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 \[3g\] of hydrogen gas?

Answer 1

Hint: Here \[1g\]of hydrogen is completely reacting with \[8\]grams of oxygen. Because, the hydrogen and oxygen are combining in the ratio, \[1:8\]. And by the combining of hydrogen and oxygen, there is a formation of water. Hence, by using the ratio, we can calculate the required amount of oxygen gas to react completely with \[3g\]of hydrogen gas.

Complete answer:
According to the law of constant proportions, the elements are present in a definite ratio by mass. Here, \[1g\]of hydrogen is completely reacting with \[8\]grams of oxygen. Because, the hydrogen and oxygen are combining in the ratio, \[1:8\]. And by the combining of hydrogen and oxygen, there is a formation of water.
Here, \[1g\]of hydrogen react with \[8\]grams oxygen
Hence, mass of oxygen gas would be required to react completely with \[3g\]of hydrogen gas is equal to, \[3 \times 8 = 24g\].
Therefore, mass of oxygen gas would be required to react completely with \[3g\]of hydrogen gas is equal to\[24g\]. Thus, we can say that, according to the law of constant proportions, the elements are present in a definite ratio by mass.

Note:
We have to know that the mass of oxygen gas would be required to react completely with \[3g\] of hydrogen gas is equal to, \[24g\]. According to the law of constant proportions, the chemical compounds are made up of elements and it is present in a fixed ratio by mass. There is no matter in the source. Water is a main example for this law, because it always contains a fixed mass ratio.