Question

The sodium salt of methyl orange has $7\%$ sodium. What is the minimum molecular weight of the compound?
A. $420$
B. $375$
C. $329$
E. $295$

Answer 1

Molecular weight is defined as the sum or total of the value of the atomic weight of the atoms in a molecule and the molecular weight of sodium is $22.98$ approximately $23g\,/\,mol$. It is also known as the molecular mass of the compound or molecule. The methyl orange is the indicator which is used in titration experiments. The number of moles is defined as the division of the given weight by the molar mass or molecular weight of the compound it is denoted by $n$.

Complete step by step answer:
The given information based on the question is sodium salt of methyl orange has $7$ percentage composition of sodium or the percentage of weight of compounds $7\%$ and we will find the minimum molecular weight of the compound.
So, as we know the formula of no. of moles. According to the definition,
${\text{Number of moles}}\left( n \right) = \dfrac{{{\text{Weight}}}}{{{\text{Molecular weight}}}}.......eq\,II$
So, we consider Molecular Weight as
$n = \dfrac{W}{M}.......eq\,II$
And so, we know that the weight of compound is $7\%$, so it is put in the $eq\,II$
$n = \dfrac{7}{{100}} \times M\,g$
And the weight of one mole of sodium is $23g$ because $1\,mole$ of sodium is present in $1\,mole$ of the given compound.
$23 = \dfrac{7}{{100}} \times M\,g/mol$
$M = \dfrac{{100}}{7} \times 23\,g/mol$
$M = \dfrac{{2300}}{7} \times \,g/mol$
$M = 329g/mol$ approximately
So, here we determine the minimum molecular weight of the compound is $M = 329g/mol$ approximately.

So, the correct answer is Option C.

Note:
The mole is defined as the unit of specific or scientific standards for measuring large quantities or amount of substance. Methyl orange indicator has textile applications. In acidic, the methyl orange indicator is in pink colour and in basic solution, it is yellowish colour.