Question

What weight of $NaOH$ will contain the same number of oxygen atoms as are present in $9.8g$ of sulfuric acid?
A. $4g$
B. $16g$
C. $40g$
D. $160g$

Answer 1

To solve this question we must know about the atomic masses for each atom or element present in a particular species. In $NaOH$ there are a total three atoms sodium, oxygen and hydrogen. Atomic mass of sodium is $23$, oxygen is $16$ and hydrogen is one.

Complete answer:
To start this question we must know about Avogadro’s number. Avogadro's number is the number of units in one mole of any substance, equals to $6.02214076 \times {10^{23}}$. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance and the character of the reaction.
Sulfuric acid has a chemical formula ${H_2}S{O_4}$, it has two hydrogen atoms, one sulfur atom and four oxygen atoms. In the question it is asked for the number of oxygen atoms in $NaOH$ to be the same as that of in $9.8g$ of sulfuric acid. In sulfuric acid there are four oxygen atoms while in sodium hydroxide there is only one oxygen atom. The molecular weight of sodium hydroxide is $40g$.
So $9.8g$ of sulfuric acid contains
$4 \times 6.02 \times {10^{23}} = 2.408 \times {10^{23}}$ atoms of oxygen
Mass of $NaOH$ containing same number of oxygen atom
Therefore,
$\dfrac{{No.of oxygen atoms in{H_2}S{O_4} \times Mol.massofNaOH}}{{AvogadroNumber}}$
Now we can substitute the known given values we get,
$= \dfrac{{4 \times 6.02 \times {{10}^{23}} \times 40}}{{6.02 \times {{10}^{23}}}}$
On simplification we get,
$= 16g$

So, the correct answer is “Option B”.

Note:
We have to know that the Avogadro's number is a proportion that relates molar mass on an atomic scale to physical mass on a human scale. Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds) per mole of a substance. It is equal to $6.02214076 \times {10^{23}}$mol-1 and is expressed as the symbol ${N_A}$.