Question

Calculate the amount of mercury obtained by the decomposition of 2.16 kg of mercuric oxide.

Answer 1

The chemical reaction involved in the solution:

$$\begin{gathered} 2\mathrm{HgO}\left(\mathrm{s}\right)\to 2\mathrm{Hg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ (\mathrm{Mercuric}\mathrm{oxide})\left(\mathrm{Mercury}\right)\left(\mathrm{Oxygen}\right) \end{gathered}$$

Step-1: Calculation of the molecular weight

Gram atomic weight of Mercury (Hg) = 200 g mol^-1

Gram atomic weight of Oxygen (O) =16 g mol^-1

Molecular weight of Mercuric oxide = Gram atomic weight of Mercury + Gram atomic weight of Oxygen

Gram molecular weight of Mercuric oxide = 200+ 16

Gram molecular weight of Mercuric oxide= 216 g mol^-1

Atomic weight of Mercury = 200 g mol^-1

Step-2: Calculation of the amount of mercury obtained by the decomposition of 2.16 kg of mercuric oxide

In a balanced chemical equation, 2 mole of mercuric oxide undergo decomposition to form 2 mole of mercury.

• According to mole concept, 1 mole of a substance= Gram molecular weight of a substance (if the substance is a molecule)
• Therefore, 2 mole of mercuric oxide= 2 ×216 g= 432 g

Similarly,

• As 1 mole of a substance= gram atomic weight of a substance (if the substance is a an element)
• Therefore, 2 mole of mercury= 2 ×200g = 400 g

So, it can be said that:

432 g of mercuric oxide decomposes to give= 400 g of mercury

1 g of mercuric oxide decomposes to give= $\frac{400}{432}$ g of mercury

2160 g of mercuric oxide decomposes to give= $\frac{400}{432}\times 2160=2000$ g of mercury

Therefore, the amount of mercury obtained by the decomposition of 2.16 kg of mercuric oxide is 2000 g or 2 kg.