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NEET 2012
Exam
NEET
Year
2012
Subject
Chemistry
Chapter
States of Matter

NEET 2012 · Chemistry · States of Matter

50 ~mL of each gas A and of gas B takes 150 and 200 ~s respectively...

50 mL50 \mathrm{~mL} of each gas AA and of gas BB takes 150 and 200 s200 \mathrm{~s} respectively for effusing through a pin hole under the similar conditions. If molecular mass of gas BB is 36 , the molecular mass of gas AA will be

Options

  1. A96
  2. B128
  3. C32
  4. D20.25

Correct answer

D. 20.25

Step-by-step solution

Given, VA=VB=50mLTA=150sTB=200sMB=36MA=?\begin{aligned} V_A & =V_B=50 \mathrm{ mL} \\ T_A & =150 \mathrm{ s} \\ T_B & =200 \mathrm{ s} \\ M_B & =36 \\ M_A & =? \end{aligned} From Graham's law of effusion rBrA=MAMB=VBTATB⋅VA⇒MA36=VA×150200×VAor MA36=1520=34MA36=916MA=9×3616=9×94=814=20.25\begin{aligned} \frac{r_B}{r_A} & =\sqrt{\frac{M_A}{M_B}}=\frac{V_B T_A}{T_B \cdot V_A} \\ \Rightarrow \sqrt{\frac{M_A}{36}} & =\frac{V_A \times 150}{200 \times V_A} \\ \text{or } \sqrt{\frac{M_A}{36}} & =\frac{15}{20}=\frac{3}{4} \\ \frac{M_A}{36} & =\frac{9}{16} \\ M_A & =\frac{9 \times 36}{16}=\frac{9 \times 9}{4}=\frac{81}{4}=20.25 \end{aligned}
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