IGCSE Chemistry - Metals extraction and Rust

IGCSE Chemistry - Metals extraction and Rust

memorize.aimemorize.ai (lvl 286)
Section 1

Preview this deck

What is coke?

Front

Star 0%
Star 0%
Star 0%
Star 0%
Star 0%

0.0

0 reviews

5
0
4
0
3
0
2
0
1
0

Active users

0

All-time users

0

Favorites

0

Last updated

2 years ago

Date created

Mar 1, 2020

Cards (83)

Section 1

(50 cards)

What is coke?

Front

impure carbon

Back

When is iron oxide reduced by C itself?

Front

in the hotter parts of the furnace

Back

How are Al cables strengthened?

Front

core of steel

Back

What is roasting?

Front

heating a compound in air to form an oxide

Back

How can the metal then be obtained from the oxide?

Front

must be reduced NEED TO ADD ELECTRONS!

Back

What is the electrolyte?

Front

solution of aluminium oxide dissolved in molten cryolite

Back

What happens first to the limestone that is put in the furnace? What type of reaction is this?

Front

V.Hot temperatures in the furnace so the limestone undergoes thermal decomposition to form calcium oxide and carbon dioxide CaCO₃ → CaO + CO₂ ENDOTHERMIC

Back

unreactive metals found...

Front

native - so unreactive that they are found naturally as the uncombined element

Back

What is the issue with aluminium oxide?

Front

HIGH MELTING POINT NOT PRACTICAL TO ELECTROLYSE THIS MOLTEN AS LOTS OF ENERGY IS NEED TO MELT IT

Back

How is Al extracted?

Front

ELECTROLYSIS - FAIRLY REACTIVE METAL

Back

What is the iron straight from the furnace?

Front

pig iron

Back

What happens to the hot waste gases at the top of the furnace?

Front

piped away used to heat the air blast at the bottom

Back

What is the blast furnace diagram?

Front

Back

What is the main reducing agent in the furnace and where?

Front

CO especially in the cooler parts

Back

What does cryolite do?

Front

it is another aluminium compound that melts at a more reasonable mixture and so allows for the Al2O3 to melt at a lower temp LOWERS COSTS

Back

What temp is the solution of pure aluminium ore and molten cryolite?

Front

about 1000 degrees

Back

What two factors govern the method used for extraction?

Front

cost of... ENERGY REDUCING AGENT

Back

Why did the Al age not occur very early on?

Front

because Al is above C in the RS so it cannot be made accidently by reacting Al₂O₃ WITH Carbon - needed to be extracted using electricity which was only discovered much later

Back

When is the CO2 reduced by more C?

Front

in the very hot parts of the furnace

Back

How else can metals be extracted (Ti)?

Front

heat the compound with a more reactive metal

Back

How does CaO remove silicon dioxide?

Front

CaO + SiO₂ → CaSiO₃

Back

Why would silicon dioxide clogging the furnace be an issue?

Front

furnace would have to be shut down whilst solid is removed VERY COSTLY

Back

Why is electrolysis not ideal?

Front

lots of electricity = EXPENSIVE PROCESS Therefore the metal product is also expensive to then buy

Back

How is a sulfide like zinc blende (sphalerite) converted into an oxide?

Front

heated in air 2ZnS + 3O₂ → 2ZnO + 2SO₂

Back

What happens to this product? What is the common name?

Front

melts and trickles to the bottom of the furnace as a molten SLAG which floats ontop of the molten iron and is tapped off separately ROAD BUILDING AND FERTILISER

Back

Why is carbon used?

Front

cheap source of heat

Back

Extract metals zinc and below?

Front

heat with C/CO REDUCING AGENT

Back

What are the stages of the extraction of iron?

Front

C + O₂ → CO₂ CO₂ + C → 2CO Fe₂O₃ + 3CO → 2Fe + 3CO₂ Fe₂O₃ + 3C → 2Fe + 3CO

Back

How is it formed?

Front

it is cooled rapidly and solidified by running into sand moulds

Back

What is silicon dioxide?

Front

a non-metal, acidic oxide

Back

Steps to the extraction of Al?

Front

Bauxite is purified to produce Al₂O₃ Al.Oxide has a very high melting point - it is dissolved in molten cryolite to make an electrolyte which has a lower MP and is a better conductor of electricity At the cathode: Al³⁺ + 3e⁻ →Al Aluminium melts and collects at the bottom of the cell - then tapped off At the anode: 2O²⁻ →O₂ + 4e⁻ Some of the oxygen produced then reacts with the C of the electrode due to the HIGH TEMPS to produce CO₂ gas. Therefore the anode gradually burns away and needs to be replaced regularly.

Back

What is done to solve this problem?

Front

the aluminium oxide is dissolved in molten cryolite

Back

What dictates the method of metal extraction?

Front

position in RS

Back

What are the issues with this?

Front

Bound to be expensive -> the mroe reactive metal itself will have had to be extracted by an expensive process

Back

What currents are used in the cell for the electrolysis of Al? WHAT BENEFIT DOES THIS HAVE?

Front

very high the heat generated by the huge currents keeps the electrolyte molten so electrolysis remains constant BUT ELECTRICITY V.EXPENSIVE

Back

Why does Al resist corrosion?

Front

it has a very strong yet thin layer of aluminium oxide on the surface this prevents anything else from getting to the surface and reacting with it

Back

What is the product called?

Front

calcium silicate

Back

Aluminium extractor diagram

Front

Carbon anodes and cathodes Outer layer is a steel tank lined with heat resistant bricks The extractor is filled with a solution of Al₂O₃ in molten cryolite and the formed molten Al collects at the bottom

Back

What is put into the BF?

Front

iron ore, coke and limestone

Back

What happens to the iron that is produced?

Front

it melts and flows to the bottom of the furnace where it can be tapped off

Back

What are the uses of Al?

Front

ALLOYS OF Al: RESIST CORROSION LOW DENSITY STRONG CONDUCT ELEC/HEAT AEROPLANE BODIES - resists corrosion, low density and strong, high strength-to-weight ratio Pots and pans - shiny, resists corrosion, heat conductor Overhead power cables - resists corrosion, low density, electricity conductor Food cans - non toxic, resists corrosion

Back

What is the first reaction?

Front

strongly exothermic

Back

How are metals above zinc extracted?

Front

electrolysis - metal ions are reduced by being given ions at the CATHODE!

Back

What are ores?

Front

oxides compounds easily converted to oxides

Back

Why is limestone added to the furnace?

Front

to remove impurities in the ore which would clog the furnace with solid material

Back

What is calcium oxide?

Front

a basic oxide - reacts with acidic oxides/acids to form salts

Back

What is a typical impurity that must be removed from the furnace?

Front

silicon dioxide SiO₂

Back

Why must you control how much limestone is put in the furnace?

Front

the thermal decomposition of limestone that occurs is ENDOTHERMIC If too much then it will begin to cool the furnace

Back

Why was the Bronze age before the Iron age?

Front

Bronze = alloy of copper and tin Both metals are low in RS Easily made from ores by heating with C Iron h/e can also be made by heating with C but at v.high temps. More diffcult to purify into a useful form than copper in bronze - so became useful much later

Back

What does this occur naturally as?

Front

quartz

Back

Section 2

(33 cards)

What is cast iron used for and why?

Front

castings manhole covers, guttering, engine blocks very fluid and molten, doesnt shrink much when solidifies

Back

What is it used for?

Front

nails, car bodies, bridges/girders, ship building

Back

What is wrought iron?

Front

PURE iron

Back

What are the uses of high-carbon steel?

Front

cutting tools, masonry nails

Back

What are the issues?

Front

EXPENSIVE

Back

What are the sacrifical anodes used in underground pipelines?

Front

sacks containing lumps of magnesum

Back

Why is Al not used in pure form for the products it makes?

Front

not very strong Al alloys are used instead that are strengthened by adding silicon, copper or magnesium

Back

How is cast iron formed?

Front

pig iron remelted cooled under controlled conditions

Back

What is mild steel?

Front

iron with up to 0.25% carbon

Back

What does salt do?

Front

rusting accelerated in the presence of electrolytes like salt

Back

What are the uses of stainless steel?

Front

kitchen sinks, saucepans, knives and forks, gardening tools, corrosion-resistant vessels in the food industry

Back

What are the issues with cast iron?

Front

very brittle - shatters if hit hard

Back

How can rusting be prevented? BARRIER METHOD

Front

keep Oxygen and water away with a barrier paint grease oil plastic less reactive metal like tin

Back

What is rusting?

Front

a chemical reaction between iron, water and oxygen

Back

Why is it very resistant to corrosion?

Front

chromium and nickel form strong oxide layers which protect the iron

Back

How does the Zinc corroding prevent the Iron eventually corroding?

Front

During the process of Zinc corroding this occurs; Zn → Zn²⁺ + 2e⁻ These electrons flow to the iron and so any iron atoms that have lost electrons regain them! If iron cannot form ions it CANNOT RUST

Back

What is it used for ? Why?

Front

decorative work like gates and railings EASY TO WORK B/C FAIRLY SOFT - NO CARBON

Back

What has happened to the iron to form rust?

Front

iron is oxidised to form Fe²⁺ ions these are then oxidised by the air to form Fe³⁺ ions

Back

IS iron used as a pure form for most of its uses?

Front

no - alloys with carbon are stronger MOST IRON IS IN THE FORM OF MILD STEEL WITH SMALL AMOUNTS OF C

Back

Why is it used for masonry nails?

Front

strong - can be hammered into concrete /brick where other nails would bend

Back

How can rust be prevented by alloying?

Front

stainless steel - alloying iron with Chromium and Nickel prevents it from rusting as the other metals form a strong impenetrable oxide layer

Back

What is the problem though?

Front

once this barrier is penetrated (scratched) iron is again exposed to oxygen and water and so will rust

Back

What is the formula for rust?

Front

hydrated iron oxide Fe₂O₃.xH₂O

Back

What is stainless steel?

Front

alloy of iron with chromium and nickel

Back

What are the benefits of mild steel?

Front

the small amount of carbon increases STRENGTH AND HARDNESS of iron

Back

What is high carbon steel?

Front

iron with 0.25-1.5% carbon

Back

What can wrought iron therefore not be used for?

Front

structural purposes - fairly soft, lack of strength

Back

What are sacrificial anodes? How are they protective?

Front

zinc blocks that are attached to the metal hulls/keels of ships...the corrosion of more reactive zinc prevents the iron from rusting

Back

What is cast iron?

Front

very impure iron 4% carbon

Back

How do they work?

Front

they are attached at regular intervals along the pipe very reactive Mg corrodes in preference to the iron electrons produced as the Mg corrodes and forms ions flow to the iron atoms and prevent their ionisation

Back

How does galvanisation prevent rusting?

Front

1. barrier to water and oxygen if not scratched 2. when scratched, Zinc corrodes instead of Iron because it is more reactive

Back

What are the problems here?

Front

more carbon means it is stronger yet more brittle!

Back

What is galvanised iron?

Front

iron coated with a layer of zinc

Back