ELECTROLYSIS [dchemlc]

label the diagram.

Answer explanation

An electrolyte is a liquid or solution that undergoes electrolysis.

The electricity is passed into and out of the electrolyte through two electrodes.

The positive electrode is called the anode.

The negative electrode is called the cathode.

what is formed at the cathode during the electrolysis of molten zinc chloride?

• zinc

• chlorine gas

• hydrogen gas

• oxygen gas

Answer explanation

If you electrolyse a molten ionic compound only containing two elements, you will get the metal at the cathode.

Reduction always occurs at the cathode and oxidation always occurs at the anode.

what is formed at the anode during the electrolysis of molten sodium iodide?

• iodine gas

• sodium

• hydrogen gas

• oxygen gas

Answer explanation

If you electrolyse a molten ionic compound only containing two elements, you will get the non-metal at the anode (because non-metals form negative ions).

• Reduction always occurs at the cathode and oxidation always occurs at the anode.

which of the following statements are false?

• all ionic compounds can be electrolysed when they are molten

• ammonia solution conducts electricity

• hydrogen chloride ionises in water

• oxidation occurs when something loses electrons

Answer explanation

Not all ionic compounds can be electrolysed when they are molten. Some break up into simpler substances before their melting point. For example, copper(II) carbonate breaks into copper(II) oxide and carbon dioxide, even on gentle heating. It is impossible to melt it.

positive ions are known as cations because they are attracted to the ___________.

Negative ions are known as anions because they are attracted to the ___________.

what is formed at the cathode during the electrolysis of copper (ll) chloride solution?

• copper

• chlorine gas

• hydrogen gas

• oxygen gas

Answer explanation

If the metal is high in the reactivity series, you get hydrogen produced at the cathode instead of the metal. • If the metal is below hydrogen in the reactivity series, you obtain the metal at the cathode.

what is formed at the anode during the electrolysis of magnesium sulfate solution?

• oxygen gas

• magnesium

• hydrogen gas

• sulfate ions

Answer explanation

• If you have solutions of halides (chlorides, bromides or iodides), you obtain the halogen (chlorine, bromine or iodine) at the anode. With other common negative ions (sulfate, nitrate, hydroxide), you obtain oxygen at the anode.

what will be produced at the anode and cathode respectively when dilute nitric acid is electrolysed?

• hydrogen gas and oxygen gas

• oxygen gas and hydrogen gas

• hydrogen gas and nitrogen gas

• nitrogen gas and hydrogen gas

Answer explanation

The only positive ions arriving at the cathode are hydrogen ions (from the acid and the water). These are discharged to give hydrogen gas.

At the anode nitrate ions and hydroxide ions (from the water) arrive. The nitrate ions are too difficult to oxidise, and so you obtain oxygen from the oxidation of hydroxide ions from the water.

which of the following is a non-electrolyte?

• sugar

• table salt

• lead (ll) bromide

• water

Answer explanation

If you tried to electrolyse a covalent compound (either molten or in solution), there wouldn't be a current flow because there aren't any ions. Nothing else would happen either. Sugar, for example, is a non-electrolyte; it doesn't undergo electrolysis. It won't conduct electricity, and won't be decomposed by it, either in solution or when molten.