AQA GCSE C4 Chemical Changes

Oxidation in terms of oxygen

When a substance gains oxygen

Reduction in terms of oxygen

When a substance loses oxygen

Metal and Oxygen equation

Metal + Oxygen -> Metal Oxide

Reactivity series of metals

The series shows the metals in order of their reactivity

Type of ion metals form

Positive Ions

Cation

A positively charged ion

Anion

A negatively charged ion

Potassium and Water reaction

• violent
• bubbles of hydrogen gas
• melts into a shiny ball that dashes around the surface
• burns with a lilac coloured flame

Sodium and Water reaction

• very quick
• bubbles of hydrogen gas
• melts into a shiny ball that dashes around the surface

Lithium and Water reaction

• quick
• Fizzes
• produces hydrogen

Calcium and Water reaction

• slow reaction
• calcium sinks
• carried back to surface with bubbles of oxygen

Calcium and Dilute Acid reaction

very quick

Magnesium and Dilute Acid reaction

quick reaction

Zinc and Dilute Acid reaction

fairly slow reaction

Iron and Dilute Acid reaction

slow reaction

Copper and Dilute Acid reaction

very slow

Reactivity series - carbon

elements more reactive than carbon will react with water and dilute acid

elements less reactive than carbon will not react with water

Reactivity series - hydrogen

elements more reactive than hydrogen react with dilute acid

Displacement reaction

A reaction where a more reactive metal displaces a less reactive metal from a compound.

Unreactive metals in Earth

Found in their natural state (like Gold)

Extraction of metals using reduction

Metals that are less reactive than carbon can be extracted from their oxides using reduction with carbon to form the pure metal

Extracting metals more reactive than carbon

Electrolysis

Oxidation in terms of electrons

Loss of electrons.

Reduction in terms of electrons

Gain of electrons.

OILRIG

oxidation is loss reduction is gain
(of electrons)

Metal and acid equation

Metal + acid → salt + hydrogen.

Redox Reaction

When oxidation and reduction both happen

What is neutralisation

the reaction between an acid and an alkali

neutralisation - base and acid

Base + acid -> salt + water.

neutralisation - alkali and acid

alkali + acid -> salt + water

difference between alkali and base

Base is a substance that can neutralise an acid
Alkali is a soluble base

Metal carbonate and acid equation

Metal carbonate + acid -> salt + water + carbon dioxide.

Metal oxides and acids equation

Metal oxide + acid → salt + water.

Formation of Soluble Salt

a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product.

Products of Acids and Alkalis

Acids produce hydrogen ions, alkalis produce hydroxide ions.

Alkali

Alkalis are soluble bases - produce hydroxide ions in aqueous solutions.

Base

Bases are compounds that neutralise acids

Acid

Acids produce hydrogen ions in aqueous solutions,

pH Scale

The measure of acidity/alkalinity of a solution; neutral solution.

Neutralisation Reaction Equation

H⁺ + OH⁻ -> H₂O.

Strong Acid

Strong acid is completely ionised in aqueous solution.

Weak Acid

Weak acid is only partially ionised in aqueous solution.

H+ concentration and pH relationship

The pH decreases as the concentration of H+ increases.

Concentrated Acid

Concentrated acid has more moles of acid per unit volume than dilute.

Dilute Acid

Dilute refers to solutions of low concentrations.

LiNO3

Lithium nitrate

K2CO3

Potassium carbonate

MgBr2

Magnesium bromide

BaSO4

Barium sulfate

Electrolysis

The passing of an electric current through ionic substances that are molten or in solution to break them down into elements

Electrolyte

The liquid/solution which conducts electricity.

Cathode

The negative electrode.

Anode

The positive electrode.

Reduction in electrolysis

Occurs at the cathode during electrolysis.

Oxidation in electrolysis

Occurs at the anode during electrolysis.

Cryolite in electrolysis

It lowers the melting point of aluminium oxide, reducing energy costs.