Redox unit assessment ANS10 (1)

2. Redox unit assessment(4U) Name:_________________________ Multiple choice (9 marks) 1. A reducing agent can be described as a substance that a. loses electrons and causes reduction. b. loses electrons and becomes reduced. c. gains electrons and causes oxidation. d. gains electrons and becomes reduced. e. gains electrons and becomes oxidized. 2. The oxidation number of the ‘S’ atom in the thiosulfate ion (S 2 O 3 2-) is a.-6 b . +6 c.+4 d . +2 e. 3 . +1 In a galvanic cell, A 4. A porous boundary, or a salt bridge, is required in a standard galvanic cell to a. conduct electrons from the anode to the cathode. b. transfer + ions to the reduction half-cells. c. keep the electrodes from contacting. d. maintain standard conditions in both half cells. e. stop current flow when electrodes are connected. 5. The corrosion of iron is accelerated by a. low humidity. b. lack of oxygen. c. low temperature. d. nonelectrolytes. e. low pH. – increases ion electrolytes 6. Cathodic protection of iron is effective because the iron a. is forced to become the anode of a cell. b. is forced to become the cathode of a cell. c. is no longer a part of any electrochemical cell. d. is attached to the positive terminal of a battery. e. is electrically prevented from gaining electrons.

7. Which of the following is the best reducing agent? A) Tin B) Sodium ion !!! C) Fluorine D) Chlorine E) Lead ** if sodium is a choice it is a better reducing agent than Pb--- my bad!!! 8. Which species(atom) is reduced in the following redox reaction? D 9. Which of the following represents a redox reaction? B Short Answer 1. Consider the following redox reaction: (3 marks) a. Identify the atom that is reduced? _ S 6+ ->4+ _ b. Which atom is oxidized?__ Se 2-  0 ___ c. Which species is the oxidizing agent? ____ SO 4 2- 2. Balance the following redox reaction in basic solution by half reaction method: (4 marks) Changed this Q--- to a better one--- Q: MnO 4 1- + CN-  MnO2(s) + CNO- RED OX 2x[MnO 4 1- +4(H+ + 4OH-)  MnO 2 (s) + 2H 2 O + 4OH-] 3x[ CN- + H 2 O  CNO- 2(H+ +2OH-)] + 3e- 2(4 H 2 O) + 2OH- +2e- 2 H 2 O ----------------------------------------------------------------- _______________________________________ -1 -4 -3 -1 ANS : 2 MnO 4 1- + 3CN-(aq) + 2 H 2 O 6e-  2MnO 2 (s) + 4 OH- (aq) + 3 CNO-(aq) + 6e- Analyze the following galvanic cell.(Zn(NO 3 ) 2 and Ni(NO 3 ) 2 ) 3. a. Which electrode is the cathode(SOA)? _______ (1) Ni2+ + 2e-  Ni(s) b. Draw or label clearly the movement of electrons.(1) c. Write the reduction and oxidation ½ cell e- 

Extra Balance Basic REDOX RED OX X3 [O 2 + 3H+ +3OH- + 2H2O +4e-  OH- + H 2 O +3OH- ] [ Au + 4 Cl1- --> AuCl 4 - + 3e-]x4 then combine ½ reactions and cancel out electrons