Question

One electrode compartment consists of an aluminum strip placed in a solution of Al(NO3)3, and the other has a nickel strip placed in a solution of NiSO4. The overall cell reaction is

2Al(s)+3Ni2+(aq)?2Al3+(aq)+3Ni(s)

1. What is being reduced?

2. Write the half-reactions that occur in the two electrode compartments.

anode reaction:

cathode reaction:

Answer 1

A voltaic cell similar to that shown in Fig. 20.5 is constructed. One electrode compartment consists of a silver strip placed in contact with a solution of Al(NO₃)₃, and the other has a nickel strip placed in a solution of NiSO₄. The overall cell reaction is

3Ni⁺²(aq) + 2Al(s) ----> 3Ni(s) + 2Al³⁺(aq).

(a) What is being oxidized and what is being reduced?

We start by sketching the voltaic cell:

From the overall cell reaction, we see that Ni²⁺ is reduced: Ni²⁺(aq) + 2e^- ----> Ni(s) and we see that Al is oxidized: Al(s) -----> Al³⁺ + 3e^-

(b) Write the half-reactions that occur in the two electrode compartments.

This was done above!

(c) Which electrode is the anode, and which is the cathode?

oxidation occurs at the anode, and reduction occurs at the cathode. Here, Al is the anode, and Ni is the cathode.

(c) Indicate the signs of the electrodes.

The anode in a voltaic cell has a (-) sign, while the cathode has a (+) sign.

(d) Do electrons flow from the Al electrode to the Ni electrode or from the Ni electrode to the Al electrode?

Electrons flow from the anode to the cathode; thus, we have current flow from the Al electrode to the Ni electrode.

(e)In which direction do anions and cations migrate through the solution? Assume the Al is not coated with its oxide.

Anions migrate towards the anode, and cations migrate towards the cathode.