Transition metals worksheet with answers for A Level chemistry (free PDF download)

Problem 1 Electron configurations ★★★

1. Write the electron configuration of an iron atom in the form [Ar] 3dˣ 4sʸ.
2. Write the configuration of Fe²⁺ and Fe³⁺.
3. Write the configuration of a copper atom.

Problem 2 Is it a transition element? ★★★

Decide whether each is a transition element and justify: scandium (forms Sc³⁺), titanium (Ti⁴⁺ and Ti³⁺), zinc (Zn²⁺), copper (Cu²⁺).

Problem 3 Match the colours ★★★

Match each ion to its colour: [Cu(H₂O)₆]²⁺, [Fe(H₂O)₆]²⁺, [Co(H₂O)₆]²⁺, MnO₄⁻ with pale green, purple, pink, pale blue.

Problem 4 Oxidation state and coordination number ★★★

For each complex give the oxidation state of the metal and the coordination number: [Fe(CN)₆]⁴⁻, [Cr(H₂O)₆]³⁺, [CuCl₄]²⁻, [Ag(NH₃)₂]⁺.

Problem 5 Classify the ligands ★★★

Classify as monodentate, bidentate or hexadentate: H₂O, Cl⁻, ethanedioate C₂O₄²⁻, EDTA⁴⁻, NH₃.

Problem 6 Writing complex formulae ★★★

1. Write the formula of the complex ion of Ni²⁺ with three ethane-1,2-diamine (en) ligands, including charge and coordination number.
2. Write the formula of the complex with Cr³⁺, four NH₃ and two Cl⁻ and give its charge.
3. Write the formula of the compound of that complex with chloride ions.

Problem 7 Colour and energy gap ★★★

A solution of [Co(H₂O)₆]²⁺ has ΔE = 3.98 × 10⁻¹⁹ J per ion.
1. Calculate the wavelength absorbed (h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹).
2. Predict the colour of the solution given that 500 nm is blue-green.
3. Explain what happens to the electrons.

Problem 8 Dichromate titration ★★★

25.0 cm³ of iron(II) sulfate solution needs 18.60 cm³ of 0.0150 mol dm⁻³ potassium dichromate(VI). Cr₂O₇²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O.
1. Calculate n(Cr₂O₇²⁻).
2. Calculate the concentration of Fe²⁺.

Problem 9 A homogeneous catalyst ★★★

Aarav studies S₂O₈²⁻ + 2I⁻ → 2SO₄²⁻ + I₂, which is slow, and speeds it up with Fe³⁺.
1. Write two equations showing how Fe³⁺ catalyses the reaction.
2. Show they add to give the overall equation.
3. Explain why the uncatalysed reaction is slow.

Problem 10 Contact process ★★★

Vanadium(V) oxide catalyses 2SO₂ + O₂ → 2SO₃.
1. Write the two steps: SO₂ + V₂O₅ → SO₃ + V₂O₄ and V₂O₄ + O₂ → V₂O₅ (balance).
2. State the change in oxidation state of vanadium in the first step.
3. Explain why the catalyst is not used up.

Problem 11 Copper and ammonia ★★★

Wanjiru adds ammonia solution drop by drop and then in excess to copper(II) sulfate solution.
1. Describe the two observations.
2. Write ionic equations for both changes.

Problem 12 Copper and chloride ★★★

Adding concentrated hydrochloric acid to [Cu(H₂O)₆]²⁺ gives a yellow-green solution: [Cu(H₂O)₆]²⁺ + 4Cl⁻ ⇌ [CuCl₄]²⁻ + 6H₂O.
1. Show that the equation balances for charge.
2. Explain the change in coordination number.
3. Predict the colour change on diluting with water, and explain.

Problem 13 Manganese oxidation states ★★★

Give the oxidation state of manganese in MnO₄⁻, MnO₄²⁻, MnO₂ and Mn²⁺, and match them to colours: purple, green, brown solid, pale pink.

Problem 14 Trends across the first row ★★★

The figure shows melting points of the first row d-block elements.
1. Identify the element with the highest melting point and the lowest.
2. Calculate the difference between the highest and the lowest.
3. State what the high values show about metallic bonding.

Problem 15 Spot the errors ★★★

Mei wrote three statements. Identify and correct the error in each.
1. Chromium is [Ar] 3d⁴ 4s².
2. Zinc is a transition metal because it is in the d-block.
3. In forming Fe²⁺, iron loses two 3d electrons first.

Problem 16 Chromium chemistry ★★★

Chromium(III) ions in solution are green. Excess sodium hydroxide gives green [Cr(OH)₆]³⁻. Hydrogen peroxide in alkali then gives yellow chromate(VI), CrO₄²⁻. Acidifying gives orange dichromate: 2CrO₄²⁻ + 2H⁺ ⇌ Cr₂O₇²⁻ + H₂O.
1. Give the oxidation state of chromium in each ion.
2. State why the chromate(VI) to dichromate change is not redox.
3. Predict the colour change when alkali is added to dichromate, and explain.

Problem 17 Cisplatin ★★★

Pt(NH₃)₂Cl₂ is square planar.
1. State the oxidation state of platinum.
2. Name the type of stereoisomerism shown in the figure.
3. The cis form binds to DNA by replacing both Cl⁻ with nitrogen donors; explain why the trans form cannot do this.

Problem 18 Tablet analysis ★★★

Bilal crushes a 2.00 g iron tablet (iron(II) sulfate) and makes it up to 250 cm³ with dilute sulfuric acid. A 25.0 cm³ portion needs 21.60 cm³ of 0.0100 mol dm⁻³ KMnO₄ (5 Fe²⁺ per MnO₄⁻).
1. Calculate n(Fe²⁺) in the 25.0 cm³ portion.
2. Calculate n(Fe²⁺) in the tablet.
3. Calculate the percentage of FeSO₄ (M_r = 151.9) in the tablet.

Problem 19 The chelate effect ★★★

[Ni(H₂O)₆]²⁺ + 3en → [Ni(en)₃]²⁺ + 6H₂O has ΔH = −12 kJ mol⁻¹ and ΔS = +120 J K⁻¹ mol⁻¹ at 298 K.
1. Explain why ΔS is positive by counting particles.
2. Calculate ΔG = ΔH − TΔS.
3. State whether the reaction is feasible.

Problem 20 Identify solution P ★★★

Solution P is pale green. Sodium hydroxide gives a green precipitate that turns brown on standing in air. Barium chloride in dilute hydrochloric acid gives a white precipitate.
1. Identify the two ions.
2. Write the ionic equation for the green precipitate.
3. Balance: Fe(OH)₂ + O₂ + H₂O → Fe(OH)₃