At a constant temperature,the vapor pressures | vedclass

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(B) The vapor pressure of a solution depends on the van't Hoff factor $(i)$ and the molality $(m)$ of the solution. For the vapor pressures to be equa

Vedclass · Accepted Answer

$0.8 \, m, 2.4 \, m, 0.6 \, m$

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(B) The vapor pressure of a solution depends on the van't Hoff factor $(i)$ and the molality $(m)$ of the solution. For the vapor pressures to be equal,the effective concentration (osmolarity) must be equal: $i_1 m_1 = i_2 m_2 = i_3 m_3 = i_4 m_4$.For $KCl$,$i = 2$ $(K^+ + Cl^-)$,so $i 	imes m = 2 	imes 1.2 = 2.4$.For $Na_2SO_4$,$i = 3$ $(2Na^+ + SO_4^{2-})$,so $3 	imes m_1 = 2.4 \implies m_1 = 0.8 \, m$.For urea (non-electrolyte),$i = 1$,so $1 	imes m_2 = 2.4 \implies m_2 = 2.4 \, m$.For $AlCl_3$,$i = 4$ $(Al^{3+} + 3Cl^-)$,so $4 	imes m_3 = 2.4 \implies m_3 = 0.6 \, m$.Thus,the molalities are $0.8 \, m, 2.4 \, m, 0.6 \, m$.

At a constant temperature,the vapor pressures of aqueous solutions of $Na_2SO_4$,urea,$AlCl_3$,and $1.2 \, m \, KCl$ are approximately equal. The molalities of the aqueous solutions of $Na_2SO_4$,urea,and $AlCl_3$ are,respectively: (Assume $100 \%$ dissociation of the solute)

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