Question
Arrange the following aqueous solutions in the order of their increasing boiling points.
$$\eqalign{
& \left( {\text{i}} \right){10^{ - 4}}\,M\,NaCl \cr
& \left( {{\text{ii}}} \right){10^{ - 4}}\,M\,\,Urea \cr
& \left( {{\text{iii}}} \right){10^{ - 3}}\,M\,MgC{l_2} \cr
& \left( {{\text{iv}}} \right){10^{ - 2}}\,M\,NaCl \cr} $$
A.
(i) < (ii) < (iv) < (iii)
B.
(ii) < (i) = (iii) < (iv)
C.
(ii) < (i) < (iii) < (iv)
D.
(iv) < (iii) < (i) = (ii)
Answer :
(ii) < (i) < (iii) < (iv)
Solution :
$$\eqalign{
& {\text{For }}{10^{ - 4}}\,M\,NaCl\,\,\,\,\,\,\,\,\,i = 2 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 4}}\,M\,\,Urea\,\,\,\,\,\,\,\,\,\,i = 1 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 3}}\,M\,MgC{l_2}\,\,\,\,\,i = 3 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,{10^{ - 2}}\,M\,NaCl\,\,\,\,\,\,\,\,i = 2 \cr} $$
More the value of $$i, C,$$ more will be the elevation in boiling point hence increasing order of boiling point is
$${10^{ - 4}}\,M\,\,Urea < {10^{ - 4}}\,M\,NaCl < {10^{ - 3}}\,M\,MgC{l_2} < {10^{ - 2}}\,M\,NaCl$$