If 8 g of a non-electrolyte solute is dissolved in 114 g of n-octane to reduce its vapour pressure to 80%, the molar mass (in g mol^{–1}) of the solute is [Given that molar mass of n-octane is 114 g mol^{–1}]

(1) 20

(2) 40

(3) 60

(4) 80

If you are commenting for the first time, please read the guidelines.

If you are answering for the first time, please read the guidelines.

Ans: (2) 40

Sol. Assuming dilute solution

${\Delta P\over P_A^0}={n_B\over n_A}={w_B\over m_B}.{m_A\over w_A}$

${20\over100}={8\over m_B}.{114\over114}$

$m_B={8\times100\over20}=40\ \text{gmol}^{-1}$

Welcome to Jee Neet QnA, where you can ask questions and receive answers from other members of the community.

Join our Telegram group for live discussion.

Subscribe our YouTube channel for video solutions with explanation.

Download Jee Neet QnA Books in PDF for offline learning.

1.2k questions

842 answers

384 comments

92 users