C6.1 Flashcards
What are the essential elements for plants?
Nitrogen
Phosphorus
Potassium
Don’t grow well if these are in limited supply, may show symptoms of mineral deficiency
What are the typical symptoms of deficiency of nitrogen, phosphorus and potassium?
Nitrogen - poor growth, yellow leaves
Phosphorus - poor root growth, discoloured leaves
Potassium - poor fruit growth, discoloured leaves
What are fertilisers?
Substances that replace the elements used by the plants when they grow
Plant roots can only absorb these is they’re in water soluble form
Nitrogen in nitrate ions or ammonium ions
Phosphorus in phosphate ions
Potassium as potassium ions
What are NPK fertilisers?
Provide nitrogen, phosphorus and potassium in water+soluble compounds
What is the haber process?
Manufactures ammonia form nitrogen and hydrogen:
N2 (g) + 2H (g) >< 2NH3 (g)
150 tonnes of ammonia made, 80% for fertilisers
How are the raw materials for the haber process obtained?
- nitrogen from fractional distillation of liquified air (78% nitrogen)
- hydrogen by reacting natural gas (mainly methane) with steam
What happens in fertiliser factories?
Many raw materials are needed
Different processes are integrated so a range of compounds for fertilised are made
Pg197
How do you make potassium sulfate (fertiliser)?
1) dilute potassium hydroxide solution into a conical flask and add a few drops of phenolphthalein indicator (changes colour at the end point of neutralisation)
2) add dilute sulfuric acid from a burette or dropping pipette, stopping when the indicator changes from pink to colourless
3) add activated charcoal which attracts the phenolphthalein and you can filter the mixture to remove the activated charcoal with the phenolphthalein attached to it
4) warm the filtrate to evaporate the water, leaving potassium sulfate behind. Must not heat this to dryness
How do you make ammonium sulfate (fertiliser)?
1) place the dilute ammonia solution in a conical flask with methyl orange indicator. Ammonia solution releases small volumes of ammonia in gas state, which has an irrating sharp smell
2) add sulfuric acid form a burette or dropping pipette, stopping when the indicator changes from yellow to red
3) when you reach the end point add a little extra ammonia solution to ensure the reaction is complete. Any a remaining ammonia will be lost during evaporation
What is the batch process?
When a small amount of the substance is made at one time
What is the continuous process?
Many industrial processes use it
Makes large amounts and go on 24/7
What are the conditions used for the haber process?
- pressure 200atm (atmospheres)
- a temperature of 450C
- iron catalyst
What happens to unreacted gases?
The ammonia leaving is liquified so the unreacted iatrogenic and hydrogen is recycled
Yield is improved to 97%
What is the contact process?
Set of reactions to produce sulfuric acid
What are the raw materials needed for the contact process?
- sulfur
- air
- water
What happens in stage 1 of the contact process?
Sulfur burns in air to produce sulfur dioxide:
S (s) + O2 (g) > SO2 (g) (-297kJ/mol)
What happens in stage 2 in the contact process?
Sulfur dioxide and oxygen react together to produce sulfur trioxide:
2SO2 (g) + O2 (g) >< 2SO3 (g)
- pressure of 2atm
- 450C
- vanadium oxide catalyst
Equilibrium yield of sulfuric trioxide is 96%
What is stage 3 of the contact process?
Sulfur trioxide is converted to sulfuric acid:
H20 (l) + SO3 (g) > H2SO4 (aq)
Why is stage 3 carried out in 2 steps?
Reaction is very exothermic so would produce a hazardous acidic mist
1) sulfur trioxide is passed through concentrated sulfuric acid to make a compound called oleum
H2SO4 (l) + SO3 (g) > H2S2O7 (l)
2) the oleum is added to water and the reaction makes a larger volume of concentrated sulfuric acid
H2S2O7 (l) + H2O (l) > 2H2SO4 (aq)
How is ethanol made from renewable materials?
Form plant sugars using fermentation
Relies on single-celes fungi called yeast to catalyse the conversion of glucose solution to carbon dioxide and ethanol
Only 15% yield
Needs filtering and fractional distillation to purify
How is ethanol made from non renewable materials?
For, the hydration of ethane which is obtained from crude oil
Ethane + steam >< ethanol
- 60atm
- 300C
- phosphoric acid catalyst
About 95% yield
No by products
What is an ore?
Rock or mineral that contains enough metal to make it economical to extract the metal
Value of metal is more than the cost of extracting it
Different metal compounds are found in different ores
Malachite = copper carbonate
Bauxite = aluminium oxide
Haematite = iron (III) oxide
What are the methods to extract metals from ores?
Can use electrolysis but electricity is expensive
If heating with is less reactive than carbon than can be extracted using carbon or carbon monoxide
How is copper extracted?
Copper can be extracted from copper (II) sulfide in two stages:
Stage 1: copper (III) sulfide is roasted in air
copper (II) sulfide + oxygen > copper (II) oxide + sulfur dioxide
2CuS (s) + 3O2 (g) > 2CuO (s) + 2SO2 (g)
Stage 2: copper (II) oxide is heated with carbon
Copper (II) oxide + carbon > copper + carbon dioxide
This is a redox reaction
Copper (II) oxide can also be reduced to copper by heating it with methane or hydrogen
What is a blast furnace?
Large reaction container where iron is extracted from its ore
What are th e raw materials needed for iron extraction?
- iron ore which contains iron(III) oxide
- coke which is mostly carbon and made by heating coal in the absence of air
- limestone which purifies the iron
What is stage 1 of the iron extraction?
Coke burns in the hot air making carbon dioxide:
C (s) + O2 (g) > CO2 (g)
What is stage 2 of the iron extraction process?
More coke reduces the carbon dioxide making carbon monoxide:
C (s) + CO2 > 2CO (g)
What is stage 3 of iron extraction?
Carbon monoxide reduces iron(III) oxide to iron at around 1500C
3CO (g) + Fe2O3(s) > 3CO2 (g) + 2Fe(l:
What happens after molten iron is produced?
The molten iron trickles downwards in the blast furnace, it contains sandy impurities from the iron ore which are removed by the limestone
What are the 2 stages for removing the sandy impurities using limestone?
Stage 1: calcium carbonate decomposes in the high temperatures
CaCO3 (s) > CaO (s) + CO2 (g)
Stage 2: calcium oxide formed reacts with silica from the sandy impurities to form calcium silicate (slag)
CaO (s) + SiO2 (g) > CaSiO3 (l)
Slag is removed separately to the iron at the Bolton of the blast furnace
What is aluminium?
Exists naturally as aluminium oxide found in an ore called bauxite
More reactive than carbon
Must be extracted with electrolysis but electrolysis works if the compound is in solution or molten
But aluminium has a very high melting point and doesn’t dissolve in water
How is aluminium electrolysed?
Aluminium oxide is dissolved in molten cryolite, which has a much lower melting point for electrolysis
How does electrolysis of aluminium take place?
Molten mixture of aluminium oxide and cryolite is contained in a huge electrolysis cell made from steel lined with graphite
The graphite lining acts as the cathode
The anode is a series of large graphite blocks
- Aluminium is produced at the cathode
- Oxygen is produced at the anodes
The oxygen reacts with the hot graphite anodes making carbon dioxide
What are the half equations for the electrolysis of aluminium?
Cathode: Al3+ + 3e- > Al
Anode: 2P2- > O2 + 4e-
What is bioleaching?
Bacteria oxidises iron and sulfide ions and use the energy transferred
Sulfuric acid forms in the presence of water and oxygen
This sulfuric acid breaks down copper sulfide ores and other minerals releasing copper ions and other metal ions
Why is bioleaching useful?
Cheaper than tradition mining and processing
Allows low-grade ores to be profitable
Bacteria occurs naturally and doesn’t need any special treatment
Doesn’t release any harmful substances but is a slow process
What is phytoextraction?
A crop is planted in soil containing a low grade ore or min waster
A competing agent may be added so the plants can absorb the metal ions more easily
The plants are harvested then burnt to produce an ash with a high concentration of metal which can be extracted just as it the ash was a high grade ore
Why is phytoextraction useful?
Cheaper than traditional mining and processing
Produces less waste and involves smaller energy transfers
Carbon neutral activity, contributes to sustainable development
Burning plants releases carbon dioxide but the plants use it for photosynthesis
What are the harms of phytoextraction?
Crops may need replanting and harvesting for several years before available metal is removed from the soil
What are alloys?
Mixture of two or more elements where at least one is metal
What are different alloys and their uses?
Steel - mainly iron, buildings, bridges, cars
Solder- mainly tin and copper, joining electrical components and copper pipes
Duralumin - aluminium and copper, aircraft parts
Brass - copper and zinc, musical instruments and coins
Bronze - copper and tin, bells, propellers for ships
What is solder like?
Melting point = 227C
Useful for joining electrical components without damaging them
What are brass and bronze like?
Strong and hard as layers cannot slide over each other due to the difference in size of atoms
Brass resists corrosion, doesn’t react easily with air or water so useful for making pins for electrical plugs
Bronze also resists corrosion and is stronger and harder than copper
Useful for propellers
