5. Electricity And Chemistry

Question 1

what does the term electrolysis mean

Answer 1

the break down of a molten or aqueous ionic compound using electricity

Question 2

what is the cathode and anode

Answer 2

cathode - negative electrode
anode - positive electrode

Question 3

what is formed at each electrode in electrolysis

Answer 3

anode - metal or hydrogen
cathode - non metal

Question 4

how can you predict whether a metal or hydrogen will form at the negative electrode during electrolysis of an aqueous compound

Answer 4

if hydrogen is above the metal in the reactivity series then the metal will form. if the metal is more reactive than hydrogen the hydrogen will form

Question 5

what forms at each electrode during the electrolysis of molten lead(II) bromide

Answer 5

anode - bromine
cathode - lead

Question 6

what forms at each electrode during the electrolysis of concentrated hydrochloric acid

Answer 6

anode - chlorine
cathode - hydrogen

Question 7

what forms at each electrode during the electrolysis of concentrated sodium chloride solution

Answer 7

anode - chlorine
cathode - hydrogen

Question 8

what forms at each electrode during the electrolysis of dilute sulfuric acid

Answer 8

anode - oxygen
cathode - hydrogen

Question 9

how can the products of electrolysis of molten electrolytes be predicted

Answer 9

anode - non-metal element
cathode - metal element

Question 10

predict what forms at each electrode during the electrolysis of molten zinc chloride

Answer 10

anode - chlorine
cathode - zinc

Question 11

what forms at each electrode during the electrolysis of copper sulfate solution using inert electrodes

Answer 11

anode - oxygen
cathode - copper

Question 12

what forms at each electrode during the electrolysis of copper sulfate solution using copper electrodes

Answer 12

anode - copper ions
cathode - copper

Question 13

describe the electrolysis of copper (II) sulfate solution using carbon electrodes

Answer 13

• place the inert carbon electrodes into a beaker of copper sulfate solution
• connect ions gain electrons t the cathode to from pure copper. oxygen ions lose electrons at the anode to form oxygen gas

Question 14

how can impure copper be purified using copper sulfate solution and copper electrodes

Answer 14

electrolysis:
- the anode is made of impure copper and the cathode is made of pure copper
- the electrodes are placed in a solution of copper sulfate
- the copper ions from the impure anode move to the cathode where they gain electrons and form pure copper
- impurities form as sludge below the anode

Question 15

where do ions in the electrolyte move to during electrolysis

Answer 15

cations move towards the cathode
anions move towards the anode

Question 16

what happens at the anode during electrolysis

Answer 16

the anions lose electrons to form their elements. this is oxidation

Question 17

what happens at the cathode during electrolysis

Answer 17

cations gain electrons to form their elements. this is reduction

Question 18

predict the products of electrolysis of concentrated potassium bromide soultion

Answer 18

anode - bromine
cathode - hydrogen

Question 19

predict the products of electrolysis of concentrated copper iodide solution

Answer 19

anode - iodine
cathode - copper

Question 20

predict the products of electrolysis of dilute zinc chloride solution

Answer 20

anode - oxygen
cathode - zinc

Question 21

what is electroplating

Answer 21

a process in which a metal is coated with a layer of another metal

Question 22

what are two reasons for using electroplating

Answer 22

• to increase resistance to corrosion
• to improve appearance

Question 23

explain how the process of electroplating works

Answer 23

similar setup to electrolysis:

the metal being coated is the cathode. the metal that will form the exterior layer is the anode. the electrolyte solution must contain ions of the metal which will form the outer coating. a power supply is connected to both electrodes

Question 24

write half equation for the reactions that occur at the electrodes when aqueous NaCl is electrolysed

Answer 24

cathode - 2H+ + 2e- –> H2
anode - 2Cl- + 2e-

Question 25

write half equations for the reactions that occur at the electrodes when molten lead(II) bromide is electrolysed

Answer 25

cathode - Pb2+ + 2e- –> Pb
anode - 2Br- –> Br2 + 2e-

Question 26

why are copper and steel-cored aluminium used in cables

Answer 26

aluminium and copper are both good conductors of electricity. aluminium is commonly used in overhead wires and copper is used one electrical wiring

Question 27

why are plastics and ceramics used as insulators

Answer 27

plastics and ceramics both do not conduct electricity. they are used as insulators as they prevent the flow of electricity

Question 28

compare the movement of electrons to the movement of ions in electrolysis

Answer 28

electrons move through the metallic conductor meaning they move through the wire from the positive electrode to the negative electrode

ions move through the electrolyte. positive ions move to the negative electrode and negative ions move to the positive electrode

Question 29

how can electrical energy be produced from simple cells

Answer 29

• two different metal electrodes are placed in an electrolyte and connected with a wire
• a current of electrons is created so electrical energy is produced
• the more reactive metal will lose electrons and the less reactive metal will gain electrons

Question 30

during the extraction of aluminium, why is aluminum oxide dissolved in molten cryolite

Answer 30

aluminium oxide has a very high melting point. dissolving it in molten cryolite reduce the melting point of the electrolyte, reducing energy usage and cost

Question 31

why does the positive electrode need to be replaced regularly during the electrolysis of aluminium oxide

Answer 31

the oxygen formed at the positive electrode reacts with the carbon electrode to form carbon dioxide. the carbon in the rod will be used up so it will need replacing

Question 32

describe how chlorine, hydrogen and sodium hydroxide can be manufactured from the electrolysis of a concentrated solution of sodium chlorie

Answer 32

• inert electrodes are placed in upside down tubes so that any gas is collected
• the electrolyte is sodium chloride
• chlorine gas formed in the tube at the positive electrode
• hydrogen gas formed in the tube at the negative electrode
• the solution left at the end is sodium hydroxide