Question

Under certain conditions, the substances iron and oxygen combine to form iron(III) oxide. If 30.9 grams of iron and 13.3 grams of oxygen combine to form iron(III) oxide, how many grams of iron(III) oxide must form?

Under certain conditions, the substance mercury(II) oxide can be broken down to form mercury and oxygen.

If 30.7 grams of mercury(II) oxide react to form 28.4 grams of mercury, how many grams of oxygen must simultaneously be formed?

Answer 1

1)
The reaction is:
4 Fe + 3 O2 -> 2 Fe2O3

Use law of conservation of mass:
Final mass of product = initial mass of reactant
So,
Mass of Fe2O3 formed = initial mass of Fe + initial mass of O2
= 30.9 g + 13.3 g
= 44.2 g

Answer: 44.2 g

2)
The reaction is:
2 HgO -> 2 Hg + O2

Use law of conservation of mass:
Final mass of product = initial mass of reactant
So,
Mass of Hg formed + Mass of O2 formed = initial mass of HgO
28.4 g + Mass of O2 formed = 30.7 g
Mass of O2 formed = 2.3 g

Answer: 2.3 g