Metallic gold is collected from below the anode when a mixture of copper and gold metals is refined by electrolysis. Explain this behavior.

Verified step by step guidance

Step 1: Understand the process of electrolysis in metal refining, which involves using an electric current to drive a non-spontaneous chemical reaction.

Step 2: Recognize that in the electrolysis of a mixture of metals, the metal with the higher reduction potential will be reduced at the cathode, while the metal with the lower reduction potential will remain in solution or be deposited elsewhere.

Step 3: Identify the standard reduction potentials for copper (Cu) and gold (Au). Gold has a higher reduction potential than copper, meaning it is more likely to be reduced and less likely to oxidize.

Step 4: During electrolysis, copper, having a lower reduction potential, will dissolve into the solution as Cu²⁺ ions at the anode, while gold, being less reactive, will not dissolve and instead will collect below the anode.

Step 5: Conclude that the behavior of gold collecting below the anode is due to its higher reduction potential, making it less reactive and more stable in its metallic form compared to copper during the electrolysis process.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction. In the context of refining metals, an electric current is passed through a solution containing metal ions, causing the metals to deposit at the electrodes. The anode is where oxidation occurs, and the cathode is where reduction takes place, allowing for the separation of metals based on their reactivity.

Electrode Reactions

In electrolysis, different metals have distinct electrode potentials, which determine their behavior at the anode and cathode. When a mixture of metals like copper and gold is subjected to electrolysis, gold, being less reactive, is preferentially deposited at the cathode, while copper ions are oxidized at the anode. This selective deposition is crucial for the effective separation and purification of metals.

Metal Reactivity Series

The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals higher in the series, such as copper, are more likely to lose electrons and form positive ions compared to those lower in the series, like gold. This concept is essential in understanding why gold is collected at the cathode during electrolysis, as it is less reactive and remains in its metallic form while copper is oxidized and dissolved into the solution.

Recommended video:

Guided course

02:02

Activity Series Chart

Related Practice

Textbook Question

(a) Calculate the mass of Li formed by electrolysis of molten LiCl by a current of 7.5 × 10⁴ A flowing for a period of 24 h. Assume the electrolytic cell is 85% efficient. (b) What is the minimum voltage required to drive the reaction?

Textbook Question

A mixture of copper and gold metals that is subjected toelectrorefining contains tellurium as an impurity. The standard reduction potential between tellurium and its lowestcommon oxidation state, Te4+, isTe4+1aq2 + 4 e- ¡ Te1s2 E°red = 0.57 VGiven this information, describe the probable fate of tellurium impurities during electrorefining. Do the impuritiesfall to the bottom of the refining bath, unchanged, as copper is oxidized, or do they go into solution as ions? If theygo into solution, do they plate out on the cathode?

Textbook Question

A disproportionation reaction is an oxidation–reduction reaction in which the same substance is oxidized and reduced. Complete and balance the following disproportionation reactions:

(b) MnO₄^2-(aq) → MnO₄^-(aq) + MnO₂(s) (acidic solution)