Chemistry C4

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Acid and Bases

An indicator is a dye that changes colour. The dye in the indicator changes colour depending on whethers its above or below a certain pH.

  • a very strong acid has pH 0
  • a very strong alkali has pH 14
  • Pure water is pH 7
  • An acid is a sunstance with a pH of less than 7. Acids form H+ ions in water. 
  • A base is a substance with a pH of greater than 7.
  • An Alkali is a base that dissolves in water. Alkalis form OH- ions in water.
  • acid + base = salt + water
  • H+ + OH- = H2O

Modern industry used tonnes of sulfuric acid

  • sulfuric acid is used in car batteries
  • used in habre proces to produce fertilisers and detergents
  • can be used to clean and prepare metal surfaces.
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Reactions of Acids

Metal Oxides and Metal Hydroxides are Bases

  • some metal oxides and metal hydroxides dissolve in water. These solube compounds are alkali.
  • even bases that dont dissolve in water still react with acid.
  • all metal oxided and hyrdoxides react with acid to form a salt and water

Acid + Metal Oxide = Salt + Water

Acid + Metal Hydroxide = Salt + Water

Acids and Carbonates Produce Carbon Dioxide

  • Acid + Carbonate = Salt + Water + Carbon Dioxide

Acids and Ammonia Produce Ammonium Salts

  • Acid + Ammonia = Ammonium Salt
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Relative Formula Mass

Relative Atomic Mass= Ar

  • this is just a way of saying how heavy different atoms are compared with the mass of an atom of carbon- 12. So carbon-12 has Ar of exactly 12.
  • It turns out that the relative atomic mass Ar is usually just the same as the mass number of the element.
  • In the periodic table, the elements all have two numbers, the smaller one is the atomic number and the bigger one is the relative atomic mass
  • If you have a compound like MgCl2, then it has the relative formula mass, Mr, which is just all the relative atomic masses added together.
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Calculating masses in Reactions

Three important steps:

  • Write out the balanced equation
  • Work out Mr- just dor the two bits you want.
  • Apply the rule: divide to get one, then multiply to get all.
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Percentage Yield

Percentage Yield compares actual and predicted yield

Formula you must know:

Percentage yield = actual yield/ predicted yield x 100

Yields are always less than 100%

  • Evaporation- liquids evaporate all the time- not just while being heated.
  • Heating- Losses while heating can be due to evaporation
  • Filtration- When you filter a liquid to remove solid particles, you nearly always lose a bit of liquid or solid.
  • Transferring Liquids- you always lose a bit of liquid when you transfer it from one container to another.
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Fertilizers

Fertilizers provide plants with the essential elements for growth

  • The three main essential elements in fertilizers are nitrogen, phosphorus and potassium.
  • Soil can lose these elements when they have been used by previous crops
  • Fertilizers replace these missing elements or provide more of them this helps to increase the crop yield.
  • The fertilizer must first dissolve in water before it can taken in by the crop root.

Ammonia can be neutralized with acids to produce fertilizers

  • Ammonia is a base and can be neutralized by acid  to make ammonium salts. 
  • Ammonia + Nitric acid = Ammonium nitrate
  • Ammonium nitrate can be produces 
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Fertilizers

Calculating Relative Formula Mass of a Fertilizer

  • Find the relative formula mass for ammonium nitrate, NH4NO3, using the following data:
  • Ar for H=1, N=14 and O=18
  • Mr= 80

Percentage mass of an element in a compound = Ar X No. of atoms (element) / Mr (of whole compound) x 100

Fertilizers damage lakes and rivers - Eutrophication 

  • Fertilizers which contain nitrates which are essential for modern farming.
  • if the fertilizers reach rivers and streams it causes problems
  • Eutrophication mean that the death of a lake or other water reserve.
  • Nitrates washed into lakes caused rapid growth of plants and algae.
  • Populations of fish who eat the plants increases and eats all the plants which are slowly dying.
  • When the plants are all dead the huge population of fish use up the remaining oxygen in the lake and render it dead.
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The Haber Process

The Haber process is a reversible reaction: N2 +3H2 <--> 2NH3 

  • the nitrogen is obtained from the air
  • the hydrogen comes from cracking of oil fractions or natural gas.
  • any nitrogen or hydrogen that is not converted will be sent round again to the beginning of the reaction.

Industrial Conditions:

  • pressure of 200 atmospheres
  • 450 degrees c
  • iron catalyst
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Haber Process Part 2

Because the reaction is reversible, there's a compromise to be made:

  • Higher pressures favor the forward reaction
  • so the pressure is set to as high as possible to give the best % yield without making the plant too expensive to build.
  • the forward reaction is exothermic, which means that increasing the temperature will actually move the equilibrium the wrong way- away from ammonia and towards N2 and H2 so the yield of ammonia would be greater at lower temperatures
  • the trouble is, lower temperatures mean a slower rate of reaction. So what they do is increase the temperature anyway, to get a much faster rate of reaction.
  • The 450oc is a compromise between maximum yield and speed of reaction. its better to wait 20 seconds for a 10% yield than 60 seconds for a 20% yield.

The Iron Catalyst

  • The iron catalyst makes the reaction go faster, which gets it to the equilibrium proportions more quickly.
  • without the catalyst the temperature would have to be raised even further to get a quick enough reaction, and that would reduce the % yield even further.
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Minimising the Cost of Production

Production cost depends on several different factors

1) Price Of Energy

2)Cost Of Raw Materials

3)Labour Costs (wages)

4)Plant Costs (equipment)

5)Rate of Production

Optimum Conditions are chosen to give the lowest cost

  • Optimum conditions are those that give the lowest production cost.
  • its ok to have a low percentage yield as long as the materials can be recycled.
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Detergents and Dry Cleaning

Washing at low temperatures saves energy!

  • high temperatures work best for getting clothes clean 
  • but some natural fabrics shrink under the heat as well as some of the dyes running.
  • you can get biological detergents which contain enzymes which break down dirt, however these enzymes denature when they get in to temperatures over 40 degrees.

Detergents work by sticking to both water and grease.

  • some dirt dissolves in water, detergents help water and oil to mix
  • detergents contain a molecule that have a hydrophilic head (water loving) head, and a hydrophobic tail (water hating)
  • The hydrophobic heads form inter molecular bonds with water.
  • when the detergent comes into contact with water it lock on with its head and locks onto grease with its tail.

Most detergents are salts 

  • organic acid + strong alkali = salt (detergent) + water
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Detergents and Dry Cleaning

Different solvents dissolve different stains:

  • when a solid dissolves in a liquid, a clear solution is formed. The liquid is called the solvent and the solid is called the solute.
  • different solids need different liquids as they need to form the correct inter molecular bond.
  • sometimes things like grease, paint and varnishes cant be removed by regular methods so have to be dry cleaning.

Dry Cleaning uses a solvent that isn't water:

  • Most commonly used dry cleaning solvent is tetrachloroethene. Most organic substances usually dissolve in a organic dry cleaning solvent. It works because the solvent is strongly attracted to the oily molecules in the stain so the bonds between the fabric and stain break and move to the solvent.

Some Cleaners are better than others but it is dependent on its circumstances.


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Chemical Production

Continuous Production- (Haber process)

  • runs without stopping, so you don't waste time stopping and restarting
  • it runs automatically
  • the quality is very consistent
  • little risk of contamination 
  • huge set up costs and not cost effective to run anything other than full capacity

Batch Production- small quantities of specialist chemicals

  • its flexible
  • start up costs are low
  • its labour intensive
  • downtime in production
  • quality is less consistent

Several factors affect the cost of pharmaceutical drugs- market research, research and development, trialing, marketing and manufacture eg a chemical need to be removed from a plant by crushing it dissolving in water then extracting it via chromatography.

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Allotropes of Carbon

Diamond is used in jewellery and cutting tools:

  • each carbon atom forms four covalent bonds in a very rigid giant covalent structure, making the diamond really hard.
  • all these strong covalent bonds gives the diamond a very high melting point.
  • does not having any free electrons so does not conduct electricity

Graphite (lead)

  • each carbon atom only forms 3 covalent bonds, creating sheets of carbon atoms which are free to slide over each other. 
  • has a high melting point
  • lots of spare electrons allowing free movement of electricity 

Fullerenes are nanoparticles

  • Fullerenes are molecules of carbon, shaped like hollow balls or close tubes, Also forms 3 covalent bonds with its neighbours allow it to conduct electricity
  • Buckminsterfullerene is the smallest which has 60 carbon atoms joined in a ball.
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Water Purity

There are a variety of limited water resources in the UK:

  • we get out water from
  • surface water- lakes, rivers and reservoirs which runs dry during the summer.
  • groundwater: aquifers in the south east 70% of the domestic water comes from groundwater.

Water is purified in water treatment plants:

  • filtration- a wire mesh screen then gravel and sand beds
  • Sedimentation- iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom.
  • Chlorination- chlorine gas is bubbled through to kill harmful bacteria and other microbes.

Tap Water can still contain impurities:

  • Nitrate Residue - from excess fertilizer run off 
  • Lead compounds from old lead pipes (very toxic)
  • Pesticide residue from run off
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Water Purity

To test for sulfate ions: add some dilute hydrochloric acid, then 10 drops of barium chloride solution to the test sample. if you see a white precipitate there are sulfate ions in the sample.

Barium chloride + sulfate ions = barium sulfate + chloride ions

Test for Halide Ions: add some dilute nitric acid, then 10 drops of silver nitrate solution to the test sample.

  • Chloride ions will produce a white precipitate
  • bromide ions will produce a cream precipitate 
  • Iodide ions will produce a pale yellow precipitate

1.4 billion people worldwide cant get clean water to drink 

  • because of contamination and needs money to set up pumps or filtration and pumping centers 

You cant get fresh water by distilling sea water

  • in countries like Kuwait sea water is distilled to produce drinking water.
  • Distillation needs loads of energy, so its expensive and not practical for producing large quantities of water.
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Comments

bethany o'malley

thankyou its really good!

Kieran Sieluzycki

your welcome!

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