Question 29 answer

Solution
STP conditions imply Standard Temperature and Pressure, i.e., P is 760 mm Hg and T is 273 K.
According to Ideal Gas Equation,
$$\begin{gathered} \frac{P_1{V}_1}{{\displaystyle \frac{w_1}{M}}\times R{T}_1}=\frac{P_2{V}_2}{{\displaystyle \frac{w_2}{M}\times R{T}_2}} \\ \frac{P_1{V}_1}{{\displaystyle w_1{T}_1}}=\frac{P_2{V}_2}{{\displaystyle w_2{T}_2}} \left(Since gas is same, M=M\right) \\ \text{Putting all the given values, we get} \\ \frac{760\times 22.4}{{\displaystyle 70\times 273}}=\frac{700\times 20}{{\displaystyle {\mathrm{w}}_2\times 300}} \\ {w}_2=52.38 \mathrm{g} \end{gathered}$$