Question

A balloon filled with helium has a volume of 6.9 L. What is the mass, in grams, of helium in the balloon?

Answer 1

Answer : The mass of helium gas in the balloon is, 1.23 grams.

Explanation : Given,

Volume of helium gas = 6.9 L

First we have to calculate moles of helium gas at STP.

As we know that, 1 mole of substance occupy 22.4 L volume of gas.

As, 22.4 L volume of helium gas present in 1 mole of helium

So, 6.9 L volume of helium gas present in $\frac{6.9L}{22.4L}\times 1mole=0.308mole$ of helium

Now we have to calculate the mass of helium gas.

$\text{Mass of He gas}=\text{Moles of He gas}\times \text{Molar mass of He gas}$

Molar mass of He gas = 4 g/mol

$\text{Mass of He gas}=0.308mol\times 4g/mol=1.23g$

Thus, the mass of helium gas in the balloon is, 1.23 grams.