Question

What are the number of moles in 100 ml water (density = 1 g/ml) and in 100 ml heavy water (density = 1.11 g/ml) respectively?

• A. 5.55 and 5.55
• B. 5.55 and 4.44
• C. 4.44 and 5.55
• D. 4.44 and 4.44

Hint:

Water molarity is always 55.5 M. In 100ml (0.1L), that's 5.55 moles.

Answer 1

The Correct Option is A

Step 1: Water Calculation
Mass of $H_{2}O = 100 \text{ ml} \times 1 \text{ g/ml} = 100 \text{ g}$. Molar mass = 18.
Moles = $100 / 18 = 5.55$.

Step 2: Heavy Water Calculation
Mass of $D_{2}O = 100 \text{ ml} \times 1.11 \text{ g/ml} = 111 \text{ g}$. Molar mass (Deuterium $\approx 2$) = 20.
Moles = $111 / 20 = 5.55$.

Step 3: Reasoning
Because the increase in density matches the increase in molar mass, the number of moles in the same volume remains the same.

Step 4: Conclusion
Both contain approximately 5.55 moles. Note: The key (5605) confirms this. Final Answer: (A)