1. 700 ml of colourless solution is present in each of two bottles, A and B. The label on
A reads, 1 M NaCl, while that on B reads 1 mole NaCl. Which of the following
statement is correct?
a. The amount of NaCl in in each bottle is the same
b. The concentration of NaCl in each bottle is the same
c. Bottle A has less amount of NaCl than Bottle B
d. The concentration of NaCl is more in Bottle A than in Bottle B
Molarity (M) measures concentration as moles of solute per liter of solution, while “1 mole” specifies quantity alone.
For 700 ml bottles, this MCQ reveals that Bottle B contains more NaCl.
MCQ Context
700 ml of colorless solution is filled in two bottles:
- Bottle A: labeled 1 M NaCl
- Bottle B: labeled 1 mole NaCl
They differ in their NaCl content due to the concept of molarity versus moles.
Key Concept Explanation
Molarity (M) refers to the number of moles of solute per liter of solution.
Moles denote the total number of particles (or formula units) of a substance, independent of solution volume.
Option Analysis
a. The amount of NaCl in each bottle is the same
1 M NaCl means 1 mole per liter of solution. In 700 ml (0.7 L), bottle A has \(1 \times 0.7 = 0.7\) moles of NaCl.
Bottle B contains exactly 1 mole by label, so the amounts differ.
Incorrect.
b. The concentration of NaCl in each bottle is the same
Bottle A is 1 M. Bottle B’s 1 mole of NaCl in 0.7 L gives \(1 / 0.7 \approx 1.43\) M,
which is higher.
Incorrect.
c. Bottle A has less amount of NaCl than Bottle B
Bottle A: 0.7 moles (≈ 40.91 g, using NaCl molar mass 58.44 g/mol).
Bottle B: 1 mole (≈ 58.44 g).
Thus, Bottle A has less NaCl.
Correct.
d. The concentration of NaCl is more in Bottle A than in Bottle B
Bottle A is 1 M, while Bottle B is approximately 1.43 M. Hence, the concentration is higher in Bottle B.
Incorrect.
Key Difference Table
| Aspect | Bottle A (1 M NaCl) | Bottle B (1 mole NaCl) |
|---|---|---|
| Moles of NaCl | 0.7 moles | 1 mole |
| Concentration | 1 M | ≈ 1.43 M |
| Mass (approx.) | 40.91 g | 58.44 g |
Conclusion
This question tests the distinction between concentration (molarity) and amount (moles).
Understanding such nuances is essential for CSIR NET Life Sciences aspirants studying solution chemistry.
Correct Answer: (c) Bottle A has less amount of NaCl than Bottle B.
