Question

Calculate the mass of

(a) An atom of silver​​​​​(b) a molecule of carbon dioxide

​(b) Three atom of copper​​​​(c) a molecule of copper sulphate

Answer 1

a) 6.022 $\times$10²³ atoms of silver = 107.86 u of silver
1 atom of silver = $\frac{107.86}{6.022\times {10}^{23}}$ = 17.91 $\times$10^-23 u

b) Molar mass of carbon dioxide (CO₂) = 12 + 16$\times$2 = 44 g/mol
6.022 $\times$10²³ molecules of CO₂ = 44 g
A molecule of CO₂ = $\frac{44}{6.022\times {10}^{23}}$ = 7.3 $\times$10^-23 g

c) 6.022$\times$10²³ atoms of copper = 63.5 g of copper
1 atom of copper = $\frac{63.5}{6.022\times {10}^{23}}$ g = 10.54 $\times$10^-23 g

3 atoms of copper = 3 $\times$10.54 $\times$10^-23 g = 31.62 $\times$10^-23 g


d) Molar mass of molecule of copper sulphate (CuSO₄) = 63.5 + 32 + 16$\times$4
= 63.5 + 32 + 64 = 159.5 g/mol
​6.022$\times$10²³ molecules = 159.5 g of CuSO_​4
1 molecule of CuSO₄ = $\frac{159.5}{6.022\times {10}^{23}}$ = 26.48 $\times$10^-23 g