How many molecules of ethane are present in 64.28 liters of ethane gas (C2H6) at STP?

A) 3.8715 × 10^25

64.28 l/22.4 l/mole at STP * 6.02 E23/mole = 1.728 E24

answer C

Source(s): Soc!!

You were given the answer already by another poster, but did you understand how that person arrived at it?

At STP, one mole of an ideal gas will occupy 22.4 liters. Ethane can be considered an ideal gas.

And, one mole of anything is an Avogadro’s number of molecules, or for an element, atoms. And that number is 6.023 x 10^23.