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1 markThe Mole Concept

CAPE Chemistry Unit 1 · 2005 · Paper 2 · Question 8(b)(ii)

A second analyst obtains a value of 290 ppm for Sample 1 (originally 250 ppm).

Identify the additional information needed to evaluate the accuracy of the result obtained at this site.

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  1. 8(a)(i)Calculate the mean and standard deviation of the calcium carbonate hardness values, showing the relevant formulae.[4 marks]
  2. 8(a)(ii)State what the standard deviation indicates regarding the variability in the water hardness values.[1 mark]
  3. 8(a)(iii)State how the reliability of the hardness data collected from the sites can be improved.[1 mark]
  4. 8(b)(i)Compare the two results with regard to precision and suggest an explanation for the discrepancy.[2 marks]
  5. 8(c)Discuss the importance of choosing appropriate volumetric apparatus when titrating 100 cm^3 water samples with EDTA using Eriochrome Black T indicator.[5 marks]
  6. 8(d)Describe the experimental procedure for calibrating and determining the accurate volume delivered by a volumetric pipette.[6 marks]

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