This question is about iron.
(a) Iron is extracted from its main ore in a blast furnace.
(i) Name the main ore of iron used in the blast furnace.
(ii) Name the substance that enters the blast furnace at A.
(iii) Name the substance that leaves the blast furnace at B.
(iv) Give two reasons for using coke in the blast furnace.
(b) Another ore of iron is iron pyrites, \(FeS_2\). Iron pyrites contains the positive ion, \(Fe^{2+}\).
Deduce the formula of the negative ion in \(FeS_2\).
(c) Iron is a transition element.
A list of properties of iron is shown.
- Iron is a good conductor of electricity.
- Iron forms soluble salts.
- Iron forms coloured compounds.
- Iron has variable oxidation states.
- Iron acts as a catalyst.
- Iron forms a basic oxide.
(i) Give two properties from the list in which iron differs from Group I elements.
(ii) Give two properties from the list in which iron is similar to Group I elements.
(d) Steel consists mainly of iron.
Iron forms rust when it reacts with water and oxygen.
Magnesium blocks can be attached to the bottom of steel boats. The magnesium does not completely cover the steel.
(i) Explain how the magnesium blocks prevent iron from rusting.
(ii) Explain why replacing the magnesium blocks with copper blocks will not prevent the bottom of the boat from rusting.
▶️ Answer/Explanation
(a) Blast furnace process:
(i) The main ore of iron is hematite (Fe2O3).
(ii) Substance entering at A: Air (O2) – Provides oxygen for combustion.
(iii) Substance leaving at B: Slag (calcium silicate, CaSiO3) – A byproduct formed from impurities.
(iv) Two roles of coke:
1. Fuel – Burns to release heat (exothermic reaction: \(C + O_2 \rightarrow CO_2\)).
2. Reducing agent – Produces carbon monoxide (\(CO\)), which reduces iron oxide (\(Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2\)).
(b) The negative ion in \(FeS_2\) is S22− (disulfide ion). The \(Fe^{2+}\) ion balances the charge of two \(S^{−}\) ions.
(c) Properties of iron vs. Group I elements:
(i) Differences:
1. Forms coloured compounds – Transition metals like iron exhibit this due to d-d electron transitions.
2. Variable oxidation states – Iron shows +2 and +3 states (e.g., \(Fe^{2+}\), \(Fe^{3+}\)), unlike Group I metals (only +1).
(ii) Similarities:
1. Good conductor of electricity – Both iron and Group I metals have delocalized electrons.
2. Forms a basic oxide – Iron oxide (\(Fe_2O_3\)) and Group I oxides (e.g., \(Na_2O\)) react with acids to form salts.
(d) Rust prevention:
(i) Sacrificial protection – Magnesium is more reactive than iron (higher in the reactivity series). It oxidizes first (\(Mg \rightarrow Mg^{2+} + 2e^−\)), preventing iron from losing electrons and rusting.
(ii) Copper is less reactive than iron. It would act as a cathode, accelerating iron’s oxidation (rusting) via galvanic corrosion.
This question is about transition elements.
(a) Transition elements are harder and stronger than Group I elements.
Describe two other differences in physical properties between transition elements and Group I elements.
(b) State one physical property of transition elements that is similar to Group I elements.
(c) State two chemical properties of transition elements.
(d) Cobalt is a transition element. Anhydrous cobalt(II) chloride is used to test for water.
State the colour change that occurs when water is added to anhydrous cobalt(II) chloride.
(e) Iron is a transition element.
(i) Which two substances react with iron to form rust?
(ii) Which metal is used to galvanize iron?
(f) The hull of a ship is made from steel (mainly iron). Metal blocks are placed on the ship’s hull to prevent rusting.
Use your knowledge of the reactivity series to explain why:
- magnesium is suitable to use as the metal blocks
- copper is not suitable to use as the metal blocks.
(g) Rust contains iron(III) oxide.
Phosphoric acid, H3PO4, can be used to remove rust from an iron object and prevent further rusting.
(i) Write a chemical equation for the reaction between iron(III) oxide and phosphoric acid to form iron(III) phosphate and water.
(ii) Iron(III) phosphate is an insoluble salt.
Suggest how the formation of iron(III) phosphate prevents further rusting.
▶️ Answer/Explanation
(a) Two physical differences:
1. Transition elements have higher melting points (e.g., iron melts at 1538°C vs. sodium at 98°C).
2. Transition elements are more dense (e.g., iron has density 7.87 g/cm³ vs. potassium 0.89 g/cm³).
(b) Similar physical property: Both are good conductors of electricity (due to metallic bonding).
(c) Two chemical properties of transition elements:
1. They act as catalysts (e.g., iron in Haber process).
2. They form colored compounds (e.g., blue CuSO₄, green FeSO₄).
(d) Anhydrous cobalt(II) chloride changes from blue to pink when hydrated.
(e)(i) Rust forms when iron reacts with:
1. Oxygen (O₂).
2. Water (H₂O).
(e)(ii) Zinc (Zn) is used for galvanizing iron.
(f) Reactivity series explanation:
– Magnesium is more reactive than iron, so it corrodes first (sacrificial protection).
– Copper is less reactive, causing iron to rust preferentially.
(g)(i) Balanced equation:
\(\text{Fe}_2\text{O}_3 + 2\text{H}_3\text{PO}_4 \rightarrow 2\text{FePO}_4 + 3\text{H}_2\text{O}\).
(g)(ii) Iron(III) phosphate forms a protective layer, blocking oxygen/water contact.