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chemistry



Explain the meaning of the word 'redox'.



Simultaneous oxidation and reduction. (=1 mark)


What colour change occurs in the Potassium manganate (VII) solution.##



Purple to colourless (pale brown) (=1 mark).




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An impure sample of Iron weighing 0.22g was dissolved in dilute sulphuric acid. The resulting solution required 34.6cm of Potassium manganate (VII) of concentration 0.02mol dm in a titration exercise. The following reactions take place:

Fe + 2H Fe + H

5 Fe + MnO + 8H 5Fe + Mn + 4HO
Calculate the number of moles of MnO used in the titration.




Hint: Use relationship



0.02 x 0.0346 = number of moles of MnO (=1 mark)

0.000692 = number of moles of MnO (=1 mark)



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Calculate the number of moles of Fe oxidised by theMnO .
Calculate the number of moles of MnO used in the titration.




Fereacts with MnO in ratio of 5:1

Number of moles of Fe = 5 x 0.000692 (=1 mark)

Number of moles of Fe = 0.00346 (=1 mark)



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Calculate the number of grammes of Fe ions used in the titration.




Hint: Use relationship


0.00346 x 56 = mass (=1 mark)

Mass = 0.19376g (=1 mark)



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Calculate the percentage purity of the original sample of Iron.