Question

Sample of ethane gas has the same mass as 1.5*10 raise to power 20 molecules of methane. How many ethane molecules does the sample of gas contain?

Answer 1

Mass of ethane (C₂H₆) = 1.5$\times$10²⁰ molecules of methane (CH₄)_​
6.022$\times$10²³ molecules ​= 16 g of CH₄
1.5$\times$10²⁰ molecules = $\frac{16}{6.022\times {10}^{23}}\times 1.5\times {10}^{20}$ = 3.98$\times$10^-3 g

Now , mass of ethane = 3.98$\times$10^-3 g
Molar mass of ethane (C₂H₆) = 2$\times$12 + 6$\times$1 = 30 g
30 g of C₂H₆ contains = 6.022$\times$10²³ molecules
3.98$\times$10^-3 of C₂H₆ contains = $\frac{6.022\times {10}^{23}}{30}\times 3.98\times {10}^{-3}$ = 0.79$\times$10²⁰ molecules