OCR A Level Chemistry B (Salters)
OCR A Level Chemistry B Developing Metals (DM) Exam Questions
Free OCR A Level Chemistry B exam questions for Developing Metals (DM), with a mark scheme for every pack. Covers transition metal electron configurations, complex ions, ligands, colour and colorimetry, precipitation reactions, electrode potentials, electrochemical cells, rusting and redox titrations.
Developing Metals (DM) exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR A Level Chemistry B Developing Metals (DM)
Developing Metals is a Year 2 storyline of OCR A Level Chemistry B (Salters) about the chemistry of metals, particularly the d-block transition metals. It covers electron configurations, variable oxidation states, complex ions with ligands and their shapes, and why transition metal compounds are coloured, including measuring concentration by colorimetry. It also develops redox through electrode potentials and electrochemical cells, applying them to corrosion of iron, and uses redox titrations to analyse metals. Examiners test configurations of transition metal ions, precipitate colours with sodium hydroxide, E cell calculations and feasibility, and redox titration calculations.
What you need to know
- Transition metals d-block elements forming at least one ion with an incomplete d subshell. Configurations lose 4s electrons before 3d; Cr and Cu have one 4s electron. They show variable oxidation states and catalytic activity.
- Complex ions Ligands donate lone pairs to form dative bonds to a central metal ion. Learn coordination number, octahedral and tetrahedral shapes, monodentate and bidentate ligands, and ligand substitution.
- Colour and colorimetry Ligands split the d orbitals; electrons absorb visible light to move to the higher level and the complementary colour is seen. A colorimeter with a calibration curve finds the concentration of a coloured solution.
- Precipitation reactions With NaOH: Cu2+ gives a blue precipitate, Fe2+ green, Fe3+ orange-brown. These are used to identify metal ions.
- Electrode potentials Half-cells are compared with the standard hydrogen electrode. E cell = E(positive) - E(negative); a positive value means the reaction is feasible. Rusting is an electrochemical process needing water and oxygen.
- Redox titrations Manganate(VII) titrations (self-indicating) and iodine-thiosulfate titrations are used, for example to determine copper: 2Cu2+ + 4I- gives 2CuI + I2.
Common mistakes in Developing Metals (DM)
- Writing Fe2+ as [Ar]3d4 4s2 instead of [Ar]3d6.
- Explaining colour as light emitted by the complex. It is due to light absorbed, with the complementary colour seen.
- Forgetting to choose a filter of the complementary colour in colorimetry.
- Subtracting electrode potentials in the wrong order, giving a negative E cell for a feasible reaction.
- Missing the 1 : 1 ratio between Cu2+ and S2O3 2- in copper determinations, which comes from combining the two equations.
Try three Developing Metals (DM) exam-style questions
1. Use E values to show that Fe3+ ions can oxidise iodide ions. Fe3+/Fe2+ = +0.77 V; I2/I- = +0.54 V. (2 marks)
Show the mark scheme answer
E cell = 0.77 - 0.54 = +0.23 V; positive so the reaction 2Fe3+ + 2I- gives 2Fe2+ + I2 is feasible.
2. Copper(II) ions in a solution react with excess KI. The iodine released requires 20.00 cm3 of 0.100 mol dm-3 sodium thiosulfate. Calculate the mass of copper in the solution. (Ar Cu = 63.5) (3 marks)
Show the mark scheme answer
Moles S2O3 2- = 0.100 x 20.00 / 1000 = 2.00 x 10^-3 mol; ratio Cu2+ : I2 : S2O3 2- is 2 : 1 : 2, so moles Cu2+ = 2.00 x 10^-3 mol; mass = 2.00 x 10^-3 x 63.5 = 0.127 g.
3. Explain how a colorimeter can be used to find the concentration of a solution of copper(II) ions. (3 marks)
Show the mark scheme answer
Choose a filter of the complementary colour to the solution; measure absorbance of standard solutions of known concentration and plot a calibration curve; measure absorbance of the unknown and read its concentration from the curve.
Developing Metals (DM) FAQs
What does OCR A Level Chemistry B Developing Metals (DM) cover?
It covers transition metal configurations, complex ions and ligands, colour and colorimetry, precipitation reactions, electrode potentials and cells, rusting and redox titrations.
Which papers is Developing Metals examined in?
In the Salters A Level, content from any storyline can be assessed in all three papers: Fundamentals of chemistry, Scientific literacy in chemistry and Practical skills in chemistry.
Which colours do I need to learn for Developing Metals?
Learn the colours of common aqueous ions and their hydroxide precipitates with sodium hydroxide, for example blue Cu2+, green Fe2+ precipitate and orange-brown Fe3+ precipitate, and the colour changes in manganate(VII) and iodine titrations.
