Question

What is the number of hydrogen atoms present in 5.4 g of urea?

• A. $9.011 \times 10^{23}$
• B. $6.022 \times 10^{23}$
• C. $2.168 \times 10^{23}$
• D. $3.011 \times 10^{23}$

Hint:

Always identify the number of atoms of the specific element per molecule first.

Answer 1

The Correct Option is C

Step 1: Molar Mass of Urea
Urea ($NH_2CONH_2$) = $14 \times 2 + 1 \times 4 + 12 + 16 = 60\text{ g/mol}$.

Step 2: Moles of Urea
$n = \frac{5.4}{60} = 0.09\text{ moles}$.

Step 3: Atoms of H
Each molecule of urea has 4 H atoms.
Number of H atoms = $0.09 \times 4 \times 6.022 \times 10^{23}$.
$= 0.36 \times 6.022 \times 10^{23} = 2.16792 \times 10^{23}$.

Step 4: Conclusion
The number of H atoms is approx $2.168 \times 10^{23}$.
Final Answer: (C)