Refining of Crude Metals Class 12: Methods and Equations
Updated 18 October 2026 · Fact-checked
Crude metal is refined by a method suited to the metal and impurity: distillation (zinc, mercury), liquation (tin), electrolytic refining (copper), zone refining (semiconductors such as germanium and silicon), vapour phase refining (Mond process for nickel, van Arkel method for zirconium and titanium) and chromatography.
Copper dissolves from the impure anode, Cu²⁺ ions travel across and plate pure copper on the cathode, while impurities fall as anode mud.
Illustration drawn for QuestionBuddy.
Understand Refining of Crude Metals
Distillation. For low-boiling metals such as zinc and mercury; the metal is evaporated and collected pure.
Liquation. A low-melting metal such as tin flows down a sloping surface, leaving higher-melting impurities behind.
Electrolytic refining. The impure metal is the anode, a strip of pure metal the cathode, and the electrolyte is a soluble salt of the same metal. More basic metals stay in solution; less basic ones collect below the anode as anode mud. For copper: impure (blister) copper anodes, pure copper cathodes, acidified copper sulphate electrolyte. At the anode Cu gives Cu2+ + 2e-; at the cathode Cu2+ + 2e- gives Cu. Anode mud contains antimony, selenium, tellurium, silver, gold and platinum, whose recovery can pay for the refining. Zinc can be refined similarly.
Zone refining. Based on impurities being more soluble in the melt than in the solid metal. A heater moves slowly along an impure rod, creating a molten zone; pure metal crystallises behind it while impurities move into the next molten zone. Repeating in the same direction drives impurities to one end, which is cut off. It gives very pure semiconductors: germanium, silicon, boron, gallium and indium.
Vapour phase refining. The metal is converted to a volatile compound, collected and decomposed. Two conditions: the metal must form a volatile compound with an available reagent, and the compound must decompose easily.
- Mond process for nickel: Ni + 4CO gives Ni(CO)4 (volatile); on heating to a higher temperature, Ni(CO)4 gives Ni + 4CO.
- van Arkel method for zirconium or titanium, removing oxygen and nitrogen: crude metal is heated with iodine in an evacuated vessel, the more covalent iodide volatilises (Zr + 2I2 gives ZrI4) and is decomposed on a tungsten filament at about 1800 K (ZrI4 gives Zr + 2I2).
Chromatography. Column chromatography purifies elements available in tiny amounts when impurities are chemically very similar to the element.
Uses (reading material). Aluminium: foil, paints, wires, light alloys, and as a reducing agent for chromium and manganese. Copper: wires, pipes, brass (with zinc), bronze (with tin). Zinc: galvanising iron, batteries, brass (60 per cent copper, 40 per cent zinc). Iron: cast iron, wrought iron, steels such as stainless steel.
Refining of Crude Metals: formulas and key facts
- Which method for which metal
Distillation Zn, Hg Liquation Sn Electrolytic Cu, Zn Zone refining Ge, Si, B, Ga, In Mond Ni van Arkel Zr, Ti - Learn as pairs.
- Electrolytic refining of copper
Anode impure Cu -> Cu2+ + 2e- Cathode Cu2+ + 2e- -> Cu Electrolyte acidified CuSO4 Anode mud Sb, Se, Te, Ag, Au, Pt - Pure copper deposits on the cathode.
- Vapour phase refining
- Mond: Ni + 4CO -> Ni(CO)4 -> Ni + 4CO | van Arkel: Zr + 2I2 -> ZrI4 -> Zr + 2I2
- Volatile compound formed, then decomposed.
How to solve Refining of Crude Metals questions
Formative (school) assessment only in 2026-27. Questions ask for the method for a metal, the electrode reactions, and Faraday-type mass calculations.
- 1Match the method to the metal property: boiling point, melting point, semiconductor purity, or volatile compound.
- 2In electrolytic refining, impure metal is the anode and pure metal the cathode.
- 3For mass of metal deposited, use Q = I x t, moles of electrons = Q / 96500, then moles of metal = electrons / n.
- 4Multiply by molar mass for grams.
- 5State the anode mud components if asked about by-products.
Refining of Crude Metals in real life
Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.
Zone refining for chips
Suppose a lab needs a silicon rod of extremely high purity for a sensor.
Which refining method suits it, and why does it work?
Try it first, then show the solutionSolution
- Zone refining is used for semiconductors.
- Impurities are more soluble in the melt than in the solid.
- The molten zone sweeps impurities to one end.
Answer: Zone refining suits silicon. Impurities are more soluble in the melt than in the solid, so a moving molten zone carries them along the rod to one end, which is cut off.
Memory hook: Impurities ride the molten zone.
Copper refining mass
Suppose a refinery cell passes 10 A for 965 s through acidified copper sulphate (invented values, Cu = 63.5).
Find the mass of pure copper deposited at the cathode.
Try it first, then show the solutionSolution
- Q = I x t = 10 x 965 = 9650 C.
- Moles of electrons = 9650 / 96500 = 0.1.
- Cu2+ + 2e- gives Cu: moles of Cu = 0.05.
- Mass = 0.05 x 63.5 = 3.175 g.
Answer: Mass of copper = 0.05 mol x 63.5 g/mol = 3.175 g.
Memory hook: Charge to electrons to moles to grams.
Tricks to remember Refining of Crude Metals
Short memory aids. Say each one aloud once, then use it on a question the same day.
Zinc and mercury distil
Low boiling points: distillation.
Use it when: Method choice.
Mond = nickel, van Arkel = Zr
Mond for nickel with CO; van Arkel for zirconium with iodine.
Use it when: Vapour phase refining.
Anode impure, cathode pure
A for ash, C for clean.
Use it when: Electrolytic refining.
Refining of Crude Metals: solved examples
Ordered from board level to HOTS. Try each one before you open the solution.
Example 1: Method for tin · 1 mark · MCQBoard level
Tin is refined by:
(a) liquation
(b) distillation
(c) zone refining
(d) the Mond process
Try it first, then show the solutionSolution
- Tin is low-melting; it flows down a slope leaving impurities: liquation (1 mark).
Answer: (a) liquation
Example 2: Zone refining principle (2 marks) · 2 marks · Very short answerBoard level
A rod of impure germanium is passed slowly through a moving heater. Where do the impurities end up and why? Name one other element refined this way. (2 marks)
Try it first, then show the solutionSolution
- Impurities are more soluble in the melt than in the solid metal, so the moving molten zone carries them to one end of the rod, which is cut off (1 mark).
- Names one other element, e.g. silicon (1 mark).
Answer: Impurities are more soluble in the molten zone than in the solid, so the moving heater carries them to one end of the rod, which is cut off. Silicon (or boron, gallium, indium) is also refined this way.
Example 3: Electrolytic refining mass (5 marks) · 5 marks · Long answerHarder board level
A current of 5.0 A is passed for 1930 s through acidified copper sulphate in a refining cell (Cu = 63.5, F = 96500 C/mol). Find the mass of copper deposited and the equal mass of impure copper that dissolves from the anode if all current dissolves copper. (5 marks)
Try it first, then show the solutionSolution
- Q = 5.0 x 1930 = 9650 C (1 mark).
- Moles of electrons = 9650 / 96500 = 0.10 (1 mark).
- Cu2+ + 2e- gives Cu: moles of Cu = 0.10 / 2 = 0.05 (1 mark).
- Mass = 0.05 x 63.5 = 3.175 g deposited (1 mark).
- If all current dissolves copper at the anode, 3.175 g dissolves (1 mark).
Answer: Q = 9650 C, electrons = 0.10 mol, copper = 0.05 mol, mass = 3.175 g deposited at the cathode, and 3.175 g of copper dissolves from the anode.
Example 4: Mond process (4 marks) · 4 marks · Short answerHarder board level
Explain the Mond process for refining nickel and the conditions that make vapour phase refining possible. (4 marks)
Try it first, then show the solutionSolution
- Nickel is heated in a stream of CO to form volatile Ni(CO)4 (1 mark).
- Ni(CO)4 decomposes at a higher temperature to give pure nickel and CO (1 mark).
- Condition 1: the metal forms a volatile compound with an available reagent (1 mark).
- Condition 2: the compound decomposes easily to give pure metal (1 mark).
Answer: Nickel is heated in a stream of carbon monoxide to form volatile nickel tetracarbonyl: Ni + 4CO gives Ni(CO)4. At a higher temperature the carbonyl decomposes: Ni(CO)4 gives Ni + 4CO, leaving pure nickel. Vapour phase refining needs the metal to form a volatile compound with an available reagent, and that compound must decompose easily.
Example 5: Anode mud and economics · 4 marks · Case-basedHOTS / competency
In the electrolytic refining of copper, (i) what collects below the anode? (1) (ii) Name two metals found there. (1) (iii) Why does their recovery matter economically? (2)
Try it first, then show the solutionSolution
- (i) Anode mud (1 mark).
- (ii) Any two of antimony, selenium, tellurium, silver, gold, platinum (1 mark).
- (iii) Less basic metals do not dissolve and collect as mud; their recovery can pay for the whole refining (2 marks).
Answer: (i) Anode mud collects below the anode. (ii) It contains metals such as silver and gold. (iii) Less basic metals do not go into solution and are recovered from the mud; their value can pay for the refining process.
Where students lose marks in Refining of Crude Metals
The slips examiners see most often, and what to write instead.
Mistake: Swapping anode and cathode
Memory slip.
Wrong working
Pure copper is the anode.
Right working
Impure copper is the anode; pure copper is the cathode.
Do this: A for ash, C for clean.
Usually costs: 2 marks.
Mistake: Wrong mole ratio of electrons
Ignoring n = 2.
Wrong working
Moles of Cu = 0.10.
Right working
Cu2+ + 2e- gives Cu, so moles of Cu = 0.10 / 2 = 0.05.
Do this: Divide electrons by 2.
Usually costs: 2 marks.
Mistake: Mixing Mond and van Arkel
Both are vapour phase methods.
Wrong working
Nickel is refined by iodine.
Right working
Nickel by CO (Mond); Zr or Ti by iodine (van Arkel).
Do this: Learn the pairs.
Usually costs: 1 mark.
Exam tips
- This chapter is formative (school) assessment only in 2026-27.
- Write electrode reactions with charges.
- Show Q, moles of electrons, moles of metal and mass in order.
Practice questions on Refining of Crude Metals
Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.
Q1 · 1 mark · MCQBoard level
In the van Arkel method, pure metal is deposited on a heated:
(a) copper plate
(b) tungsten filament
(c) iron rod
(d) graphite blockHint
About 1800 K.
Answer
(b) tungsten filament
Q2 · 2 marks · Very short answerBoard level
Name the anode, cathode and electrolyte in the electrolytic refining of copper. (2 marks)
Hint
Impure and pure.
Answer
Anode: impure copper; cathode: strip of pure copper; electrolyte: acidified copper sulphate solution.
Q3 · 3 marks · Short answerHarder board level
Calculate the mass of copper deposited when 2.0 A passes for 4825 s (Cu = 63.5, F = 96500 C/mol). (3 marks)
Hint
Q = 9650 C.
Answer
Q = 2.0 x 4825 = 9650 C; electrons = 0.10 mol; Cu = 0.05 mol; mass = 0.05 x 63.5 = 3.175 g.
Q4 · 5 marks · Long answerHarder board level
Compare the Mond process and the van Arkel method on the metals refined, reagents and the volatile compound formed, and state one common feature. (5 marks)
Hint
CO versus iodine.
Answer
Mond: nickel is heated with CO to form volatile Ni(CO)4, which decomposes at a higher temperature to pure nickel. van Arkel: zirconium or titanium is heated with iodine in an evacuated vessel to form volatile ZrI4 (or TiI4), which is decomposed on a tungsten filament at about 1800 K, removing oxygen and nitrogen impurities. Common feature: a volatile compound is formed and then decomposed to give the pure metal.
Q5 · 1 mark · Assertion-reasonHOTS / competency
Assertion (A): Zinc and mercury are refined by distillation.
Reason (R): They are low-boiling metals.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.Hint
Why distil?
Answer
(a) Both A and R are true, and R is the correct explanation of A.
Test your recall
Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.
1.Which method refines tin?Show answer
Liquation.
2.What is anode mud?Show answer
Less basic metals that collect below the anode.
3.Name a volatile compound in the Mond process.Show answer
Nickel tetracarbonyl, Ni(CO)4.
4.What is purified by chromatography?Show answer
Elements available in tiny amounts with chemically similar impurities.
Refining of Crude Metals: frequently asked questions
What is zone refining?
A method in which a moving molten zone sweeps impurities to one end of a rod.
Why is copper refined electrolytically?
To obtain very pure copper and recover valuable metals in the anode mud.
What is vapour phase refining?
Converting the metal to a volatile compound and decomposing it to give pure metal.