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

Signs of a chemical change

Change in colour, formation of gas, formation of solid, change in temperature, and 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

Highly corrosive, drain cleaner used for cleaning & soap making.

Calcium carbonate

Antacid used to treat indigestion.

Ammonia

A poisonous compound of nitrogen and hydrogen. Household cleaner.

pH

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

Ways to measure pH

pH strips or universal indicator.

Indicators

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

Neutralisation reaction

A reaction where an acid and a base combine to form a salt and water.

General word equation for neutralisation

Acid + Base → Salt + Water.

Salt

A salt is an ionic compound made of sodium and chlorine 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

Means a substance can dissolve in a liquid to form a solution

Insoluble

Means a substance doesn’t dissolve in a liquid no matter how much it is mixed

Corrosion reaction

Where a metal reacts with oxygen and water to form other compounds

Combustion reaction

Reaction between a substance and oxygen producing heat and light.

Decomposition reaction

Where a single compound breaks down into two or more 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).

rRsk assessment

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