chemistry gcse chemical changes

Cathode

Cathode

Electrode at which reduction occurs

Anode

Electrode at which oxidation occurs

Electrode

A device for conducting electricity into the liquid

Cation

A positively charged ion

Anion

A negatively charged ion

Electrolyte

An ionic compound able to conduct an electric current

Reason solid ionic substance can't conduct electricity

Ions are in fixed positions

Reason molten/dissolved ionic substances can conduct electricity

Ions are free to move and carry charge

In electrolysis ions go to

Opposite charge electrode

Positive ions go to

Cathode

Negative ions go to

Anode

Discharged

Remove an electric charge by adding/removing electrons

Oxidation in terms of electrons

Loss of electrons

Reduction in terms of electrons

Gain of electrons

When a molten compound is electrolysed the metal forms

at the cathode

When a molten compound is electrolysed the non metal forms

at the anode

Metals require electrolysis to extract

If they are more reactive than carbon, or react with carbon

Example of a metal more reactive than carbon

Aluminium

Example of a metal that reacts with carbon

Titanium

Reason electrolysis is expensive

Requires lots of energy

2 Reasons electrolysis requires lots of energy

To melt the compound and to produce the electrical current

Mixture used in electrolysis of aluminium

Cryolite and aluminium oxide

Cryolite

the substance added to aluminium oxide to lower its melting point

Reason cryolite is used

Lowers melting point so reduces energy required

Composition of anode for aluminium extraction

Graphite

Reason anode requires regular replacement in aluminium extraction

Oxygen is produced at the anode, which reacts with graphite in the anode, wearing it away.

carbon + oxygen -->

carbon dioxide

Substance formed at the anode by aluminium extraction

Oxygen

Substance formed at the cathode by aluminium extraction

Molten Aluminium

Ions in water

H+ and OH-

H+ is attracted to

Cathode

Discharge of H+

2H+ +2e- --> H2

OH- is attracted to

Anode

Discharge of OH-

4OH- --> O2 + 2H2O + 4e-

Discharged at the cathode in solution

Least reactive element

Discharged at the anode in solution

Halide ions, if present, otherwise OH-

Halide ion

a negative ion formed from a group 7 element

Test for hydrogen

Lit splint produces a squeaky pop

Metals discharged in preference to hydrogen

Copper, Silver, Gold, Platinum

Test for chlorine

Bleaches damp litmus paper

Test for oxygen

Relights a glowing splint

Metal + Acid -->

Salt + hydrogen

Acid + Base -->

Salt + water

Acid + Carbonate -->

Salt + water + carbon dioxide

Hydrochloric acid

HCl

Sulfuric acid

H2SO4

Nitric acid

HNO3

Type of salt produced by hydrochloric acid

Metal chloride

Type of salt produced by sulfuric acid

Metal sulfate

Type of salt produced by nitric acid

Metal nitrate

Acid

A substance that increases the H+ ion concentration of a solution

Base

A substance that reacts with an acid and neutralises it

Alkali

A soluble base, that produces OH- ions in solution

Types of chemicals that are bases

Metal oxides, metal hydroxides, metal carbonates, ammonia

Types of chemicals that are alkalis

Metal hydroxides, ammonia

Neutralisation reaction

The reaction of an acid and a base forming a salt and water

Ionic equation for neutralisation

H+ + OH- --> H2O

Substance reduced in metal acid reaction

Hydrogen

Substance oxidised in metal acid reaction

Metal

Acid

A substance that increases the hydrogen ion concentration of a solution.

Base

A substance that reacts with an acid and neutralises it

Alkali

A soluble base, that produces OH- ions in solution

Types of chemicals that are bases

Metal oxides, metal hydroxides, metal carbonates, ammonia

Types of chemicals that are alkalis

Metal hydroxides, ammonia

Strong acids

Acids that fully ionise in water

Weak acids

Acids that only slightly ionise in aqueous solution

Ionise

Split into ions

pH

A measure of H+ concentration

Ions produced by acids

H+

Ions produced by alkalis

OH-

Neutral pH

7

pH of acids

less than 7

pH of alkalis

more than 7

Neutralisation reaction

The reaction of an acid and a base forming a salt and water

Ionic equation for an acid and an alkali

H+(aq) + OH-(aq) --> H2O(l)

Universal indicator

An indicator with a different colour for each pH value.

If pH decreases by 1

hydrogen ion concentration increases x10

At pH 7

concentration of H+ = concentration of OH-

Strong acid

An acid that ionises completely in water

Weak acid

An acid that only partially ionises in water