chemistry

What is a mixture?

A mixture contains two or more substances that are not chemically joined — they can be physically separated.

Homogeneous mixture

A homogeneous mixture looks uniform throughout (e.g., saltwater, air). Also called a solution.

Heterogeneous mixture

A heterogeneous mixture allows you to see different parts (e.g., sand + water, oil + water).

Filtration

Technique to separate solid from liquid. The solid is too big to pass through filter paper.

Evaporation

Technique to separate dissolved solid from liquid. The liquid evaporates, leaving the solid behind.

Distillation

Technique to separate liquid from solution, keeping the liquid. The liquid boils, steam is collected and cooled.

Fractional distillation

Separates two liquids with different boiling points; each liquid boils at a different temperature.

Sieving

Technique that separates solids of different sizes; smaller particles fall through, larger do not.

Decanting

Technique to pour off the liquid carefully from settled solid.

Separating funnel

Used for two immiscible liquids (e.g., oil + water); they sit in layers, and the bottom one is drained.

Chromatography

Technique used to separate dissolved substances in a mixture. Different substances travel different distances up paper.

Crystallisation

Technique to obtain a solid from a solution by cooling the solution slowly.

Noble gases

Group 18 elements that don't react because they have a full outer shell.

Monatomic elements

Elements that exist as single atoms, found in noble gases — He, Ne, Ar, Kr, Xe.

Diatomic elements

Elements that exist as pairs — H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂. Memory trick: HOFBrINCl.

Empirical formula

The simplest whole-number ratio of atoms in a compound.

Balancing equations

Atoms are conserved; the same number of each type of atom must appear on both sides.

Limiting reagent

The reactant that runs out first in a chemical reaction, stopping the reaction.

Concentration formula

c = n/V where c = concentration in mol/L, n = moles of solute, V = volume in liters.

Standard solutions

Solutions with precisely known concentrations, made by weighing a primary standard substance.

Carbonate

Ion formula: CO₃²⁻. A polyatomic ion commonly found in minerals and is a constituent of carbonate salts.

Sulfate

Ion formula: SO₄²⁻. A polyatomic ion that is part of many important compounds, including those used in fertilizers and in industrial processes.

Nitrate

Ion formula: NO₃⁻. A polyatomic ion important in agriculture as a source of nitrogen for plants.

Hydroxide

Ion formula: OH⁻. A polyatomic ion that is a component of bases and is involved in neutralization reactions.

Phosphate

Ion formula: PO₄³⁻. A polyatomic ion essential for biological processes, including DNA and ATP formation.

Ammonium

Ion formula: NH₄⁺. A polyatomic ion that acts as a cation in many salts and is a key nutrient in fertilizers.