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Question
Silicon (Si = 28) forms a compound with chlorine (Cl = 35.5) in which 5.6 g of silicon combines with 21.3 g of chlorine. Calculate the empirical formula of the compound.
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Solution
Mass of silicon in the given compound = 5.6 g
Mass of the chlorine in the given compound = 21.3 g
The total mass of the compound = (5.6 g + 21.3)g = 26.9 g
% age of silicon in the compound = `56/26.9 × 100` = 20.82%
% age of chlorine in the compound = `21.2/26.9 × 100` = 79.18%
| Element | % age | At. wt. | Atomic ratio | Simplest ratio |
| Si | 20.82 | 28 | `20.82/28` = 0.74 | `0.74/0.74` = 1 |
| Cl | 79.18 | 35.5 | `79.18/35.5` = 2.23 | `2.23/0.74` = 3 |
∴ The empirical formula of the given compound = SiCl3
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