Question

which of the following weighs the most?
(A)10^23 molecules of H2
(B)1 mole of H2O
(C)10^22 atoms of oxygen
(D)1 mole of N2

Answer 1

1) 10²³ molecules of H₂ :
Molar mass of H = 1 g mol^-1
Mass of 6.022$\times$10²³ molecules = 2 g
Mass of 10²³ molecules = $$\begin{gathered} \frac{2}{6.022\times {10}^{23}}\times {10}^{23} \\ 0.3321g \end{gathered}$$

2) 1 mole of H₂O :
Molar mass of water = 18 g mol^-1
Mass of 1 mole of H₂O = 18 g

3) 10²² atoms of oxygen :
Atomic mass of oxygen = 16 u
Mass of 6.022$\times$10²³ atoms = 16 g
Mass of 10²² atoms = $\frac{16}{6.022\times {10}^{23}}\times {10}^{22}=0.265g$

4) 1 mole of N₂
Molar of N₂ = 28 g mol^-1
Mass of 1 mole of N₂ = 28 g

Therefore , 1 mole of N₂ weighs the most.