JEE Main 2024 · 27 January · evening · Single correct · +4 / −1
The quantity which changes with temperature is :
- (a) Molality
- (b) Molarity
- (c) Mole fraction
- (d) Mass percentage
Answer and solution
Answer (b) Molarity
Solution
Chemistry ma’am · 3 steps
Look for volume in the definition: volume swells on heating, mass and moles do not.
- What changes on heating. When a solution is warmed, it expands, so its volume goes up. The mass of solute, the mass of solvent and the number of moles stay exactly the same.
Quantity Defined as Uses volume? Changes with T? Molality moles of solute per kg of solvent No No Molarity moles of solute per litre of solution Yes Yes Mole fraction moles of one component over total moles No No Mass percentage mass of solute over mass of solution, times 100 No No - Molarity drops. In M = n/V, n is fixed but V grows on heating. So the molarity of a solution falls slightly as the temperature rises.
- So. Molarity is the only one with volume in it, so it is the one that changes with temperature. The answer is (b).
The idea to keep. Any concentration term built only from masses and moles is temperature-independent. The moment volume enters (molarity, normality), it changes with temperature.
Answer from the NTA final answer key. Solution by PrepWiser.