Question

A sample of ethane gas has same mass as 1.5 into 10 to the power 20 molecules of methane how many ethane molecules does the sample of gas contain

Answer 1

$mass \: of \: 6.022 \times {10}^{23} \: molecules \: \\ of \: methane \: = 16g \\ mass \: of \: 1.5 \times {10}^{20} \: molecules \: of \\ methane \: = \frac{16 \times 1.5 \times {10}^{20} }{6.022 \times {10}^{23} } = 0.003985g$

and,

$30g \: of \: ethane \: contains \: molecules = 6.022 \times {10}^{23} \\ 0.003238g \: of \: ethane \: contains \: molecules \: = \frac{6.022 \times {10}^{23} \times 0.003238 }{30} = 6.5 \times {10}^{19} molecules$