Electrolytic Processes Flashcards
All 23 cards in this deck
What is an electrolyte?
An ionic compound that is molten or dissolved in water, so that its ions are free to move.
What is meant by the term electrolysis?
Using electrical energy from a direct current supply to decompose (break down) an electrolyte, i.e. an ionic compound.
During electrolysis, which electrode does each type of ion move to?
Positive ions (cations) move to the cathode, the negative electrode; negative ions (anions) move to the anode, the positive electrode.
True or false? Solid sodium chloride conducts electricity.
False. Its ions are held in a lattice and cannot move, so no current flows; it conducts only when molten or dissolved in water.
Give two reasons why graphite is a suitable material for electrodes in electrolysis.
It conducts electricity, and it is inert so it does not react with the electrolyte or the products.
What are the products of the electrolysis of copper chloride solution using inert electrodes?
Copper (solid) at the cathode and chlorine (gas) at the anode.
What are the products of the electrolysis of sodium chloride solution using inert electrodes?
Hydrogen at the cathode and chlorine at the anode.
What are the products of the electrolysis of sodium sulfate solution using inert electrodes?
Hydrogen at the cathode and oxygen at the anode.
In the electrolysis of water acidified with sulfuric acid, how do the volumes of the two gases compare?
The volume of hydrogen (at the cathode) is twice the volume of oxygen (at the anode), a 2 : 1 ratio.
In the electrolysis of an aqueous solution, which product forms at the cathode?
Hydrogen, unless the metal is less reactive than hydrogen (e.g. copper), when the metal is formed instead.
In the electrolysis of an aqueous solution, which product forms at the anode?
Oxygen, unless a halide ion is present (e.g. chloride), when the halogen is formed instead.
What are the products of the electrolysis of molten lead bromide?
Lead at the cathode and bromine at the anode.
What two changes must be made to normal electrolysis apparatus to electrolyse molten lead bromide?
Use a crucible (not a beaker) that will not break or melt when heated strongly, and heat it with a Bunsen burner to melt the lead bromide.
What are the products of electrolysing a molten binary ionic compound?
e.g. molten zinc chloride
The metal forms at the cathode and the non-metal at the anode — zinc at the cathode, chlorine at the anode.
What are the products when copper sulfate solution is electrolysed using inert (graphite) electrodes?
Copper deposited at the cathode and oxygen at the anode.
What happens at the anode when copper sulfate solution is electrolysed with copper electrodes?
Copper atoms form copper ions () that pass into the solution, so the anode loses mass.
What happens at the cathode when copper sulfate solution is electrolysed with copper electrodes?
Copper ions form copper atoms, so solid pink/brown copper is deposited and the cathode gains mass.
True or false? The blue colour of copper sulfate solution fades during electrolysis with copper electrodes.
False. The colour and concentration stay the same, because for every copper ion entering the solution at the anode, one is removed at the cathode.
When impure copper is purified by electrolysis, what is the solid that collects beneath the anode?
The insoluble impurities that fall from the impure copper anode.
True or false? Calcium nitrate mixed with water behaves as an electrolyte, but calcium carbonate mixed with water does not.
True. Calcium nitrate dissolves so its ions are free to move; calcium carbonate is insoluble, so its ions stay fixed in the solid.
When copper is purified by electrolysis, what are the anode, the cathode and the electrolyte?
Anode: impure copper. Cathode: pure copper. Electrolyte: copper sulfate solution.
In the copper sulfate core practical, why are the copper electrodes washed and dried before they are weighed?
So no copper sulfate solution or water is left on them, which would make the measured mass too high.
When molten lead bromide is electrolysed, what do the bromine and the lead look like?
Bromine: a red-brown gas given off at the anode. Lead: a silvery liquid that collects at the cathode.