How many moles of argon atoms are present in 11.2 L of argon gas at STP?

2 Answers
Jan 8, 2017

Answer:

What is the molar volume at #"STP"?#

Explanation:

Well, the molar volume at #"STP"# is #22.4*L#. You have to be careful to quote this now, because different curricula have different standards, and some quote standard pressure as #100*kPa# not #"1 atmosphere"#.

So you have a volume of #11.2*L#; given the molar volume, and this represents, #(11.2*cancelL)/(22.4*cancelL*mol^-1)=??mol#.

We note that #1/(mol^-1)=1/(1/(mol))=mol#, as required for a molar quantity.

Jan 8, 2017

Answer:

Using the current recommended STP values of #"0"^@"C"# and #"100 kPa"#, #"11.2 L"# of Ar atoms contain #"0.493 mol Ar"#.

Using the older standard, as indicated in the explanation, #"11.2 L"# of Ar atoms contain #"0.500 mol"#.

Explanation:

Current values for STP are #0^@"C"# or #"273.15 K"# for temperature, and pressure of #"10"^5color(white)(.) "Pa"#, which is usually written as #"100 kPa"#, or #"1 bar"#.

At these current values, the molar volume of a gas is #"22.710 L/mol"#.

In order to determine the number of moles of the given volume of Ar, divide the given volume by the molar volume of an ideal gas, #"22.710 L/mol"#.

#(11.2"L")/(22.710"L"/"mol")#

Simplify by multiplying by the inverse of the molar volume.

#11.2cancel"L"xx(1"mol")/(22.710cancel"L")="0.493 mol Ar"#

Using the older STP values of #"0"^@"C"# or #"273.15 K"#, and pressure of #"1 atm"#, molar volume is #"22.414 L/mol"#.

#11.2cancel"L"xx(1"mol")/(22.414cancel"L")="0.500 mol Ar"#