Chemistry 3 (Grade 12)
Mixtures and solutions, acids and bases, redox, and electrochemistry.
Mixtures and solutions, acids and bases, redox, and electrochemistry.
Units of the book
| Unit | What to know |
|---|---|
| Mixtures and solutions | types, concentration, solubility, colligative properties |
| Acids and bases | Arrhenius, Brønsted, Lewis, strength, pH, neutralization |
| Redox | oxidation numbers, oxidizing and reducing agents, balancing |
| Electrochemistry | galvanic cells, batteries, electrolysis |
| Organic and biochemistry | hydrocarbons and naming, functional groups, organic reactions, carbohydrates, proteins and fats |
Formulas to remember
- M = n/V: molarity
- M₁V₁ = M₂V₂: dilution
- pH = −log[H⁺]: pH
- pH + pOH = 14: pH and pOH
- MₐVₐ = M b V b: titration
- E°cell = E°cathode − E°anode: cell potential
🧠 Memory kit: Chemistry 3 formulas
| Formula | In plain words | How to remember it |
|---|---|---|
| M = n / V(L) | Molarity: moles of solute per litre of solution. | M = “moles per litre”. |
| m = n / kg(مذيب) | Molality: moles of solute per kilogram of solvent. | The “l” in molality is the “l” in kilogram. |
| X = n A / n total | Mole fraction; all fractions add to 1. | Part ÷ whole. |
| M₁V₁ = M₂V₂ | Dilution: the same moles before and after adding water. | Water adds volume, never solute. |
| ΔT b = K b · m · i, ΔT f = K f · m · i | Boiling-point rise and freezing-point drop (colligative properties). | They depend only on the number of particles: i = 2 for NaCl, 3 for CaCl₂, 1 for sugar. |
| pH = −log[H⁺], pOH = −log[OH⁻] | pH. | Each drop of 1 in pH → ten times more acidic. |
| pH + pOH = 14, [H⁺][OH⁻] = 1 × 10⁻¹⁴ | Their link at 25 °C. | Below 7 acidic, 7 neutral, above 7 basic. |
| MₐVₐ = M b V b | Titration at the equivalence point (one H⁺ and one OH⁻ each). | Moles of H⁺ = moles of OH⁻. For H₂SO₄, multiply by 2. |
| E°cell = E°cathode − E°anode | Galvanic cell potential; positive means spontaneous. | “Cathode minus anode.” |
| CₙH₂ₙ₊₂ | CₙH₂ₙ | CₙH₂ₙ₋₂ | Alkanes (single bonds, -ane), alkenes (double, -ene), alkynes (triple, -yne). | Every extra bond costs two hydrogens. |
🧠 Memory kit: acids, redox and organic chemistry
| Topic | What to know |
|---|---|
| Acid–base definitions | Arrhenius: an acid gives H⁺ in water, a base gives OH⁻. Brønsted–Lowry: acid = proton donor, base = acceptor. Lewis: acid = electron-pair acceptor, base = donor. |
| Strong acids | HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄. The rest (like vinegar CH₃COOH) are weak. |
| Strong bases | group 1 hydroxides (NaOH, KOH) and Ca(OH)₂, Sr(OH)₂, Ba(OH)₂. Ammonia NH₃ is weak. |
| Indicators | litmus: red in acid, blue in base. Phenolphthalein: colourless in acid, pink in base. |
| Neutralization | acid + base → salt + water. |
| Oxidation-number rules | a free element is 0, oxygen −2 (−1 in peroxides), hydrogen +1 (−1 with metals), group 1 +1, group 2 +2, fluorine −1, and the total = the charge. |
| Oxidizing and reducing agents | the oxidizing agent is reduced (gains electrons); the reducing agent is oxidized (loses them). Each does to the other the opposite of what happens to it. |
| Cells | galvanic: a spontaneous reaction makes electricity; anode negative. Electrolysis: electricity forces a reaction; anode positive. In both, oxidation at the anode and reduction at the cathode. |
| Organic name prefixes | meth 1, eth 2, prop 3, but 4, pent 5, hex 6, hept 7, oct 8, non 9, dec 10. |
| Functional groups | alcohol −OH (-ol), aldehyde −CHO (-al), ketone C=O inside the chain (-one), carboxylic acid −COOH (-oic acid), ester −COO− (-oate), ether R−O−R, amine −NH₂, alkyl halide R−X. |
| Organic reactions | substitution (alkanes), addition (alkenes and alkynes open the double bond), condensation (water comes out), esterification: acid + alcohol → ester + water, polymerization: small monomers → a polymer. |
| Organic boiling points | rise with chain length and fall with branching. Alcohols boil higher than similar alkanes thanks to hydrogen bonds. |
| Biomolecules | carbohydrates → monosaccharides (glucose). Proteins → amino acids (peptide bonds). Fats → fatty acids + glycerol. Nucleic acids → nucleotides. |
- OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
- AN OX, RED CAT: oxidation at the anode, reduction at the cathode.
- “Molarity → litres of solution, molality → kilograms of solvent.” The “l” in molality is the “l” in kilogram.
- Carbon prefixes: “Monkeys Eat Peeled Bananas” = meth, eth, prop, but (1–4); after that the Greek numbers you know: pent, hex, hept, oct …
A way of memorizing that sticks
- Understand before you memorize: read “in plain words” for each formula and say out loud what it measures and why each quantity is multiplied or divided. A formula you understand takes a minute to learn.
- Active recall: cover the formula column and write it from memory, then check. Writing from memory beats rereading by far.
- Spaced repetition: review the same sheet after 1 day, 3 days, a week and two weeks. Four short reviews lock it in until test day.
- Your own formula page: write every formula of a book on one page by hand. If it does not fit, you are writing things you can derive, so cut them.
- Teach it: explain the formula to a friend, or to yourself in a mirror, in two sentences. If you cannot explain it, you do not know it yet.
- Use it at once: after each group, press “Try one” in the patterns below. Memory sets when you use it.
Question patterns
Concentration and colligative properties
Dilution does not change moles. NaCl gives 2 particles; CaCl₂ gives 3.
pH and neutralization
Below 7 acidic, 7 neutral, above 7 basic.
Conjugate pairs
Conjugate base = acid − H⁺; conjugate acid = base + H⁺.
Oxidation numbers
H = +1, O = −2, and the sum is zero in a neutral compound.
Electrochemical cells
Anode: oxidation (negative in a galvanic cell); cathode: reduction. E = cathode − anode.
- Gas solubility falls with heat, unlike most solids.
- The oxidizing agent is the one reduced.
Functional groups
| Group | Formula | Example |
|---|---|---|
| alcohol | R−OH | CH₃OH methanol |
| ether | R−O−R′ | CH₃OCH₃ |
| aldehyde | RCHO | HCHO methanal |
| ketone | RCOR′ | CH₃COCH₃ acetone |
| carboxylic acid | RCOOH | CH₃COOH |
| ester | RCOOR′ | CH₃COOCH₃ |
| amine | R−NH₂ | CH₃NH₂ methylamine |
| alkyl halide | R−X | CH₃Cl |
Hydrocarbons
- CₙH₂ₙ₊₂: alkane
- CₙH₂ₙ: alkene
- CₙH₂ₙ₋₂: alkyne
- m = mol ÷ kg: molality
More patterns (figures and calculations)
Molality, pOH and temperature
m = mol/kg, pH + pOH = 14, K = °C + 273
Alkanes and alkenes
Find the hydrogens from the general formula.
Organic boiling points
Hydrogen bonding → higher. Longer chain or bigger halogen → higher.
Naming organic compounds
Find the functional group, then count the carbons.