times 0.1 = 0.2$ mol of particles ($\mathrm{Na^+}$ and $\mathrm{Cl^-}$)
Increasing order of osmotic pressure: urea < sodium chloride < glucose.
Answer (b)
Official answer key$n_{\mathrm{C_2H_5OH}} = 92/46 = 2\text{ mol}$; $n_{\mathrm{H_2O}} = 540/18 = 30\text{ mol}$
$x_{\mathrm{C_2H_5OH}} = \dfrac{2}{2+30} = 0.0625$
$x_{\mathrm{H_2O}} = \dfrac{30}{2+30} = 0.9375$
Final answer: 0.0625 (ethanol), 0.9375 (water)
Answer (c)
Official answer keyChloroform and acetone form a maximum boiling azeotrope. The solution shows negative deviation from Raoult's law, because the chloroform-acetone attractions (hydrogen bonding between the C-H of chloroform and the C=O of acetone) are stronger than the attractions in the pure liquids, so the vapour pressure is lower and the boiling point is higher.
From ISC 2027 Specimen Chemistry Paper 1, question 21(ii).
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