Molarity drifts with temperature, molality does not
"Molarity drifts with temperature, molality does not" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "Reactions in solutions: concentration terms" in Some Basic Concepts of Chemistry. A flask of solute in water shows molarity, molality and mole fraction side by side; warming expands the solution volume so molarity drifts while molality stays fixed. JEE Main asked 45 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Reactions in solutions: concentration terms in Some Basic Concepts of Chemistry. Change the values and watch what happens.
What it shows
NCERT § "Reactions in Solutions"
A flask of solute in water shows molarity, molality and mole fraction side by side; warming expands the solution volume so molarity drifts while molality stays fixed.
Controls
4 to try
- Slidersolute 0–2 mol (NaOH, 40 g/mol)
- Slidersolvent water 100–1000 g
- Slidertemperature 10–80 °C (solution volume expands)
- Readoutdensity, solution volume
Try this
Make a 1.0 m solution, then heat it from 20 °C to 70 °C and keep molality at 1.00 while the molarity readout falls below its 20 °C value; goal checks both.
Common mistake
Using mass of solution for molality or volume of solvent for molarity; thinking molarity is temperature independent.
In JEE Main
42 shifts analysed
45 questions from Some Basic Concepts of Chemistry across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Reactions in Solutions"
- Mass percent = (mass of solute / mass of solution) × 100.
- Mole fraction of a component = its moles / total moles of all components; the mole fractions of all components add up to 1.
- Molarity (M) = moles of solute per litre of solution; it changes with temperature because volume changes.
- Molality (m) = moles of solute per kilogram of solvent; it does not depend on temperature because it uses masses only.
- Dilution keeps the moles of solute fixed, so M₁V₁ = M₂V₂.
- Converting molarity to molality needs the solution's density: find the mass of 1 L of solution, subtract the solute's mass to get the solvent's mass, then divide the moles of solute by that mass in kg.
- Converting molality to molarity goes the other way: mass of solution = mass of solvent + mass of solute, then use density to get the volume.
Questions
4 answers
- What does the "Molarity drifts with temperature, molality does not" simulation show?
- A flask of solute in water shows molarity, molality and mole fraction side by side; warming expands the solution volume so molarity drifts while molality stays fixed.
- What mistake does the "Molarity drifts with temperature, molality does not" simulation fix?
- A common mistake it clears up: using mass of solution for molality or volume of solvent for molarity; thinking molarity is temperature independent.
- Does JEE Main ask questions from Some Basic Concepts of Chemistry?
- Yes. JEE Main asked 45 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Reactions in solutions: concentration terms" in Some Basic Concepts of Chemistry (Class 11 Chemistry).
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