✅ 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

positives of using fermentation?

Answer 3

• has a renewable resource (plant sugars)
• can carry out in a school lab
  NOT A REVERSIBLE REACTION

Question 4

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

Answer 4

• not a reversible reaction
• 35C (too low = yeast cells inactive, too high = enzymes denature)
• atmospheric pressure

Question 5

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

Answer 5

ethene + steam ⇌ ethanol

Question 6

what are the conditions needed for hydration to produce ethanol?

Answer 6

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

REVERSIBLE REACTION

Question 7

compare fermentation of sugars and hydration of ethene (6)

Answer 7

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 8

define an alloy

Answer 8

a mixture of two or more elements, at least one of which is a metal

Question 9

STEEL

a) describe composition
b) property
c) uses

Answer 9

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

Question 10

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

Answer 10

can be stretched/pulled a lot before breaking

Question 11

why can steel alloys be designed for specific uses?

and give examples

Answer 11

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

Question 12

DURALUMIN

a) describe composition
b) properties
c) uses

Answer 12

a) aluminium + copper
b) low density (stronger than pure aluminium)
c) aircraft parts

Question 13

SOLDER

a) describe composition
b) properties
c) uses

Answer 13

a) tin + Lead

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

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

Question 14

BRONZE

a) describe composition
b) properties
c) uses

Answer 14

a) copper + tin
b) stronger + harder than copper, resists corrosion (= useful for making propellers for ships)

c)
statues- metal artwork (resist corrosion)
Bells, cymbals

Question 15

BRASS

a) describe composition
b) properties
c) uses

Answer 15

a) copper + zinc
b) conducts electricity, resists corrosion (=so useful for making pins in electrical plugs)
c)
- musical instruments and coins

Question 16

why are alloys harder + stronger than pure metals?

Answer 16

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

Question 17

neg of alloys disturbing regular lattice structure of pure metals?

Answer 17

alloys are less malleable + ductile than pure metal

Question 18

what is corrosion?

Answer 18

the reaction of a metal with substances in the surroundings, such as air and water

Question 19

what is the difference between rusting and corroding?

Answer 19

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

corroding is any metal’s reaction with surroundings

Question 20

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

Answer 20

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 21

describe how the rusting of iron is a redox reaction

Answer 21

iron loses electrons (is oxidised)

oxygen gains electrons (is reduced)

Question 22

describe how a piece of iron would completely corrode away

Answer 22

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 23

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

Answer 23

silver + hydrogen sulfide -> silver sulfide + hydrogen

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

Question 24

how is hydrogen sulfide produced?

Answer 24

naturally by bacteria

Question 25

which part of an object corrodes?

Answer 25

only the outer exposed surface

Question 26

what is the familiar orange-brown rust we see?

Answer 26

hydrated iron(III) oxide

Question 27

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

Answer 27

• get 3 nails + 3 test tubes
• first (with stopper/bung)
  with anhydrous calcium chloride (absorbs water vapour, keeps nail dry)
• second with boiled water (w/ no dissolved oxygen) (with stopper)
• third with air + water (no stopper on top)
• record appearance
  rust on only 3rd test tube

Question 28

what conditions causes corrosion to occur?

Answer 28

the presence of water and oxygen

Question 29

how can you reduce corrosion?

Answer 29

make a physical barrier between the environment and the surface of the metal
- stopping air and water reaching the surface of the metal

Question 30

what are the 2 main ways corrosion can be prevented?

Answer 30

• barrier methods

- sacrificial methods

Question 31

how does sacrificial protection work?

Answer 31

• the metal (iron) you want to protect is in contact with with a more reactive metal, such as iron/zinc
• more reactive metal corrodes first - it ‘sacrifices’ itself to protect the iron or steel

Question 32

in terms of electrons how does sacrificial protection work?

Answer 32

• the more reactive the metal, the more easily it loses electrons
• sacrical metals like zinc and magnesium lose electrons more easily than iron does
• they are more readily oxidised than iron

Question 33

what is galvanising?

Answer 33

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

Question 34

how do barrier methods work?

and give 4 examples

Answer 34

prevent oxygen and water from touching iron/(surface of the metal)

• painting
• coating with oil,grease, or plastic

Question 35

explain galvanising, incl 2 things it does

Answer 35

MD..

Galvanising involves dipping the metal object in molten zinc. After it has cooled and solidified, the thin layer of zinc does 2 things:

• it stops air and water from reaching the iron or steel below
• it acts as a sacrificial metal so that the object is protected, even if the zinc layer is damaged

//AD…

• 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

Question 36

Alloys topic;

How is bronze helpful in artists work - due to its molten property

Answer 36

Molten bronze expands slightly as it solidifies, so it fills in tiny details in an artist’s mould

Question 37

Corrosion topic:

Tell me about the corrosion of silver. (4)
And how this is seen in objects made out of silver (trophies, jewellery)

Answer 37

• silver does not easily react with oxygen in the air or with water
• however, it will corrode in the presence of hydrogen sulfide, H2S, a gas produced naturally by bacteria
• the hydrogen sulfide reacts with silver when oxygen and water are also present
• the reaction corrodes silver, producing a thin layer of black silver sulfide, Ag2S
• this makes objects made out of silver, such as trophies and jewellery, turn black, so they need to be cleaned

Question 38

The familiar orange-brown rust seen is ___.

Tell me about it.

Answer 38

Hydrated iron (III) oxide.
It easily flakes off the surface of the object, exposing fresh metal underneath.

Question 39

When can rusting continue until

Answer 39

Rusting can continue until an iron or steel object has completely corrodes away

Question 40

4 methods of rust prevention :

Answer 40

• Painting
• Coating with oil, grease, or plastic
• Plating with zinc (galvanising)
• Plating with tin

Question 41

Problems with paint, oil, grease, plastic coatings

Answer 41

• If paint is damaged, rusting starts on the exposed metal
• it continues underneath the paint
• the paint eventually flakes off, exposing fresh metal to air and water
• oil/grease/plastic coatings have similar problems

Question 42

Ferrous meaning

Answer 42

(chiefly of metals) containing or consisting of iron.

Question 43

Sacrificial protection is useful where __ is difficult

W/ example

Answer 43

Painting

• ships have zinc or magnesium blocks bolted onto their hulls below the waterline
• these protect the hull from rusting, but gradually corrode away and have to be replaced

Question 44

Iron rusting, half equation

Answer 44

During rusting, iron atoms lose electrons and are oxidised to iron(III) ions:

Fe -> Fe 3+ + 3e-

Question 45

How does metal plating work, in general

Answer 45

A layer of metal plated onto an iron or steel metal object prevents air and water from reaching the iron or steel below

Question 46

Tin plating, and its disadvantage

Answer 46

• tin plating involves electroplating the steel object with tin, or dipping it in molten tin
  (- the inside of steel food cans is protected by tin plating)
• however, tin is less reactive than iron
• if the tin layer is damaged, the steel acts as a sacrificial metal for the tin, and it rusts even faster than normal