States of Matter - Result Question 88
88. Oxygen is present in one litre flask at a pressure of $7.6 \times 10^{-10}$ mm Hg . Calculate the number of oxygen molecules in the flask at $0^{\circ} \mathrm{C}$.
$(1983,2 M)$
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Answer:
Correct Answer: 88. $\left(2.7 \times 10^{10} \mathrm{~g} \mathrm{~mol}^{-1}\right)$
Solution:
$\begin{aligned} & \text { Number of moles }(n)=\frac{p V}{R T} \\ & \text { and } \quad n=\frac{N \text { (Number of molecules) }}{N_A \text { (Avogadro number) }} \\ & \Rightarrow \quad N=n N_A=\left(\frac{p V}{R T}\right) N_A \\ & =\left(\frac{7.6 \times 10^{-10}}{760} \times \frac{1}{0.082 \times 273}\right) \times 6.023 \times 10^{23} \\ & =2.7 \times 10^{10} \text { molecules } \\ & \end{aligned}$
BETA
