How many mercuric chloride must react to give 5.35 grams of Hg?

Method 1 :

Molar mass of HgCl₂ = (200.6 + 35.45×2) = 271.5 g/mol
Molar mass of Hg = 200.6 g/mol

HgCl₂ → Hg + Cl₂
OR: Mole ratio HgCl₂ : Hg = 1 : 1

No. of moles of Hg produced = (5.35 g) / (200.6 g/mol) = 0.02667 mol
No. of moles of HgCl₂ needed = 0.02667 mol
Mass of HgCl₂ needed = (271.5 g/mol) × (0.02667 mol) = 7.24 g


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Method 2 :

In 1 mole of HgCl₂ :
Mass of HgCl₂ = (200.6 + 35.45×2) g = 271.5 g
Mass of Hg contained = 200.6 g

When the mass of Hg is 5.35 g :
Mass of HgCl₂ = (5.35 g) × (271.5/200.6) = 7.24 g