Question

The formula and molecular mass of caustic soda is:
\[
  A.{\text{ }}NaOH = 40{\text{ }}g{\text{ }}mo{l^{-1}} \\
  B.{\text{ }}N{a_2}OH = 63{\text{ }}g{\text{ }}mo{l^{-1}} \\
  C.{\text{ }}Na{\left( {OH} \right)_2} = 57{\text{ }}g{\text{ }}mo{l^{-1}} \\
  D.{\text{ None of these}} \\
 \]

Answer 1

Hint- In order to deal with this question first we will define the term molecular mass of any compound further we will discuss the caustic soda and write its formula according to it we will evaluate the molecular mass of caustic soda.

Complete step-by-step answer:
Molecular mass: The mass of a given molecule is the molecular mass (m): it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses, because they contain different element isotopes. The related amount of relative molecular mass, as defined by IUPAC, is the ratio of a molecule's mass to the unified unit of atomic mass (also known as the dalton) and is unitless.

Sodium hydroxide is an inorganic compound with formula $NaOH$ , also known as lye and caustic soda. It is a white solid ionic complex made up of sodium cations $N{a^ + }$ and anions of hydroxide $O{H^ - }$ . Sodium hydroxide is an extremely caustic base and alkali that at ordinary atmospheric temperatures decomposes proteins and can cause extreme chemical burns. It is highly water soluble, and extracts moisture and carbon dioxide from the soil readily.

Molar mass of this can be calculated by the sum of the atomic masses of the elements present in the compound.
Molar mass of $NaOH$
= Atomic mass of $Na$ + atomic mass of $O$ + atomic mass of $H$
$
   = 23 + 16 + 1 \\
   = 40g/mol \\
 $
Hence the formula and molecular mass of caustic soda is \[NaOH = 40{\text{ }}g{\text{ }}mo{l^{-1}}\]
So, the correct answer is option A.

Note- The molecular mass and the relative molecular mass is distinct from the molar mass, but is related. The molar mass is defined as the mass of a given substance divided by a substance's quantity and expressed in g / mol.
Molecular masses are calculated from the atomic masses of every nuclide present in the molecule, while molar masses are calculated from each element's standard atomic weights. The standard atomic weight takes into account the element's isotopic distribution (usually assumed to be "normal") in a given sample.