Question

If 25.3 grams of mercury(II) oxide react to form 23.4 grams of mercury, how many grams of oxygen must simultaneously be formed?

Answer 1

Answer : The mass of oxygen formed must be 3.8 grams.

Explanation :

Law of conservation of mass : It states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.

This also means that total mass on the reactant side must be equal to the total mass on the product side.

The balanced chemical reaction will be,

$2HgO\rightarrow 2Hg+O_2$

According to the law of conservation of mass,

Total mass of reactant side = Total mass of product side

Total mass of $2HgO$ = Total mass of $2Hg+O_2$

As we are given :

The mass of $HgO$ = 25.3 grams

The mass of $Hg$ = 23.4 grams

So,

$2\times 25.3g=2\times 23.4g+\text{Mass of }O_2$

$50.6g=46.8g+\text{Mass of }O_2$

$\text{Mass of }O_2=3.8g$

Therefore, the mass of oxygen formed must be 3.8 grams.