Finding Molar Mass using Ideal Gas Law

Question

Mass of Unknown Metal	0.0527g
Volume of H2 Gas Produced	25.5 mL
Barometric Pressure	755 mm Hg
Temperature of Water	298 K

What is the molar mass of the metal used in this experiment? Make sure to attach your work. Use correct number of significant figures.

Answer 1

What is molar mass? Molar mass is the number of g/mol. The table gives us grams but we do not know how many mols we were given because the metal is unknown. Luckily, the ideal gas law can help us here.

PV=nRT

Rearrange to find n (the number of mols)

(PV/RT) = n

755 mmHG = 1 atm

Thus we will use the gas constant of 0.082 L x ATM x mol^-1 x K ^-1. (You just need to find the gas constant number that matches the rest of your units.)

Plugged in you get

(1 atm x 0.0255L)/(0.082 x 298 K) = n

n= 0.00107 mols

We were given 0.0527g. We need g/mol so divide this number by the number of mols we found.

Answer should be 49.3 g/mol rounded to 3 sig figs.