# The Number of Molecules in a Liter of Oxygen at STP

## What is the number of molecules in a liter of oxygen at STP compared to the number of molecules of hydrogen in 1L at STP?

a) Half the number of molecules of hydrogen in 1L at STP.

b) Identical to the number of molecules of hydrogen in 1L at STP.

c) One sixteenth the number of molecules of hydrogen in 1L at STP.

d) Twice the number of molecules of hydrogen in 1L at STP.

## Answer:

The number of molecules in a liter of oxygen at STP is identical to the number of molecules of hydrogen in 1L at STP.

The answer to this question is c) one sixteenth the number of molecules of hydrogen in 1 L at STP.

At STP (standard temperature and pressure), 1 mole of any gas occupies 22.4 L. Therefore, 1 L of oxygen at STP contains 1/22.4 or approximately 0.04464 moles of oxygen. Using Avogadro's principle, we know that 1 mole of any gas contains 6.022 x 10^23 molecules. So, 0.04464 moles of oxygen contains (6.022 x 10^23) x 0.04464 or approximately 2.68 x 10^22 molecules of oxygen.

Similarly, 1 L of hydrogen at STP also contains 0.04464 moles of hydrogen, which means that there are also 2.68 x 10^22 molecules of hydrogen in 1 L at STP. Therefore, the number of molecules in a liter of oxygen at STP is identical to the number of molecules of hydrogen in 1 L at STP.