Q76 (2024)
Identify the correct statements:
(A) The molality of 2.5 g of ethanoic acid (Molar mass: $60 \text{ g mol}^{-1}$) in 75 g of benzene solution is 0.556 m.
(B) The molarity of a solution containing 5 g of NaOH (molar mass: $40 \text{ g mol}^{-1}$) in 450 mL of solution is 0.278 M at 298 K.
(C) Aquatic species are more comfortable in cold water.
(D) The solubility of gas increases with decrease in pressure.
(E) For a binary mixture of A and B, the number of moles of A and B are $n_A$ and $n_B$ respectively. The mole fraction of B will be $x_B = \frac{n_A}{n_A \times n_B}$.
Choose the correct answer from the options given below:
- (1) A and C only
- (2) A, B and C only
- (3) A, D and E only
- (4) A and B only
### Related Formula
$$m = \frac{w_B}{M_B} \times \frac{1000}{w_A(g)}, \quad M = \frac{w_B}{M_B} \times \frac{1000}{V(mL)}$$
### Core Logic
(A) $m = \frac{2.5}{60} \times \frac{1000}{75} = 0.556 \text{ m}$ (Correct).
(B) $M = \frac{5}{40} \times \frac{1000}{450} = 0.278 \text{ M}$ (Correct).
(C) Lower temp $\implies$ higher gas solubility $\implies$ more $O_2$ in cold water (Correct).
(D) Gas solubility increases with increase in pressure (Incorrect).
(E) $x_B = \frac{n_B}{n_A + n_B}$ (Incorrect).
### Step 1: Conclusion
Statements A, B and C are correct (Option 2).
### Pattern Recognition
Verify numerical formulas for molality, molarity, and Henry's law temperature dependence.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Solutions
