Chemistry: Reactions, Acids, Bases, and Safety Symbols

Reactants

The starting substances in a chemical reaction.

Products

The new substances formed by the reaction.

Law of Conservation of Mass

Mass cannot be created or destroyed in an isolated system.

Physical change

When a substance changes form or state but not chemical structure

Chemical change

Produces new substances, usually irreversible (e.g., rusting iron).

Signs of a chemical change

Change in colour, formation of gas (bubbles), formation of solid (precipitate), change in temperature, production of odour.

Endothermic reaction

Absorbs energy from surroundings. Example: Photosynthesis.

Exothermic reaction

Releases energy to surroundings. Example: Burning wood.

Properties of acids

Sour taste, corrosive, pH below 7.

Properties of bases

Bitter taste, slippery feel, pH above 7.

Hydrochloric acid

Stomach acid used for digestion.

Citric acid

Found in fruit, used for flavour & preservation.

Sulfuric acid

Used in fertiliser production.

Sodium hydroxide

Drain cleaner used for cleaning & soap making.

Calcium carbonate

Antacid used to treat indigestion.

Ammonia

Household cleaner.

pH

It measures acidity or alkalinity on a scale of 0-14.

Ways to measure pH

pH strips or universal indicator.

pH of common substances

Pure water: 7, Lemon juice: 2.

Indicators

Indicators change colour based on pH, showing if a solution is acidic, neutral, or basic.

Neutralisation reaction

An acid and a base combine to form a salt and water.

General word equation for neutralisation

Acid + Base → Salt + Water.

Neutralisation example 1

Treating acid spills with baking soda — the fizzing neutralises the acid into salt and water.

Neutralisation example 2

Deodorising with vinegar or baking soda — acids neutralise bases and vice versa to remove odours.

Salt

A salt is an ionic compound formed from an acid and a base.

solute

The substance that is dissolved (lesser amount).

solvent

The substance that does the dissolving (greater amount, e.g., water).

solution

A homogeneous mixture formed when a solute dissolves in a solvent.

precipitation reaction

When two solutions react to form an insoluble solid (precipitate).

soluble

Able to dissolve in a solvent to form a clear solution.

insoluble

Cannot dissolve significantly in a solvent.

metal activity series

A ranking of metals by their reactivity, from most reactive to least reactive.

corrosion reaction

Gradual degradation of a metal through oxidation.

combustion reaction

Reaction between a substance and oxygen producing heat and light.

decomposition reaction

A compound breaks into simpler substances.

combination reaction

Two or more reactants form one product.

Dangerous Good

Risks like fire/explosion (transport safety).

Hazardous Substance

Risks to health (toxicity, irritation).

Explosive symbol

Exploding Bomb.

Flammable substance symbol

Flame.

Toxic substance symbol

Skull and Crossbones.

Radioactive material symbol

Trefoil symbol.

Infectious substance symbol

Biohazard symbol.

Corrosive substance symbol

Corrosion (test tubes damaging hand and surface).

risk assessment

Includes hazard identification, risk assessment (likelihood/severity), control measures, disposal procedures, first aid procedures.