Chemistry C3 - Edexcel

GCSE Extension Science Edexcel - Chemistry C3

From the CGP revision guide and school notes.

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Testing for POSITIVE Ions - Flame Test

1) Dip hoop in HCl and heat - remove any unwanted ions.

2) Dip hoop in the unknown salt and then into the roaring flame. See flame colour.

Flame Test Colours

Calcium (Ca+) - Brick Red

Sodium (Na+) - Yellow

Barium - Apple Green

Copper (Cu2+)- Green

Potassium (K+) - Lilac

Magnesium - Bright White

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Testing for POSITIVE Ions - Precipitate Test

1) Create a soloution by adding water to the unknown salt.

2) Add a few drops of NaOH to the solution. See the colour of the precipitate formed.

Precipitate Colours

Aluminium (Al3+) - White

Calcium (Ca2+) - White

Magnesium (Mg2+) - White

Copper (Cu2+) - Blue

Iron (Fe2+) - Green

Iron (Fe3+) - Brown

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Test For NEGATIVE Ions

Carbonates (CO3 2-) give off CO2 with dilute HCl.

Sulphites (SO3 2-) give of SO2 with dilute HCl.

Sulphates (SO4 2-) produce a white precipitate. Add dilute HCl (to remove any other ions) followed by Barium Chloride (BaCl2).

Halides (Cl-, Br-, I-) add nitric acid (HNO3) followed by Silver Nitrate (AgNO3):

  • Cloride (Cl-) gives a white precipitate of Silver Chloride.
  • Bromide (Br-) gives a cream precipitate of Silver Bromide.
  • Iodide (I-) gives a yellow precipitate of Silver Iodide.
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Test For Acids And Alkalis

1) Litmus:

  • Blue Litmus paper turns red if H+ Ions are present = Acidic
  • Red Litmus paper turns blue if OH- ions are present = Alkali.

2) Phenolphthalein. Pink but turns colourless in acids.

3) Methyl Orange. Yellow in alkalis but Red in acids.

4) Universal Indicator. Estimates pH of solution. Red = Acid, Green = Neutral, Purple/Blue = Alkali.

5) Add substance to metal to test for Acids (H+ Ions). Gives of Hydrogen = Squeeky Pop Test.

6) Heat Substance with Ammonium Salt to test for Alkalis (OH- Ions) Hydroxides give off ammonium gas when heated with ammonium salt. Ammonia gas is smelly or use universal indictor (goes purple) to show it's there.

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Maths Stuff

1 Mole = 6.023 x 10(23)

Number of Moles = Mass (g)  /  Mr

1000 cm3 = 1 dm3

Volume (dm3) = Number of Moles x 24 (1 mole of any substance, in gaseous form occupies 24 dm3)

Concentration =   M   /   Volume (dm3)   (M = either Mass or Number of Moles depending on what you are asked to find out)

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To find out exactly how much acid is needed to neutralise an alkali (or vice versa).

1) Use a pipette to pour 25cm3 of alkali into a conical flask. Add a few drops of Phenolphthalein indicator.

2) Fill a burette with acid.

3) Use a burette, add the acid to the alkali whilst stirring the conical flask.

4) The indicator changes colour at the point of neutralisation.

5) Repeat, remove any anomalies, take an average.

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Water is a solvent. It disolves in most ionic compounds by surrounding the ions attracting them more than they attract eachother - so the solid nature falls apart.

Water treatment is very expensive. It is filtered twice then chlorinated to kill any harmful bacteria.

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Transition Metals

Common metals:

  • good heat/electricty conductors
  • Dense, strong and shiny.
  • High melting points
  • Much less reactive than Group 1 metals.

Copper is hard strong and has a high melting point and is a good conductor. Used for wires and pipes. Doesn't react with water. = Electric wire and plumbing.

Iron pure it is malleable.

  • Cast Iron = 3% Carbon. Brittle, conducts heat well = Cooking Pots etc...
  • Steels. Low carbon = Cheap, strong, malleable = Car bodies etc. High Carbon = Cheap, hard = Drill Bits. Stainless Steels = Don't rust or react much with acid = Cutlery, containers etc...

They make good catalysts (Haber Process)

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1)Methanol 2)Ethanol 3)Propanol 4)Butanol 5)Pentanol

  • Have an -OH Functional group.
  • Clear colourless liquids at room temp.
  • Flammable + evaporate easily
  • React with Oxygen to form Carboxylic Acids.
  • React with Carboxylic Acids to produce Esters.
  • Toxic

Used as solvents as can disolve in most substances. The -OH group can mix with water and ionic compounds. E.g. in purfumes

Used as a fuel in spirit burners, and cars (mixed with petrol and can be fermented from sugar cane so is renewable)

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Carboxylic Acids

1)Methanoic Acid 2)Ethanoic Acid 3)Propanoic Acid 4)Butanoic Acid 5)Pentanoic

  • -COOH functional group
  • They react with any other acids to form salts with '-anoate' endings. E.g. Methanoic Acid will form Methanoate.
  • Corrosive
  • Used to make Soaps and Esters.

They're common

  • Vinegar contains ethanoic acid
  • ethanol in drinks is oxidised into ethanoic acid.
  • Citric acid = Carboxylic Acid
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  • Alcohol + Carboxylic Acid --> Ester + Water         = Esterification
  • Methanol + Ethanoic Acid --> Methyl Ethanoate + water
  • Butanol + Propanoic Acid --> Butyl Propanoate + water
  • Have a pleasant smell (used in flavourings and purfumes)
  • Colourless + low boiling points
  • Flammable
  • Don't mix well with water, but do with alcohols and organic solvents.
  • Can be toxic
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The loss and gain of electrons: Oxidation Is Loss, Reduction Is Gain.

Positive Anode, Negative Is Cathode

Copper is purified by electrolysis.

The electrons are stripped off the anode causing them to turn positive (Cu2+ ions) which are attracted by the cathode.

Pure copper is depositied on the Cathode.

Electrode mud is deposited = great value.

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The Alkali Metals (Group 1)

  • Shiny and soft
  • Low density
  • lower melting and boiling points
  • Metalic bonding in the metals is a lot weaker.

As you go down they become; more reactive, higher density, softer, lower melting point, lower boiling point.

React with water to produce Hydrogen Gas.

  • Can fizz and move around the surface of the water.
  • Potassium sparks a flame.

Sodium Carbonate = for glass and washing soda crystals.

Sodium Hydroxide = Strong alkali with many industrial uses.

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Sulphuric Acid

Made by the contact process:

  • 1)Burn sulphur in air to make Sulphur Dioxide. S + O2 --> SO2
  • 2)Sulphur dioxide is oxidised to form sulphur trioxide. 2SO2 + O2 <--> 2SO3
  • 3) Sulphur trioxide is dissolved in concentrated sulphuric acid to form fuming sulphuric acid. SO3 + H2SO4 --> H2S2O7
  • 4) Fuming sulphuric acid is diluted to form concentrated sulphuric acid.                   H2S2O7 + H2O --> 2H2SO4

Catalyst is very important in step two. Use Vanadium Pentoxide.

Uses of Sulphuric Acid:

  • Car batteries
  • Petrolium Refining
  • Clean metal surfaces.
  • fertilisers, soaps and detergents etc...
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  • Hydrophobic Tail: dislikes water and loves oil and grease = hydrocarbon chain/tail.
  • Hydrophilic Head: loves water and hates oil and grease = small and ionic/head.

The contain surfactants which lower the surface tension of water to help water soak into the fibres of clothes.

Surfactants also help oil and water mix. The oil forms droplets surrounded by a coating of surfactant. This helps to lift oily dirt out of fabric.

Made from an ester (fatty acid) and an alkali. Natural fats are boiled up with sodium hydroxide.

Soaps form Scum in Hard Water Areas.

Biological detergents contain enzymes but non-bios don't. Help to break down some insoluable molecules into smaller soluable ones.

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fay bower

this is really good thankyou!

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