Question

How many grams of methanol ($C{H_3}OH$) must be added to 2 moles of ${H_2}O$ to make a solution containing equal numbers of molecules of ${H_2}O$ and $C{H_3}OH$?

Answer 1

Hint: The scientific unit mole in chemistry is used for measuring large quantities of very small entities such as atoms, molecules, or other particles. The number of particles in one mole of a substance is fixed and is equal to $6.022 \times {10^{23}}$.

Complete step by step answer:
Mole is the unit of measurement for the amount of substance in the International System of Units (SI). In a mole of a substance, the number of particles is fixed and is equal to $6.022 \times {10^{23}}$. The substance can be atoms, molecules, ions or electrons.
The number $6.022 \times {10^{23}}$ i.e. the Avogadro number was chosen so that the mass of one mole of a chemical compound in grams is numerically equal to the average mass of one molecule of the compound, in Daltons.
Now, in the given question, to get the equal number of molecules as that of 2 moles of ${H_2}O$, we would need exactly two moles of methanol.

Molecular weight of methanol is equal to 32 g
i.e. Weight of one mole of methanol = 32 g

Hence, weight of two moles of methanol = 2 $\times$ 32 g = 64 g

Thus, the correct answer is 64 grams.

Note: Remember that the number of molecules in one mole of a substance is constant and is equal to the Avogadro’s number. It is independent of the nature of the molecule.