Question

$0.5\, M\, NaCl$ aqueous solution is isotonic with______ $\%$ W/V aqueous solution of urea.
(Molar mass of urea $=60\, g\, mol ^{-1}$ )

Answer 1

For isotonic solutions,
$\pi_{1}=\pi_{2}$
$i _{1} C _{1}= i _{2} C _{2}$
($\because$ constant temperature)
$\therefore 2 \times 0.5=1 \times C _{2}$
$C _{2}=1\, M$
$1$ molar aqueous solution of urea
$=60\, g$ of urea in $1000\, mL$ of solution
$=6\, g$ urea in $100\, mL$ solution
$=6 \% W / V$ aqueous solution of urea