Question

The molarity of pure water is

• A. $18.36\mathrm{M}$
• B. $1.16\mathrm{M}$
• C. $55.56\mathrm{M}$
• D. $5.56\mathrm{M}$

Answer 1

The correct option is C

$55.56\mathrm{M}$

Explanation for correct option:

C. $55.56\mathrm{M}$

Step 1: Molarity:

• “Molarity $\left(\mathrm{M}\right)$ is defined as the number of moles of solute dissolved in one liter (or one cubic decimetre) of solution.”

Step 2: Formula used for calculating Molarity:

• Molarity can be expressed as:
• $\mathrm{Molarity}=\frac{\mathrm{Moles}\mathrm{of}\mathrm{solute}}{\mathrm{Volume}\mathrm{of}\mathrm{solution}\mathrm{in}\mathrm{litre}}$

Step 3: Given Information:

• The molar mass of pure water = $18\mathrm{g}{\mathrm{mol}}^{-1}$.
• Mass of pure water = $1000\mathrm{g}$

Step 4: Calculation for molarity:

$$\begin{gathered} \mathrm{Molarity}=\frac{\mathrm{Moles}\mathrm{of}\mathrm{solute}}{\mathrm{Volume}\mathrm{of}\mathrm{solution}\mathrm{in}\mathrm{litre}} \\ \mathrm{Molarity}=\frac{{\displaystyle \frac{1000\mathrm{g}}{18\mathrm{g}{\mathrm{mol}}^{-1}}}}{1\mathrm{L}}=55.56\mathrm{mol}{\mathrm{L}}^{-1}\mathrm{or}55.56\mathrm{M} \end{gathered}$$

Thus, the molarity of pure water is $55.56\mathrm{M}$.

Explanation for incorrect options:

The molarity of pure water is $55.56\mathrm{M}$. Thus, options A, B, and D are incorrect.

Hence, the correct option is C i.e. $55.56\mathrm{M}$.