4. Electrochemistry
A section of Chemistry, 0620
Listing 10 of 500 questions
The diagram shows an electrolysis cell for extracting sodium from molten sodium chloride. – – + – + B C D A sodium E molten sodium chloride sodium power supply Which letter on the diagram represents the electrolyte? the cathode? Which one of the following substances is most likely to be used as the anode? Put a ring around the correct answer. graphite sodium sulfur zinc What information from the diagram suggests that sodium is less dense than molten sodium chloride? Predict the product formed at the anode during this electrolysis. Name the gases formed at the anode and cathode when an aqueous solution of sodium chloride is electrolysed. product at the anode product at the cathode
0620_w11_qp_21
THEORY
2011
Paper 2, Variant 1
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Lithium has two naturally-occurring isotopes, Li and Li . What do you understand by the term isotope? Draw a labelled diagram to show the atomic structure of an atom of Li . Show the particles in the nucleus as well as the electrons. Lithium reacts with oxygen to form lithium oxide, Li2O. Complete the equation for this reaction. Li + → Li2O Aqueous lithium chloride is electrolysed using the apparatus shown below. + – On the diagram above, label: ● the electrolyte ● the anode. What do you understand by the term aqueous? Explain why aqueous lithium chloride is able to conduct electricity.
0620_w12_qp_21
THEORY
2012
Paper 2, Variant 1
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During electrolysis, ions move in the electrolyte and electrons move in the external circuit. Reactions occur at the electrodes. The diagram shows the electrolysis of molten lithium iodide. molten lithium iodide electrode electrode + – external circuit heat Draw an arrow on the diagram to show the direction of the electron fl ow in the external circuit. Electrons are supplied to the external circuit. How and where is this done? Explain why solid lithium iodide does not conduct electricity but when molten it is a good conductor. The results of experiments on electrolysis are shown in the following table. Complete the table. The fi rst line has been done as an example. electrolyte electrodes product at cathode product at anode change to electrolyte molten lithium iodide carbon lithium iodine used up aqueous copper(sulfate platinum oxygen concentrated aqueous potassium chloride carbon chlorine The diagram below shows the electrolysis of dilute sulfuric acid. Hydrogen is formed at the negative electrode and oxygen at the positive electrode and the concentration of sulfuric acid increases. carbon cathode dilute sulfuric acid bubbles of hydrogen gas bubbles of oxygen gas carbon anode + – The ions present in the dilute acid are H+, OH–and SO4 2–. Write an equation for the reaction at the negative electrode . Complete the equation for the reaction at the positive electrode . 4OH–→ O2+ H2O+ Suggest an explanation of why the concentration of the sulfuric acid increases. In the apparatus used in , the power supply is removed and immediately replaced by a voltmeter. carbon cathode dilute sulfuric acid bubbles of hydrogen gas bubbles of oxygen gas carbon anode V voltmeter A reading on the voltmeter shows that electrical energy is being produced. Suggest an explanation for how this energy is produced.
0620_w12_qp_32
THEORY
2012
Paper 3, Variant 2
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Questions Discovered
500