Question

What volume does a `"5.0-g"` sample of hydrogen gas occupy at STP?

The molar volume of a gas at STP `= "22.4 L mol"^(-1)`

Answer 1

`"56 L"`

Explanation:

The problem provides you with the molar volume of a gas at STP

`V_"n STP" = "22.4 L mol"^(-1)`

So, you know that under STP conditions for pressure and temperature, `1` mole of any ideal gas will occupy `"22.4 L"`.

You can use the molar volume of a gas at STP as a conversion factor to help you determine the volume a sample of gas will occupy when kept under STP conditions.

In your case, you need to find volume, so rearrange the molar volume of a gas as

`"22.4 L"/"1 mole H"_2 ->` this takes you from moles of `"H"_2` to liters

Now, in order to find the number of moles present in `"5.0 g"` of hydrogen gas, you can use the gas' molar mass

`5.0 color(red)(cancel(color(black)("g"))) * "1 mole H"_2/(2.016color(red)(cancel(color(black)("g")))) = "2.48 moles H"_2`

This sample of hydrogen gas will thus occupy

`2.48 color(red)(cancel(color(black)("moles H"_2))) * "22.4 L"/(1color(red)(cancel(color(black)("mole H"_2)))) = color(darkgreen)(ul(color(black)("56 L")))`

The answer is rounded to two sig figs, the number of sig figs you have for the mass of hydrogen gas.