How many moles are in a gas in 890mL at 21 °C and 750 mmHg?

Mar 3, 2016

$n = \text{0.036 mol}$

Explanation:

Use the ideal gas law. The formula is $P V = n R T$, where $P$ is pressure, $V$ is volume, $n$ is moles, $R$ is the gas constant, and $T$ is the Kelvin temperature.

Given/Known
$P = \text{750 mmHg"="750 Torr}$
$V = 890 \cancel{\text{mL"xx(1"L")/(1000cancel"mL")="0.89 L}}$
$R = {\text{62.363577 L Torr K"^(-1) "mol}}^{- 1}$
https://en.m.wikipedia.org/wiki/Gas_constant
$T = \text{21"^@"C"+273.15"=294 K}$

Unknown
$n$

Solution
Rearrange the formula to isolate $n$. Substitute the given/known values into the formula and solve.

$P V = n R T$

$n = \frac{P V}{R T}$

n=(750cancel"Torr" * 0.89cancel"L")/((62.363577 cancel"L" cancel"Torr" cancel"K"^(-1)" mol"^(-1))xx(294cancel"K"))="0.036 mol" rounded to two significant figures