Chemistry 30
Redox Reactions & Electrochemistry					60

I.	Multiple Choice				20

	1.	B
	2.	C
	3.	D
	4.	B
	5.	B	
6.	A
7.	C
8.	D
9.	B
10.	C
11.	C
12.	C
13.	C
14.	A
15.	C
16.	D
17.	D
18.	D
19.	B
20.	C

II.	Short Answer				35

	1.	Determine the oxidation number of each element in the following:	4 marks

	a.	MgCl2		Mg = ____+2____	Cl = _____-1________

	b.	H2SO4		H = ____+1______	S = _____+6_________	O = ____-2______

	c.	PO43-		P = ____+5______	O = _____-2_________

	d.	NH4+		N = ____-3______	H = _____+1__________

2.	a.	Show, by the change in oxidation numbers, that the following equation represents a redox reaction.
	b.	Identify the elements that undergo oxidation and reduction.
	c.	Also identify the oxidizing agent and the reducing agent.		3 marks			
			I2 + SO32- + 2 OH-  H2O + SO42- + 2I-

		Element oxidized:  __________S__________		Element reduced: ______I______________

		Oxidizing agent:	_________I2__________		Reducing agent:   ____SO32-____________

3.	Balance the following redox reactions, using either the oxidation number method or the half-reaction method.
							6 marks
	a.	    2 HBr  +   1  H2SO4       1  SO2   +    1  Br2   +   2  H2O

	b.	     2 MnO4-   +    5  H2S   +     6 H+      5  S   +    2  Mn2+   +  8  H2O

	c.	   2 NF3   +     2 AlCl3        1 N2   +    3  Cl2   +   2   AlF3

4.	Will a reaction occur if a copper(II) sulfate solution is stored in an aluminum container?  Explain and support your answer (a “yes” or “no” alone is not worth any marks) and provide a balanced equation.	3 marks

		2 Al + 3 Cu2+  2 Al3+ + 3 Cu
		There are different ways to solve this question. One method is to calculate Eo. This is found to be +2.00 (students should show work to support this). Because Eo is positive, the reaction will be spontaneous.
		An activity series may be used instead.

5.	Write the two balanced half-reaction equations for the following reaction, and identify each half-reaction as oxidation or reduction.			4 marks

		Ca(s) + F2(g)  CaF2(s)
	
			oxidation:  Ca  Ca2+ + 2e-
			reduction: F2 + 2e-  2 F-

6.	Use a table of standard reduction potentials to determine the voltage of the following electrode pairs.  
							4 marks
	a.	Co|Co2+   and   Mg|Mg2+

				Co2+ + 2 e-  Co	Eo = -0.28
				Mg  Mg2+ + 2 e-	Eo = +2.37
				net voltage:	Eo = +2.09

	b.	Cl-|Cl2   and   Ni|Ni2+
			
			Cl2 + 2 e-  2 Cl-	Eo =  +1.36
			Ni  Ni2+ + 2 e-	Eo = +0.26
			net voltage:	Eo = 1.62

7.	Use a table of standard reduction potentials or activity series to determine whether or not the following reactions will occur spontaneously. If it does, write a balanced equation for the reaction. Write N.R. if a reaction does not occur.			4 marks

	a	Cr3+ + K(s)   Cr + 3 K+

	b.	Mn2+ + Zn(s)  NR	Eo = -0.43.  Not a spontaneous reaction

8.	Refer to a table of standard reduction potentials to complete the following diagram and questions concerning the electrochemical cell created using copper and silver half-cells:	8 marks

	a.	Write the equation for the oxidation half-reaction:	(1 mark)

			Cu  Cu2+ + 2 e-

	b.	Write the equation for the reduction half-reaction:	(1 mark)

			Ag+ + e-  Ag

	c.	What is the voltage produced by this cell:	(2 marks)

			0.46 V
	d.	Label the following items on the diagram:	(4 marks)
•	
•	anode
•	cathode
•	positive post
•	negative post
•	direction of flow of electrons
•	direction of flow of cations and anions from the salt bridge (show on the diagram or describe below)

9.	In the electrolytic cell shown here, an iron nail is being plated with copper.	4 marks

	a.	Which object, the iron nail or the copper bar, should be connected to the negative post of the battery?

			the iron nail

	b.	Write the equation for the half-reaction that occurs at the cathode of the electrolytic cell.

			Cu2+ + 2 e-  Cu

	c.	Write the equation for the half-reaction that occurs at the anode of the electrolytic cell.

			Cu  Cu2+ + 2 e-

	d.	Show on the diagram the flow of electrons both entering and leaving the battery.

			see diagram above