Question

A cylinder of argon gas contains 50.0 L of `Ar` at 18.4 atm and 127 °C. How many moles of argon are in the cylinder?

Answer 1

The cylinder contains `"28.0 mol Ar"`.

Explanation:

Use the ideal gas law.

`PV=nRT`, where `n` is moles and `R` is the gas constant.

Known
`P="18.4 atm"`
`V="50.0 L"`
`T=127^@"C+273.15=400 K"`
`R="L atm K"^(-1) "mol"^(-1)`
https://en.m.wikipedia.org/wiki/Gas_constant

Unknown
`n`

Solution
Rearrange the equation to isolate `n`. Substitute the known values into the equation and solve for `n`.

`PV=nRT`

`n=(PV)/(RT)`

`n=(18.4cancel"atm" * 50.0cancel"L")/(0.082057338 cancel"L" * cancel"atm" * cancel"K"^(-1) * "mol"^(-1) * 400"K")="28.0 mol Ar"`