Compare and contrast Galvanic and Electrolytic cells and design a galvanic cell diagram for Cu/Cu2+ and Ag/Ag+.

Here are the solutions to questions 20 and 21.

Question 20:

i) The two main types of electrochemical cells are:

• Galvanic (or Voltaic) cells
• Electrolytic cells

ii) Two similarities between the two electrochemical cells are:

• Both involve redox reactions (oxidation and reduction).
• Both have electrodes (anode and cathode) where these reactions occur.

iii) Two differences between the two electrochemical cells are:

• Galvanic cells produce electrical energy from spontaneous chemical reactions, while electrolytic cells use electrical energy to drive non-spontaneous chemical reactions.
• In a galvanic cell, the anode is the negative electrode and the cathode is the positive electrode. In an electrolytic cell, the anode is the positive electrode and the cathode is the negative electrode.

iv) To design an electrochemical (Galvanic) cell diagram between $Cu^{2+}/Cu$ and $Ag^{+}/Ag$:
Given standard reduction potentials:
$Cu^{2+}(aq) + 2e^- \rightleftharpoons Cu(s) \quad E^\circ = +0.34V$
$Ag^{+}(aq) + e^- \rightleftharpoons Ag(s) \quad E^\circ = +0.80V$

Since $Ag^{+}/Ag$ has a higher standard reduction potential ($+0.80V$) than $Cu^{2+}/Cu$ ($+0.34V$), silver will be reduced at the cathode, and copper will be oxidized at the anode.

• Anode (Oxidation): A copper electrode immersed in a copper nitrate solution ($Cu(NO_3)_2(aq)$). Oxidation occurs here: $Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-$.
• Cathode (Reduction): A silver electrode immersed in a silver nitrate solution ($AgNO_3(aq)$). Reduction occurs here: $Ag^{+}(aq) + e^- \rightarrow Ag(s)$.
• External Circuit: The copper and silver electrodes are connected externally by a wire through a voltmeter, which measures the cell potential. Electrons flow from the copper anode to the silver cathode.
• Salt Bridge: A salt bridge (e.g., containing $KNO_3$) connects the two half-cells to maintain electrical neutrality by allowing ion migration. Anions flow towards the anode compartment, and cations flow towards the cathode compartment.

The cell notation is:

$$Cu(s) | Cu^{2+}(aq) || Ag^{+}(aq) | Ag(s)$$

Question 21:

i) Considering the compounds $NH_4OH$, $KBr$, $H_2SO_4$:

a) The compound that will turn blue litmus paper into red is sulfuric acid ($H_2SO_4$), as it is an acid.

b) The compound that will turn red litmus paper into blue is ammonium hydroxide ($NH_4OH$), as it is a base.

c) The compound that will have no action on neither red nor blue litmus paper is potassium bromide ($KBr$), as it is a neutral salt.

ii) Complete and balance the following equations of reactions, with all state symbols:

a)

$$2HNO_3(aq) + Ca(OH)_2(aq) \longrightarrow Ca(NO_3)_2(aq) + 2H_2O(l)$$

b)

$$H_2SO_4(aq) + 2NH_4OH(aq) \longrightarrow (NH_4)_2SO_4(aq) + 2H_2O(l)$$

iii) The compounds to be prepared are not specified in the question. Please provide the list of compounds for this part.