C4 - Chemical Changes

Reactivity series

Potassium

Sodium

Lithium

Calcium

Magnesium

Aluminium

Carbon

Zinc

Iron

Tin

Lead

Hydrogen

Copper

Silver

Gold 

Platinum

*carbon and hydrogen are not metals but are a useful comparison

Displacement Reaction

Occurs when a more reactive metal displaces (kicks out) a less reactive metal from a compound

Most metals react with acids to produce what?

A salt and hydrogen

Metal carbonates react with acids to produce what?

A salt, carbon dioxide and water

Group 1 metals are more reactive than hydrogen, so they displace it to form what?

Hydrogen gas and a metal hydroxide

What can we use displacement reactions for?

Extracting metals from their ores by displacing with a more reactive, less valuable metal

Oxidation

Loss of electrons

Reduction

Gain of electrons

acid + alkali →

salt + water

Using sulphuric acid results in what type of salt?

Metal sulphate salt

Using nitric acid results in what type of salt?

Metal nitrate salt

When an acid and an alkali are reacted together the salt produced is left in solution, which means that we have a mixture of dissociated ions. How can we obtain crystals of salt?

By gently heating and evaporating the water, leaving behind the salt crystals

Why does an acid have a pH < 7?

Due to its H⁺ ions

Why does an alkali have a pH > 7?

Due to its OH^- ions

A neutral substance has what?

An equal number oh H⁺ and OH^- ions

A change in 1 pH is equal to what?

A 10x change in concentration of H⁺ or OH^- ions

A strong acid dissociates more completely. If at the same concentration, it will have a lower/higher? pH than a weak acid

lower

Examples of strong acids

Hydrochloric

Sulphuric

Nitric

Examples of weak acids

Ethanoic

Citric

Carbonic

Electrolysis

Involves passing an electrical current through a substance to cause oxidation and reduction at the anode and cathode

Electrolysis can only happen when ions are …

Free to move

In ionic compounds in what state must it be in for electrolysis

Molten or in solution

What can electrolysis be used for?

To obtain pure metals from a compund/ore

1?

Anode (graphite)

2?

Cathode

3?

Cryolite and aluminium oxide

4?

The positive ions e.g. Al³⁺ are attracted to the cathode, where they are reduced

Al³⁺ _(l) + 3e^- → Al _(l)

5?

The negative ions e.g. O^2- are attracted to the anode, where they are oxidised

2O^2- _(l) → O_{2 (g)} + 4e^-

Oxygen reacts with carbon in the anodes to produce CO₂ , this means what?

They need to be replaced periodically

Why is cryolite added to electrolysis with molten compounds?

Lowers the melting point of the aluminium oxide - cheaper

What is happening with the H⁺ ions?

H⁺ ions are less reactive than Na⁺ ions, so they move to the cathode to be reduced

2H⁺ _(aq) + 2e^- → H_{2 (g)}

The more reactive cation (positive ion) remains in solution while the less reactive one is reduced at the cathode

What happens to halide ions (F^-, Cl^-, Br^-)

They are always oxidised at the anode. If the anion (negative ion) isn’t a halide, the oxygen is oxidised instead and oxygen gas is produced

2Cl_(aq) → Cl_{2 (g)} + 2e^-