C6.1 (2) - ethanol, alloys, corrosion

Question 1

what are the two methods of making ethanol? (and describe each one briefly)

Answer 1

fermentation - using yeast to catalyse the conversion of glucose solution to carbon dioxide and ethanol

hydration - obtaining ethene from crude oil and reacting it with steam

Question 2

why is yeast added to the glucose solution in order for it to ferment?

Answer 2

as it contains enzymes which catalyse the conversion of glucose to ethanol and carbon dioxide

Question 3

conditions for fermentation to take place? (and explain why)

Answer 3

• 35C (too low = yeast cells inactive, too high = enzymes denature)
• atmospheric pressure

Question 4

what is the word equation for hydration to occur (to produce ethanol)?

Answer 4

ethene + steam ⇌ ethanol

Question 5

what are the conditions needed for hydration to produce ethanol?

Answer 5

• 300C
• 60 atmospheres
• phosphoric acid catalyst
• therefore only occurs in a laboratory
• exothermic reaction

REVERSIBLE REACTION

Question 6

compare fermentation of sugars and hydration of ethene (6)

Answer 6

fermentation
- low raw material cost
- normal pressure + temp
- low energy needed
BUT
- low percentage yield
- low rate of reaction
- low purity (more energy needed to extract product further)

hydration
- high material cost
- high pressure + temp
- high energy needed
BUT
- high percentage yield (95%)
- high purity (no by-products)

Question 7

define an alloy

Answer 7

a mixture of a metal and one other element

Question 8

STEEL

a) describe composition
b) property
c) uses

Answer 8

a) iron + carbon + other metals
b) high tensile strength, ductile
c) buildings, briges, car doors

Question 9

what does it mean if a material has high tensile strength (simply)?

Answer 9

can be stretched/pulled a lot before breaking

Question 10

why can steel alloys be designed for specific uses?

and give examples

Answer 10

• as more carbon added = harder - chisels (brittle)
• low carbon = easily shaped/softer - car body
• stainless steel = resistant to corrosion

Question 11

DURALUMIN

a) describe composition
b) properties
c) uses

Answer 11

a) aluminium + copper
b) low density, moderate tensile strength (stronger than pure aluminium)
c) aircraft parts

Question 12

SOLDER

a) describe composition
b) properties
c) uses

Answer 12

a) tin + copper

b) melts at a low temp (compared to tin and copper individually)
good electric conductors

c) joining electric components (without damaging)
- liquid solder into gap + solidifies fast

Question 13

BRONZE

a) describe composition
b) properties
c) uses

Answer 13

a) copper + tin

b) stronger + harder than copper
resists corrosion

c) propellers for ship (hard)
wires
statues (resist corrosion)

Question 14

BRASS

a) describe composition
b) properties
c) uses

Answer 14

a) copper + zinc
b) conducts electricity, resists corrosion

c)
- pins in electrical plugs conducts)
- instruments and coins

Question 15

why are alloys harder than pure metals?

Answer 15

• different-sized atoms (due to diff elements)
• so particles cannot slide over each other
• disrupts regular lattice structure of pure metal

Question 16

neg of alloys disturbing regular lattice structure of pure metals?

Answer 16

alloys are less malleable + ductile than pure metal

Question 17

what is corrosion?

Answer 17

the reaction of a metal with substances in the surroundings

Question 18

what is the difference between rusting and corroding?

Answer 18

rusting is when either iron or steel corrode with oxygen and water

corroding is any metal’s reaction with surroundings

Question 19

what is the word and symbol equation for the rusting of iron?

Answer 19

iron + oxygen + water -> hydrated iron (III) oxide

4Fe(s) + 3O (g) + 2H O (l) -> 2Fe O H O(s)
2 2 2 3 2

Question 20

describe how the rusting of iron is a redox reaction

Answer 20

iron loses electrons (is oxidised)

oxygen gains electrons (is reduced)

Question 21

describe how a piece of iron would completely corrode away

Answer 21

1) surface reacts with surroundings
2) rust produce from corrosion flakes off
3) exposing fresh metal
4) which then reacts with surroundings
and the process repeats

Question 22

what is the word and then the symbol equation for how silver corrodes?

Answer 22

silver + hydrogen sulfide -> silver sulfide + hydrogen

2Ag(s) + H S(g) -> Ag S(s) + H (g)
2 2 2

Question 23

which part of an object corrodes?

Answer 23

only the outer exposed surface

Question 24

what is the familiar orange-brown rust we see?

Answer 24

hydrated iron(III) oxide

Question 25

how would you set up an investigation to see what substances are needed for rusting to happen?

Answer 25

• get 3 nails + 3 test tubes
• full first with air + no water (with stopper)
  with anhydrous calcium chloride (absorbs water vapour)
• second with boiled water (ie. no oxygen) (with stopper)
• third with air + water (no stopper on top)
• record appearance
  rust on only 3rd test tube

Question 26

what conditions causes rusting to occur?

Answer 26

the presence of water and oxygen

Question 27

how can you reduce corrosion?

Answer 27

make a physical barrier between the environment and the surface of the metal

Question 28

what are the 2 main ways corrosion can be prevented?

Answer 28

• physical barrier methods
• sacrificial methods

Question 29

how does sacrificial protection work?

Answer 29

• coating the metal you want to protect with a more reactive metal
• more reactive metal corrodes first, protecting the metal within

Question 30

in terms of electrons how does sacrifical protection work?

Answer 30

• more reactive element loses electrons more easily

Question 31

what is galvanising?

Answer 31

plating a layer of molten zinc onto an object to prevent air + water reaching the metal below
(acts as a sacrifical metal)

Question 32

how do barrier methods work?

and give 4 examples

Answer 32

prevent oxygen and water from touching iron

• paint/oil/grease/electroplating w/ tin/plastic

Question 33

explain galvanising and how it is special (answer on here is a bit terrible)

Answer 33

• is a barrier and sacrificial method
• forms barrier around metal (reacts with surroundings and creates a ‘seal’)
• but even when scratched/barrier is removed, acts as a sacrificial method as it is very reactive
• so metal still does not corrode