electrolysis

Question 1

What is electric current?

Answer 1

flow of electrons or ions

Question 2

what can electrons or ions act as?

Answer 2

charge carriers

Question 3

why do covalent compounds not conduct electricity?

Answer 3

they don’t contain ions because they make bonds by sharing electrons so they dont have any charge carriers that are free to move - cant carry an electric current

Question 4

why do ionic compounds only conduct electricity when in molten or in solution?

Answer 4

made of lattice of positive or negative ions but they arent free to move in a solid, when an ionic compound is dissolved the ions seperate - free to move and carry an electric current. the same when an ionic compound melts

Question 5

describe an experiment to distinguish between eletrolytes and non-electrolytes

Answer 5

set up an electrolytic cell, put the conductivity probe in the substance you are testing, measure the conductivity, current flows if it’s an eletrolyte. if not you will get a reading of zero conductivity

Question 6

what is the definition of electrolysis?

Answer 6

the formation of new substances when ionic compounds conduct electricity

Question 7

describe an experiment to investigate electrolysis (molten salts)

Answer 7

use inert electrodes (so it doesn’t affect the reaction just transfers electrons) of molten salts such as lead (II) bromide (PbBr2) set up the experiment with the electrolysis equipment. lead bromide will make lead and bromine you can use chemical tests to check

Question 8

describe an experiment to investigate electroylsis (aqueous solutions)

Answer 8

place inert eletrodes (so it doesn’t affect the reaction just transfers electrons) into an aqueous solution

eg. sodium chloride (product sodium chloride: Hydrogen at the negative; chlorine at the positive)

, copper (II) sulfate (copper at the negative; oxygen at the positive)

and dilute sulfuric acid (dilute sulfuric acid: Hydrogen at the negative; oxygen at the positive)

At the positive electrode the negatively charged ion from the compound will form an atom. At the negative electrode the atom of the positive ion will form.If the metal in the solution is more reactive then hydrogen, the hydrogen from the water will be a product, as the metal will bond with the oxygen.

Test the products using known methods: eg damp blue litmus paper turned red by chlorine.

Question 9

what are the ionic half equations for sulfuric acid at cathode and anode?

Answer 9

solution of sulfuric acid ( H2SO4) contains the ions SO4 2- H+ AND OH-
cathode: hydrogen gas is produced
2H+ + 2e- –> h2

anode: hydroxide ions lose electrons more easily than sulfate ions so oxygen and water are produced
4OH- –> O2 + 2H20 + 4e-

Question 10

what are the ionic half equations for sodium chloride?

Answer 10

NaCl contains the ions Na+ Cl- OH- H+
cathode: hydrogen gas is produced
2H+ + 2e- –> h2

anode: chloride ions lose electrons more easily than hydroxide ions so chlorine gas is produced:
2Cl- –> Cl2 + 2e-

Question 11

what are the ionic half equations for copper (II) sulfate?

Answer 11

CuSO4 contains the ions Cu2+ SO4 2- H+ and OH-
cathode: copper metal is produced
Cu2+ + 2e- –> Cu

anode: oxygen and water are produced
4OH- –> O2 + 2H20 + 4e-

Question 12

what does one faraday represent?

Answer 12

one mole of electrons

Question 13

how do you calculate the amount of products of the electrolysis of molten salts and aqueous solutions?

Answer 13

• write out the balanced half equation for the cathode
• calculate the number of faradays:
  charge (coloumbs) = current (amps) x time (seconds) eg. QIT number of faradays divide answer by 96 000
• calculate number of moles ( divide the number of faradays by the number of electrons in the half equation)
• work out the mass by moles = mass/mr