C6.1 Improving processes and products Flashcards
What elements do plants need?
Nitrogen , Phosphorus , Potassium
If a plant receives a limited supply of these elements…
Plants will not grow well and show symptoms of mineral deficiency
Lack of nitrogen causes?
Poor growth , yellow leaves
Lack of phosphorus causes?
Poor root growth , discoloured leaves
Lack of Potassium causes?
Poor fruit growth , discoloured leaves
Fertilisers
Substance that replenish and replace elements used by plants as they grow
In what form can plant roots absorb these elements
When they are in a water soluble form :
- nitrate ions ( NO3-)
-phosphate ions ( PO34-)
-potassium ions ( K+)
-ammonium ions ( NH4+)
NPK fertilisers
Provide nitrogen phosphorus and potassium in water soluble compounds
What is the Haber Process ?
Manufactures Ammonia from nitrogen and hydrogen
-reversible reaction
Word Equation for the Haber Process:
N2 ( g ) + 3H2 ( g ) <——> 2NH3 ( g )
Which raw materials are required for the Haber Process?
-air
-natural gas
-steam
What percent of ammonia is used to make fertilisers?
80%
The atmosphere consists of ___% nitrogen
78%
How is nitrogen manufactured for the Haber Process?
Fractional distillation of liquified air
How is hydrogen manufactured for the Haber Process?
Reacting natural gas ( methane ) with steam
What are the conditions required for the Haber Process?
-presence of iron catalyst
-high temperature
-high pressure
Ammonium nitrate
NH4NO3
Ammonium sulfate
(NH4)2SO4
Ammonium Phosphate
(NH4)3PO4
Potassium Nitrate
KNO3
Which compounds of fertilisers can we make in the lab ?
-potassium sulfate
-ammonium sulfate
Describe the method of making potassium sulfate in the lab (6)
Made from potassium hydroxide ( KOH) and sulphuric acid ( H2S04 )
-add KOH to a conical flask alongside a few drops of phenolphthalein indicator
-add dilute sulphuric acid from a burette , stopping when the indicator changes from pink to colourless
-add ‘activated charcoal’ , this binds/attracts to the phenolphthalein which can then be easily filtered out of the mixture to avoid including any impurities
-warm the filtrate to gently evaporate the water , leaving potassium sulfate behind
Why is single indicator ( phenolphthalein or methyl orange ) used instead of universal indicator ?
This provides a distinct colour changes , so adding this enables you to determine the exact point when the alkali has been neutralised
How can the experiment be made more accurate ?
- use a white tile which makes the colour change more distinct and easier to see
How is ammonium sulfate made in the lab?
-place dilute ammonia solution in a conical flask with methyl orange indicator
-add dilute sulphuric acid from a burette / dropping pipette , stopping when the indicator changes from yellow to red
-when reaching the end point ( distinct colour change ) , add a little extra ammonia solution to ensure the reaction is complete
What are some hazards when making ammonium sulfate and how can these be prevented ?
-ammonia and potassium hydroxide are highly alkaline and irritant : wear gloves , eye protection and lab coat
-ammonia gives off an irritating sharp smell : carry out the experiment in a fume cupboard or be cautious when inhaling near the experiment
Batch process
Small amount at one time eg in a school lab
Continuous process
Large amounts and continue all the time eg large industrial processes
Features of batch process are?
-low rate of production
-low cost
-large no of people / workers needed
-frequent shut down periods
-low ease of automating the process
Features of continuous processes are?
-high rate of production - ADV
-high cost of equipment - DISADV
-small no of workers needed - ADV
-rare shut down periods - ADV
-high ease of automating
What is the difference between making substances in a lab vs industrially in a factory ?
Lab starts off with pure substances bought from chemical manufacturers , whereas fertiliser factors start with raw materials ( which must be purified either before or the whole substance after )
What type of reaction is the Haber Process?
Exothermic
Conditions for the Haber Process ?
-pressure of 200 ATM ( 20MPa )
-a temperature of 450 degrees Celsius
-an iron catalyst
Under these usual conditions , what is the equilibrium yield of ammonia ?
30%
Despite the low equilibrium yield , why is ammonia still made ( The Haber Process ) conducted under such conditions?
- if pressure is increased , equilibrium position moves to the right and equilibrium yield of ammonia increase
-however this is extremely hazardous and also expensive
-the higher equilibrium yield does not justify the additional costs , so manufacturers must comprise with a lower pressure
What factors determine the temperature chosen for the Haber Process?
-if temp is increased, equilibrium position moves to the left , decreasing yield of ammonia therefore a high equilibrium yield is favoured by a low temperature
-therefore manufacturers have to compromise with temp and pick a temperature ( 450 C ) low enough to produce a reasonable yield but high enough to achieve a good rate of reaction
-additionally , the iron catalyst works more efficiently about 400 C
What other conditions are chosen to increase yield of ammonia during the Haber Process?
-mixture of gases leaving the reaction vessel is cooled so that ammonia is liquefied
-this allows ammonia to be removed and products ( unreacted nitrogen and hydrogen ) to be recycled
-this improves the overall yield to 95%
Uses of sulfuric acid?
Fertilisers , oil refining , metal extraction , making paints and polymers
How many steps are needed to synthesise sulfuric acid?
3 steps , including the Contact process
Which raw materials are required to make sulfuric acid?
-sulfur
-air ( any source of oxygen )
-water
Stage 1
sulfur burns in air to produce sulfur dioxide
-exothermic reaction
Word equation for stage 1 of synthesising sulfuric acid?
S + O2 ——> SO2
Stage 2 of producing sulfuric acid?
The Contact Process:
-sulfur dioxide and oxygen react together to produce sulfur trioxide
-exothermic reaction
Word equation for the Contact Process ( Stage 2 ) ?
2SO + O2 <——> 2SO3
What are the conditions chosen for the (reversible) Contact process?
-pressure of 2ATM
-temperature of 450 degrees Celsius
-a vanadium oxide catalyst , V2O5
Produces an equilibrium yield of 96%
Stage 3 of producing sulfuric acid?
Sulfur trioxide is converted tosulfuric acid
Word equation for stage 3?
H20 + SO3 ——> H2SO4
Renewable raw materials can be…
Replaced as they are used , and technically should not run out
How is ethanol made?
Via the process of fermentation , relies on yeast
What is the role of yeast during fermentation?
-it contains enzymes which catalyse the conversion of glucose solution to carbon dioxide and ethanol
Word equation for fermentation ?
Glucose ——> Carbon Dioxide + Ethanol
Chemical equation for fermentation including state symbols?
C6H12O6 (aq) ——> 2CO2 (g) + 2C2H5OH (aq)
How can fermentation be carried out in a school laboratory?
-place glucose solution and yeast in a conical flask
-use a rubber bung to seal the conical flask , collecting the gas and bubbling it through limewater
Non renewable materials are…
Materials that are used faster than they can be replaced
How is ethanol produced from non renewable materials
Ethene is obtained from crude oil , and is then hydrated to form ethanol
What type of reaction is the hydration of ethene ?
Exothermic and reversible
Chemical equation for the hydration of ethene?
C2H4 (g) + H2O (g) <——> C2H5OH ( g )
What is the state of steam?
Gas
- H2O with the state symbol (g)
Why can’t the hydration of ethene be carried out in a school laboratory?
-requires temp of 300 degrees Celsius
-pressure of 60ATM
-presence of a phosphoric acid catalyst
What are the ways in which ethanol is produced?
Fermentation of sugars and Hydration of ethene
Positive features of fermentation of sugars?
-low costs of raw materials
-can be carried out in school lab ; as it is carried out in moderate conditions
-low energy requirements
Negative features of fermentation of sugars?
-low rate of reaction
-low percentage yield
-low purity of product ( requires fractional distillation and filtering )
Positives of hydration of ethene?
-high rate of reaction
-high percentage yield
-high purity of product ( no by products )
Negatives of hydration of ethene?
-high cost of raw materials
-high temp and pressure
-high energy requirements
What is an ore?
A rock or mineral which contains enough metal to make it economical to extract it - the value of the metal is more than the cost of extracting it
What metal compound is found in malachite?
Copper carbonate
What metal compound is found in bauxite?
Aluminium oxide
What metal compound is found in haematite?
Iron ( III ) oxide
Where does carbon lie in the reaction series?
In between aluminium and zinc
What possible methods could be used to extract metal from its ores?
-electrolysis
-if the metal is less reactive than carbon , cheaper methods are used instead by heating the metal with carbon or carbon monoxide
Why is electrolysis not used to extract metal from its ores?
Electricity is expensive
Describe the first stage of extracting copper from copper (II) sulfide : word equation , chemical equation
Stage 1 : the copper (II) sulfide is “roasted” in air
Copper (II) sulfide + oxygen ——> copper (II) oxide + sulfur dioxide
2CuS(s) + 3O2(g) ——> 2Cu(s) + CO2(g)
Describe the second stage of extracting copper from copper (II) sulfide: word equation , chemical equation
Stage 2:Copper oxide is heated with carbon
Copper(II) oxide + carbon ——> copper + carbon dioxide
2CuO(s) + C(s) ——> 2Cu(s) + CO2(g)
Is the extraction of copper a redox reaction?
Yes
In the extraction of copper what is reduced?
Copper(II) oxide is reduced and is the oxidising agent
In the extraction of copper , what becomes oxidised?
Carbon gains oxygen and acts as the reducing agent
How else can copper oxide be reduced to copper?
-heating it with methane or with hydrogen
Why is copper extracted by heating copper oxide with carbon?
It is less reactive and is therefore displaced
It is a much cheaper process than electrolysis
How is iron extracted from its ore ?
Using a large reaction container called a blast furnace
What ore is iron extracted from?
Haematite
Which raw materials are used for the extraction of iron ( added to the top of the blast furnace)
-iron ore ( eg haematite which contains iron (II) oxide
-coke
-limestone
(Hot air is forced in at the bottom of the blast furnace)
Why is limestone added to the blast furnace?
It is used to purify the iron
Describe what occurs in the blast furnace (6)
Carbon reduces iron (III) oxide to iron , but carbon monoxide is the main reducing agent. So it is formed when coke reacts with carbon dioxide . The CO then reduces the iron oxide to iron . Molten iron trickles downwards in the blast furnace , but also contains sandy impurities from the iron ore . These impurities are removed using limestone , forming molten calcium silicate ( slag ) . This floats on top of the molten iron , and both the iron and slag are removed separately at the bottom of the furnace.
Describe the steps taken ( and chemical equation ) to reduce iron (iii) oxide to iron:
Stage 1 : Coke burns in hot air , producing CO2
C + O2 —> CO2
Stage 2 : More coke reduces the carbon dioxide , forming carbon monoxide
C + O2 —> 2CO
Stage 3 : Carbon monoxide reduces iron oxide to iron at around 1500:
3CO + Fe2O3 —> 3CO2 + 2Fe
What is slag?
Molten calcium silicate
After iron (III) oxide is reduced to iron , what happens?
At temps of 1500 degrees Celsius , the iron becomes molten and trickles downwards in the blast furnace , which contains sandy impurities from the iron ore . This is removed using limestone , which is mostly calcium carbonate
How are impurities removed from the molten iron?
Stage 1 : Calcium carbonate decomposes in high temperatures
CaCO3 ( s) —> CaO (s) + CO2 ( g)
Stage 2 : Calcium oxide reacts with silica from sandy impurities forming calcium silicate
CaO (s) + SiO2 (g) —> CaSiO3 (l)
After the iron is purified , what happens?
The slag floats on top of the molten iron , and they are both separately removed at the bottom of the blast furnace in the liquid state
Which ore is aluminium found in?
Bauxite
Why can’t aluminium be extracted from its ore in the same way as iron or copper?
It is more reactive than carbon , and must be extracted via electrolysis as opposed to heating compounds
Why is it a problem to electrolyse aluminium oxide?
It does not dissolve in water and has a very high melting point ( over 2000 degrees Celsius ) which would be costly to maintain
Electrolysis only works if the compound is in solution or molten - why?
So the ions are free to move throughout the fluid and towards their respective electrode
How is aluminium oxide electrolysed ?
-it is dissolved in molten cryolite ( which has a much lower BP )
-the mixture is contained in a huge electrolysis cell made with steel and lined with graphite
-the graphite lining acts as the cathode
-a series of large graphite blocks acts as the anode
Why is cryolite used in the electrolysis of aluminium oxide?
It is mixed with the aluminium oxide as it has a much lower boiling point and therefore can be molten at temperatures of around 900 as opposed to 1500
This reduces energy costs , which is the most important factor determining the cost of aluminium extraction
The cathode during electrolysis of aluminium oxide is:
The graphite lining of the electrolysis cell
The anode during electrolysis of aluminium oxide is:
A series of large graphite boocks
What happens at the cathode during electrolysis of aluminium oxide?
Aluminium is produced
Al3+ + 3e- —> Al
What happens at the anode of the electrolysis of aluminium oxide?
Oxygen is produced at the anode(s)
2O2- —> O2 + 4e-
Why might the anodes in an aluminium electrolysis cell need to be sometimes replaced?
They will react and lose mass , eventually decreasing in size
-graphite is a form of carbon so will form carbon dioxide
What is acid mine drainage?
Mines often flood , causing metal sulfides to be oxidised underwater . This produces sulfuric acid , and also other metal ores . This forms soluble metal compounds which leave with the water as it drains from the mine
What do bacteria do in bioleaching?
They oxides iron (II) and sulfide ions and use the energy transferred , sulfuric acid is also produced in the presence of water and oxygen . This breaks down copper sulfide ores and other minerals , releasing copper (II) ions and other metal ions
Low grades ores
Ores that contain too little metal for traditional methods to be profitable
Advantages of bioleaching?
It’s cheaper than traditional mining and processing
Utilises low grade ores
Natural process which does not need any special treatment
Disadvantages of bioleaching :
Slow process
May sometimes produce toxic substances
Care must be take to avoid these , and sulfuric acid, escaping into water and soil
What is phytoextraction?
When a crop is planted in a soil containing low grade ore or mine waste . A “complexing agent” is added so plants can absorb mineral ions more easily . The plants are then harvested and burnt to produced an ash with a high concentration of the metal . The metal can then be extracted , as if the ash was a high grade ore.
Advantages of phytoextraction:
Cheaper than traditional mining and processing
Produces less waste and involves smaller energy transferred
Closer to being a carbon neutral activity as it releases CO2 ( when plants are burnt ) but also absorbs it ( during photosynthesis of the plants growth )
Disadvantages of phytoextraction:
-slow process , crops may need replanting and harvesting for several years
-dependent on weather for photosynthesis
Compare the processes of phytoextraction and bioleaching
-phytoextraction uses certain plants to extract metals from low grade ores whereas bioleaching makes use of bacteria to break down copper sulfide
-both are relatively cheap
-phytoextraction adds to pollution as co2 is produced , whereas bioleaching does not have any effects ( unless toxic substances are produced)
-both processes are slow
What is an alloy?
A mixture of two or more elements , at least one of which is metal
Alloy of steel contains which metal?
Iron
Properties of steel
High tensile strength and ductile
Uses of steel
Buildings , bridges , cars
Duralumin allot contains which metals?
Aluminium and copper
Properties of duralumin
Strong and lightweight
Uses of duralumin
Aircraft parts
Solder contains which metals?
Tin and copper
Uses of solder?
Joining electrical components and copper pipes
Brass is made of which metals?
Copper and zinc
Uses of brass
Musical instruments and coins
Bronze is made up of which metals?
Copper and tin
What is bronze used for?
Bells , propellers for ships , musical instruments , metal artworks
Solders melting point ?
227 degrees Celsius
Why is the melting point of solder ( 227 ) useful for electrical components?
-it can join them without damaging them
-as it can easily become molten and flow into gaps between components , and then solidify quickly
-metals are good conductors of electricity , so the soldered joint allows an electric current to pass
When metals are bent or stretched , what happens to their atoms?
The layers of metal ions slide over one another
Why are alloys often stronger and harder than their individual metals? Example?
-the difference metal atoms are difference sizes , making it hard for the same metal ions to slide over one another
An example of this would be copper
Features of brass?
-conducts electricity ( not as well as copper )
-stronger then copper
-resists corrosion
Brass resists corrosion , meaning ?
It does not react easily with wir or water
Features of bronze?
-harder and stronger than copper
-resists corrosion
Corrosion
The reaction of a metal with substances in its surroundings , such as air and water
Why does silver corrode? What is formed?
( does not react easily with oxygen or water )
-corrodes in the presence of hydrogen sulfide , a gas naturally produced by bacteria
-this reacts with silver in the presence of oxygen or water
-this produces a think layer of black silver sulphide
How is the corrosion of silver avoided?
By constantly cleaning objects made of sikver
Hydrogen sulfide formula
H2S
Silver sulphide formula
Ag2S
Which type of metals do nor corrode?
Highly unreactive metals, such as gold and platinum
What type of reaction is rusting?
A redox reaction , iron is oxidised and oxygen is reduced
Word equation for when iron rusts
Iron + oxygen + water ——> hydrated iron (III) oxide
What must be present for rusting to occur?
Water and oxygen
What else speeds up rate of rusting?
Salt water , dissolved salts
How is rusting prevented?
-painting
-coating with oil , grease , or plastic
-plating with zinc ( galvanising )
-plating with tin
What is the downside to using methods such as painting and coating to prevent rusting?
If the paint , oil , or grease is damage , rusting will start on the exposed metal and continue underneath the paint , causing it to flake off . Eventually more and more fresh metal will be exposed to air and water
Name better ways of preventing rusting:
-sacrificial protection
-galvanising
When is sacrification used?
When a low reactivity metal is coated with a higher reactivity metal
Describe how sacrificial protection works
-metal is coated with another metal more reactive than it, such as magnesium or zinc
-as long as the metal remains in contact with the coated metal, the more reactive metal corrodes frost - hence sacrificing itself to protect the iron/steel
-
Why is sacrificial protection useful?
It is convenient for when painting or coating is difficult
Example of sacrificial protection?
Ships have zinc or magnesium bolts boosted into their hulls below the waterline , protecting it from rusting
-they have to be replaced as they gradually corrode
Explain why a more reactive metal will corrode first and quicker than a less reactive metal
Sacrificial metals such as magnesium and zinc lose electrons more easily than iron does ( more reactive = more easily loses electrons ) , and are also more readily oxidised than iron
What happens to iron during rusting?
The atoms lose electrons and are oxidised to iron (III) ions
Fe ——> Fe3+ + 3e-
How does metal plating work?
A layer of metal is plated onto an iron or steel metal object , preventing air and water reaching the metal below
What is the difference between metal playing and galvanising
Galvanising is specific to plating with molten zinc
Galvanising
Dipping the metal object into molten zinc , allowing it to cool and solidify
What does galvanising do?
- Stops air and water reaching iron or steel below
- Acts as a sacrificial metal so object is protected , even if zinc layer is damaged
Another example of metal plating:
Tin plating
What is tin plating?
Electroplating the steel object with tin , or dipping it in molten tin
Example of tin plating?
Insides of steel food cans are protected by tin plating
Farm gates
Disadvantages of Tin plating:
Tin is less reactive than iron , so if it becomes damaged , the steel would act as a sacrificial metal and rust even faster than normal
What are ceramics ?
Hard , non metallic metals
Examples of ceramics
Brick , China , Porcelain , Glass
Describe the structure of ceramics
-contain metals and non metals
-forming giant ionic lattices or giant covalent structures
Typical properties of ceramics?
-high MP
-hard and stiff , but brittle
-poor conductors of electricity and heat
Why are ceramics so unreactive?
The compounds in them are mainly oxides
How is glass made?
Melting sand , and then allowing it to cool and solidify
-has an irregular giant structure without crystals , and is therefore usually transparent
How are other ceramics produced?
-heating clay to high temps
-forming tiny crystals , joined together by glass
How do China and porcelain appear glassy ?
Coated in a glaze and reheated , forming a smooth , hard and waterproof surface
What are the ideal properties for a material used for an overhead electrical cable?
-good conductor of electricity
-lightweight
-strong ( does not snap easily )
-resist corrosion
Which metals are suitable for overhead electrical cables?
-aluminium ( good conductor , good tensile strength , lightweight )
-copper ( best conductor , low tensile strength , very high density )
-steel ( low conductor , best tensile strength , heavy )
Which materials are good for insulators?
-glass
-porcelain - best for insulators
-poly (propene)
What is poly(propene)?
A tough , flexible polymer
What is a composite material?
Material made from two or more materials with different properties are combined
How are composite materials used in clothes?
Polyester cotton = cotton thread and polyester fibre
-more hardwearing and easier to wash and dry
Describe another composite material :
Fibre ( carbon ) glass = glass ( carbon ) fibres in a resin
Strong , tough , lightweight
Uses of fibreglass :
Canoes , boats , surfboard
Carbon fibre : sports equipment and racing cars
What materials is concrete made from?
Aggregate , sand , and cement ( and water )
Properties of concrete
High compressive strength - good for foundations
Low tensile strength - cracks and breaks under high pressure
How is the low tensile nature of concrete resolved?
By embedding steel rods in concrete ( which have a high tensile strength )
-creates the composite material called steel-reinforced concrete
Plywood
A composite material in which thin sheets of wood are glued together in layers so the grains are at right angles to each other
-resists bending
-used for floors and walls
What is a life cycle assessment ?
A cradle-to-grave analysis of the impact of making , using , and disposing of a manufactured product
What data should a LCA include?
-sustainability
-environmental impact
-life span of the product and whether it can be recycled
-disposal / how easily the materials decompose
What happens to materials and products if they are unable to be recycled?
They will end up in landfill sites as waste , which is not an efficient use of resources
Reasons for the importance of recycling are…
-conserving limited raw materials and energy resources
-reducing release of harmful substances into the environment
-reducing waste
Factors affecting whether or not a product should be recycled are…(4)
-how easily waste can be collected and sorted
-amount and type of any by products released by recycling
-cost of recycling compared to disposal in landfill or incineration
-amount of energy involved at each stage
Why is it important for materials to be sorted before they are recycled?
So that materials are not contaminated and can be used for their purposes
How are metals recycled?
Melted by heating until molten , and poured into moulds to produce blocks called ingots
How is paper recycled?
Mixed with water , cleaned , rolled and heated to make new paper
How is glass recycled?
Melted by heating , and moulded into new glass objects
How are polymers like PET and poly(propene) recycled?
Melted and formed into new objects
