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 differences in physical properties:
1. Higher melting/boiling points (transition elements have stronger metallic bonds).
2. Higher density (transition elements are more compact).
(b) Both are good conductors of heat/electricity (metallic bonding allows free electron movement).
(c) Two chemical properties:
1. Form colored compounds (due to d-d electron transitions).
2. Act as catalysts (e.g., Fe in Haber process).
(d) The color change is from blue (anhydrous) to pink (hydrated).
(e) (i) Rust forms when iron reacts with oxygen and water.
(ii) The metal used for galvanization is zinc (Zn).
(f) Magnesium is suitable because it is more reactive than iron (sacrificial protection). Copper is unsuitable because it is less reactive than iron (accelerates rusting).
(g) (i) The equation is: \(\text{Fe}_2\text{O}_3 + 2\text{H}_3\text{PO}_4 \rightarrow 2\text{FePO}_4 + 3\text{H}_2\text{O}\).
(ii) Iron(III) phosphate forms a protective layer, preventing contact with water/oxygen.
Zinc and copper are elements next to each other in the Periodic Table.
(a) Zinc is obtained from zinc blende in a two-step process.
- In step 1, zinc blende is converted into zinc oxide.
- In step 2, zinc oxide is converted into zinc in a blast furnace.
Outline how each of these steps are done.
In your answer:
- give one chemical equation for each step
- describe how zinc is removed from the blast furnace in step 2.
(b) Name the alloy formed when zinc is mixed with copper.
(c) Copper is a transition element. It can have variable oxidation states.
State two other chemical properties of transition elements which make them different from Group I elements.
(d) A compound of copper can be used to test for water.
(i) State the full name of this compound of copper.
(ii) State the colour change that occurs when water is added to this compound of copper.
(e) Aqueous potassium iodide reacts with aqueous copper(II) sulfate to produce iodine.
(i) Balance the chemical equation for this reaction.
(ii) Deduce the charge on the copper ion in CuI.
(iii) In terms of electron transfer, explain why copper is reduced in this reaction.
(iv) Identify the reducing agent.
▶️ Answer/Explanation
(a)
Step 1: Zinc blende (ZnS) is roasted in air to form zinc oxide (ZnO) and sulfur dioxide (SO₂).
Equation: \(2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2\)
Step 2: Zinc oxide is reduced by carbon (coke) in a blast furnace to produce zinc vapor and carbon monoxide (CO).
Equation: \(ZnO + C \rightarrow Zn + CO\)
Removal of zinc: Zinc vapor is distilled and condensed to collect pure zinc.
(b) The alloy formed is brass (a mixture of zinc and copper).
(c) Two properties of transition elements:
1. Formation of colored compounds (e.g., blue Cu²⁺ solutions).
2. Catalytic activity (e.g., nickel in hydrogenation).
(d)
(i) The compound is anhydrous copper(II) sulfate.
(ii) Color changes from white to blue when water is added.
(e)
(i) Balanced equation: \(4KI + 2CuSO_4 \rightarrow 2CuI + I_2 + 2K_2SO_4\)
(ii) The charge on copper in CuI is +1 (Cu⁺).
(iii) Copper is reduced because it gains an electron (Cu²⁺ → Cu⁺).
(iv) The reducing agent is potassium iodide (KI) or iodide ions (I⁻).