Chemical Change chemistry

What happens when metals react with oxygen?

Metals react with oxygen to produce metal oxides — the metal gains oxygen — this is an oxidation reaction

Write the general word equation for a metal reacting with oxygen

Metal + oxygen → metal oxide

Write the word equation for magnesium burning in oxygen

Magnesium + oxygen → magnesium oxide

Write the balanced symbol equation for magnesium burning in oxygen

2Mg + O₂ → 2MgO

Write the word equation for iron reacting with oxygen

Iron + oxygen → iron oxide

What is oxidation in terms of oxygen?

Gain of oxygen

What is reduction in terms of oxygen?

Loss of oxygen

What is a redox reaction?

A reaction where both oxidation and reduction occur simultaneously — one substance gains oxygen while another loses it — or one loses electrons while another gains them

What is the reactivity series in order from most to least reactive?

Potassium — sodium — lithium — calcium — magnesium — aluminium — zinc — iron — copper — silver — gold — hydrogen and carbon are also included

Why is the reactivity series useful?

It allows us to predict whether displacement reactions will occur — which metals can be extracted by reduction with carbon — and how vigorously metals react with water and acids

How does the reactivity of a metal relate to its tendency to form positive ions?

More reactive metals form positive ions more readily — they lose electrons more easily — less reactive metals form positive ions less readily

How do potassium sodium and lithium react with water?

Very vigorously — metal + water → metal hydroxide + hydrogen — potassium ignites with a lilac flame — sodium melts and moves rapidly — lithium moves and fizzes

How does calcium react with water?

Fizzes steadily — calcium + water → calcium hydroxide + hydrogen — produces a white cloudy solution as calcium hydroxide is sparingly soluble

How does magnesium react with water?

Very slowly with cold water — reacts more vigorously with steam — magnesium + steam → magnesium oxide + hydrogen

How does zinc react with dilute acid?

Steadily — zinc + hydrochloric acid → zinc chloride + hydrogen

How does iron react with dilute acid?

Slowly — iron + hydrochloric acid → iron chloride + hydrogen

Does copper react with dilute acid?

No — copper is less reactive than hydrogen — it does not displace hydrogen from acids

What is a displacement reaction?

A more reactive element displaces a less reactive element from a compound — the more reactive element takes the place of the less reactive one

Give an example of a metal displacement reaction with equation

Zinc + copper sulfate → zinc sulfate + copper — Zn + CuSO₄ → ZnSO₄ + Cu — zinc is more reactive than copper so displaces it

Give an example of a halogen displacement reaction

Chlorine + potassium bromide → potassium chloride + bromine — chlorine is more reactive than bromine so displaces it

What observations would you make when zinc is added to copper sulfate solution?

The blue solution becomes colourless — a reddish-brown copper deposit forms on the zinc — the solution warms up slightly — zinc dissolves

What observations would you make when iron is added to copper sulfate solution?

The blue solution becomes pale green — reddish-brown copper deposits on the iron — iron dissolves — the solution changes from blue to green as Fe²⁺ replaces Cu²⁺

What is oxidation in terms of electrons? (HT)

Loss of electrons — OIL — Oxidation Is Loss

What is reduction in terms of electrons? (HT)

Gain of electrons — RIG — Reduction Is Gain

What does OIL RIG stand for? (HT)

Oxidation Is Loss — Reduction Is Gain — a memory aid for electron transfer in redox reactions

In the displacement reaction Zn + CuSO₄ → ZnSO₄ + Cu which species is oxidised and which is reduced? (HT)

Zinc is oxidised — it loses electrons — Zn → Zn²⁺ + 2e⁻. Copper ions are reduced — they gain electrons — Cu²⁺ + 2e⁻ → Cu

Write the ionic equation for zinc displacing copper (HT)

Zn + Cu²⁺ → Zn²⁺ + Cu

Write the half equation for zinc being oxidised (HT)

Zn → Zn²⁺ + 2e⁻

Write the half equation for copper ions being reduced (HT)

Cu²⁺ + 2e⁻ → Cu

Write the half equation for iron being oxidised to Fe²⁺ (HT)

Fe → Fe²⁺ + 2e⁻

Write the half equation for iron being oxidised to Fe³⁺ (HT)

Fe → Fe³⁺ + 3e⁻

In a displacement reaction which species is oxidised and which is reduced? (HT)

The more reactive metal is oxidised — it loses electrons to become positive ions. The less reactive metal ion is reduced — it gains electrons to become neutral atoms

How are unreactive metals found in the Earth?

As the metal itself — for example gold is found as pure gold nuggets because it is so unreactive it does not form compounds

How are most metals found in the Earth?

As compounds in ores — they require chemical reactions to extract the metal — the more reactive the metal the harder it is to extract

How are metals less reactive than carbon extracted?

By reduction with carbon — carbon displaces the metal from its oxide — the metal oxide is reduced — carbon is oxidised

Give an example of metal extraction by reduction with carbon

Iron extraction in the blast furnace — iron oxide + carbon → iron + carbon dioxide — carbon reduces the iron oxide by removing oxygen

Write the word equation for iron extraction by reduction with carbon

Iron oxide + carbon → iron + carbon dioxide

Why can carbon reduce iron oxide but not aluminium oxide?

Carbon is more reactive than iron — it displaces iron from its oxide. Carbon is less reactive than aluminium — it cannot displace aluminium from its oxide

How are metals more reactive than carbon extracted?

By electrolysis — this requires large amounts of energy — used for aluminium potassium sodium calcium and lithium

What is the relationship between reactivity and ease of extraction?

More reactive metals form more stable compounds — require more energy to extract — less reactive metals form less stable compounds — easier to extract

How do you name a salt?

First part comes from the metal or base — second part comes from the acid — hydrochloric acid gives chlorides — sulfuric acid gives sulfates — nitric acid gives nitrates

What salt is formed when hydrochloric acid reacts with sodium hydroxide?

Sodium chloride — NaCl

What salt is formed when sulfuric acid reacts with copper oxide?

Copper sulfate — CuSO₄

What salt is formed when nitric acid reacts with potassium carbonate?

Potassium nitrate — KNO₃

What salt is formed when hydrochloric acid reacts with zinc?

Zinc chloride — ZnCl₂

What are the products of acid reacting with a metal?

Salt + hydrogen gas — acid + metal → salt + hydrogen

Write the word equation for hydrochloric acid reacting with magnesium

Magnesium + hydrochloric acid → magnesium chloride + hydrogen

Write the balanced symbol equation for hydrochloric acid reacting with magnesium

Mg + 2HCl → MgCl₂ + H₂

Write the word equation for sulfuric acid reacting with zinc

Zinc + sulfuric acid → zinc sulfate + hydrogen

Write the balanced symbol equation for sulfuric acid reacting with zinc

Zn + H₂SO₄ → ZnSO₄ + H₂

Write the balanced symbol equation for hydrochloric acid reacting with iron

Fe + 2HCl → FeCl₂ + H₂

Explain the reaction of metals with acids in terms of electrons (HT)

The metal loses electrons — is oxidised — forms positive metal ions. Hydrogen ions from the acid gain electrons — are reduced — form hydrogen gas

Write the half equation for magnesium reacting with acid (HT)

Mg → Mg²⁺ + 2e⁻ — magnesium loses two electrons and is oxidised

Write the half equation for hydrogen ions being reduced in acid reactions (HT)

2H⁺ + 2e⁻ → H₂ — hydrogen ions gain electrons and are reduced

Which metals react with hydrochloric and sulfuric acid?

Magnesium — zinc — iron — these are the reactions required for the spec — reactions at room temperature only — not steam reactions

What are the products when acids react with alkalis?

Salt + water — this is neutralisation — acid + alkali → salt + water

Write the word equation for hydrochloric acid reacting with sodium hydroxide

Hydrochloric acid + sodium hydroxide → sodium chloride + water

Write the balanced symbol equation for hydrochloric acid reacting with sodium hydroxide

HCl + NaOH → NaCl + H₂O

Write the word equation for sulfuric acid reacting with potassium hydroxide

Sulfuric acid + potassium hydroxide → potassium sulfate + water

Write the balanced symbol equation for sulfuric acid reacting with potassium hydroxide

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

What are the products when acids react with insoluble bases (metal oxides)?

Salt + water — acid + metal oxide → salt + water

Write the word equation for hydrochloric acid reacting with copper oxide

Hydrochloric acid + copper oxide → copper chloride + water

Write the balanced symbol equation for hydrochloric acid reacting with copper oxide

2HCl + CuO → CuCl₂ + H₂O

Write the word equation for sulfuric acid reacting with zinc oxide

Sulfuric acid + zinc oxide → zinc sulfate + water

Write the balanced symbol equation for sulfuric acid reacting with zinc oxide

H₂SO₄ + ZnO → ZnSO₄ + H₂O

What are the products when acids react with metal carbonates?

Salt + water + carbon dioxide — acid + metal carbonate → salt + water + carbon dioxide

Write the word equation for hydrochloric acid reacting with calcium carbonate

Hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide

Write the balanced symbol equation for hydrochloric acid reacting with calcium carbonate

2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂

Write the word equation for hydrochloric acid reacting with sodium carbonate

Hydrochloric acid + sodium carbonate → sodium chloride + water + carbon dioxide

Write the balanced symbol equation for hydrochloric acid reacting with sodium carbonate

2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂

Write the balanced symbol equation for sulfuric acid reacting with copper carbonate

H₂SO₄ + CuCO₃ → CuSO₄ + H₂O + CO₂

How can you make a soluble salt from an insoluble base or carbonate?

Add excess insoluble base or carbonate to warm acid — stir until no more dissolves — filter off excess solid — evaporate solution to crystallise — dry the crystals

Why is excess solid base or carbonate added during salt preparation?

To ensure all the acid is neutralised — any excess solid can be filtered off — adding excess acid would contaminate the product

What is the method for making copper sulfate crystals from copper oxide and sulfuric acid?

Add excess copper oxide to warm dilute sulfuric acid — stir until no more dissolves — filter to remove excess copper oxide — evaporate filtrate to crystallise copper sulfate — dry crystals between filter paper

What colour change would you observe when making copper sulfate from copper oxide?

The colourless acid gradually turns blue as copper sulfate forms — when the solution no longer changes colour the acid is fully neutralised — excess black copper oxide remains

What is the pH scale?

A measure of acidity and alkalinity — scale from 0 to 14 — below 7 is acidic — 7 is neutral — above 7 is alkaline

What ions do acids produce in aqueous solution?

Hydrogen ions H⁺

What ions do alkalis produce in aqueous solution?

Hydroxide ions OH⁻

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O — hydrogen ions and hydroxide ions react to form water

How can you measure pH?

Using universal indicator — gives an approximate pH from colour change. Using a pH probe/meter — gives a precise numerical value

What colour does universal indicator turn in strongly acidic solutions?

Red

What colour does universal indicator turn in neutral solutions?

Green

What colour does universal indicator turn in strongly alkaline solutions?

Purple/violet

What is a strong acid? (HT)

An acid that completely ionises in aqueous solution — all molecules dissociate to produce H⁺ ions — the ionisation is essentially complete and irreversible

What is a weak acid? (HT)

An acid that only partially ionises in aqueous solution — only some molecules dissociate — an equilibrium exists between the dissociated ions and undissociated molecules

Give examples of strong acids (HT)

Hydrochloric acid HCl — sulfuric acid H₂SO₄ — nitric acid HNO₃

Give examples of weak acids (HT)

Ethanoic acid — citric acid — carbonic acid

What is the difference between a dilute acid and a weak acid? (HT)

Dilute/concentrated refers to the amount of acid dissolved in a given volume — concentration. Weak/strong refers to the degree of ionisation — how completely the acid dissociates — these are independent properties

Do strong and weak acids of the same concentration have the same pH? (HT)

No — a strong acid of a given concentration has a lower pH than a weak acid of the same concentration — because the strong acid fully ionises producing more H⁺ ions

What happens to hydrogen ion concentration when pH decreases by one unit? (HT)

The hydrogen ion concentration increases by a factor of 10 — pH is a logarithmic scale

What happens to hydrogen ion concentration when pH decreases by two units? (HT)

The hydrogen ion concentration increases by a factor of 100 — each unit decrease multiplies H⁺ concentration by 10

What is electrolysis?

The breakdown of an ionic compound using electricity — the compound must be molten or dissolved in water so ions are free to move

What is an electrolyte?

An ionic compound that is melted or dissolved in water — the free ions allow electrical charge to flow — making electrolysis possible

What is the cathode?

The negative electrode — positive ions move towards it — reduction occurs here — positive ions gain electrons

What is the anode?

The positive electrode — negative ions move towards it — oxidation occurs here — negative ions lose electrons

What are inert electrodes?

Electrodes that do not react with the electrolyte or products — usually made of platinum or carbon — they do not change during electrolysis

What happens at the cathode during electrolysis?

Positively charged ions move to the cathode — gain electrons — are reduced — metals or hydrogen are produced

What happens at the anode during electrolysis?

Negatively charged ions move to the anode — lose electrons — are oxidised — non-metals are produced

What is produced when molten lead bromide is electrolysed?

Cathode — lead metal. Anode — bromine gas — the molten state allows lead and bromide ions to move freely

Write the half equation for lead deposited at the cathode during electrolysis of molten lead bromide (HT)

Pb²⁺ + 2e⁻ → Pb — lead ions gain electrons and are reduced