redox and electrolysis

Question 1

define the term “redox reaction”

Answer 1

a reaction where both oxidation and reduction take place

Question 2

define the term ‘oxidation’

Answer 2

gain of oxygen
loss of electrons
loss of hydrogen

Question 3

define the term ‘reduction’

Answer 3

loss of oxygen
gain of electrons
gain of hydrogen

Question 4

define the term ‘oxidant’ and mention an example

Answer 4

oxidizing agent ( a substance which itself is reduced)
KMnO4 (potassium manganate) purple to colourless

Question 5

define the term ‘reducing agent’ and mention a few examples

Answer 5

a substance which itself is oxidized
CO, CO2, H2, KI (colourless to orange brown)

Question 6

define the term ‘electrolysis’

Answer 6

the breakdown of an ionic compound (1)
when molten or aqueous (1)
by the passage of electricity (1)

Question 7

in an electrolysis cell, which two components are part of the ‘external circuit’

Answer 7

wire and electrodes

Question 8

the cathode represents the ___ charge whereas the ____ represents the opposing charge

Answer 8

negative (1)
anode (1)

Question 9

electrodes are…

Answer 9

rods that carry charge
or
rods that allow the passage of electricity

Question 10

why must the electrolyte be molten or aqueous?

Answer 10

to have free moving ions to carry the charge

Question 11

why must electrodes be made of graphite or platinum?

Answer 11

due to them being inert and good conductors

Question 12

fluorine is _____ in colour at gas state

Answer 12

pale yellow

Question 13

bromine is _____ in colour in gas state

Answer 13

orange brown

Question 14

iodine is ____ in colour in gas state

Answer 14

purple

Question 15

chlorine is ____ in colour in gas state

Answer 15

yellowish green

Question 16

oxygen, hydrogen and nitrogen are ___ in colour in gas state

Answer 16

colourless

Question 17

copper is a ___ metal (colour)

Answer 17

reddish brown

Question 18

gold is a ___ metal (colour)

Answer 18

yellow

Question 19

negatively charged ions move towards the ___

Answer 19

anode

Question 20

positively charged ions move towards the ____

Answer 20

cathode

Question 21

the current in electrolyte are (ions/electrons)

Answer 21

ions

Question 22

the current in electrodes are (ions/electrons)

Answer 22

electrodes

Question 23

why can ionic compounds conduct electricity when molten or aqueous?

Answer 23

due to free moving ions which carry charges

Question 24

products of electrolysis of molten lead bromide

Answer 24

cathode: lead metal
anode: bromine gas
electrolyte: used up

Question 25

products of the electrolysis of molten calcium iodide

Answer 25

cathode: calcium metal anode: iodine gas electrolyte: used up

Question 26

give the observations seen after the electrolysis of molten zinc chloride

Answer 26

deposition of silvery grey metal at cathode bubbles of yellowish green gas at anode bulb lights up

Question 27

give the products of the electrolysis of conc. aqueous sodium chloride

Answer 27

cathode: hydrogen gas anode: chlorine gas electrolyte: sodium hydroxide

Question 28

give the products and observations of the electrolysis of dilute copper sulfate

Answer 28

**products** cathode: copper metal anode: oxygen gas electrolyte: sulfuric acid **observations** deposition of reddish brown metal at cathode bubbles of colourless gas at anode bulb lights up blue colour of electrolyte fades

Question 29

define the term ‘electroplating’

Answer 29

a process where a thin layer of one metal is put on top of another object by electrolysis

Question 30

give two uses of electrolysis

Answer 30

1. protects metal from corrosion (rusting) 2. gives an attractive and shiny appearance

Question 31

the object being electroplated is always the (cathode/anode)

Answer 31

cathode

Question 32

the plating metal is always the (cathode/anode)

Answer 32

anode

Question 33

the electrolyte in electroplating should always be

Answer 33

solution of the plating metal’s ionic compound

Question 34

how to electroplate a spoon with silver (mention cathodes, anodes and electrolyte)

Answer 34

cathode: spoon anode: silver electrolyte: silver nitrate (or any ionic compound of silver)

Question 35

why must an object be cleaned with sandpaper before electroplating?

Answer 35

to remove dirt or grease for a perfect coating

Question 36

how to achieve uniform coating during electroplating?

Answer 36

by rotating and fully immersing the object being electroplated in the electrolyte

Question 37

define the term ‘insulator’

Answer 37

a substance that resists the flow of current, and doesnt have any free moving electrons

Question 38

define the term ‘conductor’

Answer 38

a substance that allows electricity to flow through it, and has free moving electrons

Question 39

give 2 examples of insulators

Answer 39

plastic, wood, paper, glass, etc.

Question 40

give 2 examples of conductors

Answer 40

metals, graphite, etc.

Question 41

define the term ‘ore’

Answer 41

rock which a metal is naturally created and found in

Question 42

what method is used to extract the most reactive metals?

Answer 42

electrolysis

Question 43

what method is used to extract metals below carbon (in the reactivity series)

Answer 43

heating with carbon in a blast furnace

Question 44

how are least reactive metals found?

Answer 44

native, only need purification

Question 45

bauxite is the ore of (aluminum/iron)

Answer 45

aluminum

Question 46

bauxite consists of alumina which has a molecular formula of ___ and an impurity which is ___

Answer 46

Al2O3 Fe2O3 (iron oxide)

Question 47

what step is taken to remove impurities from bauxite?

Answer 47

crush the ore and mix with sodium hydroxide

Question 48

molten aluminium is collected at the (bottom graphite lining/anode graphite rods)

Answer 48

bottom graphite lining

Question 49

give molten cryolite’s molecular formula

Answer 49

Na3AlF6

Question 50

why do we dissolve alumina in molten cryolite?

Answer 50

1. dec. mp. from 2040°C to 900° which saves time, cost and energy 2. improves electrical conductivity of electrolyte

Question 51

what is seen in the cathode lining after the electrolysis of alumina?

Answer 51

aluminum metal (molten)

Question 52

after the electrolysis of alumina, what gases are present in the anode

Answer 52

oxygen gas (from Al2O3) CO (incomplete combustion of graphite at anode) CO2 (complete combustion of graphite at anode) F2 (from cryolite)

Question 53

why must the anode be replaced periodically?

Answer 53

carbon anode ‘burn away’ due to complete and incomplete combustion reactions of hot carbon with oxygen (producing CO and CO2)

Question 54

name 4 uses of aluminum and what properties of aluminium allow it to be suitable for each use

Answer 54

1. aircraft bodies: low density, high tensile strength 2. food/drink cans: nontoxic, non porous protective oxide layer that makes it resistant to corrosion 3. saucepans: nontoxic, non porous protective oxide layer that makes it resistant to corrosion + high mp. + good conductor of heat 4. overhead cables: high electrical conductivity, low density

Question 55

why do overhead cables use a steel core

Answer 55

to strengthen the cable (which prevents sagging)

Question 56

what is irons ore

Answer 56

hematite

Question 57

what does the ore hematite consist of

Answer 57

iron oxide and silicon oxide

Question 58

list 5 raw materials needed for the extraction of iron

Answer 58

1. hematite (ore) 2. carbon (coke/coal) 3. limestone (CaCO3) 4. water (coolant) 5. hot air

Question 59

what step heats up the blast furnace (1000°C - 2000°C)

Answer 59

oxidation of carbon

Question 60

why does slag lay on top of molten iron

Answer 60

its less dense

Question 61

steel is an alloy of iron with?

Answer 61

carbon

Question 62

define the term alloy

Answer 62

mixture of two or more metals not chemically bonded/combined

Question 63

give 3 reasons for the production of alloys

Answer 63

inc hardness more resistant to corrosion improved appearance

Question 64

how to make alloys

Answer 64

by melting the metals and allowing them to cool together

Question 65

what increases the hardness of an alloy of steel

Answer 65

inc the percentage of carbon

Question 66

describe the composition of mild steel

Answer 66

99.75% iron 0.25% carbon

Question 67

give the used of mild steel

Answer 67

car bodies machinery

Question 68

give the composition of hard steel

Answer 68

99% iron 1% carbon

Question 69

give the uses of hard steel

Answer 69

railway lines building constructions hammers bridges

Question 70

give the composition of stainless steel

Answer 70

chromium nickel iron

Question 71

uses of stainless steel

Answer 71

cutlery kitchen sinks chemical plants surgical tools

Question 72

brass composition

Answer 72

copper zinc

Question 73

brass uses

Answer 73

instruments door knockers

Question 74

bronze composition

Answer 74

copper tin

Question 75

bronze uses

Answer 75

castings

Question 76

solder composition

Answer 76

50% lead 50% tin

Question 77

solder use

Answer 77

electrical conductors