Question

6.022 × \(10^{20}\) molecules of urea are present in 100 mL of its solution. The concentration of the solution is

• A. 0.10 M
• B. 0.02 M
• C. 0.01 M
• D. 0.001 M

Hint:

Always convert molecules to moles before calculating molarity.

Answer 1

The Correct Option is C

Step 1: Converting number of molecules into moles.
Avogadro number = \(6.022 \times 10^{23}\) molecules per mole
\[ \text{Moles of urea} = \frac{6.022 \times 10^{20}}{6.022 \times 10^{23}} = 10^{-3}\ \text{mol} \]

Step 2: Converting volume into litres.
\[ 100\ \text{mL} = 0.1\ \text{L} \]

Step 3: Calculating molarity.
\[ \text{Molarity} = \frac{\text{moles}}{\text{volume}} = \frac{10^{-3}}{0.1} = 0.01\ \text{M} \]

Step 4: Conclusion.
The concentration of the solution is 0.01 M.