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: Roasting zinc blende (ZnS) in air converts it to zinc oxide (ZnO).
Chemical equation: \(2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2\).
Step 2: Reduction of ZnO with coke (carbon) in a blast furnace produces zinc.
Chemical equation: \(ZnO + C \rightarrow Zn + CO\).
Removal of zinc: Zinc is distilled due to its low boiling point.
(b) The alloy formed is brass.
(c) Two properties of transition elements:
1. Form colored compounds/ions (e.g., blue Cu²⁺ solutions).
2. Act as catalysts (e.g., platinum in catalytic converters).
(d) (i) The compound is anhydrous copper(II) sulfate.
(ii) Colour change: white → blue (due to hydration).
(e) (i) Balanced equation: \(4KI + 2CuSO_4 \rightarrow 2CuI + I_2 + 2K_2SO_4\).
(ii) Charge on Cu in CuI: +1 (since I has a −1 charge).
(iii) Copper is reduced as it gains an electron (Cu²⁺ → Cu⁺).
(iv) Reducing agent: KI / iodide ions (I⁻) (donates electrons).
A student used chromatography to separate the dyes in the blue ink from a ball-point pen. She used the equipment shown in the diagrams below.
(a) Complete the diagram below to show how she set up the apparatus.
(b) Describe how chromatography could be used by the student to separate the dyes.
(c) The student used water as a solvent. Suggest a different solvent that she could use.
(d) The diagram below shows the results of the chromatography using the blue ink, B, and several pure dyes, W, X, Y and Z.
(i) Which of the dyes, W, X, Y and Z, were in the blue ink?
(ii) How many dyes in the ink had been separated by this chromatography?
(e) The diagram shows the ball-point pen used in the experiment.
(i) The cap of the pen is made of poly(ethene).
Describe the formation of poly(ethene) from ethene. In your answer, include the words:
- monomer,
- polymer.
(ii) The tip of the pen is made from an alloy.
What is meant by the term alloy ?
(f) The table shows some properties of four alloys.
(i) How does the strength of the steel and aluminum alloys vary with their thermal conductivity?
(ii) Which one of these alloys is the best one to use to make the body of an aircraft? Give two reasons for your answer.
▶️ Answer/Explanation
(a) The setup includes:
– A chromatography paper not touching the sides of the beaker.
– The solvent (e.g., water) at the bottom, with the paper dipping into it.
– A watch glass covering the beaker to prevent solvent evaporation.
(b) Steps to separate dyes:
1. Place a small spot of ink above the solvent level on the paper.
2. Allow the solvent to rise up the paper, carrying the dyes at different rates.
3. Dyes separate based on their solubility and affinity for the paper.
(c) Alternative solvents: ethanol, propanone, or ethyl acetate (any organic solvent).
(d)(i) The blue ink contains dyes W, X, and Y (their spots align with B’s separated components).
(d)(ii) The ink contains 4 dyes (W, X, Y, and an unidentified component).
(e)(i) Poly(ethene) forms when ethene monomers (C₂H₄) undergo addition polymerization, linking into long polymer chains.
(e)(ii) An alloy is a mixture of metals (or a metal with a non-metal) to enhance properties like strength.
(f)(i) Higher strength alloys have lower thermal conductivity (e.g., steel is stronger but less conductive than aluminum).
(f)(ii) Best aircraft alloy: High-strength aluminum.
Reasons:
1. High strength-to-weight ratio (lightweight but strong).
2. Low density (reduces overall aircraft weight).