Solubility product (Ksp)

“It predicts whether a precipitate will form when solutions are mixed.”

The equilibrium constant for a sparingly soluble salt dissolving.

Memory trick: Exceed Ksp → it precipitates.

Salt hydrolysis

“Baking soda solution is mildly basic because of hydrolysis.”

Salts of weak acids or bases react with water to give acidic or basic solutions.

Memory trick: Weak parent → non-neutral salt.

Nernst equation

“It's why a battery's voltage sags as it drains.”

Adjusts electrode potential for non-standard concentrations.

Memory trick: Concentration shifts the voltage.

Corrosion

“Rust silently costs the world billions each year.”

The slow electrochemical oxidation of metals, like iron rusting.

Memory trick: An unwanted galvanic cell.

Fuel cell

“Hydrogen fuel cells power spacecraft and emit only water.”

Converts a fuel's chemical energy directly and cleanly into electricity.

Memory trick: Clean direct-to-electricity.

Molecularity vs order

“Order is measured; molecularity is mechanistic.”

Molecularity is the number of species in an elementary step (a whole number); order is experimental and can be fractional.

Memory trick: Molecularity is always a whole number.

First-order half-life

“Radioactive decay's steady half-life is first-order kinetics.”

For a first-order reaction, the half-life is constant, independent of concentration.

t½ = 0.693/k

Memory trick: Constant half-life = first order.

SN1 vs SN2

“Bulky groups jam the backside attack, pushing the reaction toward SN1.”

SN1 goes via a carbocation in two steps (favours 3°); SN2 is a one-step backside attack (favours 1°).

Memory trick: 3°→SN1, 1°→SN2.

Haloarenes are less reactive

“Chlorobenzene stubbornly holds its chlorine, unlike a simple alkyl halide.”

The C–X bond in haloarenes resists substitution due to resonance and partial double-bond character.

Memory trick: Resonance strengthens the C–X bond.

Oxidation of alcohols

“A breathalyser detects alcohol by oxidising it and reading the colour change.”

Primary alcohols oxidise to aldehydes then acids; secondary to ketones; tertiary resist oxidation.

Memory trick: 1°→acid, 2°→ketone, 3°→no.

Acidity of phenol

“The ring 'spreads out' the negative charge, making phenol give up its H more easily.”

Phenol is more acidic than alcohols because its conjugate base is resonance-stabilised.

Memory trick: Resonance makes phenol acidic.

Aldol condensation

“A classic carbon–carbon bond-builder in organic synthesis.”

Aldehydes/ketones with α-hydrogens combine to form β-hydroxy carbonyl compounds.

Memory trick: Needs an α-hydrogen.

Cannizzaro reaction

“One molecule is oxidised while another is reduced — a chemical see-saw.”

Aldehydes without α-hydrogens disproportionate into an alcohol and an acid.

Memory trick: No α-H → self redox.

Basicity of amines

“That lone pair is what makes amines grab H⁺ and smell fishy.”

Amines are basic because nitrogen's lone pair accepts a proton.

Memory trick: Lone pair → base.

Diazonium salts

“The bright azo dyes in clothes start life as diazonium salts.”

Aryl diazonium salts are versatile intermediates for making dyes and substituted benzenes.

Memory trick: Gateway to azo dyes.

Amino acids

“String amino acids in the right order and you get anything from muscle to enzyme.”

The 20 building blocks of proteins, each with an amino and a carboxyl group.

Memory trick: Protein's alphabet.

Nucleic acids

“The recipe for you is written in a four-letter nucleotide code.”

DNA and RNA are polymers of nucleotides that store and express genetic information.

Memory trick: Store genetic code.

Essential vs non-essential amino acids

“A balanced diet supplies the amino acids your body can't build.”

Essential amino acids must come from diet; the body makes the rest.

Memory trick: Essential = from food.

Soaps vs detergents

“Detergents were invented so cleaning wouldn't fail in mineral-rich water.”

Soaps are salts of fatty acids (fail in hard water); detergents work even in hard water.

Memory trick: Detergents beat hard water.

How soap cleans

“Each soap molecule is a tiny tadpole that traps dirt in the middle.”

Soap molecules have a water-loving head and an oil-loving tail, lifting grease into water.

Memory trick: Head loves water, tail loves grease.

Antacids

“That chalky tablet after a spicy meal is simply neutralising acid.”

Basic compounds that neutralise excess stomach acid.

Memory trick: Base neutralises acid.

Antibiotics

“Penicillin, found by accident, launched the antibiotic age.”

Chemicals that kill or inhibit bacteria; ineffective against viruses.

Memory trick: Target bacteria, not viruses.

Catalysts in industry

“A metal catalyst quietly feeds nearly half the planet.”

Iron catalyses the Haber process that fixes nitrogen into ammonia for fertiliser.

Memory trick: Catalysts make industry viable.

Acid-base: Arrhenius, Bronsted, Lewis

“Three lenses, widening from H⁺ to full electron-pair chemistry.”

Acids give H⁺ (Arrhenius/Bronsted) or accept electron pairs (Lewis); bases do the opposite.

Memory trick: Lewis is the broadest definition.