Question

A solution containing 8.6 g $L^{-1}$ of urea is isotonic with a 5% (w/v) solution of unknown solute. The molar mass of the solute will be

• A. 348.9 g $mo{l}^{-1}$
• B. 174.5 g $mo{l}^{-1}$
• C. 87.3 g $mo{l}^{-1}$
• D. 34.89 g $mo{l}^{-1}$

Answer 1

The correct option is A 348.9 g $mo{l}^{-1}$

Given:

No of moles of urea $=8.6/60$

$5$% of unknown solution $=5g/100ml$

$=50g/1000ml$

$=5g/litre$

No of moles of unknown solute =$50/m$

$8.6/60=50/m$

$m=348.9$

Option A is the correct answer.