Quelpr
3 marksMole Concept

CSEC Chemistry · January 2016 · Paper 2 · Question 1(b)(i)

Carol investigated the effect of concentration on reaction rate using aqueous potassium iodate (KIO₃) and aqueous sodium hydrogen sulfite (NaHSO₃) with sulfuric acid and starch. The time for a blue-black color to appear was noted. The reactions are: NaHSO₃ + H₂SO₄ → H₂SO₄ + NaHSO₄; KIO₃ + 3H₂SO₃ → KI + 3H₂SO₄; KIO₃ + 3H₂SO₃ + 5KI → 3K₂SO₄ + 3H₂O + 3I₂; I₂ + starch → starch-I₂ complex (blue-black). Solution 1 is 100 cm³ of aqueous KIO₃ (0.214 g). Solution 2 is 100 cm³ of a mixture of aqueous NaHSO₃, sulfuric acid, and starch. Solution X is 50 cm³ of aqueous KIO₃ of unknown concentration. Experiment 6 replaced Solution 1 with Solution X. Results are in Table 1.

Calculate the concentration, in mol dm⁻³, of KIO₃ in Solution 1. [RAM: K = 39.1, I = 126.9, O = 16.0]

This question uses a figure or table from the paper — you'll see it when you practise.

The mark scheme is shown once you've answered.

Practise this question

Other parts of this question

  1. 1(a)(i)Define the term 'rate of reaction'.[1 mark]
  2. 1(a)(ii)State TWO factors, other than concentration, which affect the rate of a chemical reaction.[2 marks]
  3. 1(b)(ii)The final concentration of NaHSO₃ in all experiments was 0.0008 mol dm⁻³. Using the information provided in Table 1 on page 6, determine the concentration of…[2 marks]
  4. 1(c)(i)From the stopwatches displayed in Figure 1 on page 7, record the times taken for the blue-black colour to appear in the appropriate spaces in Table 1. The time…[3 marks]
  5. 1(c)(ii)Calculate the reciprocal times (1/time) and record them to 3 decimal places in the appropriate spaces in Table 1. One of the times has already been recorded…[3 marks]
  6. 1(c)(iii)Using the axes provided on page 8, plot a graph of concentration of KIO₃ versus reciprocal time for Experiments 1-5, and draw the best straight line through…[5 marks]
  7. 1(d)Based on the graph drawn in (c) (iii) on page 8, what deduction can be made about the effect of concentration of aqueous KIO₃ on the rate of reaction?[2 marks]
  8. 1(e)Experiment 6 was carried out using Solution X, which contained an unknown concentration of KIO₃. Using the reciprocal time calculated in Experiment 6,…[2 marks]
  9. 1(f)(i)State the responding variable.[1 mark]
  10. 1(f)(ii)State the controlled variable.[1 mark]

More practice: the rest of this paper · more Mole Concept questions · all CSEC Chemistry past papers