AQA GCSE chemistry - 4.4 chemical changes

What is oxidation?

When a substance gains oxygen (and loses electrons)

What is reduction?

When a substance loses oxygen (and gains electrons)

What do metals react with oxygen to produce?

Metal oxides

What is the reactivity series (of metals)?

• The series shows the metals in order of their reactivity

• Metals above H₂ in reactivity series react with acid to produce H₂. The more reactive the metal is, the quicker and more violent reaction with acid occurs

• Metals below H₂ don’t react with acids

• Not all metals above H₂ react with water - mostly group 1 and 2 metals

What is the order of the reactivity series?

Potassium, sodium, lithium, calcium, magnesium, aluminium, carbon (non-metal), zinc, iron, hydrogen (non-metal), copper, silver, gold

What is a mnemonic for the reactivity series?

Please Send Lions, Cats, Monkeys And Cute Zebras Into Hot Countries Signed Gordon

What do metals form when they react with other substances?

Positive ions

What is the reactivity of a metal related to?

Its tendency to form positive ions. A metal higher up in the reactivity series will lose electrons more easily and is thus more reactive than one which i lower down on the series

What happens when a metal reacts with water?

A metal hydroxide and hydrogen are formed

What happens when a metal reacts with a dilute acid?

A salt and hydrogen are formed

What will a more reactive metal displace from a compound?

A less reactive metal

How would one deduce the reactivity of a metal from experimental results?

Based on the number of reactions of each metal. The metal with the most reactions is the most reactive and least reactions is the least reactive

How are unreactive metals found in Earth?

In their natural state as the metal itself (e.g gold)

How are most other metals found in earth?

Compounds called ores that require chemical reactions to extract the metal

How can metals less reactive than carbon be extracted from their oxides?

By reduction with carbon

What is the extraction method for the metal (from the ore) dependent upon?

The metal’s position in the reactivity series

How can a metal that is less reactive than carbon be extracted from its compounds?

By heating with carbon for a displacement reaction

Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal

How can a metal that is more reactive than carbon be extracted from its compounds?

Electrolysis of molten compounds

What is an displacement reaction?

When a more reactive metal displaces a less reactive metal from its compound (e.g magnesium is more reactive than copper so it displaces copper from a copper sulphate solution)

What is a redox reaction?

A reaction in which reduction and oxidation occur at the same size,

What are some examples of redox reactions?

Displacement reactions and electrolysis

What can a balanced ionic equation be split into (redox reaction)?

Two half equations

What does OIL RIG stand for?

Oxidation Is Loss Reduction Is Gain

What do acids react with some metals to produce?

Salt and hydrogen

This is a redox reaction, also a displacement reaction

What solutions do acids form in water?

Acidic solutions with a pH less than 7

What solution do alkalis form in water?

Alkaline solutions with a pH more than 7

What are acids neutralised by?

Alkalis and bases

What is the equation for the neutralisation reaction?

Acid + Alkali → Salt + Water (+ carbon dioxide)

What does the salt produced in any reaction between an acid and a base or alkali depend on?

The acid used and the positive ions in the base/alkali/carbonate

How do you name a salt?

First name - metal in the base

Last name - acid (ending in -ide or -ate)

What are some acids I should know?

• Hydrochloric acid (HCl) - forms negative chloride ion Cl^-

• Sulfuric acid (H₂SO₄) - forms negative sulfate ion SO₄^2-

• Nitric acid (HNO₃) - forms negative nitrate ion NO₃^-

What are some bases I should know?

• Metal hydroxides

• Metal oxides

• Metal carbonates

Are alkalis or bases soluble in water?

Alkalis are soluble in water

Bases are insoluble in water

Alkalis are soluble bases

What is the test for the presence of hydrogen?

Test: lit splint in test tube

Result if present: pop sound

What is the test for the presence of carbon dioxide?

Test: limewater

Result if present: limewater goes cloudy

What are the four reactions to form soluble salts?

• Metal oxide + acid → salt + water

• Metal hydroxide + acid → salt + water

• Metal carbonate + acid → salt + water + carbon dioxide

• Metal + acid → salt + hydrogen

In the last two reactions, we will see effervescence/fizzing because a gas is produced in a liquid

How can a soluble salt be formed?

From one of the four reactions. The solid is added to the acid until no more reacts and the excess solid is filtered off to produce the solution of the salt

How do you form a solid salt?

Salt solutions can be crystallised to produce solid salts

What type of ions do acids produce in aqueous solutions?

Hydrogen ions (H⁺)

What type of ions do aqueous solutions of alkalis contain?

Hydroxide ions (OH^-)

What would the results of a test with litmus paper be on acids and alkalis?

Red: acid (remain red), alkali (turn blue)

Blue: acid (turn red), alkali (remain blue)

What is the pH of a neutral solution?

7

What happens during a neutralisation reaction between an acid and an alkali?

Hydrogen ions react with hydroxide ions to produce water. This can be represented by the equation:

H⁺_(aq) + OH^-_(aq) → H₂O_(l)

How can the universal indicator test show us what pH a solution is?

Universal indicator can be added to a solution to change it to a colour corresponding to a pH

• Brick red- strong acid

• Orange/yellow - weak acid

• Green - neutral

• Blue - weak alkali

• Indigo/blue-black - strong alkali

A more accurate value can be obtained using a pH probe

How can the volumes of acid and alkali solution that react with each other to neutralise a solution be measured?

With a titration

What happens to a strong acid in an aqueous solution?

It fully dissociates/ionises

What happens to a weak acid in an aqueous solution?

It partially dissociates/ionises