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3 marksTitrimetric (Volumetric) Methods of Analysis

CAPE Chemistry Unit 2 · May/June 2021 · Paper 2 · Question 2(b)(i)

Sodium hydrogen carbonate (NaHCO₃) is sometimes used as a primary standard, yet its molecular mass is only 84 g mol⁻¹.

List THREE reasons why NaHCO₃ can be used as a primary standard.

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  1. 2(a)(i)Define EACH of the following terms: Accuracy[4 marks]
  2. 2(a)(ii)Define EACH of the following terms: Precision[4 marks]
  3. 2(b)(ii)State ONE reason why NaOH may NOT be used as a primary standard.[1 mark]
  4. 2(c)(i)Write the balanced equation for the reaction between sodium hydrogen carbonate and sulfuric acid.[2 marks]
  5. 2(c)(ii)Calculate the mass (in grams) of the sodium hydrogen carbonate that the student would use to neutralize the acid, if 23.50 cm³ of the acid were used from the…[4 marks]
  6. 2(d)(i)Define the term 'mean volume'.[1 mark]
  7. 2(d)(ii)Determine the mean volume from the titre values (to be used in the calculations).[2 marks]
  8. 2(d)(iii)Define the term 'standard deviation'.[1 mark]
  9. 2(d)(iv)Using the following equation, justify the choice of the titre values selected in (d)(ii). S = √[Σ(x-x)² / (n-1)][3 marks]
  10. 2(e)When 0.612 g of hydrated barium chloride is heated to constant mass, 0.522 g of residue is formed. Deduce the formula of hydrated barium chloride.[4 marks]
  11. 2(f)Outline FIVE experimental steps that should be carried out to determine the ethanoic acid content of the vinegar.[5 marks]

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