Question

2. Mass of 112 mL of a certain gas is 0.22 g at STP. How many molecules are there in the sample of gas ? What is the molar mass of the gas ?​

Answer 1

Given :-

Volume of certain gas at STP = 112 ml

Mass of gas at STP = W = 0.22 g

We can find number of moles using relation,

n = Given Volume/Volume at STP

Here 'n' represents number of moles.

n = 112/22400

$\bf{n\:=\:0.005\:mole}$

As we know the moles we can find the number of molecules,

No. of molecules = n × 6.02 × 10²³

N = 0.005 × 6.02 × 10²³

N = 3.01 × 10²¹ molecules

Again,

For Molar mass we use simple forumla,

W/M = n

0.22/0.005 = M

$\bf{M\:=\:44\:g}$