Chemistry_Grade_10-12 (1).pdf

A the anode in an electrolytic cell has a negative

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(a) The anode in an electrolytic cell has a negative charge. (b) The reaction 2KClO 3 2KCl + 3O 2 is an example of a redox reaction. (c) Lead is a stronger oxidising agent than nickel. 2. For each of the following questions, choose the one correct answer. (a) Which one of the following reactions is a redox reaction? i. HCl + NaOH NaCl + H 2 O ii. AgNO 3 + NaI AgI + NaNO 3 iii. 2 FeCl 3 + 2 H 2 O + SO 2 H 2 SO 4 + 2 HCl + 2 FeCl 2 iv. BaCl 2 + MgSO 4 MgCl 2 + BaSO 4 (IEB Paper 2, 2003) (b) Consider the reaction represented by the following equation: Br 2( l ) + 2 I aq 2 Br aq + I 2( s ) Which one of the following statements about this reaction is correct? i. bromine is oxidised ii. bromine acts as a reducing agent iii. the iodide ions are oxidised iv. iodine acts as a reducing agent (IEB Paper 2, 2002) (c) The following equations represent two hypothetical half-reactions: X 2 + 2 e 2 X (+1.09 V) and Y + + e Y (-2.80 V) Which one of the following substances from these half-reactions has the greatest tendency to donate electrons? i. X ii. X 2 iii. Y iv. Y + (d) Which one of the following redox reactions will not occur spontaneously at room temperature? i. Mn + Cu 2+ Mn 2+ + Cu ii. Zn + SO 2 4 + 4 H + Zn 2+ + SO 2 + 2 H 2 O iii. Fe 3+ + 3 NO 2 + 3 H 2 O Fe + 3 NO 3 + 6 H + iv. 5 H 2 S + 2 MnO 4 + 6 H + 5 S + 2 Mn 2+ + 8 H 2 O (e) Which statement is CORRECT for a Zn-Cu galvanic cell that operates under standard conditions? i. The concentration of the Zn 2+ ions in the zinc half-cell gradually de- creases. ii. The concentration of the Cu 2+ ions in the copper half-cell gradually increases. iii. Negative ions migrate from the zinc half-cell to the copper half-cell. iv. The intensity of the colour of the electrolyte in the copper half-cell gradually decreases. (DoE Exemplar Paper 2, 2008) 3. In order to investigate the rate at which a reaction proceeds, a learner places a beaker containing concentrated nitric acid on a sensitive balance. A few pieces of copper metal are dropped into the nitric acid. (a) Use the relevant half-reactions from the table of Standard Reduction Po- tentials to derive the balanced nett ionic equation for the reaction that takes place in the beaker. (b) What chemical property of nitric acid is illustrated by this reaction? (c) List three observations that this learner would make during the investiga- tion. 351
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17.7 CHAPTER 17. ELECTROCHEMICAL REACTIONS - GRADE 12 (IEB Paper 2, 2005) 4. The following reaction takes place in an electrochemical cell: Cu ( s ) + 2 AgNO 3 ( aq ) Cu ( NO 3 ) 2 ( aq ) + 2 Ag ( s ) (a) Give an equation for the oxidation half reaction. (b) Which metal is used as the anode? (c) Determine the emf of the cell under standard conditions. (IEB Paper 2, 2003) 5. The nickel-cadmium (NiCad) battery is small and light and is made in a sealed unit. It is used in portable appliances such as calculators and electric razors.
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