Question

How do you calculate the percent composition of water?

Answer 1

Hint: As we know that the mass percentage of any element is about 100 times the mass of the element divided by the total mass. We can calculate the percent composition of water by using the formula:
$Mass \ \% \ of \ Element = \dfrac{Mass \ of \ Element}{Mass \ of \ Compound} \times 100$

Complete step by step answer:
In the lower classes, we have come across the calculation of several parameters which also includes mass percent. Let us see this in detail.
- As we know that the percentage composition is the ratio of the individual element to the to the total amount of individual elements present in the compound, that is whole multiplied by 100.
- As we know that the molecular weight of water is about 18 g/mol. And the mass of oxygen is about 16 g/mol. And the mass of hydrogen is about 2 g/mol.
- We can calculate the percentage of oxygen in the water as:
$\text{Mass of Element} = \dfrac{\text{Mass of Element}}{\text{Mass of Compound}} \times 100$
$\begin{align}
& =\dfrac{16}{18} \times 100 \\ 
& =88.88\% \\ 
\end{align}$                                                                                                                                                                 -

Hence, we get the percentage of oxygen in the water as 88.88%.
- Now, we will calculate the percentage of hydrogen in the water as:
 $\begin{align}
& \text{Mass of Element} = \dfrac{\text{Mass of Element}}{\text{Mass of Compound}} \times 100 \\ 
& =\dfrac{2}{18} \times 100 \\ 
& =11.11\% \\ 
\end{align}$                                                                                                   
 - Hence, we get the percentage of hydrogen in the water as $11.11\%$.
Therefore, in this way we can calculate the percent composition of water, that is the percentage of hydrogen in the water is $11.11\%$ and percentage of oxygen in the water is $88.88\%$.

Note: It is found that the percentage composition can be measured experimentally and also if the percentage composition of the element is given, then we can calculate the empirical formula of the compound, which is basically the simplest whole ratio of each type of atom present in the compound.