Suggest two reasons why the mass deposited was different from the expected value

1) Dissolution of the copper anode

2) Time of the reaction

Explanation:

The figure shows the electrolysis of Copper Chloride using copper electrodes.

In aqueous solution, the ions present in the solution include:  H⁺, OH⁻. Cu²⁺ Cl⁻

The half equations for the reaction  are:

At rhe Anode (positive electrode) : 2Cl⁻(aq) - 2e = Cl₂(g)

At the Cathode (negative electrode) Cu²⁺ (aq) + 2e = Cu (s)

Hence copper ions are reduced at the cathode by gaining two electrons to form copper solid deposits. It is the mass of the deposited copper that the student measured over time.

Reasons why the actual mass is different  from the expected mass

1) Dissolution of the copper Anode: The electrodes used for this experiment are copper electrodes as both the positive and negative electrode.

Under the influence of an electric current, the copper anode will dissolve by gaining electrons and go into solution as copper II ions (Cu²⁺). thereby increasing the amount of copper ions in solution.

The aqueous copper ions from the anode and from the copper chloride (CuCl₂ (aq) electrolyte will migrate to the negative cathode, gain electrons, and get deposited as pure copper solid.  This increases the mass of copper solid deposited at the cathode.

2) Time: As the time of the reaction from zero to sixty (60) minutes under the influence of an electric current, more of the copper anode will dissolve, migrate to the cathode and get deposited as copper solid.

Hence as the time of the reaction increases, more of the copper ions will be deposited as copper solid thereby increasing the value of the actual mass of copper deposited.