"Published in Newark, California, USA"
A certain gas weighs 2.478 grams and occupies a volume of 712.5 mL at 25°C and 1.2 atm. What is the molecular formula of the gas?
Solution:
In the given word problem, the weight of a gas is given. We need to solve for the number of moles of a gas in order to get its molecular weight as well as its molecular formula.
The absolute temperature of a gas is
The universal gas law constant for L, gmole, K, and atm is
.Hence, by Ideal Gas Law, the number of moles of a gas is
The molecular weight of a gas is
Next, we need to get the Periodic Table of Elements and check the atomic mass of the gas elements (except the noble gasses). The molecular weight of a gas is equal to twice the atomic mass of a gas element. The molecular weight of the gasses are:
By comparing the calculated molecular weight of a gas with the molecular weight of the gasses above, chlorine gas is the closest value.
Therefore, the molecular formula of a certain gas is Cl2.