Chapter 5: Chemical Changes

How is the reactivity of a metal determined?

The reactivity of a metal is determined by its tendency to form positive ions (lose electrons).

What is the order of the Reactivity Series (from most to least reactive)?

Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold, Platinum.

What is a displacement reaction?

A reaction where a more reactive metal takes the place of a less reactive metal in a compound.

Define oxidation and reduction in terms of oxygen.

• Oxidation: The gain of oxygen.

• Reduction: The loss of oxygen.

Define oxidation and reduction in terms of electrons.

• Oxidation: Oxidation is loss of electrons (e^{-}).

• Reduction: Reduction is gain of electrons (e^{-}).

How are metals less reactive than carbon extracted from their ores?

They are extracted by reduction using carbon (e.g., 2Fe{2}O{3} + 3C \rightarrow 4Fe + 3CO_{2}).

How are metals more reactive than carbon extracted from their ores?

They are extracted using electrolysis, which requires large amounts of energy to melt the compounds and produce electricity.

What are the products of a reaction between a metal and an acid?

Metal + Acid \rightarrow Salt + Hydrogen (H_{2}).

What is the general ionic equation for a neutralisation reaction?

H^{+}(aq) + OH^{-}(aq) \rightarrow H_{2}O(l)

What is the difference between a strong acid and a weak acid (Higher Tier)?

• Strong Acid: Completely ionised in aqueous solution (e.g., HCl, H{2}SO{4}, HNO_{3}).

• Weak Acid: Only partially ionised in aqueous solution (e.g., ethanoic acid, citric acid).

How does pH relate to the concentration of hydrogen ions (H^{+})?

As pH decreases by 1 unit, the concentration of hydrogen ions increases by a factor of 10.

In electrolysis, which ions move to which electrode?

• Cations (positive ions) move to the Cathode (negative electrode).

• Anions (negative ions) move to the Anode (positive electrode).

What are the rules for electrolysis of an aqueous solution at the Cathode?

Hydrogen is produced if the metal is more reactive than hydrogen. The metal is produced if it is less reactive than hydrogen.

What are the rules for electrolysis of an aqueous solution at the Anode?

Oxygen gas is produced unless the solution contains halide ions (Cl^{-}, Br^{-}, I^{-}), in which case the halogen is produced.

Write a half equation for the production of oxygen at the anode.

4OH^{-} \rightarrow O{2} + 2H{2}O + 4e^{-} OR 4OH^{-} - 4e^{-} \rightarrow O{2} + 2H{2}O

How is the reactivity of a metal determined?

The reactivity of a metal is determined by its tendency to form positive ions (lose electrons).

What is the order of the Reactivity Series (from most to least reactive)?

Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold, Platinum.

What is a displacement reaction?

A reaction where a more reactive metal takes the place of a less reactive metal in a compound.

Define oxidation and reduction in terms of oxygen.

• Oxidation: The gain of oxygen.

• Reduction: The loss of oxygen.

Define oxidation and reduction in terms of electrons.

• Oxidation: Oxidation is loss of electrons (e^{-}).

• Reduction: Reduction is gain of electrons (e^{-}).

How are metals less reactive than carbon extracted from their ores?

They are extracted by reduction using carbon (e.g., 2Fe{2}O{3} + 3C \rightarrow 4Fe + 3CO_{2}).

How are metals more reactive than carbon extracted from their ores?

They are extracted using electrolysis, which requires large amounts of energy to melt the compounds and produce electricity.

What are the products of a reaction between a metal and an acid?

Metal + Acid \rightarrow Salt + Hydrogen (H_{2}).

What are the products of a reaction between an acid and a metal hydroxide or metal oxide?

Acid + Metal Oxide/Hydroxide \rightarrow Salt + Water (H_{2}O).

What are the products of a reaction between an acid and a metal carbonate?

Acid + Metal Carbonate \rightarrow Salt + Water + Carbon Dioxide (CO_{2}).

What is the general ionic equation for a neutralisation reaction?

H^{+}(aq) + OH^{-}(aq) \rightarrow H_{2}O(l)

What is the difference between an alkali and a base?

A base is a substance that neutralises an acid (e.g., metal oxides). An alkali is a soluble base that produces OH^{-} ions in aqueous solution.

What is the difference between a strong acid and a weak acid (Higher Tier)?

• Strong Acid: Completely ionised in aqueous solution (e.g., HCl, H{2}SO{4}, HNO_{3}).

• Weak Acid: Only partially ionised in aqueous solution (e.g., ethanoic acid, citric acid).

How does pH relate to the concentration of hydrogen ions (H^{+})?

As pH decreases by 1 unit, the concentration of hydrogen ions increases by a factor of 10.

In electrolysis, which ions move to which electrode?

• Cations (positive ions) move to the Cathode (negative electrode).

• Anions (negative ions) move to the Anode (positive electrode).

Why is cryolite used in the electrolysis of aluminium oxide?

Cryolite is used to lower the melting point of the aluminium oxide, which reduces the energy costs required for the process.

Why must the positive electrode (anode) be regularly replaced during the electrolysis of aluminium oxide?

The oxygen produced at the anode reacts with the carbon (graphite) electrode to form carbon dioxide gas (CO_{2}), gradually burning it away.

What are the rules for electrolysis of an aqueous solution at the Cathode?

Hydrogen is produced if the metal is more reactive than hydrogen. The metal is produced if it is less reactive than hydrogen.

What are the rules for electrolysis of an aqueous solution at the Anode?

Oxygen gas is produced unless the solution contains halide ions (Cl^{-}, Br^{-}, I^{-}), in which case the halogen is produced.

Write a half equation for the production of oxygen at the anode.

4OH^{-} \rightarrow O{2} + 2H{2}O + 4e^{-} OR 4OH^{-} - 4e^{-} \rightarrow O{2} + 2H{2}O

How is the reactivity of a metal determined?

The reactivity of a metal is determined by its tendency to form positive ions (lose electrons).

What is the order of the Reactivity Series (from most to least reactive)?

Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold, Platinum.

What is a displacement reaction?

A reaction where a more reactive metal takes the place of a less reactive metal in a compound.

Define oxidation and reduction in terms of oxygen.

• Oxidation: The gain of oxygen.\n- Reduction: The loss of oxygen.

Define oxidation and reduction in terms of electrons.

• Oxidation: Oxidation is loss of electrons (e^{-}).\n- Reduction: Reduction is gain of electrons (e^{-}).

How are metals less reactive than carbon extracted from their ores?

They are extracted by reduction using carbon (e.g., 2Fe{2}O{3} + 3C \rightarrow 4Fe + 3CO_{2}).

How are metals more reactive than carbon extracted from their ores?

They are extracted using electrolysis, which requires large amounts of energy to melt the compounds and produce electricity.

What are the products of a reaction between a metal and an acid?

Metal + Acid \rightarrow Salt + Hydrogen (H_{2}).

What are the products of a reaction between an acid and a metal hydroxide or metal oxide?

Acid + Metal Oxide/Hydroxide \rightarrow Salt + Water (H_{2}O).

What are the products of a reaction between an acid and a metal carbonate?

Acid + Metal Carbonate \rightarrow Salt + Water + Carbon Dioxide (CO_{2}).

What is the general ionic equation for a neutralisation reaction?

H^{+}(aq) + OH^{-}(aq) \rightarrow H_{2}O(l)

What is the difference between an alkali and a base?

A base is a substance that neutralises an acid (e.g., metal oxides). An alkali is a soluble base that produces OH^{-} ions in aqueous solution.

What is the difference between a strong acid and a weak acid (Higher Tier)?

• Strong Acid: Completely ionised in aqueous solution (e.g., HCl, H{2}SO{4}, HNO_{3}).\n- Weak Acid: Only partially ionised in aqueous solution (e.g., ethanoic acid, citric acid).

How does pH relate to the concentration of hydrogen ions (H^{+})?

As pH decreases by 1 unit, the concentration of hydrogen ions increases by a factor of 10.

In electrolysis, which ions move to which electrode?

• Cations (positive ions) move to the Cathode (negative electrode).\n- Anions (negative ions) move to the Anode (positive electrode).

Why is cryolite used in the electrolysis of aluminium oxide?

Cryolite is used to lower the melting point of the aluminium oxide, which reduces the energy costs required for the process.

Why must the positive electrode (anode) be regularly replaced during the electrolysis of aluminium oxide?

The oxygen produced at the anode reacts with the carbon (graphite) electrode to form carbon dioxide gas (CO_{2}), gradually burning it away.

What are the rules for electrolysis of an aqueous solution at the Cathode?

Hydrogen is produced if the metal is more reactive than hydrogen. The metal is produced if it is less reactive than hydrogen.

What are the rules for electrolysis of an aqueous solution at the Anode?

Oxygen gas is produced unless the solution contains halide ions (Cl^{-}, Br^{-}, I^{-}), in which case the halogen is produced.

Write a half equation for the production of oxygen at the anode.

4OH^{-} \rightarrow O{2} + 2H{2}O + 4e^{-} OR 4OH^{-} - 4e^{-} \rightarrow O{2} + 2H{2}O

What ion is responsible for acidity in solution?

The hydrogen ion (H^{+}).

What ion is responsible for alkalinity in solution?

The hydroxide ion (OH^{-}).

What is an alkali?

A soluble base with a pH greater than 7.

If pH changes from 4 to 2, how does [H^{+}] change?

It increases by 100 times (10 \times 10).

What is the difference between acid concentration and acid strength?

Strength refers to the degree of ionisation; concentration refers to the amount of acid substance in a given volume of solution.

How do you name the salt produced by sulfuric acid?

A sulfate.

In the preparation of a soluble salt, why is the metal oxide/carbonate added in excess?

To ensure all the acid has reacted and been used up.

How is the excess unreacted solid removed during the preparation of a soluble salt?

By filtration.

How are pure crystals produced from a salt solution in a practical?

By heating the solution in an evaporating dish until the crystallisation point, then leaving it to cool and dry.

Which two non-metals are often included in the reactivity series?

Carbon and Hydrogen.

What is an ionic equation?

A chemical equation that shows only the species that change during the reaction (ignoring spectator ions).

Write the half equation for the oxidation of Magnesium.

Mg \rightarrow Mg^{2+} + 2e^{-}