C6.1 (2) - ethanol, alloys, corrosion Flashcards
c6.1.5 - making ethanol c6.1.10 - alloys c6.1.11 - corrosion c6.1.12 - reducing corrosion
what are the two methods of making ethanol? (and describe each one briefly)
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
why is yeast added to the glucose solution in order for it to ferment?
as it contains enzymes which catalyse the conversion of glucose to ethanol and carbon dioxide
conditions for fermentation to take place? (and explain why)
- 35C (too low = yeast cells inactive, too high = enzymes denature)
- atmospheric pressure
what is the word equation for hydration to occur (to produce ethanol)?
ethene + steam ⇌ ethanol
what are the conditions needed for hydration to produce ethanol?
- 300C
- 60 atmospheres
- phosphoric acid catalyst
- therefore only occurs in a laboratory
- exothermic reaction
REVERSIBLE REACTION
compare fermentation of sugars and hydration of ethene (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)
define an alloy
a mixture of a metal and one other element
STEEL
a) describe composition
b) property
c) uses
a) iron + carbon + other metals
b) high tensile strength, ductile
c) buildings, briges, car doors
what does it mean if a material has high tensile strength (simply)?
can be stretched/pulled a lot before breaking
why can steel alloys be designed for specific uses?
and give examples
- as more carbon added = harder - chisels (brittle)
- low carbon = easily shaped/softer - car body
- stainless steel = resistant to corrosion
DURALUMIN
a) describe composition
b) properties
c) uses
a) aluminium + copper
b) low density, moderate tensile strength (stronger than pure aluminium)
c) aircraft parts
SOLDER
a) describe composition
b) properties
c) uses
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
BRONZE
a) describe composition
b) properties
c) uses
a) copper + tin
b) stronger + harder than copper
resists corrosion
c) propellers for ship (hard)
wires
statues (resist corrosion)
BRASS
a) describe composition
b) properties
c) uses
a) copper + zinc
b) conducts electricity, resists corrosion
c)
- pins in electrical plugs conducts)
- instruments and coins
why are alloys harder than pure metals?
- different-sized atoms (due to diff elements)
- so particles cannot slide over each other
- disrupts regular lattice structure of pure metal
neg of alloys disturbing regular lattice structure of pure metals?
alloys are less malleable + ductile than pure metal
what is corrosion?
the reaction of a metal with substances in the surroundings
what is the difference between rusting and corroding?
rusting is when either iron or steel corrode with oxygen and water
corroding is any metal’s reaction with surroundings
what is the word and symbol equation for the rusting of iron?
iron + oxygen + water -> hydrated iron (III) oxide
4Fe(s) + 3O (g) + 2H O (l) -> 2Fe O H O(s)
2 2 2 3 2
describe how the rusting of iron is a redox reaction
iron loses electrons (is oxidised)
oxygen gains electrons (is reduced)
describe how a piece of iron would completely corrode away
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
what is the word and then the symbol equation for how silver corrodes?
silver + hydrogen sulfide -> silver sulfide + hydrogen
2Ag(s) + H S(g) -> Ag S(s) + H (g)
2 2 2
which part of an object corrodes?
only the outer exposed surface
what is the familiar orange-brown rust we see?
hydrated iron(III) oxide
how would you set up an investigation to see what substances are needed for rusting to happen?
- 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
what conditions causes rusting to occur?
the presence of water and oxygen
how can you reduce corrosion?
make a physical barrier between the environment and the surface of the metal
what are the 2 main ways corrosion can be prevented?
- physical barrier methods
- sacrificial methods
how does sacrificial protection work?
- coating the metal you want to protect with a more reactive metal
- more reactive metal corrodes first, protecting the metal within
in terms of electrons how does sacrifical protection work?
- more reactive element loses electrons more easily
what is galvanising?
plating a layer of molten zinc onto an object to prevent air + water reaching the metal below
(acts as a sacrifical metal)
how do barrier methods work?
and give 4 examples
prevent oxygen and water from touching iron
- paint/oil/grease/electroplating w/ tin/plastic
explain galvanising and how it is special (answer on here is a bit terrible)
- 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
