Chemistry 30

Print out the practice set	Word	RTF	PDF
Print out the answers	Word	RTF	PDF

---

1. Using either an activity series (Table 11.2) or Table of Standard Reduction Potentials, predict whether a reaction takes place, and if so, give a balanced reaction equation.

   a. Ag_(s) + HCl_(aq)

   Answer:

    Using Activity Series we determine no reaction will occur since Ag is lower on the list than H.

    Using Standard Reduction Potentials:

   Write out half-reactions in a way that will produce the equation in question (that is with solid Ag and aqueous H⁺ ions as reactants (Cl^- will be a spectator ion). Remember to reverse the sign of E° if you reverse an equation:

	E°
Ag(s) → Ag+ + e-	-0.80
2H+ + 2e- → H2	0.00
Net Voltage	-0.80

Conclusion – since the voltage (E°) is negative, the reaction WILL NOT BE spontaneous. No reaction will occur.

---

 b. Mg_(s) + FeSO_4(aq)

Answer:

 Using Activity Series we find that a reaction will occur because Mg is higher on the list than Fe.

Using Standard Reduction Potentials:

SO₄^2- will be a spectator ion.

	E°
Mg(s) → Mg2+ + 2e-	+2.37
Fe2+ + 2e- →Fe	-0.45
Net Voltage	+1.92

Conclusion – since a positive voltage results, the reaction WILL BE spontaneous.

The balanced equation for the reaction will be:

Mg_(s) + FeSO_4(s) → MgSO_4(aq) + Fe_(s)

---

c. Cu_(s) + AuCl_3(aq)

Answer:

Using Activity Series we find that a reaction will occur because Cu is higher on the list than Au

Using Standard Reduction Potentials:

Cl^- will be a spectator ion.

	E°
Cu(s) → Cu2+ + 2e-	-0.34
Au3+ + 3e- → Au	+1.50
Net Voltage	+1.1

Conclusion – since a positive voltage results, the reaction WILL BE spontaneous.

The balanced equation for the reaction will be:

3 Cu_(s) + AuCl_3(aq) → 3 CuCl_{2 (aq)} + 2 Au_(s)

---

d. Sn_(s)+ Al₂(SO₄)_3(s)

Answer:

Using Activity Series - no reaction. Sn is lower on the list than Al

Using Standard Reduction Potentials:

SO₄^2- will be a spectator ion.

	E°
Sn(s) → Sn2+ + 2e-	+0.14
Al3+ + 3e- → Al	-1.66
Net Voltage	-1.52

Conclusion – since the voltage is negative, this reaction WILL NOT BE spontaneous.

---

2. Consider the electrolysis of water. Describe the events at the anode in terms of

a. the reaction	Oxidation always occurs at the anode. Thus the anode reaction is 2 H2O(l) → O2 (g) + 4 H+(aq) + 4 e-
b. pH	H+ is being produced. As [H+] increases, pH decreases (the solution becomes more acidic)
c. gas produced	O2 gas is produced at the anode

Return to Notes