12188 12 The reaction between iron(III) and iodide ions may be studied in a cell as shown below. voltmeter – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – - – – – – – – – – – – – – – – – – – – – – – – – – V salt bridge solution of potassium iodide solution of iron(III) chloride Pt Pt A solution of iron(III) chloride is placed in one beaker and a solution of potassium iodide in the other beaker. A salt bridge connects the beakers. (a) The salt bridge can be made using a glass tube or paper. (i) Name a chemical which is usually used to make a salt bridge. [1] (ii) Describe how you would make a salt bridge from paper in the laboratory. [1] (iii) State two reasons for using a salt bridge in an electrochemical cell. [2] 12188 [Turn over (b) The electrode potentials for the two half-cells taking place in the reaction are: Fe3+(aq)  +  e ⇌ Fe2+(aq) +0.77 V I2(aq)  +  2e ⇌ 2I−(aq) +0.54 V (i) Calculate the emf of the cell. [2] (ii) Write a conventional representation for the cell. [2] (iii) Write the equation for the reaction taking place. [1] (iv) Explain which way electrons will flow in the cell. [2] 12188 (c) Before the cell operates Fe3+ ions and I− ions are present. After the cell operates Fe2+ ions are present together with I2 molecules. State how you would test for each of these species and the results expected for positive tests. (i) Fe3+ [2] (ii) Fe2+ [2] (iii) I− [2] (iv) I2 [2] 12188 BLANK PAGE DO NOT WRITE ON THIS PAGE (Questions continue overleaf) [Turn over