Calculate the percentage composition of oxygen and hydrogen in Water $H_{2} O$ .
Given : Atomic weight of H = 1u, O = 16u

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Solution

Step 1: Given data
Atomic weight of H = 1u, O = 16u
Step 2: Finding the mass for the given data
The molecular mass of $H_{2} O$ = (Number of hydrogen atoms x atomic mass of hydrogen) + (Number of oxygen atoms x atomic mass of oxygen)
The molecular mass of $H_{2} O$ = $(2 \times 1) + (1 \times 16)$
The molecular mass of $H_{2} O$ = $2 + 16 = 18$ u
Step 3: Finding the mass for each element
Mass of $H$ = (Number of hydrogen atoms x atomic mass of hydrogen) $= (2 \times 1) = 2 u$
Mass of $O$ = (Number of oxygen atoms x atomic mass of oxygen) $= (1 \times 16) = 16 u$
Step 4: Finding the % composition
% composition is the proportion by mass of each element present in a compound.
% composition of $H = \frac{2}{18} = 11.11 %$
% composition of $O = \frac{16}{18} = 88.89 %$
Thus, the percentage composition of hydrogen and oxygen in Water $H_{2} O$ is $11.11 %, and 88.89 %$ respectively.

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