Question

Calculate the total pressure in a 10.0 L cylinder which contains 0.4 g helium, 1.6 g oxygen and 1.4 g nitrogen at $27\text{℃}.$
{R = 0.082 L atm K^-1 mol^-1}

• A. 0.492 atm
• B. 49.2 atm
• C. 4.92 atm
• D. 0.0492 atm

Answer 1

Answer: (A)

$\text{N}\text{u}\text{m}\text{b}\text{e}\text{r} \, \text{o}\text{f} \, \text{m}\text{o}\text{l}\text{e}\text{s} \, \text{o}\text{f} \, \text{H}\text{e}=\frac{0.4}{4}=0.1$
$\text{N}\text{u}\text{m}\text{b}\text{e}\text{r} \, \text{o}\text{f} \, \text{m}\text{o}\text{l}\text{e}\text{s} \, \text{o}\text{f} \, \text{o}\text{x}\text{y}\text{g}\text{e}\text{n}=\frac{1.6}{32}=0.05$
$\text{N}\text{u}\text{m}\text{b}\text{e}\text{r} \, \text{o}\text{f} \, \text{m}\text{o}\text{l}\text{e}\text{s} \, \text{o}\text{f} \, \text{n}\text{i}\text{t}\text{r}\text{o}\text{g}\text{e}\text{n}=\frac{1.4}{28}=0.05$
$\text{T}\text{o}\text{t}\text{a}\text{l} \, \text{m}\text{o}\text{l}\text{e}\text{s} \, \text{i}\text{n} \, \text{t}\text{h}\text{e} \, 10.0 \, \text{L} \, \text{c}\text{y}\text{l}\text{i}\text{n}\text{d}\text{e}\text{r} \, \text{a}\text{t} \, 27\text{℃}$
$=0.1+0.05+0.05$
$=0.2 \, \text{m}\text{o}\text{l}$
$\text{p}_{\text{T}}=\frac{\text{n} \text{R} \text{T}}{\text{V}}=\frac{0.2 \times 0.082 \times 300}{10}=0.492 \, \text{a}\text{t}\text{m}$