Download Electrolysis Test 1.pdf and more Exams Analytical Chemistry in PDF only on Docsity!
Most experiments involving electrolysis use inert electrodes, which do not take part in the reactions. However, in some experiments the electrodes do take part in the reactions. A student investigates the electrolysis of copper(II) sulfate solution using copper electrodes which do take part in the reaction. She uses this apparatus. She uses this method.
t weigh two clean strips of copper
t use one strip as the positive electrode and the other as the negative electrode
t after electrolysis wash the strips of copper with ethanol (a liquid that boils at 78°C)
t dry the strips of copper and reweigh them
The ionic half-equations for the reactions at the electrodes are Positive electrode Cu(s) – 2e–^ → Cu2+(aq) Negative electrode Cu2+(aq) + 2e–^ → Cu(s) (a) Suggest why the copper strips would dry more quickly when washed with ethanol rather than with water. (1) .................................................................................................................................................................................................................................................................................... power supply positive electrode lamp negative electrode copper(II) sulfate solution
Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
(b) The student’s results are shown in the table. Positive electrode Negative electrode Mass of electrode before electrolysis in g 8.78 7. Mass of electrode after electrolysis in g 8.46 8. The table shows that the decrease in mass of the positive electrode was 0.32 g. (i) Calculate the increase in mass, in grams, of the negative electrode. (1) Increase in mass = .........................................g (ii) The ionic half-equations show that the increase in mass of the negative electrode should be the same as the decrease in mass of the positive electrode. Suggest two reasons why the increase in mass of the negative electrode in the student’s experiment was less than expected. (2) 1 ............................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 2 ............................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
(iii) Suggest why the straight line should go through the origin. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iv) Explain why the graph shows that the increase in mass is directly proportional to the electrical charge passed. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (v) Use your graph to estimate the increase in mass, in grams, of the copper electrode that would be produced by passing an electrical charge of 0.55 faradays. (2) Increase in mass = ..............................................................................g (Total for Question = 12 marks) Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
The diagram shows how sodium chloride solution can be electrolysed and the products of electrolysis collected. (a) (i) Draw an arrow on the diagram to show the direction of electron flow at point X. (1) (ii) The diagram shows one of the gases being collected in test tube Q. Identify this gas. (1) .................................................................................................................................................................................................................................................................................... (iii) When the concentration of the sodium chloride solution is low, the gas collected in test tube P is mostly oxygen. The formation of this gas can be represented by an ionic half-equation. Balance the equation. (1) ..........................OH−^ !" ..........................H 2 O + ..........................O 2 + ..........................e−
P Q
sodium chloride solution X power supply
- – Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
(d) Chlorine is used in the manufacture of phosphorus pentachloride, PCl 5 The equation for the reaction is: PCl 3 (g) + Cl 2 (g) !"PCl 5 (g) !H = −124 kJ/mol (i) What does the !"symbol indicate about this reaction? (1) .................................................................................................................................................................................................................................................................................... (ii) Predict and explain the effect of increasing the pressure on the equilibrium position of this reaction. (2) Prediction ...................................................................................................................................................................................................................................................... Explanation .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question = 12 marks) Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
The apparatus shown in the diagram can be used to investigate the colours of the cobalt(II) ion (Co2+) and the chromate ion (CrO 4 2–) in cobalt(II) chromate. electrode A power supply water cobalt(II) chromate solution electrode B
These are the results of the experiment. Ɣ a pink colour moves towards electrode A Ɣ a yellow colour moves towards electrode B (a) Explain how the results show that the chromate ion is yellow. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) (i) Chromate ions in aqueous solution can be converted into dichromate ions (Cr 2 O 72 −) by the addition of hydrogen ions. Balance the equation that represents this reaction. (1) ................CrO 42 −(aq) + ................H+(aq) o ................Cr 2 O 72 −(aq) + ................H 2 O(l) (ii) Which solution is a source of hydrogen ions for this reaction? (1) A H 2 O 2 (aq) B HCl(aq) C NaOH(aq) D NH 3 (aq) Fo moe aeome GCSE and A leel eoceǡ ii a ZZZ.VaYem\e[amV.co.Xk/
