Question

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water .What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas ?

Answer 1

Answer:

Mass of oxygen gas required to react completely with 3g of hydrogen gas is

8x3g = 24g.

Answer 2

Answer:

The law of constant proportions states that in a chemical substance, the elements are always present in definite proportions by mass. Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.

1g of hydrogen reacts with oxygen = 8g

Thus, in order to form water, 3 x 8 = 24 g of oxygen will react completely with 3 g of hydrogen gas.

Concept insight: Recall the law of constant proportions and then apply that in a chemical substance, the elements are always present in definite proportions by mass.

OR

2H

2

+O

2

→2H

2

O

4g 32g 36g

Since, 32 g of oxygen reacts with 4g of H

2

.

So, 3g of H

2

will require =

4

3×32

=24 grams of O

2