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Atoms and reactions

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Question 1
82%

An iron ore sample was dissolved in acid and all the iron converted to Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) ions. A 25.00 cm3 sample of this Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) solution was titrated against a standard solution of potassium dichromate(VI), K2Cr2O7\text{K}_2\text{Cr}_2\text{O}_7K2​Cr2​O7​. The complete oxidation of Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) required 20.00 cm3 of 0.0150 mol dm-3 K2Cr2O7(aq)\text{K}_2\text{Cr}_2\text{O}_7(aq)K2​Cr2​O7​(aq) according to the equation below:

Cr2O72−(aq)+14H+(aq)+6Fe2+(aq)⟶2Cr3+(aq)+6Fe3+(aq)+7H2O(l) \text{Cr}_2\text{O}_7^{2-}(aq) + 14\text{H}^+(aq) + 6\text{Fe}^{2+}(aq) \longrightarrow 2\text{Cr}^{3+}(aq) + 6\text{Fe}^{3+}(aq) + 7\text{H}_2\text{O}(l) Cr2​O72−​(aq)+14H+(aq)+6Fe2+(aq)⟶2Cr3+(aq)+6Fe3+(aq)+7H2​O(l)

What is the concentration of Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq), in mol dm−3\text{mol dm}^{-3}mol dm−3, in the sample?

A

0.01200.01200.0120

B

0.07200.07200.0720

C

0.1130.1130.113

D

0.002000.002000.00200

Markscheme

Atoms and reactions Questions

  1. A Level
  2. /Chemistry
  3. /Atoms and reactions

199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.

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