NEET · Chemistry —

Solutions appeared 2 times across 1 year — 4.4% of Chemistry. This question is from Concentration Terms and Gas Solubility.

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Identify the correct statements : (A) The molality of 2.5 g of ethanoic acid (Molar mass: 60 ~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 ~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 nA and nB respectively. The mole fraction of B will be xB = nAnA + nB. Choose the correct answer from the options given below:

Solution & Explanation

Core Logic

(A) Molality (m) = Moles of soluteMass of solvent (kg) = (2.5 / 60)/(75 / 1000) = (2.5)/(60) × (1000)/(75) = 0.5555 ≈ 0.556 m. (Correct) (B) Molarity (M) = Moles of soluteVolume of solution (L) = (5 / 40)/(450 / 1000) = (5)/(40) × (1000)/(450) = 0.2777 ≈ 0.278 M. (Correct) (C) Aquatic species are more comfortable in cold water because the solubility of dissolved oxygen is higher at lower temperatures (Henry's Law constant KH increases with temperature, implying solubility decreases as T increases). (Correct) (D) According to Henry's Law (P = KH χ), solubility of a gas is directly proportional to partial pressure. So, solubility decreases with a decrease in pressure. (Incorrect) (E) Mole fraction of B (xB) should be (nB)/(nA + nB). The given formula has nA in the numerator, which is for xA. (Incorrect)

Step 1: Final Conclusion

Only statements A, B, and C are correct.

Pattern Recognition

Henry's Law facts are staples: Higher T = Lower solubility (fishes prefer cold). Higher P = Higher solubility (soda fizzes when pressure drops).

Chapter Mix

Class 12 Chemistry: Solutions

Reference Study Guides

Solutions

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Q77 neet_2026_03_may_morning Non-Ideal Solutions
Mixture of chloroform and acetone forms a solution with negative deviation from Raoult's law due to :
  • A. Formation of hydrogen bonding between acetone and chloroform
  • B. Increase in escaping tendency of molecules of each component.
  • C. Stronger intermolecular forces between chloroform molecules than those between chloroform and acetone molecules.
  • D. Repulsive forces.

Solution

Core Logic

Acetone (CH₃COCH₃) and Chloroform (CHCl₃) mix to form a non-ideal solution with a negative deviation from Raoult's law. This occurs because a new, strong intermolecular hydrogen bond forms between the highly electronegative oxygen of the acetone carbonyl group and the hydrogen of chloroform (which is acidic due to three highly electronegative chlorine atoms).

(CH₃)₂C=O ⋯ H-C(Cl)₃

This strong A-B interaction reduces the escaping tendency of both molecules compared to their pure states (A-A and B-B interactions), leading to a lower vapor pressure (negative deviation) and an increased boiling point.

Step 1: Final Conclusion

The negative deviation is due to the formation of hydrogen bonding between acetone and chloroform.

Pattern Recognition

Acetone + Chloroform is the canonical textbook example for Negative Deviation due to H-bonding. Ethanol + Acetone is the canonical example for Positive Deviation.

Chapter Mix

Class 12 Chemistry: Solutions

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