Question

The percentage of oxygen in NaOH is:
(A)- $16$
(B)- $4$
(C)- $40$
(D)- $8$

Answer 1

Often the percentage is known as the ratio of the amount of element per mole present in the molecule to the total amount of the molecule per mole. This way, also taking the mass in grams the percentage is calculated.

Complete step by step answer:
A percentage of a constituent element to its compound is known as its percentage composition with respect to the compound.
It is the ratio of the amount of element present in the compound to the total amount of the compound, multiplied by 100, where the amount is measured in grams. So, we consider the molar mass during calculation.
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Then, in the NaOH molecule, the percentage composition of the oxygen atom can be calculated as follows:
The molar mass of Sodium atom = $23\,g/mol$
Oxygen atom = $16\,g/mol$
Hydrogen atom = $1\,g/mol$
Then, total molar mass of NaOH $=23+16+1=40\,g/mol$.
Percentage composition of oxygen $=\dfrac{\text{mass of oxygen}}{\text{mass of NaOH}}\text{ }\\!\\!\times\\!\\!\text{ }100$
$=\dfrac{16}{40}\times 100\,=\,40\,$
This way, it has great significance in the chemical analysis of the compound, as it gives us information of the mole to mole ratio of the constituent atoms present in the compound. This can further be used to obtain the ion to ion ratio. Thus, the empirical formula and the molecular formula of the given compound can be generated in this manner.

Therefore, the percentage of the oxygen atom in NaOH is option (C)- $40$.

Note: Similarly, the percent of sodium and hydrogen in the sodium hydroxide molecule can also be calculated. Such that, the sum of the individual percent composition of the constituent elements in the molecule is $100$ .