C6

What are Fertilisers

Substances that replace elements used by plants as they grow
Plant roots can only absorb these elements if they are in soluble form

What 3 elements do plants need and their ionic forms

Nitrogen (Nitrates and Ammonium ions)
Phosphorus (Phosphate ions)
Potassium (Potassium ions)

How do you know if a plant is deficient in any of these elements?

Nitrogen- Poor growth, yellow leaves
Phosphorus- Poor root growth, discoloured leaves
Potassium- Poor fruit growth, discoloured leaves

What are NPK Fertilisers

Fertilisers that contain Potassium Nitrate and Ammonium Phosphate
Provide plants with essential elements, increasing yield

How is ammonia made?

Made from Nitrogen and Hydrogen in the Haber process
Nitrogen used to make plant proteins for growth

What is the Haber process and why is it important?

Turns air into fertiliser, essential for world food supply.
Plants can’t take in nitrogen from air due to strong triple bonds

3H₂ + N₂ = 2NH₃
Hydrogen + Nitrogen = Ammonia

What happens in a fertiliser factory?

Variety of raw materials needed eg. Sulphur (H₂SO₄) and Phosphate for phosphoric acid
Different processes in fertiliser factory integrated so range of compounds for fertilisers can be made

What is the contact process?

Sulphuric acid made in a multistep process.
You need:
Sulphur from underground by mining
Oxygen from air
Water

What are the steps of the contact process

1. Sulphur + Oxygen → Sulphur dioxide
S + O₂ → SO₂

2. Sulphur dioxide + Oxygen = Sulphur Trioxide
2SO₂ + O₂ = 2SO₃

3. Sulphur trioxide + Water → Sulphuric acid
SO₃ + H₂O → H₂SO₄

What are the conditions required for the contact process?

Temp: 450 Degrees Celsius
Pressure: 2 Atmospheres (200kPA)
Catalyst: Vanadium Oxide
Equilibrium yield usually 95%

Why are these specific conditions used?

Increasing temp increases ROR but decreased yield. Use optimum temp
Increasing pressure increases both ROR and yield but very expensive and needs specialist equipment

How are Hazards controlled?

Reaction in stage 3 very exothermic which produces a very acidic mist. Stage 3 carried out in two steps

Sulphur trioxide passed through concentrated sulphuric acid to make Oleum (H₂S₂O₇)

Oleum added to water and reaction makes a larger volume of acid

Define Hydrocarbons

Hydrocarbons- Compounds that only contain hydrogen and carbon atoms

What are the different prefixes for alkenes and alkanes

Meth- 1
Eth- 2
Prop- 3
But- 4
Pent- 5
Hex- 6
Hept- 7
Oct- 8
Non- 9
Dec- 10

Properties of Alkanes?

Form a homologous series as they have similar features:
-Carbon atoms joined by single covalent bonds (saturated)
-Same general formula (C_nH_2n+2) eg. methane = CH₄
-Each successive

What reactions can alkanes undergo?

Combustion: If there’s plentiful supply of oxygen
-C₃H₈ + 5O₂ → 4H₂O + 3CO₂ + Heat and light
-Carbon atoms oxidised to CO₂ and hydrogen atoms oxidised to H₂O

Incomplete combustion: limited supply of oxygen
4CH₄ + 5O₂ → 2C + 2CO + 8H₂O
-Some carbon atoms oxidised to Carbon monoxide whilst some stay as carbon
-Hydrogen atoms oxidised to water

Properties of alkenes

Unsaturated- contain atleast one Carbon-carbon double bond
Similar chemical and physical properties
Same general formula (C_nH_2n) eg. Ethene = C₂H₄

What are addition reactions for alkenes

Carbon carbon functional group lets alkenes undergo addition reactions
Atoms combine with a molecule to form larger molecule and no other product

eg. Ethene + Bromine → Dibromethane
(double bond always breaks so ethene → ethane)

What is the test for alkenes using bromine water

Bromine water yellow-brown due to Br-Br bond
When it meets an alkene, they will react to produce bromoalkane
If alkene present in solution, turns colourless from yellow

Properties of alcohol

Same functional group (Hydroxyl: OH)
Same general formula (C_nH_2n+1OH)

What reactions can Alcohol undergo

Incomplete combustion
C₂H₅OH + 2O₂ → C + CO + 3H₂O

Complete combustion
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

How to make alcohol from fermenting with yeast

Yeast + Sugar → Alcohol + CO₂ + Heat

Temp: 25-35*C
Anaerobic conditions (no air)
-Yeast contains enzymes that break sugars down to alcohol
-Sugars dissolved in water turns into ethanol and CO₂
-Air lock: CO₂ can escape but prevents air from entering

Advantages and disadvantages of making alcohol from fermenting with yeast

+Easy
+Cheap, doesn’t need special equipment
+Reliable

-Pure ethanol not produced
-Low yield of ethanol
-CO₂ produced

How to make alcohol with hydration of alkenes

Ethene + Water → Ethanol

Temp: 300*C
Pressure: 60-70 atmospheres
Catalyst: Strong acid eg. sulphuric acid

Advantages and disadvantages of making alcohol with hydration of alkenes

+Fast and continuous
+Pure product (100% atom economy)
+High yield (around 100%)

-Non renewable (ethene from crude oil)
-Expensive
-Requires advanced equipment
-Atmospheric effects (pollutant from burning fossil fuels)

Properties of carboxylic acids

Not hydrocarbons (contain oxygen)
Carboxyl functional group (COOH)
Same formula (C_n-1H_2nCOOH) as n subtracted by 1 as other carbon in functional group
Ends in -anoic acid eg. Methanoic acid = HCOOH

How are carboxylic acids formed

Produced when alcohols oxidised by an oxidising agent
eg. Ethanol + Oxygen → Ethanoic acid + water
Weak acids so undergo same reactions that acids do

How do fractionating columns work?

Crude oil put in which is mixture of many hydrocarbons and fossil fuels
Really high temp at the bottom, boils crude oil
As vapour goes up, it cools and condenses
Low boiling point low viscosity fractions at the top (short-chain HC) whilst high (long chain HC) at the bottom

Difference between short and long chain molecules

Short chains need less energy to break intermolecular bonds as they’re weak whilst long chains need lots of energy

Low BP, Low viscosity for short chain. High BP, High viscosity for long chain

Define Cracking

Cracking- Chemical reaction that breaks covalent bonds of long alkane molecules into smaller, more alkane and alkene molecules

Eg. Heptane → Pentane + ethene
Sometimes hydrogen can be a product.

Why is cracking used?

Carried out on large alkanes as not useful as fuels due to:
-Do not flow easily
-Difficult to ignite
-High boiling points

Small alkanes better fuels due to low BP so flows and ignites easier.

Requires: High temp (600*C) + Hot catalyst of alumina or silica

Advantages and disadvantages of Fractional distillation over cracking

-F.D. produces more fractions with larger molecules, more than can be sold
-Doesn’t produce enough small molecules which are high in demand
+F.D. can handle crude oil as feedstock

How are plastics made?

Plastics made from long molecules called polymer molecules
Polymer molecules made from monomer (smaller, short) molecules

What is addtion polymerisation?

Addition reaction as monomers (alkene) undergo addition reaction when they join
Due to the Carbon-carbon double bond
All atoms in monomer used to form polymer

What are some common polymers

Polyethene- Used in shopping bags
Polypropylene- Used in plastic bottles
Polyvinylchloride (PVC)- used in packaging

What is condensation polymerisation?

Two molecules react together to form one larger and one smaller molecule (often water)
Polyesters and polyamides both made from condensation reactions
Each monomer has two functional groups

Properties of polyester

Functional group COO
Formula (COORR) Where R is hydrocarbon
Polyesters made from dicarboxylic acid molecule which has 2 carboxyl groups (2xCOOH) and alcohol molecule with 2 hydroxyl groups (2x OH) known as diol
Made by carboxyl end of acid reacting with hydroxyl end of alcohol

Carboxylic acid + alcohol → ester + water

Properties of polyamides

Made from a Dicarboxylic acid molecule with 2 Carboxyl groups and an amine molecule with 2 amino groups (-NH₂)

Some common biological polymers

DNA- Nucleotides join together to form polynucleotides which spiral round each other for double helix structure. Hydrogen bonds between strands hold them together

Protein- Amino acids → polypeptides → proteins
Made of amino group (NH₂) and carboxyl group (COOH) and reactive functional group (sidecchain based on specific acid) Around 20 diff. natural amino acids

Carbs- Compounds containing oxygen, carbon and hydrogen. Includes simple sugars eg. glucose and sucrose. Complex carbs made of simple sugars joined by glycosidic bonds

How do batteries produce electricity?

Exothermic cells occur in chemical cell. Produces voltage between its 2 ends. To make a cell, need atleast anode and cathode and 2 diff. electrolytes

Cell connected to a circuit, current flows through cell and circuit. Continues until one of the reactants in cell used up

Order of reactivity series?

Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Further apart elements, more p.d. as more vigorous reaction. Electrolyte also affects p.d.

How does a hydrogen fuel cell work

Hydrogen enters through left (negative anode) and oxidised to become hydrogen ion (H₂ → 2H⁺ + 2e^-)
Electrons travel along wire to cathode, H⁺travels along electrolyte to cathode
Both react with oxygen entering through right (positive cathode) to make water (O₂ + 4H⁺ + 4e^- → 2H₂O)
As fuel enters the cell, it becomes oxidised which sets up a p.d. which generates electricity

2H₂ + O₂ → 2H₂O

Advantages and disadvantages of fuel cells

+Replace powerstations
+Replace fossil fuel engines (not polluting)
+Only requires hydrogen + oxygen (no waste and abundant)
+Last longer than batteries and simpler
+Less polluting to dispose of

-Hydrogen gas so needs space to store than fossil fuels
-Explosive when mixed with air (dangerous to store)
-Making hydrogen fuel requires energy

What are ores

Most elements exist as compounds (Metal oxides as part of ores)
Metal ion must be split from oxygen ion
Ores contain enough metal or metal compound for it be economical to extract the metal

What are common ores

Malachite- copper carbonate
Bauxite- Aluminium oxide
Haematite- Iron(III) Oxide

Advantages and disadvantages of metal extraction using electrolysis

+Most powerful (work for any ore)
-Most expensive
-Only used where electricity is abundant

Advantages and disadvantages of metal extraction using reduction with carbon

+Cheaper than electrolysis
-Labour intensive
-Expensive to startup as industrial equipment needed

Advantages and disadvantages of metal extraction using heat

+cheap
-can only be used on most unreactive metals

How is copper extracted?

1.Copper(II) sulphide + oxygen → Copper(II) oxide + Sulphur dioxide
2CuS + 3O₂ → 2CuO + 2SO₂

2.Copper(II) oxide + Carbon → Copper + Carbon Dioxide
2CuO + C → 2Cu + CO₂
OR
2.Methane + Copper(II) Oxide → copper + water + Carbon dioxide

What is a blast furnace

30m High reaction container
Raw materials added at top: Iron ore (haematite), Coke (coal heated in absence of air), Limestone purifies air or Calcium Carbonate
Hot air blasted into furnace

How is iron extracted?

1. Iron ore, limestone and coke delivered to top of furnace (800*C) Coke burns in hot air (C+O₂→CO₂)

2. More coke reduces carbon dioxide (C +CO₂ → 2CO)

3. Carbon monoxide reduces Iron (III) oxide at around 1500*C (Fe₂O₃ + 3CO → 2Fe(I) + 3CO₂) Impurities removed using limestone

4. Calcium carbonate decoomposes (CaCO₃ → CaO + CO₂)
Calcium oxide reacts with silica from impurities to form calcium silicate (slag)
CaO + SiO₂ → CaSiO₃

How is aluminium extracted?

Bauxite dissolved in cryotite to lower melting point

Positive aluminium ions move towards negative cathode where they gain electrons and turn into aluminium atoms (Al³⁺ + 3e^- → Al)

Negatively charged oxide ions move to positive anode, lose 2 electrons to turn into oxygen atoms and rapidly join in pairs to form oxygen gas (2O²—>O₂ + 4e^-)

What is Rusting?

Specific name given to corrosion of iron
Chemical reaction between iron, oxygen and water
Chemical name- hydrated iron(III) oxide

Iron + Oxygen + water → Hydrated iron(III) oxide or Iron(III) hydroxide

4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

How to reduce corrosion

Need to stop material reacting with oxygen or water
Done by:
-Painting
-Coating iron with oil, grease or plastic
-Plating with tin
-Galvanising- plating with zinc

How does stainless steel stop corrosion

Chromium in stainless steel oxidises to chromium oxide when exposed to air
Oxide forms thin film on surface of steel
Layers stop air and water from reacting with metal below

What is sacrificial protection

More reactive metal than iron or steel in contact with the body of the ship (eg. magnesium or zinc)
The more reactive metal corrodes first, protecting hulls of ships below water line
More reactive metal loses electrons more readily than iron (oxidised faster) so has to be replaced eventually

Difference between galvanising and tin plating?

Galvanising- plating surface of metal with zinc (used to protect car body parts and metal work)
Tin plating- Electroplating steel objects with tin (inside of steel food cans as it’s less reactive so doesn’t affect food but rusts even faster than normal)

What is phytoextraction?

Process in which metals removed from contaminated soil
Certain plants (hyperaccumalators) absorb metal compounds through roots and store in leaves and stems
Plants harvested and burnt, metals extracted from ash

Useful for cleaning polluted land and obtain valuable metals

Advantages and disadvantages of Phytoextraction

+Environmetally-friendly: reduces need for mining which causes pollution and habitat destruction
+Cost-effective: Cheaper than other methods
+Sustainable: Allows recovery of valuable metals from plants

-Slow process: Takes long time for plants to absorb enough metal
-Limited: Only works for specific metals
-Dependent on plant growth: Process depends on right conditions eg. climate, soil, plant species. Not always suitable

What is Bioleaching?

Process uses bacteria to extract metals from ores
Bacteria breaks down metal compounds, releases metal ions
Collected then purified

What are leachates?

Solution that contains dissolved metal ions
Formed when bacteria breaks down metal sulfides in ores, releasing metal ions into liquid solution
Leachate processed to extract and purify metal using displacement or electrolysis

Advantages and disadvantages of Bioleaching

+Environmentally-friendly: Reduces need for traditional mining
+Extracts metals from low-grade ores: Allows use of ores otherwise were too poor for extraction
+Lower energy costs: Uses biological processes not furnaces so less energy consumption

-Slow process: takes weeks or months to extract significant amount
-Produces toxic substances: can release harmful chemicals eg. sulfuric acid
-Not suitable for all metals: Mainly used for metals such as copper

Properties of ceramics

Hard non-metallic materials eg. brick, porcelain
Contain metal and non-metal combined to form giant ionic structure
High melting points
Hard, Stiff, Brittle
Poor conductors of heat and electricity

How are glass and other ceramics made?

Glass made by smelting sand, cooling then solidifying
Irregular giant structure without crystals, usually transparent

Other ceramics made by heating clay to very high temperature

Define tensile strength and compressive strength

Tensile strength- Ability of material to withstand pulling force without stretching
Compressive strength- Ability of material to withstand pushing force without squashig

What are composite materials and some examples

Made from two or more materials combined together, each with different properties
One is the reinforcement- Hard, long solid fibres or fragments
Other the matrix- Binds reinforcement together, soft→Hard
Properties of a composite material different from the materials it contains

Eg. Polyester cotton- harder than cotton, easier to wash + dry

How is concrete made for buildings?

Concrete made from aggregate (small stones), cement and water
When water’s added to mixture, chemical reaction binds them together

Sand + Gravel + Water → Cement

Properties of concerete?

High compressive strength- Useful for foundations
Low tensile strength- Beams cracked if pulled with heavy loads
Steel rods embedded into concrete as it sets- High compressive and tensile strength

What’s Reinforced concrete?

Steel rods used to increase strength and flexibility of concrete
Can support 300-500x combined mass of steel + concrete its made from
Many uses- lamp posts, railways, building support

What are alloys and properties of alloys

Alloys- Mixture of two or more elements where atleast one is a metal

Can be different properties from metals they contain
Contains atoms of diff. sizes, distort regular arrangement of metal atoms
Disrupts layers, difficult to slide over each other so stronger and harder than pure metals

What are some examples of alloys

Duralumin (Aluminium + copper)- used in aircraft parts as it’s lightweight (less fuel consumption), strong (withstand force), corrosion resistant

Solder (Tin + Copper)- Joins copper pipes and electrical components as low melting points (joins things without damage), good electrical conductivity and strong

Brass (Copper + Zinc)- Used in coins and instruments as it’s malleable (shaped easily), strong and hard

Bronze (Copper + tin) used in bells and ship propellers as it’s resistant to corrosion, strong and hard

What is a life cycle assessment?

Way of analysing life of product to see how much energy and water used and effects on environment of each stage
Split into 3 main stages: Cradle (further split into raw materials, manufacturing, distribution) Use and Grave (disposal)
By analysing data at each stage, improvements can be made to save energy and harm environment less

What data is used?

Sustainability- Including use of raw materials
Environmental impact- waste products + pollution
Life span of product and if recyclable
Disposal- how easily materials decompose (biodegradable?)

What factors affect whether a material should be recycled?

Collection and sorting- difficult?
By-products released by recycling
Cost of recycling compared to disposal
Amount of energy involved at each stage

How are certain materials recycled?

Metals melted by heating, molten metal poured into moulds to produce new ingots

Paper mixed with water, cleaned, rolled and heated to make new paper

Glass melted by heating and moulded into new glass objects

Polymers melted and formed into new products

What is our atmosphere made up of?

Nitrogen (78%)
Oxygen (21%)
Argon (0.8%)
CO₂ (0.03%)
Other (0.07%)

What was the first atmosphere like?

Earth molten for millions of years with no atmospheres, surface cooled down to form thin crusts with volcanoes
Released hydrogen sulfide, methane and CO₂, water vapour and ammonia
Gravity prevented gas escaping into space which formed first atmosphere

How did the current atmosphere come about?

3.8 billion years ago, Earth cooled enough to condensate water vapour which formed liquid
3.7 billion years ago, first microscopic organisms were formed
Supercontinent formed after cratons rose from ocean 3.3 billion years ago
CO₂ dissolved in oceans, green plants evolved and photosynthesised (oxygen in atmosphere) 2.4 billion years ago
N₂ in atmosphere from ammonia reacting with oxygen and released by denitrifying bacteria

How did CO₂ decrease in the early atmopshere?

Photosynthesis- cyanobacteria evolved to photosynthesise, later evolved to algae and aquatic plants
Ocean absorption- CO₂ dissolved in water
Precipitation by sedimentary rocks formation- carbon absorbed by marine organisms (eg. shellfish) and carbonate sediments (eg. limestone which locked away more CO₂)

How did oxygen collect in the atmosphere?

At first, O₂ produced oxidised metals in rocks (metal oxides)
Once most metals oxidised, O₂ accumulated in atmosphere
Build up killed early organisms but supported evidence of more complex organisms
Oxygen creates ozone which supports evolution of more complex organisms

How do acidic oxides create acid rain?

Nitrogen monoxide (NO) formed in car engines, oxidised in air to form Nitrogen Dioxide (NO₂)
NO₂ dissolves in clouds to form acid rain
SO₂ formed when fossil fuels burnt which dissolves in clouds to form acid rain

What are particulates and why are they harmful

Small particles produced in incomplete combustion and vehicle engines
Settle deep into lungs when breathed
Can cause bronchitis and increased risk of heart disease

What is carbon monoxide and why is it harmful

Produced during incomplete combustion of fuels
Toxic without taste or smell
Attaches to haemoglobin in red blood cells, reducing amount of oxygen blood can carry
Causes drowsiness, breathing difficulty or even death

Outline the greenhouse effect

Energy transferred by radiation from sun reaches Earth’s surface
Radiation warms Earth’s surface
IR emitted by surface, some goes directly into space, some absorbed by Greenhouse gas molecules in atmosphere
GG molecules emit IR radiation in all directions, warming Earth

Examples of some greenhouse gases?

Methane (CH₄)- More active than CO₂ but less abundant
Water vapour- Most abundant
Nitrous oxide (N₂O)- From fertilisers, fuel combustion and biomass burning
CO₂

How do we reduce Greenhouse gas emissions?

Use less fossil fuels
Use renewable energy sources for electricity
Carbon capture to reduce amount of CO₂ released when fuels burnt

Methods expensive so steps taken to protect against global warming instead

What did the Intergovernmental panel say on climate change (IPCC)

Extremely likely that human influence main cause of global warming between 1951-2010
“Extremely likely” as Earth and atmosphere very large and complex system

Impossible for scientists to carry out controlled fair tests so make predictions based on observations and measurements and models
Actual outcome only evident in future

What is potable water?

Safe to drink (not necessarily pure)
Should have low levels of dissolved salts and microbesO

How do we obtain potable water in UK?

Rainwater dissolves gases from air as it falls to ground
Rainwater collects underground, in lakes or in rivers (fresh water)
Soluble and insoluble contaminants must be removed

How is potable water produced?

Choose appropriate source of fresh water
Pass water through filter beds
Pass through sterilising beds (eg. chlorine, ozone or UV light) to kill microorganisms

What is desalination and what are the 2 methods?

If freshwater supplies limited, may have to remove salt from sea/salty water

Done through:
Distillation (separates mixture with diff. boiling points, salt from pure water)
Reverse osmosis (water moves against conc. gradient against a membrane)

Both methods require lots of energy (to heat up mixture to boiling points or pressurise water in reverse osmosis) which is very expensive so desalination rarely used.

How do we get potable water from waste water

Urban lifestyles and industrial processes produce large amounts of waste water that requires treatment before being released.
Must remove organic matter and harmful microbes
Done through various processes such as screening, sedimentation, digestion

How is waste water treated?

1. Screening- remove large solid particles eg. grit
2. Sedimentation- Solids sink to form sludge but liquid remains above (effluent)
3. Sludge dried and anaerobically digested (removes organic matter.) Produces biogas to make electricity. Dried sludge used as fertiliser
4. Effluent aerobically digested to remove organic matter and harmful microbes
5. Still contains harmful micro-organisms. Chlorine added to remove (less than 5ppm in drinking water)