Chemistry C4

Ocr Gateway chemistry C4

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Acids and bases

universal indicator produces the pH scale- Acid= 0 and red, Alkali= 14 and blue

An indicator is a dye that changes colour

pH scale goes from 0-14

Acids and bases neutralise each other

An Acid is a substance with a pH less than 7- form h+ ions in water

A base is a substance with a pH greater than 7

An alkali is a base that dissolves in water to form OH- ions

neutralisation- acid+base--> salt+water, H+ + OH- ---> H2O

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Sulfuric Acid

sulfuric acid is used in car batteries,

  • where its concentrated enough to cause severe burns

it can also be used in many manufacturing processes

  • making fertilisers and detergents

you can also use it to clean and prepare metal surfaces

  • e.g. before painting or welding- metal surface is usually covered with a layer of insoluble metal oxide, the sulfuric acid reacts with these forming soluble metal salts that wash away
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Metal oxides and Metal Hydroxides

are bases

some metal hydroxides and metal oxides dissolve in water, soluble compounds are alkalis

even bases that won't dissolve in water will react with acids

metal oxides and metal hydroxides react with acids to form salt and water

Acid+metal oxide----> salt + water

Acid + metal hydroxides ---> salt +water

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carbonates and ammonia

acids and carbonates produce carbon dioxides

acid + carbonate ----> salt + water + carbon dioxide

acids and ammonia produce ammonium salts

acid+ammonia ---> ammonium salt

ammonia= NH4

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Relative atomic mass and relative formula mass

  • way of saying how heavy different atoms are compared with the mass of carbon 12
  • same as relative atomic mass
  • the bigger number on the periodic table is the relative atomic mass

relative formula mass= atomic masses added together

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Caluculating masses

1. write out balanced symbol equation out the relative formula masses of the bits you want

3. apply the rule: divide to get one, multiply to get all

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Percentage Yield

percentage yield compares the actual and predicted yield

percentage yield= actual yield (g's) / predicted yield * 100

Yields are always less than 100% because of the reaction taking place:

  • evaporation- liquids evaporate all the time
  • heating- heating can be due to evaporation, in reversible reactions increasing the temperature moves the position of equilibrium
  • filtration- when filter a liquid to move solid particles
    • if want to keep liquid always lose some that is left on the paper
    • if want to keep the solid some gets left on the paper
  • transferring liquids- always lose some when transfer containers and always some left on the inside surface
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  • provide plants with the essential nutrients to grow- nitrogen, phosphorus and potassium
  • sometimes these elements are missing from the soil because they have been used up by previous crop
  • fertilisers replace the missing elements or provide more- increase crop yield
  • fertiliser must dissolve in water to be absorbed by plant roots

Ammonia can be neutralised with acids to produce fertilisers

  • ammonia= a base, neutralised to make ammonium salts
  • ammonium nitrate is an especially good fertiliser because it has nitrogen from two sources
    • ammonia + Nitric acid ----> ammonium nitrate
  • ammonium sulfate can be used as a fertiliser
    • ammonia + sulfuric acid ----> ammonium sulfate
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Making Ammonium Nitrate in the lab

made by titration

  • add few drops of methyl orange indicator to ammonia- turns yellow
  • slowly add nitric acid from the burette into ammonia until the yellow colour just changes to red. gently swirl flask as you add acid. go especially slowly when think alkali's almost neutralised.
    • methyl orange yellow in alkali, red in acid- so when colour changes know all the ammonia has been neutralised
  • to get solid ammonium nitrate crystals gently evaporate the solution until only a bit is left, leave to crystallise
  • the ammonium crystals aren't pure as have methyl orange indicator in them.
  • To get pure crystals need to take exactly how much nitric acid it took to neutralise the ammonia and then repeat the titration using that volume of acid and no indicator
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relative formula mass- same as calculating any other formula mass

calculating the mass of an essential element in a fertiliser:

percentage mass of an element of a compound=

relative atomic mass*number of atoms (of that element) / formula mass (whole compound) * 100

Fertilisers damage lakes and rivers by eutrophication

  • excess nitrates wash into rivers, causing rapid growth of plants and algae
  • some plants start dying due to competition for light
  • decomposers feed on the dead plants and increase in population size
  • they use all the oxygen in the water and fish die
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The haber process

  • Is an important process as it makes ammonia
  • it is a reversible reaction
  • N2 + 3H2 <----> 2HH3
  • nitrogen obtained from air
  • hydrogen comes from cracking of oil fractions or natural gas
  • its reversible so not all the nitrogen and hydrogen will convert to ammonia
  • industrial conditions=
    • pressure= 200 atmospheres,
    •  temperature= 450'C
    • catalyst= iron

Iron catalyst makes the reaction go faster which gets equilibrium proportions quicker, without the catalyst the temperature would have to be raised even further to get a quick enough reaction, also keeps cost down

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Compromise in Haber Process

  • higher pressure favour the forward reaction
  • pressure is set as high as possible without making the plant too expensive to build- so 200 atmospheres operating pressure is chosen
  • the forward reaction is exothermic which means increasing temperature will move equilibrium the wrong way- yield of ammonia lower at higher temperatures
  • problem is at lower temperatures the rate of reaction is slower
  • 450'c is a compromise between maximum yield and speed of reaction
  • the unused hydrogen and nitrogen are recycled so nothing is wasted
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Cost of production

five main things that affect the cost of making a new substance

  • price of energy- needs to keep energy bills as low as possible
  • cost of raw materials- kept to a minimum by recycling any materials that haven't reacted
  • labour costs- labour intensive processes can be expensive, automation cuts running costs by reducing the number of people
  • plant costs (equipment)- depends on conditions have to cope with
  • Rate of production- faster the reaction goes the better it is in terms of reducing the time and cost of production

Optimum conditions are those that give the lowest production cost

however the rate of reaction and percentage yield must be high enough to make sufficient amount of the product each day.

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active detergent- removes dirt from clothes

water softeners- remove chemicals that cause hardness

bleaches- remove coloured stains

optical brighteners make whites even whiter

enzymes to digest food stains


washing up liquids- rinsing agent so washing up water drains off quickly

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Low temperature washes

Save energy and your clothes:

  • some clothes shrink in high temperature washes
  • some lose shape
  • some dyes run at high temperatures
  • enzymes are denatured and stop working at high temperatures
  • saves environment as less carbon dioxide emissions which reduces greenhouse effect and climate change
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Detergents help water and oil mix

have a hydrophilic head  (water loving) and hydrophobic tail (water hating)

  • hydrophilic heads from intermolecular bonds with water
  • hydrophobic tails bond to the fat molecules in greasy dirt
  • when fabric is moved around (in washing machine) the detergent molecules find their way between the grease and wet fabric
  • the detergent molecule eventually surrounds the grease and bond to it (pulls it away)
  • hydrophilic coat stops the grease droplets reattaching themselves to the fabri
  • Also: molecules are held together in the liquid phase by intermolecular forces- 2 types, polar and non-polar- the oxygen side of water is slightly negative and the hydrogen side positive
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Most Detergents are salts

Modern synthetic detergents are made using big organic molecules from crude oil

detergents are salts made by neutralisation reactions between an acid and an alkali:

  • organic acid + strong acid ----> salt (detergent) + water

soapless detergents don't form a scum with water

soapless and detergents containing soap work in the same way:

  • covalent hydrocarbon chain is the hydrophobic tail
  • the ionic bit on the end is the hydrophilic head
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Different solvents dissolve different stains

solution= when solid dissolves in a liquid

solvent= liquid that the solid dissolves into

solute= solid being dissolved

How?- if the solvent is water and solute lump of sugar

  • water molecules form strong intermolecular bonds with the sugar molecules
  • as water-sugar bonds form, they pull apart sugar-sugar bonds and the lump breaks up
  • the water molecules surround the sugar molecules- solution forms
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Dry cleaning

Dry cleaning uses a solvent that isn't water

  • usually used for clothes that would be damaged if washed them in water
    • clothes with fibres that would swell up and change shape when wet
  • also useful when you have a stain that won't dissolve in water or detergent

Dry cleaning works because the solvent is strongly attracted to the oily molecules in the stain. The intermolecular bonds between the 'stain' molecules break and are replaced by bonds with the solvent- stain dissolves

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Continuous Production

large scale industrial manufacture for popular chemicals e.g. the haber process

  • production never stops- no time wasted emptying the reactor and restarting
  • it runs automatically- only need to interfere when something goes wrong
  • The quality is consistent
  • usually the manufacturing plant only makes one product so there's little risk of contamination
  • start up costs to build the plant are huge and it isn't cost effective to run at less than full capacity
  • heat given out in exothermic reaction used to heat next lot of reactants
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Batch production

Small quantities of specialist chemicals e.g. pharmaceutical drugs

  • its flexible- several different products can be made with same equipment
  • start up costs are relatively low- small scale
  • labour intensive- equipment needs to be set up and manually controlled for each batch and cleaned at the end
  • 'downtime'  between batches means that nothing is being produced
  • it is harder to keep same quality from batch to batch
  • more chance of contamination
  • easier to match supply with demand

pharmaceutical drugs are complicated to make and there's relatively low demand for them. so batch production is often the most cost effective way to produce them

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Cost Pharmaceutical drugs

  • Market research
  • research and developing- wages for highly paid scientists 
  • Trialling- time consuming and requires animals and humans
  • Marketing- advertising in medical magazines
  • Manufacture- batch production- labour intensive
  • energy
  • raw materials- often rare and from plants

Extracting chemicals from plants

  • crushing the plant to break open the plant cells
  • dissolve the crushed plant in a solvent to dissolve the required chemical and filtering off undissolved substances
  • chromatography to separate the required chemical from other dissolved chemicals
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  • used in jewellery and cutting tools
  • diamonds are sparkly, colourless and clear
  • each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure which makes diamond really hard- ideal as cutting tools
  • strong covalent bonds give a high melting point
  • doesn't conduct electricity as no free electrons
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  • black and opaque but still kind of shiny
  • each carbon atom only forms 3 covalent bonds creating sheets of carbon atoms which are free to slide over each other
  • the layers are held together so loosely that they can be rubbed off onto layers of paper to leave a black mark- how a pencil works
  • this also makes graphite slippery- good lubricating material
  • got a high melting point- covalent bonds need lots of energy to break
  • lots of spare electrons so can conduct electricity- used for electrodes
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Fullerenes are nanoparticles

fullerenes are a molecules of carbon shaped like hollow balls or closed tubes, each carbon atom forms three covalent bonds with its neighbour leaving free electrons that can conduct electricity

The smallest fullerene= buckminsterfullerene which has 60 carbon atoms joined in a ball

Fullerenes can be used to 'cage' other molecules-

  • fullerene structure forms around another atom or molecule which is trapped inside
  • could be a new way of delivering a drug into the body
  • e.g. for slow release
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Nanotubes and Nanoparticles

Fullerenes can be joined together to form nanotubes:

  • covalent bonds make carbon nanotubes very strong- used to reinforce graphite in tennis racquets
  • conduct electricity- used to make tiny electric circuits for computer chips
  • huge surface area so could help make good industrial catalysts


  • normally unreactive silver can kill bacteria
  • colour of gold nanoparticles varies from red to purple
  • can be made by molecular engineering- has to be done molecule by molecule to a specific design
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Water and its conservation

Where it comes from:

  • surface water: lakes, rivers and reservoirs
  • groundwater- aquifers

conservation methods:

  • stopping leaks in pipes
  • not wasting water at home- not leaving taps running
  • recycling water
  • installing a water meter
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Water Purification

  • Filtration- a wire mesh screens out large twig and then gravel and sand beds filter out any other solid bits
  • Sedimentation- iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom- insoluble sediment
  • Chlorination- chlorine gas is bubbled through to kill harmful bacteria and microbes

Tap water can still contain impurities:

  • nitrate residues
  • lead compounds
  • pesticide residues
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Testing water for dissolved ions

Test for Sulfate ions-

  • add 10 drops of barium chloride (BaCl2) solution to test sample
  • if white precipitate there are sulfate ions present

Test for halide ions-

  • add some silver nitrate solution (AgNO3)
  • chloride ions will produce a white precipitate
  • bromide ions will produce a cream precipitate
  • Iodide ions will produce a pale yellow precipitate
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people who can't get clean water

1.4 billion people worldwide can't get clean water to drink

  • communities in some developing countries don't have access to clean water
  • people often have to walk miles for water every day
  • dirty water can carry dangerous microbes
  • giving a community a clean water source and teaching them the skills to maintain it can save many lives

can get water by distilling sea water:

  • in dry countries sea water is distilled
  • needs loads of energy and is expensive so is not practical for producing large quantities of fresh water
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Deslie Thomas


These are really good and detailed thank you

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