ACSBR 16 Electrolysis - Assignment

Anglo-Chinese School (Barker Road) A Methodist Institution Founded in 1886 CHEMISTRY DEPARTMENT OF SCIENCE Name: ( ) Class: SEC 4 ELECTROLYSIS – ASSIGNMENT ALEX LEE/2010 PAGE 1 OF 7 PURE Multiple-Choice Questions [20 Marks] TOTAL SCORE / 30 Write in your selected answer for the multiple-choice questions in the boxes provided. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1. The circuit below was set-up, using an unknown substance Q. It was observed that the bulb lit, but there were no decomposition products at the electrodes. What is Q? A aqueous sodium chloride C molten sodium chloride B mercury D sugar solution 2. When the experiment below was set-up, the ammeter showed that no current was flowing. A few drops of dilute sulfuric acid were dissolved in liquid Z and the ammeter then showed that a current was flowing. What could Z be? A aqueous NaOH C ethanol B concentrated NaCl D water

ALEX LEE/2010 PAGE 2 OF 7 3. Two cells, containing substances X a n d Y r e s p e c t i v e l y, were connected in series with a battery and a light bulb, as shown in the diagram below. In which of the following pairs of substances did the bulb light up? in X in Y A aqueous copper(II) sulfate solid lead(II) bromide B aqueous potassium sulfate dilute hydrochloric acid C concentrated hydrochloric acid pure ethanoic acid D concentrated sodium chloride concentrated sugar solution 4. Which one of the following does not yield any gaseous products? electrolyte electrodes A aqueous copper(II) sulfate platinum B aqueous silver nitrate copper C concentrated sodium chloride copper D dilute sulfuric acid platinum 5. A liquid is to be electrolysed, and two test-tubes full of the liquid are placed over carbon electrodes. The diagram below shows the apparatus after some time. Which one of the following could be the liquid undergoing electrolysis? A aqueous CuSO4 C concentrated NaCl B concentrated HCl D dilute H2SO4 6. Electrolysis of molten lead(II) bromide gives lead at the cathode. Why does lead form? A Lead(II) bromide decomposes on heating. B Lead is less reactive than hydrogen. C Positive lead(II) ions are discharged at the cathode. D The anode dissolves to form lead(II) ions. X Y

ALEX LEE/2010 PAGE 3 OF 7 7. Four electrolysis experiments, each using aqueous copper(II) sulfate as the electrolyte, were set-up as shown below. In which of these four experiments did the concentration of the copper(II) sulfate electrolyte remain constant? A C B D 8. In which one of the following instances is there no change in the pH of the solution during electrolysis? A concentrated sodium chloride solution between platinum electrodes B copper(II) chloride solution between platinum electrodes C copper(II) sulfate solution between copper electrodes D dilute sulfuric acid between copper electrodes 9. The electrolysis shown in the diagram is set up. What is observed? at positive electrode at negative electrode A bubbles of colourless gas bubbles of colourless gas B bubbles of colourless gas solution turns brown C solution turns brown bubbles of colourless gas D solution turns brown silvery droplets 10. An aqueous sample of zinc chloride is electrolyzed using iron electrodes. Which of the following statements, pertaining to the above experiment, is false? A Bubbles of colourless gas are formed at the positive electrode. B The pH of the solution gradually increases. C The solution gradually turns green. D Zinc ions are attracted to the negative electrode. copper platinum platinum graphite copper carbon platinum copper carbon electrodes concentrated aqueous rubidium iodide

ALEX LEE/2010 PAGE 4 OF 7 11. What change always takes place when aqueous copper(II) sulfate is electrolysed? A Copper is deposited at the negative electrode. B Oxygen is evolved at the positive electrode. C Sulfate ions move towards the negative electrode. D The colour of the solution fades. 12. In the diagram below each cell contains an aqueous solution of a single salt and all four electrodes are platinum. Electrodes Q and S increase in mass during the electrolysis but no gas is given off at Q or S. If an increase in mass of Q i s g r e a t e r t h a n t h e i n c r e a s e o f ma s s o f S i n t h e s a me t i me , which of the following statements is necessarily true? A The anions of the solutions in Cells A and B are different. B The cations of the solutions in Cells A and B are different. C The current flowing in Cell A is greater than the current flowing in Cell B. D The solution in Cell A is more concentrated than the solution in Cell B. 13. Which one of the following involves the largest number of electrons for complete discharge during electrolysis? A 3 mol of P3- ions C 5 mol of O2- ions B 4 mol of Al3+ ions D 8 mol of Na+ ions 14. In an electrolysis experiment, the same quantity of electricity deposited 16 g of copper and 6 g of titanium. What was the charge on the titanium ion? A 1+ C 3+ B 2+ D 4+ 15. Dilute sulfuric acid was electrolysed using inert electrodes. What volumes (at r.t.p.) of hydrogen and oxygen were formed by the passage of one mole of electrons? volume of H2 / dm3 volume of O2 / dm3 A 12 6 B 12 24 C 24 12 D 24 24 P Q R S Cell A Cell B

ALEX LEE/2010 PAGE 5 OF 7 16. A sample of copper contained, as an impurity, a metal below it in the reactivity series. The diagram shows the apparatus used for refining the sample. The loss in mass of the positive electrode was 50 g and the gain in mass of the negative electrode was 45 g. What was the percentage purity of this sample of copper? A 10.0% C 90.0% B 11.1% D 95.0% 17. The diagram below shows the electrolysis of an unknown electrolyte. Which of the following could be the electrolyte? A aqueous potassium iodide C concentrated copper(II) sulfate B concentrated copper(II) chloride D concentrated hydrochloric acid 18. A metal spoon is to be electroplated with silver using aqueous silver nitrate as the electrolyte. Which of the following should be used as the cathode? A copper block C silver block B platinum block D spoon 19. The heat-reflecting shields of some space rockets are gold-plated, using electrolysis. Which electrodes and electrolyte would be used to gold-plate the heat shield? negative electrode positive electrode electrolyte A carbon heat shield gold compound B gold heat shield copper compound C heat shield carbon copper compound D heat shield gold gold compound impure copper anode pure copper cathode aqueous copper(II) sulfate

ALEX LEE/2010 PAGE 6 OF 7 20. Aqueous sodium sulfate is electrolysed using copper electrodes. The current is constant and the cathode is weighed at regular intervals over a long period of time. Which graph is obtained when the mass of the cathode is plotted against time? A C B D Structured Questions [10 Marks] 21. A strip of moistened filter paper is laid on a microscope slide. A drop of silver nitrate solution is placed near one end of the paper and a drop of potassium iodide solution is placed near the other end. Using inert electrodes, the apparatus is connected to a suitable d.c. supply. After some time, a pale yellow streak appears as shown below. (a) Briefly explain why a pale yellow streak is formed. [2] (b) Suggest why the streak appears nearer the cathode than the anode. [1] mass time mass time mass time mass time pale yellow streak potassium iodide solution silver nitrate solution damp filter paper cathode anode

ALEX LEE/2010 PAGE 7 OF 7 22. An aqueous solution of calcium hydroxide is electrolyzed between graphite electrodes. (a) State the formula of the produc