Question

If $$4\text{g}$$ of $$\text{NaOH}$$ are contained in one deciliter of solution, its molarity would be:
A.$$4\text{M}$$
B.$$2\text{M}$$
C.$$1\text{M}$$
D.$$1.5\text{M}$$

Answer 1

Hint: To find molarity, we need to calculate moles of solute present in per litre of the solution. Moles of a substance is a SI unit of amount of substance, it can be calculated from mass, volume and number of a substance.

Complete step by step answer:
In order to find molarity of $$\text{NaOH}$$ or sodium hydroxide, we need to first find moles of sodium hydroxide present in the given volume of solution. As the given mass of sodium hydroxide is $$4\text{g}$$ and as molar mass of sodium hydroxide means mass of 1 mole sodium hydroxide molecules and that is $$40\text{g}$$ , from this data we can easily calculate moles of sodium hydroxide and moles of a substance can be given as:
$$\text{no of moles}={\displaystyle \frac{\text{given mass}}{\text{molar mass}}}$$ ,
putting values of mass of sodium hydroxide given and molar mass of sodium hydroxide.
We get, number of moles of sodium hydroxide as: $$\text{no of moles}={\displaystyle \frac{4}{40}}=0.1\text{mol}$$ .
Now volume of the solution can be determine from the given data in question as it is given that $$\text{NaOH}$$ are contained in one deciliter of solution, it means volume of solution is $$0.1\text{L}$$ .
Now molarity of the solution is defined as the number of moles of a solute present in $$1\text{L}$$ or $$1000\text{mL}$$ of the solution. In our case, solute is sodium hydroxide, thereby molarity of the solution can be given as:
$$\text{Molarity}={\displaystyle \frac{\text{moles of NaOH}}{\text{Volume of solution}\left(\text{in L}\right)}}={\displaystyle \frac{0.1}{0.1}}=1\text{M}$$ .

Thus, the correct option is C.

Note:
Molality of a solution is defined as the number of moles of solute present in $$1000\text{g}$$ or $$1\text{kg}$$ of a solvent. Mole fraction is the ratio of number of moles of solute or solvent present in the solution and the total number of moles present in the solution of the substance.