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.

Answer 1

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