Question

The density of air at N.T.P. is 1.293 gm/lit. If the pressure is tripled keeping its temperature constant its density becomes

• A. 3.87 gm/Itr
• B. 1.293 gm/Itr
• C. 2.586 gm/Itr
• D. 0.431 gm/Itr

Answer 1

Answer: (A)

3.87 gm/Itr

Answer 2

First we derive an expression for density of a gas. Density $=\frac{\operatorname{mass}( w )}{\operatorname{volume}( V )}$ but we know that PV = nRT now $n =\frac{ w }{ M }$ where $M$ is molecular weight So, $PV =\frac{ w }{ M } RT$ this gives $\frac{ w }{ V }=\frac{ PM }{ RT }=$ density $= d$ Clearly at a constant temperature, $\frac{ d _{1}}{ P _{1}}=\frac{ d _{2}}{ P _{2}}$ so since pressure is tripled, density also triples new density $=$ old density $x_{3}$ $=1.293 \times 3$ $=3.87 gm / ltr$