Topic 5 Flashcards
(23 cards)
Explain how the methods of extraction of the metals in this section are related to their positions in the reactivity series
Reactivity Series (Most to Least Reactive): Potassium, Sodium, Calcium, Magnesium, Aluminium, (CARBON), Zinc, Iron, Tin, Lead, (HYDROGEN), Copper, Silver, Gold, Platinum
Anything LESS reactive than carbon can be displaced from its ore by carbon (eg iron)
Anything MORE reactive than carbon can’t and so is extracted by electrolysis (eg aluminium)
Describe and explain the extraction of aluminium from purified aluminium oxide by electrolysis, including:
i the use of molten cryolite as a solvent and to decrease the required operating temperature
ii the need to replace the positive electrodes
iii the cost of the electricity as a major factor
Aluminium oxide has a very high melting point and hence it is dissolved in molten cryolite to make the electrolyte. The mixture has a much lower melting point and is also better conductor of electricity than molten aluminium oxide.
The electrodes are made of graphite (carbon) and they need to be replaced regularly because of the hot temps and the carbon anodes burn with oxygen to create carbon dioxide. This means that they all need to be replaced regularly and this adds to the costs of the extraction.
Large amounts of energy are needed to produce aluminium, this is why using molten cryolite saves quite a lot of money, as it has a reasonably low melting point and acts as a solvent for aluminium oxide.
Write ionic half-equations for the reactions at the electrodes in aluminium extraction
Two equations that I need to know:
Al^3 + 3e^- —> Al
2O^2- —> O2 + 4e^-
(The Al and the O2 come from the aluminium oxide which is broken down via electrolysis)
Describe and explain the main reactions involved in the extraction of iron from iron ore (haematite), using coke, limestone and air in a blast furnace
In order to extract iron from hematite (iron ore), you need a blast furnace, coke (for reducing the iron oxide to iron metal) and limestone (for taking away impurities). The process is as follows…
- Hot air is blasted into the furnace, this makes the coke burn much faster than normal, and also raises the temp to around 1500 degrees Celsius. The coke burns to produce carbon dioxide (C + 02 —> CO2)
- The CO2 then reacts with unburnt/leftover coke, producing carbon monoxide (CO2 + C —> 2CO)
- The carbon monoxide will then react with the iron ore, producing iron (3CO + Fe2O3 —> 3CO2 + 2Fe)
- The limestone removes the silicon dioxide (SiO2) that is the main impurity. This happens as the limestone is decomposed by the heat into calcium oxide and carbon dioxide (CaCO3 —> CaO + CO2). The calcium oxide then reacts with the silicon dioxide forming calcium silicate, aka slag (CaO + SiO2 —> CaSiO3).
- The iron and slag are both molten so sink to the bottom of the furnace. However, slag is less dense than iron so the slag sits into of the iron, they are both tapped off. (Weird ass english)
NOTE: Although the slag is useless in this, the process is still sustainable as the slag is not wasted. It can be used in fertilisers and road building
NOTE NOTE: It is very important understand that this a reduction reaction (the iron is reduced as it loses oxygen).
Explain the uses of aluminium and iron, in terms of their properties
Aluminium:
- Airplane bodies: high strength-to-weight ratio
- Overhead power cables: Good conductor of electricity
- Saucepans: Good conductor of heat
- Food cans: Non-toxic
- Window frames: resists corrosion
Iron:
- Car bodies: Strong
- iron Nails: Strong
- Ships, girders and bridges : Strong
Understand that crude oil is a mixture of hydrocarbons
Crude oil is made up of different hydrocarbons (molecules with ONLY hydrogen and carbon atoms in them)
Describe and explain how the industrial process of fractional distillation separates crude oil into fractions
Fractional Distillation:
Crude oil, as such, has no direct use. it has to be refined before it is any use. The first step in the refining of crude oil is fraction distillation.
Fractional distillation is carried out in a fractionating column, The column is hot at the bottom and gradually becomes cooler at the top.
The crude oil is split into various fractions as described below. A fraction is a mixture of hydrocarbons with very similar boiling points.
Crude oil is heated to convert it into a vapour. The vapour is then fed into the bottom of the fractionating column.
The hydrocarbons with very high boiling points (fuel, oil and bitumen) immediately turn into liquid and are tapped off at the bottom of the column.
Recall the names and uses of the main fractions obtained from crude oil: refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen
Refinery Gases - Bottled gas Gasoline (Petrol) - Fuel for cars *Naptha* - Making chemicals Kerosene - Aircraft fuel Diesel - Fuel for cars, lorries, buses Fuel Oil - Fuel for ships, power stations Bitumen - For roads and roofs
Describe the trend in boiling point and viscosity of the main fractions
The lower the boiling point, the lower the viscosity, and vice verse
NOTE: The lower the viscosity, the thinner the substance runs, the higher the viscosity, the thicker something is (as liquid). For example, water has a super low viscosity, whilst syrup has a higher viscosity than water.
Understand that incomplete combustion of fuels may produce carbon monoxide and explain that carbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen
Usually hydrocarbons combust with oxygen to give carbon dioxide and water, like so:
- Hydrocarbons + Oxygen -> Carbon Dioxide + Water
However, if there is not enough oxygen, resulting in an incomplete combustion, the following reaction will be produced:
- Hydrocarbons + Oxygen -> Carbon Monoxide + Carbon + Water
Carbon monoxide is poisonous because tit bonds with haemoglobin in the blood instead of oxygen, meaning that the oxygen isn’t carried around the body.
Understand that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming nitrogen oxides
The temperature in a car engine is high enough for nitrogen and oxygen from the air to react to form oxides of nitrogen. These oxides are also passed out through the exhaust of the car and when they get into the atmosphere, they can dissolve in the water in the air to form acid rain.
Understand that nitrogen oxides and sulfur dioxide are pollutant gases which contribute to acid rain, and describe the problems caused by acid rain
Sulfur dioxide mix with clouds forming dilute sulfuric acid, which is very acidic. Nitrous oxide also mixes with clouds, forming nitric acid. These fall as acid rain which causes lakes to become acid which kills plants, animals, trees and damages limestone buildings and statues.
Understand that fractional distillation of crude oil produces more long-chain hydrocarbons than can be used directly and fewer short-chain hydrocarbons than required and explain why this makes cracking necessary
Fractional distillation produces more long-chain hydrocarbons:
- They are saturated (all single bonds)
- Less reactive
- Alkanes are less flammable (less volatile)
- Alkanes are more viscous (thick fluid)
Fractional distillation produces less short-chain hydrocarbons:
- Unsaturated (double bonds, triples bonds)
- More reactive
- Alkenes are more flammable (more volatile)
- Alkenes are less viscous (thin & runny liquid)
Why is cracking necessary?
- Less useful longer-chain (alkanes) produced are converted into more useful shorter-chain (alkanes)
- They are converted by catalytic cracking
- Cracking is the decomposition of longer hydrocarbon chains to shorter hydrocarbon chains using heat and a catalyst
- Longer chain (alkane) —> alkene + alkane
- Longer chain (alkane) —> alkene + hydrogen (for shorter chain alkene)
- Cracking is always cracking an alkane to produce 1 alkene and 1 alkane
- eg. C6H14 -> C2H6 (ethane) + C4H8 (butene)
- Cracking is always cracking an alkane to produce 1 alkene and 1 alkane
- Alkanes are always CnH2n+2
- Alkenes are always CnH2n
Describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking, using silica or alumina as the catalyst and a temperature in the range of 600–700 degrees celcius
Catalyic Cracking:
- Long chain hydrocarbons are passed over a hot catalyst; solica or alumina, at 600-700 degrees Celsius
- Causing them to break into smaller molecules
- As some atoms are lost from molecules, they become unsaturated (alkenes); they can form double bodns
- Produces alkenes and shorter chain alkanes.
Understand that an addition polymer is formed by joining up many small molecules called monomers
A polymer is just a very long saturated chain (saturated as it has no carbon double bonds). Small molecules called monomers join together to make polymers. One type of polymer is an addition polymer. The monomers that make up additional polymers are alkenes as they have a carbon-carbon double bond. If alkenes are put under a high pressure with a catalyst, they will break their carbon-carbon double bond and polymerise (join together), forming a polymer.
Draw the repeat unit of addition polymers, including poly(ethene) and poly(propene)
GOOGLE FOR IMAGES
To find the repeating unit, just find the section of the polymer that is repeated and draw it out, writing the number of monomers there are next to it (if you don’t know how many monomers there are, you just put an ‘n’)
Deduce the structure of a monomer from the repeat unit of an addition polymer
In the simplest terms: take away the two ‘floating’/empty bonds at the sides and make a carbon-carbon double bond between 2 carbons instead.
Describe some uses for polymers, including poly(ethene), poly(propene)
Polyethene is light and stretchy making it ideal for packaging such as plastic bags, water bottles/food containers and carpets.
Polypropene is a tough polymer but is quite flexible and heat resistant too, this makes it ideal for making things like crates.
Explain that addition polymers are hard to dispose of as their inertness means that they do not easily biodegrade
Addition polymers are unreactive because they are saturated, which means they don’t biodegrade (decompose by bacteria or other living organisms) easily. Solutions used today include:
- Burning (not good, produces harmful gases)
- Landfills (takes up a lot of useful land and harmful chemicals leak into the soil)
- Recycling (good for the environment but uses up energy and isn’t always cheap)
Understand that nitrogen from air, and hydrogen from natural gas or the cracking of hydrocarbons, are used in the manufacture of ammonia
Ammonia is manufactured using hydrogen and nitrogen (as ammonia is NH3). The equation for the reaction is…
N2 (g) + 3H2(G) ⇌ 2NH3 (g) (+heat)
Hydrogen is sourced from natural gas. Nitrogen is sourced from the air (as the air is 78% nitrogen).
The manufacture of ammonia with hydrogen and nitrogen is reversible, therefore, as soon as ammonia is made, it starts to turn back into nitrogen and hydrogen. This means that not all of the nitrogen and hydrogen is converted to ammonia and not all ammonia is converted into nitrogen and hydrogen (because, as soon as nitrogen and hydrogen are produced, it starts to turn into ammonia). This means the reaction reached a dynamic equilibrium.
Describe the manufacture of ammonia by the Haber process, including the essential conditions:
i a temperature of about 450°C
ii a pressure of about 200 atmospheres
iii an iron catalyst
Nitrogen + Hydrogen ⇌ Ammonia
N2 + 3H2 ⇌ 2NH3
Temperature: 450°C (higher temp increases reaction, but reduces yield)
Pressure: 200 atm (higher pressure used to increase yield, but is expensive)
Using an iron catalyst (increases rate of reaction)
Nitrogen and Hydrogen (whilst combining) 1:3 by volume
Understand how the cooling of the reaction mixture liquefies the ammonia produced and allows the unused hydrogen and nitrogen to be recirculated
Ammonia is removed by cooling down the reaction mixture and condensing ammonia into liquid ammonia
The unused/unreacted hydrogen and nitrogen is then recycled.
Describe the use of ammonia in the manufacture of nitric acid and fertilisers
Uses of Ammonia:
- Put into fertilisers; contains nitrate ions, which plants need to make amino acids and so proteins plants need to grow
- Reacts with oxygen to make nitric acids
4NH3 + 802 —> 4HNO3 + 4H20
