Section B Bahagian B. [20 marks] [20 markah] Answer any one questions from this section. Jawab mana-mana satu soalan daripada bahagian ini.

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1 Section B Bahagian B [20 marks] [20 markah] Answer any one questions from this section. Jawab mana-mana satu soalan daripada bahagian ini. 1. (a) What is meant by electrolysis? Apakah yang dimaksudkan dengan elektrolisis? [2 marks/markah] (b) Diagram below shows the apparatus set up for the electrolysis molten lead (II) bromide. Rajah di bawah menunjukkan susunan radas bagi elektrolisis plumbum (II) bromida lebur. Diagram/Rajah (i) Explain why lead (II) bromide is heated during electrolysis. Terangkan mengapakah plumbum(ii) klorida dipanaskan semasa elektrolisis. [6 marks/markah] (ii) What can be observed in this experiment? Explain how the products are formed at the electrodes. Apakah yang dapat diperhatikan dalam eksperiment tersebut? Terangkan bagaimana hasil tindak balas terbentuk pada elektrod-elektrod. [12 marks/markah]

2 2. (a) Table below shows the results of a series of experiments carried out to construct the electrochemical series. The positive terminal and value for the potential difference for the pair of metals X and copper, Cu are not given. W, X and Y are not the actual symbols of the metals. Jadual di bawah menunjukkan keputusan satu siri eksperimen yang telah dijalankan untuk membina siri elektrokimia. Terminal positif dan nilai beza keupayaan bagi pasangan logam X dan kuprum, Cu tidak diberi. W, X dan Y bukan simbol sebenar logam-logam itu. Table Jadual (i) Based on the values of the potential differences, arrange the metals in descending order in the electrochemical series. Berdasarkan nilai beza keupayaan, susun logam-logam tersebut dalam tertib menurun dalam siri elektrokimia. [1 mark] [1 markah] (ii) Predict the value of the positive terminal and the potential difference for the pair of metals X and Cu. Explain your answer. Ramal nilai terminal positif dan beza keupayaan bagi pasangan logam X dan Cu. Jelaskan jawapan anda. [3 marks] [3 markah]

3 (b) Diagram below shows a voltaic cell. Metal Q is situated below copper in the electrochemical series. Rajah di bawah menunjukkan suatu sel voltan. Logam Q terletak di bawah kuprum dalam siri elektrokimia. Diagram Rajah State the positive terminal and the negative terminal of this cell. Suggest a metal that is suitable as metal Q and a solution that is suitable as solution R. Nyatakan terminal positif dan terminal negatif bagi sel ini. Cadangkan logam yang sesuai sebagai logam Q dan larutan yang sesuai sebagai larutan R. [4 marks] [4 markah] (c) Experiment I and experiment II are carried out to investigate the factors affecting the discharge of ions at the electrodes. Table below shows the apparatus set-up and the observations for experiment I and experiment II. Eksperimen I dan eksperimen II dijalankan untuk menyiasat faktor yang mempengaruhi nyahcas ionion pada elektrod-elektrod. Jadual di bawah menunjukkan susunan radas dan pemerhatian bagi eksperimen I dan eksperimen II.

4 Table Jadual (i) Name the products formed at the anodes and cathodes in experiment I and experiment II. Explain your answer using half-equations. Namakan hasil yang terbentuk di anod dan di katod dalam eksperimen I dan eksperimen II. Jelaskan jawapan anda dengan menggunakan setengah persamaan. [10 marks] [10 markah] (ii) A solution of common salt, sodium chloride, is electrolysed using carbon electrodes. Write a half-equation for the reaction at the cathode. Larutan garam biasa, natrium klorida, dielektrolisis menggunakan elektrod karbon. Tulis setengah persamaan bagi tindak balas yang berlaku di katod. [2 marks] [2 markah]

5 Answer Scheme Chapter 6 Form 4 Paper 2 1. (a) A process by which a compound in the molten or aqueous state is broken down into its constituent elements [1 m] when an electric currents is passed through it. [1 m] (b) i. In solid lead (II) chloride, lead (II), Pb 2+ ions and bromide Br ions are not free to move. [1 m] Lead (II) bromide is heated until molten [1 m] to obtain free moving lead(ii) ions and bromide ions. [1 m] lead(ii), Pb 2+ ions are attracted to the cathode while [1 m] bromide Br ions are attracted to the anode [1 m] when the switch is on and the circuit is completed. [1 m] ii. The pointer of the ammeter deflected when the switch is on. [1 m] A grey solid is deposited at the cathode and [1 m] a brown gas is collected in syringe [1 m] In molten lead(ii) bromide, the lead(ii), Pb 2+ ions and bromide, Br ions are free to move. [2 m] The Pb 2+ ions are attracted to the anode when the carbon electrodes are dipped into the switch and the switch in on. [3 m] The Pb 2+ ions are discharged at the cathode by accepting electrons to form lead [1 m Br ions are discharged at the anode by donating electrons to form bromine gas [1 m] cathode: Pb e Pb [1 m] anode: 2Br Br + 2e [1 m] 2.(a) (i) (ii) Positive terminal is Cu. Terminal positif ialah Cu. The potential difference is 1.3 V Perbezaan keupayaan ialah 1.3 V (b) The positive terminal is Q and the negative terminal is Cu. Terminal positif ialah Q dan terminal negatif ialah Cu. Suitable metal for Q = silver Logam sesuai untuk Q = argentum Suitable Solution for R = silver nitrate solution Larutan sesuai untuk R = larutan argentum nirat (c) (i) Experiment I: Eksperimen I: Product formed at the anode is oxygen. Hasil yang dibentuk pada anod ialah oksigen. The anions presence are OH and I Anion-anion yang ada ialah OH dan I OH ions are preferentially to be discharged as shown in the equation below. Ion OH diutamakan untuk dinyahcas seperti yang ditunjukkan dalam persamaan berikut. 4OH 2H 2 O + O 2 + 4e

6 This happens because the concentration of I is too low. Ini berlaku kerana kepekatan I terlalu rendah. The product formed at the cathode is hydrogen. The cations present are H + and K +. Hasil yang dibentuk pada katod ialah hidrogen. Kation-kation yang hadir ialah H + dan K +. Potassium occupies too high a position in the electrochemical series. Thus, H+ ions are preferentially discharged as shown in the equation below. 2H + + 2e H 2 Kalium mengambil kedudukan yang terlalu tinggi dalam siri elektrokimia. Jadi ion H + diutamakan untuk dinyahcas seperti yang ditunjukkan dalam persamaan di bawah. 2H + + 2e H 2 Experiment II: Eksperimen II: The product formed at the anode is iodine. Hasil yang dibentuk pada anod ialah iodin. The electrolyte used is a concentrated solution of potassium iodide. Thus, the concentration of I is very high. Due to its high concentration it is, preferentially to be discharged compared to OH. 2I I 2 + 2e Elektrolit yang digunakan mempunyai larutan pekat kalium iodida. Jadi larutan pekat I turut menjadi tinggi. Disebabkan kepekatan yang tinggi maka ia diutamakan untuk menyahcas berbanding dengan OH. 2I I 2 + 2e The product formed at the cathode is hydrogen. Hasil yang dibentuk pada katod ialah hidrogen. Both H + ions and K + ions are attracted to the cathode but H + ions are preferentially discharged because of the lower position in the electrochemical series. 2H + + 2e H 2 Kedua-dua ion H + dan ion K + adalah ditarik ke katod. Akan tetapi cuma ion H + dinyahcaskan kerana kedudukan yang lebih rendah dalam siri elektrokimia. 2H + + 2e H 2 (ii) At the cathode: 2H + + 2e H 2 Pada katod : 2H + + 2e H 2

Section B Bahagian B. [20 marks] [20 markah] Answer any one questions from this section. Jawab mana-mana satu soalan daripada bahagian ini.

Section B Bahagian B. [20 marks] [20 markah] Answer any one questions from this section. Jawab mana-mana satu soalan daripada bahagian ini. Section B Bahagian B [20 marks] [20 markah] Answer any one questions from this section. Jawab mana-mana satu soalan daripada bahagian ini. 1. (a) Diagram below shows the structural formulae of four organic