Each student in a class of nine students performs an experiment to find the formula of a chloride of iron. Each student prepares the chloride of iron by passing a stream of chlorine gas over a sample of iron wire as shown in the diagram. [Figure 2.1]

1. (a)(i)Each student carries out the following steps in the order shown in the list. Some of the measurement steps are missing from the list. • Weigh the reaction tube containing a quantity of iron wire. • Set up the apparatus as shown in the diagram. • Start the flow of dry chlorine gas. • Heat the iron wire until it has completely reacted. • Allow the apparatus to cool, with chlorine gas still flowing. • Weigh the side-arm conical flask containing the chloride of iron. State the two additional measurement steps that each student must perform in order to find the formula of the chloride of iron. 1 2[1]
2. (a)(ii)The flow of dry chlorine gas must start before the iron wire is heated. Explain why.[1]
3. (a)(iii)State an assumption that has to be made for the measurements made in this experiment to be valid.[1]
4. (b)(i)The class results are shown in the table. student | mass of iron wire /g | mass of iron chloride /g | mass of chlorine /g | amount of iron /mol | amount of chlorine atoms /mol ---|---|---|---|---|--- 1 | 0.57 | 1.64 | | | 2 | 1.10 | 3.16 | | | 3 | 1.40 | 4.03 | | | 4 | 1.95 | 5.61 | | | 5 | 2.18 | 5.89 | | | 6 | 2.75 | 7.90 | | | 7 | 3.05 | 8.77 | | | 8 | 3.45 | 9.80 | | | 9 | 3.90 | 11.18 | | | Calculate the mass of chlorine that reacts with the iron wire in each experiment. Record each mass to two decimal places. Calculate the amount of iron, in mol, and amount of chlorine atoms, in mol, that reacts in each experiment. Record the number of moles to three significant figures. [Ar: Fe, 55.8; Cl, 35.5][3]
5. (b)(ii)Plot a graph on the grid of the amount of chlorine atoms against the amount of iron. Use a cross (x) to plot each data point. Draw a line of best fit through the plotted points. You should consider whether (0,0) should be on the line of best fit.[2]
6. (b)(iii)Circle the point on the graph you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure.[2]
7. (c)Use the graph to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be on your line of best fit. Give your answer to three significant figures. coordinates 1 coordinates 2 gradient =[2]
8. (d)The formula of the chloride of iron produced in this experiment is FeCl₃. State how the results student 4 obtains could be used to determine this formula.[1]
9. (e)(i)Student 3 weighs the conical flask using a balance accurate to two decimal places and records its mass. After the chloride of iron is produced the mass increases by 4.03 g. Calculate the percentage error in measuring the mass of this chloride of iron. percentage error =[1]
10. (e)(ii)Student 8 follows the same procedure as student 3. State whether the results from student 8 will have more or less percentage error than those from student 3. Explain your answer.[1]
11. (f)(i)Another student suggested that the chloride of iron could also be prepared by the reaction between iron wire and hydrochloric acid. A sample of a chloride of iron prepared in this way contains 44% iron by mass. Show that the formula of this chloride of iron is FeCl₂. [Ar: Fe, 55.8; Cl, 35.5][1]
12. (f)(ii)Explain, using the electrode potential values in the table, why the methods in (a) and (f) do not produce the same chlorides of iron. reaction | electrode potential, E/V ---|--- Fe²⁺(aq) + 2e⁻ ⇌ Fe(s) | -0.44 2H⁺(aq) + 2e⁻ ⇌ H₂(g) | 0.00 Fe³⁺(aq) + e⁻ ⇌ Fe²⁺(aq) | +0.77[1]

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