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6 marksThe Mole Concept

CAPE Chemistry Unit 1 · 2017 · Paper 2 · Question 4(c)

A solution of potassium iodide was made by dissolving 20 g in 1 dm³ of water. A mixture of 25 cm³ of this solution and an equal volume of dilute sulfuric acid on titration with 0.02 mol dm⁻³ potassium dichromate(VI) solution needed 24.80 cm³ for complete oxidation.

Calculate the molar ratio of Cr₂O₇²⁻ to I⁻ and hence derive the ionic equation for the reaction which has occurred. Molar ratio: Ionic equation:

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  1. 4(a)Apply the concept of the 'hybridization of atomic orbitals' to explain the planarity of the ethene molecule.[3 marks]
  2. 4(b)(i)State TWO principles which form the basis of the valence-shell electron pair repulsion (VSEPR) theory.[2 marks]
  3. 4(b)(ii)Use the VSEPR theory to account for the difference in shape between the ammonia molecule (NH₃) and the ammonium ion (NH₄⁺). Ammonia molecule (NH₃): Ammonium…[4 marks]

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