Chemistry 202 Unit Section Assignment

Chemistry 3202 Unit 4 Section 2 HWP 2006 Page of

Chemistry 3202 Unit 4 Section 2 Lessons 1-4 Homework Portfolio

2006
Value 2 points
1. Consider this cell notation: Zn|Zn²⁺||Eu³⁺,Eu²⁺|Pt.

(2) (a) Identify the anode and the cathode.

In cell notation, the anode is the solid species listed on the left and the cathode is the species listed on the right. Thus zinc is the anode and platinum is the cathode.

(2) (b) Sketch and label the diagram for the electrochemical cell represented by the cell notation. Include a salt bridge with a suitable electrolyte.

(1) (c) Which species is the reducing agent? Zinc

(1) (d) Which species loses electrons? Zinc

(2) (e) How will the mass of the zinc electrode change? It will decrease. Zinc atoms are oxidized at the anode resulting in formation of zinc ions.

(4) 2. For each item, write the cell notation, calculate the cell potential () for each redox reaction, and state whether the reaction is spontaneous or non-spontaneous.

(a)

Cr | Cr²⁺ || Pb²⁺ | Pb



The reaction is spontaneous because E_cell is a positive value for the equation as it is written.

(b) (assume one of the electrodes is carbon)

Ni | Ni²⁺ || Cl^- | Cl_2(g) | C



The reaction is spontaneous because E_cell is a positive value for the equation as it is written.

(2) 3. Describe the two key differences between electrolytic and galvanic cells.

The first difference is that an external power source has to be connected to the cell in order to drive the redox reaction in an electrolytic cell whereas in an electrochemical cells, electrons flow from a region of high potential (anode) to the area of lower potential (the cathode).

The second difference is in the charges on the anode and cathode. In an electrochemical cell, the anode is negative and the cathode is positive. in an electrolytic cell, the anode is positive and the cathode is negative.

4. for No|No³⁺||Cu²⁺|Cu is 2.842 V.

(2) a) Write the oxidation and reduction half reactions for the redox reaction.

(2) b) Calculate the reduction potential of the nobelium half-cell.

(3) 5. Consider these spontaneous redox reactions involving gallium, manganese, and neptunium and their aqueous ions:

List the reducing agents from worst to best. Justify your order.

The order is: In, Ga, Mn, Np.

Reasoning: Equation 1 shows Np to be a better reducing agent than Mn. Reaction 2 shows Ga to be a better reducing agent than In. Since the third equation does not proceed in a forward direction, the reverse reaction must be spontaneous, so Mn is a better reducing agent than Ga.

6. An electrolytic cell contains a solution of iridium bromide. A 0.200 A current is passed through the cell for 1.00 h resulting in the deposition of 0.478 g of iridium metal at the cathode.

(3) (a) Calculate the charge of the iridium ion in a solution of iridium bromide.

Given:

I = 0.200 A

t = 1.00 h = 3600 s

m = 0.478 g

Strategy:

1. 
   Calculate the quantity of charge applied in coulombs.
   
2. 
   Calculate the moles of electrons supplied.
   
3. 
   Calculate the moles of iridium metal plated.
   
4. 
   Determine the ratio of moles of iridium to moles of electrons transferred.
   

Therefore, iridium ions must be gaining three electrons each.

(1) (b) Write the reduction half reaction for the redox reaction.