Quick answer: Solutions is the first Class 12 Chemistry chapter and gives a 3–5 mark numerical almost every year — usually on molar mass from a colligative property. Here are the formulas and the numericals.
Concentration terms
- Molarity M = moles/volume (L); molality m = moles/kg solvent (temperature independent)
- Mole fraction xA = nA/(nA + nB); ppm = mass × 10⁶/total mass
Laws
- Henry: p = KH x (higher KH → lower solubility); used in soda bottles, scuba (bends), high altitude anoxia
- Raoult: pA = p°A xA; ideal solution obeys it (benzene–toluene). Positive deviation (ethanol–acetone, weaker forces, minimum boiling azeotrope); negative deviation (acetone–chloroform, H-bonding, maximum boiling azeotrope)
Colligative properties (depend on number of particles)
| Property | Formula |
|---|---|
| Relative lowering of vapour pressure | (p° − p)/p° = xsolute |
| Elevation of boiling point | ΔTb = i Kb m |
| Depression of freezing point | ΔTf = i Kf m |
| Osmotic pressure | π = i CRT |
van’t Hoff factor
- i = observed particles/expected. NaCl → 2, CaCl₂ → 3, glucose → 1, acetic acid in benzene (dimer) → 0.5
- Degree of dissociation α = (i − 1)/(n − 1); association α = (1 − i)/(1 − 1/n)
Numericals
1. 5 g of a non-volatile solute in 100 g water lowers freezing point by 0.93 K (Kf = 1.86): m = 0.5 → moles = 0.05 → M = 5/0.05 = 100 g/mol.
Stuck on a question? Ask it here and get a step-by-step answer in seconds — pay only per answer, no subscription. Ask your doubt now →
2. Osmotic pressure of 0.1 M NaCl at 300 K: π = 2 × 0.1 × 0.0821 × 300 = 4.93 atm.
3. Boiling point of 1 m urea solution (Kb = 0.52): 100.52°C.
Common mistakes
- Using molarity in ΔT formulas (they need molality)
- Forgetting i for electrolytes
- Using litres instead of kilograms of solvent
Related: Electrochemistry notes.
Stuck on a solutions chemistry question?
Type the exact question (or attach a photo), choose your class or exam and your language — Hindi, Hinglish, English or 9 more — and ask your doubt on DoubtPay AI. You get step-by-step working with a labelled diagram where it helps, and you can ask for a hint, an attempt check, practice questions or flashcards instead. No subscription: packs start at ₹9 for 15 answers, unused credits stay in your account.
Frequently asked questions
Are these Solutions Class 12 Chemistry notes enough for the exam?
They cover every formula, definition and question type that appears in school and board papers for this chapter. Use them with the NCERT examples, exercise questions and the last five years' papers to be fully prepared.
How should I revise Solutions Class 12 Chemistry?
Revise the notes after 1 day, 7 days and 30 days. Solve five questions each time instead of only reading, and keep an error list of the steps you get wrong.
What if I get stuck on a solutions class 12 question?
Type or photograph the exact question on DoubtPay AI, choose your class and language, and get a step-by-step answer with a diagram. You can also ask for a hint or have your own attempt checked. Packs start at ₹9 for 15 answers.
Stuck on a question? Ask it here and get a step-by-step answer in seconds — pay only per answer, no subscription. Ask your doubt now →