Question

What is the mass in grams of 120 liters at STP oh He gas​

Answer 1

The mass of He gas = 21.428 g

Further explanation

Given

120 liters of He gas​

Required

the mass in grams

Solution

Conditions at T 0 ° C and P 1 atm are stated by STP (Standard Temperature and Pressure). At STP, Vm is 22.4 liters/mol.

Mol for 120 L :

$\tt \dfrac{120}{22.4}=5.357~moles$

Mass of He gas(MW=4 g/mol) :

$\tt mass=mol\times Ar\\\\mass=5.357\times 4=21.428~g$