2

2. Spinach leaves were boiled in water for varying times. The water was cooled and tested for the presence of Fe$^{2+}$ ions by titration with standardized potassium manganate(VII) solution, KMnO$_4$ (aq).

(a) Three trials were performed for each boiling time. In each trial, 10.0 g of spinach was boiled in a beaker containing 250 cm$^3$ of tap water for 5, 10, 15, and 20 minutes. The spinach was removed by filtration and the solution was bottled and stored in a refrigerator until titration was performed.

(i) State the independent and dependent variables. [1]

(ii) Suggest two additional experimental conditions that should be controlled to ensure that the methodology of this investigation is valid. [2]

(iii) Suggest an additional trial that should be performed so that it can be determined how much Fe$^{2+}$ was extracted only from the spinach leaves. [1]

(iv) Discuss two difficulties that a student might experience when determining the end point of this titration. [2]

(b) The average results from (a) were graphed.

{{figure_desc:fig-2|graph of Amount of Fe$^{2+}$ (×10⁻³ mol) vs Boiling time (minutes)}}

(i) State the relationship shown in the graph between the amount of Fe$^{2+}$ released from the spinach and the boiling time. [1]

(ii) Comment on the range and quantity of measurements used in the investigation. [2]

(c) The initial hypothesis was that more Fe$^{2+}$ would be extracted from the spinach leaves as the boiling time increased.

(i) Evaluate, giving a reason, whether the results support the hypothesis. [1]

(ii) Suggest one modification to the investigation that would make it more suitable for testing the hypothesis. [1]