Question

Which of the following weighs the most?

• A. ${10}^{23}$ molecules of $H_2$
• B. 1 mole of $H_2$O
• C. 1 mole of $N_2$
• D. ${10}^{22}$ molecules of $O_2$

Answer 1

Answer: (C)

1 mole of $N_2$

Molecular weight of $H_2=2$ g/mol. 1 mole of $H_2$ weighs 2 g and contains $6.02\times {10}^{23}$ (Avogadro's number ) molecules.

Weight of ${10}^{23}$ molecules of H${}_2$ $=\frac{1\times {10}^{23}}{6.02\times {10}^{23}}\times 2=0.33$ g

Weight of 1 mole of H${}_2$O $=$ molecular weight $=2\left(1\right)+16=18$ g.

Weight of 1 mole of N${}_2$ $=$ molecular weight $=2\left(14\right)=28$ g.

Molecular weight of $O_2=32$ g/mol. 1 mole of $O_2$ weighs 32 g and contains $6.02\times {10}^{23}$ (Avogadro's number ) molecules.

Weight of ${10}^{22}$ atoms of oxygen $=\frac{1\times {10}^{22}}{6.02\times {10}^{23}}\times 32=0.53$ g

Hence, 1 mole of N${}_2$ weighs the most.