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CBSE Class 12 · Chemistry

Solutions

Official NCERT chapter from Chemistry Part I–II (book code lech1). ExamMaster notes are original teaching at CBSE Class 12 depth.

This lesson follows the official chapter “Solutions” in Chemistry Part I–II. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 12
  • Medium level
  • 8 concepts

1Types of Solutions

Types of solutions: gas, liquid, or solid dissolved in a taught solvent-look — homogeneous mix. A type is a look-pair (solute-solvent states), not a brand. Air as a gas-in-gas if named; brine as solid-in-liquid.

A suspension as a solution because it “looks wet” is a miss.

Figure. A solution is solute sitting inside a solvent. Gas-in-liquid, liquid-in-liquid, and solid-in-liquid are three types, not three colours.

How it works

  1. Name solute and solvent looksThe type.
  2. Keep homogeneous as the testOne look.
  3. Refuse a cloudy settle as this headingNot a solution.

2Expressing Concentration of Solutions

Concentration: mole fraction, molarity, molality as taught. M = n/V_L; m = n/kg_solvent. A 2 mol in 1 L is 2 M. Concentration is a number-write, not a taste.

Using kg of solution as the molality denominator is a miss.

Figure. Molarity divides moles by litres of solution. Molality divides the same moles by kilograms of solvent. 2 M and 2 m are different tests even when the number matches.

How it works

  1. Pick M, m, or x as taughtThe measure.
  2. Write n over the matching denominatorThe number.
  3. Keep litres for M, kg solvent for mTwo words.

Molarity

2 mol solute in 0.50 L solution. Find M.

  • n/V2/0.50
  • M4 mol/L
  • Read4 M

Pro tip. Litres of solution, not kg.

3Solubility

Solubility: how much sits at a T as taught. Gas solubility often falls as T rises (as framed); a pressure-look (Henry) if named. Solubility is a sit-limit, not a rate.

A kinetic “dissolves fast” as solubility is a miss.

Figure. Solid KNO3 dissolves more as water warms. The curve rises; it does not start at the origin, because some salt already dissolves when cold.

How it works

  1. Name the T (and P if a gas)The given.
  2. Read how much sitsSolubility.
  3. Keep Henry only if taughtHonest extra.

4Vapour Pressure of Liquid Solutions

Vapour pressure of a liquid solution: solvent VP drops when a non-volatile solute sits as taught (Raoult). p = x_solvent p° as framed. VP is a surface-look, not a boiling-slogan.

A solute that raises VP as the default non-volatile case is a miss.

Figure. Raoult: the partial pressure of A is its mole fraction times the pure vapour pressure. The line starts at the origin — no A, no P_A — and ends at P_A*.

How it works

  1. Name the solvent fractionThe given.
  2. Form x p° as taughtRaoult.
  3. Keep non-volatile as the simple caseThe heading.

5Ideal and Non-ideal Solutions

Ideal versus non-ideal: ideal follows Raoult as taught; non-ideal shows + or − deviations and may have an azeotrope if named. Ideal is a follow-the-line, not “good”.

Calling every mix ideal is a steal.

Figure. An ideal mix is the straight join from P_B* to P_A*. Positive deviation bows above that join: A–B attractions are weaker than A–A and B–B, so more vapour escapes.

How it works

  1. Ask whether p matches x p°Ideal?
  2. Name a deviation or azeotrope if taughtNon-ideal.
  3. Refuse good/bad as the testA line-test.

6Colligative Properties and Determination of Molar Mass

Colligative properties: depend on number of solute bits as taught — VP lowering, boiling rise, freezing drop, osmotic π. Molar mass from a measured colligative if framed. Colligative is a count-story, not an identity-story.

Using the solute’s colour as a colligative is a miss.

Figure. Boiling-point elevation tracks molality, not the solute’s name. At Kb = 0.52 K kg/mol, 0.1 / 0.2 / 0.3 molal lift the boiling point by 0.52 K, 1.04 K, 1.56 K.

How it works

  1. Name the property (ΔTb, ΔTf, π, …)The look.
  2. Read it as a bit-countColligative.
  3. Keep i later if van’t Hoff was taughtNext heading.

7Abnormal Molar Masses

Abnormal molar mass: ions or association change the bit-count as taught; i = observed/calculated. NaCl i≈2 if fully split. Abnormal is a count-adjust, not a wrong balance.

Ignoring split on NaCl as i=1 is a miss if the lesson used i.

Figure. A colligative formula that ignores van’t Hoff i reports an abnormal molar mass. Urea stays i = 1; NaCl near i = 2; CaCl2 near i = 3. Observed M is M_true / i.

How it works

  1. Ask whether bits split or clumpThe reason.
  2. Write i as the factorThe adjust.
  3. Keep i=1 for a non-electrolyte as taughtHonest.

8A definition is a test you can run

Solution-word is a test: a type, a concentration-write, Raoult, or a colligative. If you only say “mix”, you have a heading.

A glass-sticker is not the test.

Figure. Mole fraction is a test you can run: every x in the mix must add to 1. If 0.4 + 0.6 is not 1, the composition was miscounted.

How it works

  1. Name M, x p°, or ΔTfThe object.
  2. Give the school sentenceThe test.
  3. Then the word has contentThe definition ran.
2 mol in 0.50 L is
  1. 4 M
  2. 2 M
  3. 0.5 M

n/V.

Notes

  • Mapped to the official NCERT chapter “Solutions”. Original teaching only — no textbook sentences.
  • Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.

Formulas

  • M=n/V_L
  • m=n/kg_solvent
  • p = x_solvent p° (Raoult, as taught)

Recap

Hold these pegs from the official chapter “Solutions”. The wording is ExamMaster’s teaching, not a textbook recap.

Types of Solutions
Types of solutions: gas, liquid, or solid dissolved in a taught solvent-look — homogeneous mix.
Expressing Concentration of Solutions
Concentration: mole fraction, molarity, molality as taught.
Solubility
Solubility: how much sits at a T as taught.
Vapour Pressure of Liquid Solutions
Vapour pressure of a liquid solution: solvent VP drops when a non-volatile solute sits as taught (Raoult).
Ideal and Non-ideal Solutions
Ideal versus non-ideal: ideal follows Raoult as taught; non-ideal shows + or − deviations and may have an azeotrope if named.
Colligative Properties and Determination of Molar Mass
Colligative properties: depend on number of solute bits as taught — VP lowering, boiling rise, freezing drop, osmotic π.

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