• # question_answer 86)   A vessel contains 1.6 g of dioxygen at STP (273.15 K. 1 atm pressure). The gas is now transferred to another vessel at constant temperature, where pressure becomes half of the original pressure. Calculate : (a) volume of the new vessel. (b) number of molecules of dioxygen.

(i) Volume of 1.6 g${{O}_{2}}$  at STP $=\frac{1.6}{32}\times 22.4=1.12L$ ${{P}_{1}}{{V}_{1}}={{P}_{2}}{{V}_{2}}$ or         $1\times 1.12=0.5\times {{V}_{2}}$ or           ${{V}_{2}}=2.24L$ (ii) Number of molecules = $\frac{Mass}{molar\,mass}\times 6.023\times {{10}^{23}}$ $=\frac{1.6}{32}\times 6.023\times {{10}^{23}}$ $\mathbf{=3}\mathbf{.0115\times 1}{{\mathbf{0}}^{\mathbf{22}}}$