Buffer solution

“Your blood is buffered near pH 7.4 — stray far and you're in danger.”

A mix that resists pH change when small amounts of acid or base are added.

Memory trick: Weak acid + its salt.

Common ion effect

“Adding NaCl to salty water can push extra salt out of solution.”

Adding an ion already present in an equilibrium suppresses ionisation.

Memory trick: Shared ion → less dissociation.

Oxidation and reduction

“A cut apple browning and iron rusting are oxidation in slow motion.”

Oxidation is loss of electrons; reduction is gain (OIL RIG).

Memory trick: OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Oxidising vs reducing agent

“The agent always does the opposite to itself — an oxidising agent is itself reduced.”

An oxidising agent gains electrons (is reduced); a reducing agent loses them (is oxidised).

Memory trick: Agent = opposite of its own name.

Galvanic vs electrolytic cell

“A battery is galvanic; electroplating jewellery is electrolytic.”

A galvanic cell makes electricity from a spontaneous reaction; an electrolytic cell uses electricity to force a non-spontaneous one.

Memory trick: Galvanic gives; electrolytic needs power.

Anode and cathode

“In every cell, 'An-Ox, Red-Cat' holds true.”

Oxidation always happens at the anode; reduction at the cathode.

Memory trick: Anode = Oxidation.

Electrochemical series

“Zinc protects iron ships because zinc gives up electrons more readily than iron.”

Metals ranked by their tendency to lose electrons; reactive metals sit at the top.

Memory trick: Higher up = more reactive.

Faraday's laws of electrolysis

“Exactly how much metal electroplates depends on how much current you run and for how long.”

The mass deposited during electrolysis is proportional to the charge passed.

Memory trick: More charge → more metal.

Rate of reaction

“Fireworks react in a flash; rusting takes years — same chemistry, vastly different rates.”

How fast reactant is consumed or product formed per unit time.

Memory trick: Steeper concentration change = faster.

Order of reaction

“Order is measured, not read off the balanced equation.”

The power of a reactant's concentration in the experimentally-found rate law.

Memory trick: Order comes from experiment.

Activation energy

“A matchstick needs a strike's energy to get the reaction over the hill.”

The minimum energy barrier reactants must cross to react.

Eₐ

Memory trick: Barrier every reaction must climb.

Catalyst

“Your body's enzymes are catalysts making life's reactions fast enough to live.”

Speeds a reaction by lowering activation energy, without being consumed or shifting equilibrium.

Memory trick: Lowers the hill; not used up.

Effect of temperature on rate

“Milk spoils fast on the counter but slowly in the fridge.”

Raising temperature increases reaction rate, roughly doubling it every 10°C.

Memory trick: Hotter → faster.

Catenation of carbon

“From plastics to proteins, everything organic is built on carbon chains.”

Carbon's ability to bond with itself in long chains and rings underlies all organic chemistry.

Memory trick: Carbon links endlessly.

Functional group

“Swap the functional group and alcohol becomes acid — different smell, different reactions.”

The reactive atom or group that decides an organic molecule's chemistry (–OH, –COOH, etc.).

Memory trick: The group runs the chemistry.

Isomerism

“Two molecules with identical formulas can be a medicine and a poison.”

Same molecular formula, different arrangement of atoms.

Memory trick: Same formula, different structure.

Electrophile vs nucleophile

“Chemistry is a dance: electron-rich meets electron-poor.”

Electrophiles are electron-poor (accept electrons); nucleophiles are electron-rich (donate them).

Memory trick: Nucleophile = electron donor.

Resonance

“Benzene's electrons are smeared into a stable ring, not fixed double bonds.”

Delocalisation of electrons across a molecule, giving extra stability.

Memory trick: Real molecule = hybrid of structures.

Carbocation stability

“More alkyl 'friends' steady the positive charge.”

Stability order 3° > 2° > 1°, because alkyl groups donate electron density.

Memory trick: More alkyl groups → more stable.

Alkanes, alkenes, alkynes

“Cooking gas (alkane), ripening agent ethene (alkene), welding gas ethyne (alkyne).”

Alkanes have single bonds (saturated); alkenes have C=C; alkynes have C≡C (unsaturated).

Memory trick: -ane single, -ene double, -yne triple.

Saturated vs unsaturated

“Unsaturated fats have C=C 'kinks' that keep oils liquid.”

Saturated hydrocarbons have only single bonds and maximum hydrogens; unsaturated have double/triple bonds.

Memory trick: Double/triple bond = unsaturated.

Markovnikov's rule

“'The rich get richer' — the H-rich carbon gains the H.”

In HX addition to an alkene, H adds to the carbon already having more hydrogens.

Memory trick: H to the H-rich carbon.

Aromaticity of benzene

“Benzene refuses to behave like a normal alkene because breaking its ring costs stability.”

Benzene's planar ring with 6 delocalised electrons is extra stable and prefers substitution to addition.

Memory trick: Aromatic → substitutes, not adds.

Combustion of hydrocarbons

“Every engine and gas stove runs on this reaction.”

Hydrocarbons burn in oxygen to give CO₂ and water, releasing energy.

Memory trick: Fuel + O₂ → CO₂ + H₂O + energy.