y11 electrolysis test

Question 1

how to describe current in metal/graphite

Answer 1

the flow of electrons

Question 2

how to describe current in liquid/dissolved ionic compound

Answer 2

the flow of ions

Question 3

when are ionic compounds able to conduct and why

Answer 3

only when molten or dissolved in water, because the ions are able to move and carry charge

Question 4

why can’t simple covalent molecules conduct

Answer 4

because they have no overall charge or free elctrons to carry charge

Question 5

positive ion =

Answer 5

cation

Question 6

negative ion =

Answer 6

anion

Question 7

what is electrolysis

Answer 7

the decomposition of compounds using electricity

Question 8

oxidation means…

Answer 8

the loss of electrons

Question 9

reduction means…

Answer 9

the gain of electrons

Question 10

Describe the electrolysis of molten lead bromide

Answer 10

-Pb 2+ ions are attracted to the cathode (negatively charged electrode) and gain electrons, becoming Pb atoms
- Br- ions are attracted to anode (positively charged electrode) and lose electrons, becoming Br2 molecules
- at cathode grey lead metal is deposited on surface of electrode
-at anode brown bromine gas is given off

Question 11

Using example of electrolysis of PbBr2, write half equation at cathode, and whether it’s reduction or oxidation

Answer 11

Pb2+ + 2e- => Pb
Reduction

Question 12

Using example of electrolysis of PbBr2, write half equation at anode, and whether it’s reduction or oxidation

Answer 12

2Br- => Br2 + 2e-
Oxidation

Question 13

what is an ore

Answer 13

a rock that contains enough metal for profitable extraction of that metal

Question 14

how can carbon be used to extract metals

Answer 14

Due to a displacement reaction, carbon can displace metals below it in the reactivity series, and seperate it from the ore.

Question 15

method of extraction for elements above carbon in reactivity series

Answer 15

electrolysis

Question 16

disadvantage of electrolysis

Answer 16

high energy cost for both heat and electricity

Question 17

which metals don’t require extraction

Answer 17

metals at bottom of reactivity series: copper, silver, gold, platinum are found ‘native’ and don’t need to be extracted

Question 18

ions present in water

Answer 18

small amount of H+ and OH- ions

Question 19

what happens at the anode (which types of ions are oxidised)

Answer 19

If present, halide ions will be oxidised to form halogen molecules, but if not hydroxide ions are oxidised to form oxygen (gas)

Question 20

what happens at cathode (which elements are reduced)

Answer 20

If the element present is lower than hydrogen in the reactivity, that metal will be formed. If higher, hydrogen gas will form. In other words, it’s whatever is lower in reactivity series.

Question 21

what are the products from the electrolysis of sodium chloride solution

Answer 21

hydrogen, chlorine and sodium hydroxide

Question 22

test for:
- H2 gas
- O2 gas
- Cl2 gas

Answer 22

H2 = extinguishes lit splint with a squeaky pop
O2 = relights a glowing splint
Cl2 = bleaches damp (preferably blue) litmus paper

Question 23

test for
H+ ions
OH- ions
in a solution

Answer 23

Acids contain H+ ions, and bases contain OH- ions, so you can use a few drops of universal indicator. If H+ - would go red/orange, if OH- would go purple/blue

Question 24

what is electroplating

Answer 24

when electrolysis is used to create a thin layer of a metal on a conductive object

Question 25

explain the mass changes during the electrolysis of copper sulphate

Answer 25

-in this set up, instead of using a graphite electrode, your cathode is a thin sheet of pure copper, and your anode is impure copper
-the electrolyte (CuSO4) is added
-the copper atoms at the anode lose electrons (oxidised), becoming ions
-the anode becomes thinner due to atom loss, and the impurities fall to the bottom (as sludge)
-the copper ions are attracted to the cathode, and are reduced to form purified copper atoms
-the cathode gradually becomes thicker
-gain in mass at cathode is same as loss in mass at anode