1.
At $${80^ \circ }C,$$ the vapour pressure of pure liquid $$'A’$$ is $$520\,mm\,Hg$$ and that of pure liquid $$'B'$$ is $$1000\,mm\,Hg.$$ If a mixture solution of $$'A'$$ and $$'B'$$ boils at $${80^ \circ }C$$ and $$1\,atm$$ pressure, the amount of $$'A'$$ in the mixture is $$\left( {1\,atm = 760\,mm\,Hg} \right)$$
At 1 atmospheric pressure the boiling point of mixture is $${\text{8}}{{\text{0}}^ \circ }C.$$
At boiling point the vapour pressure of mixture, $${P_T} = 1$$ atmosphere $$ = 760\,mm\,Hg.$$
Using the relation,
$$\eqalign{
& {P_T} = P_A^ \circ {x_A} + P_B^ \circ {x_B},{\text{we get}} \cr
& {{\text{P}}_T} = 520{x_A} + 1000\left( {1 - {x_A}} \right) \cr
& \left\{ {\because \,P_A^ \circ = 520\,mm\,Hg,} \right. \cr
& P_B^ \circ = 1000\,mm\,Hg;\,{x_A} + {x_B} = 1 \cr
& {\text{or}}\,\,760 = 520{x_A} + 1000 - 1000{x_A}\,{\text{or}}\,\,{\text{480}}{{\text{x}}_A} = 240 \cr
& {\text{or}}\,\,{x_A} = \frac{{240}}{{480}} = \frac{1}{2}\,\,{\text{or}}\,\,50\,mol\,{\text{percent}} \cr} $$
2.
$${P_A}$$ and $${P_B}$$ are the vapour pressure of pure liquid components, $$A$$ and $$B,$$ respectively of an ideal binary solution. If $${X_A}$$ represents the mole fraction of component $$A,$$ the total pressure of the solution will be.
A.
$${P_A} + {X_A}\left( {{P_B} - {P_A}} \right)$$
B.
$${P_A} + {X_A}\left( {{P_A} - {P_B}} \right)$$
C.
$${P_B} + {X_A}\left( {{P_B} - {P_A}} \right)$$
D.
$${P_B} + {X_A}\left( {{P_A} - {P_B}} \right)$$
Acetonitrile $$\left( {\mathop {C{H_3}}\limits^{\delta + } - C \equiv \,\mathop N\limits^{\delta - } } \right)$$ and acetone both are polar molecules, hence dipole-dipole interaction exist between them. Between $$KCl$$ and water ion-dipole interaction is found and in Benzene ethanol and Benzene-Carbon tetra chloride dispersion force is present
4.
Which one of the following electrolytes has the same value of van't Hoff's factor $$(i)$$ as that of $$A{l_2}{\left( {S{O_4}} \right)_3}$$ ( if all are $$100\% $$ ionised ) ?
A.
$${K_2}S{O_4}$$
B.
$${K_3}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$$
C.
$$Al{\left( {N{O_3}} \right)_3}$$
D.
$${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$$
Osmotic pressure is a colligative property which is used to find the molecular weight of polymer because other colligative properties give so low value of molecular weight that it cannot be measured accurately.
6.
The vapour pressure of acetone at $${20^ \circ }C$$ is 185 $$torr.$$ When $$1.2 g$$ of a non-volatile substance was dissolved in $$100 g$$ of acetone at $${20^ \circ }C,$$ its vapour pressure was 183 $$torr.$$ The molar mass $$\left( {g\,mo{l^{ - 1}}} \right)$$ of the substance is :
Using relation,
$$\frac{{{p^ \circ } - {p_s}}}{{{p_s}}} = \frac{{{w_2}{M_1}}}{{{w_1}{M_2}}}$$
where $${w_1},{M_1} = $$ mass in $$g$$ and $$mol.$$ mass of solven
$${w_2},{M_2} = $$ mass in $$g$$ and $$mol.$$ mass of solute
Let $${{\text{M}}_2} = x$$
$${p^ \circ } = 185\,torr\,;\,{p_s} = 183\,torr$$
$$\frac{{185 - 183}}{{183}} = \frac{{1.2 \times 58}}{{100x}}$$ ( $$Mol.$$ mass of acetone = 58 )
$$x = 64$$
∴ Molar mass of substance $${\text{ = 64}}$$
7.
Which of the following solutions shows positive deviation from Raoult's law ?
Acetone + ethanol is an example of solutions showing positive deviation from Raoult's law. Since acetone-ethanol attractions are weaker than acetone-acetone and ethanol-ethanol attractions.
8.
The vapour pressures of ethanol and methanol are $$44.5\,\,mm\,\,Hg$$ and $$88.7\,\,mm\,\,Hg$$ respectively. An ideal solution is formed at the same temperature by mixing $$60\,g$$ of ethanol with $$40\,g$$ of methanol. The total vapour pressure of the solution and the mole fraction of methanol in the vapour are respectively
A.
$$43.46\,\,mm\,\,{\text{and}}\,\,{\text{0}}{\text{.51}}$$
$$\eqalign{
& {\text{For }}{10^{ - 4}}\,M\,NaCl\,\,\,\,\,\,\,\,\,i = 2 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 4}}\,M\,\,Urea\,\,\,\,\,\,\,\,\,\,i = 1 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 3}}\,M\,MgC{l_2}\,\,\,\,\,i = 3 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 2}}\,M\,NaCl\,\,\,\,\,\,\,\,i = 2 \cr} $$
More the value of $$i, C,$$ more will be the elevation in boiling point hence increasing order of boiling point is
$${10^{ - 4}}\,M\,\,Urea < {10^{ - 4}}\,M\,NaCl < {10^{ - 3}}\,M\,MgC{l_2} < {10^{ - 2}}\,M\,NaCl$$
10.
At equilibrium the rate of dissolution of a solid solute in a volatile liquid solvent is ______________.