Page 472 - SUBSEC October 2017_Neat

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2. After being opened and used, a bottle of AR iron (II) sulphate was left on the laboratory shelf
for some time. 10 g of the sample were then dissolved in some dilute suphuric acid and 1 dm 3
of solution was prepared. 20 cm of this solution was placed in a conical flask and titrated with
3
0.02 mol dm KMnO (aq) / H (aq). The ionic equation for the reaction is
+
-3
4
5Fe (aq) + MnO (aq) + 8H (aq) → 5Fe (aq) + Mn (aq) + 4H O (l).
2+
+
3+
2+−
4− 2
Figure 1 below shows the readings on the burette before and after each titration. DO NOT WRITE IN THIS AREA

Figure 1. Readings on the burette DO NOT WRITE IN THIS AREA

(a) (i) What colour change would you expect at the end point of the reaction?

................................................................................................................................
[1 mark]

(ii) Complete Table 2 to record the tritration results. You should include the initial and
final burette readings and the volumes of KMnO (aq)/H (aq) used.
+
4
TABLE 2: TITRATION RESULTS

1 2 3

Final burette reading (cm )
3
Initial burette reading (cm )
3
Volume of KMnO used (cm ) DO NOT WRITE IN THIS AREA
3
4
[4 marks]

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