electrolysis

Question 1

describe an ELECTROLYTE

Answer 1

an IONIC compound in molten state (liquid) or dissolved in water

Question 2

describe the process of ELECTROLYSIS

Answer 2

process in which electrical energy from a direct current supply decomposes an electrolyte

Question 3

describe ANIONS and CATIONS

Answer 3

ANIONS - negatively charged ions move to positive electrode (anode)

CATIONS - positively charged ions move to negative electrode (cathode)

Question 4

explain the formation of the products in the electrolysis:

copper chloride
sodium chloride
sodium sulfate
molten lead bromide

Answer 4

COPPER CHLORIDE - copper at cathode, chlorine at anode

SODIUM CHLORIDE - hydrogen at cathode, chlorine at anode

SODIUM SULFATE - hydrogen at cathode, oxygen at anode

MOLTEN LEAD BROMIDE - produces lead at cathode, bromine at anode

Question 5

how can you predict which metal forms at which electrode

Answer 5

CATHODE - hydrogen produced unless compound contains ions less reactive than hydrogen then that metal is produced instead (copper, silver, gold)

ANODE - oxygen produced unless compound contains halide ions (chlorine, bromine or iodine)

Question 6

Explain oxidation and reduction

Answer 6

positively charged ions GAIN electrons and are REDUCED. reduction - cathode

negatively charged ions LOSE electrons and are OXIDISED. oxidation - anode

electrons are shown as e- in half equations

Question 7

explain what happens when copper can be purified by the electrolysis of copper sulfate solution

Answer 7

in pure copper cathode, copper ions move to copper electrode gain electrons and discharged as pure copper

in impure copper cathode, ions are replaced by copper ions from the impure copper anode

impurities form ‘sludge’ below anode

Question 8

describe the copper purification electrolysis practical results

Answer 8

cathode gains mass as copper ions gain electrons

anode loses mass as copper atoms lose electrons