Electrolytic Processes Flashcards

All 21 cards in this deck

What is an electrolyte?

An ionic compound in the molten state or dissolved in water, so that its ions are free to move.

What is meant by the term electrolysis?

The use of electrical energy, from a direct current supply, to decompose (break down) an electrolyte.

During electrolysis, which electrode do cations move to, and which do anions move to?

Cations (positive ions) move to the cathode (negative electrode); anions (negative ions) move to the anode (positive electrode).

True or false? Molten zinc chloride conducts electricity because it contains delocalised electrons.

False. It conducts because it contains ions that are free to move.

What are the steps to predict the products of electrolysing an aqueous solution using inert electrodes?
e.g. copper chloride solution

1. Cathode: the metal is formed if it is less reactive than hydrogen, otherwise hydrogen — copper.
2. Anode: the halogen is formed if a halide is present, otherwise oxygen — chlorine.

What are the products of the electrolysis of sodium chloride solution using inert electrodes?

Hydrogen at the cathode and chlorine at the anode.

What is produced at each electrode when water acidified with sulfuric acid is electrolysed, and in what volume ratio?

Hydrogen at the negative electrode and oxygen at the positive electrode, in a 2 : 1 volume ratio (hydrogen is double the volume of oxygen).

How is impure copper purified by electrolysis?

The impure copper is the anode and pure copper the cathode, in copper sulfate solution; copper dissolves from the anode and pure copper is deposited on the cathode.

What are the products of the electrolysis of molten lead bromide?

Lead at the cathode and bromine at the anode.

What are the steps to predict the products of electrolysing a molten binary ionic compound?
e.g. molten potassium bromide

1. The positive metal ions go to the cathode and form the metal: potassium at the cathode.
2. The negative non-metal ions go to the anode and form the non-metal: bromine at the anode.

In electrolysis, what happens at the cathode in terms of electrons?

Positive ions gain electrons, so reduction occurs at the cathode.

In electrolysis, what happens at the anode in terms of electrons?

Negative ions lose electrons, so oxidation occurs at the anode.

What are the steps to write a half equation for a reaction at the cathode?
e.g. hydrogen ions forming hydrogen gas, $H_2$

1. Write the ions on the left and the product on the right: $2H^+ \rightarrow H_2$
2. Add electrons to the left-hand side to balance the charges: $2H^+ + 2e^- \rightarrow H_2$

What is the balanced half equation for the formation of oxygen from hydroxide ions at the positive electrode?

$4OH^- \rightarrow O_2 + 2H_2O + 4e^-$

Why are copper electrodes cleaned with emery paper before their masses are determined?

To remove surface oxide, grease or other impurities.

In the copper sulfate electrolysis practical, what must be done to the cathode before its final mass is measured?

Rinse it with distilled water and dry it before weighing; the increase in mass is the mass of copper deposited.

In the electrolysis of copper sulfate solution with copper electrodes, what happens to the mass of each electrode?

The anode gets smaller (copper atoms are oxidised to ions that go into solution) and the cathode gets larger (copper ions are reduced to copper atoms).

True or false? When copper sulfate solution is electrolysed with copper electrodes, the solution stays the same shade of blue.

True. The same number of copper ions enter the solution at the anode as leave it at the cathode, so the concentration of $Cu^{2+}$ does not change.

What are the products of the electrolysis of sodium sulfate solution using inert electrodes?

Hydrogen at the cathode (sodium is more reactive than hydrogen) and oxygen at the anode (no halide ions are present).

What is produced at each electrode when copper sulfate solution is electrolysed with inert electrodes?

Copper at the cathode (copper is less reactive than hydrogen) and oxygen at the anode (no halide ions are present).

When copper is purified by electrolysis, what happens to the impurities in the impure copper anode?

As the anode dissolves, insoluble impurities are released and fall to the bottom of the cell, where they collect as a sludge.