GCSE Chemistry 3B - AQA

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  • Created on: 19-05-13 16:29

Titration - Experiment and Calculation

Titration experiments are used to find out concentrations

Step 1: Put 25.00 cm3 of alkali in a flask and add a few drops of indicator like methyl orange

Step 2: Add 50.00 cmof acid from the burette abit at a time, swirling it. When it turns clear, add the acid in drops so you can tell when the acid had neutralized as it goes clear

Step 3: Record the result and take that away from 50.00 cm3. Repeat the experiment a few times to get a mean - no anomilies

Titration Calculations:      A x Vb x Cb = B x Va x Ca

A = ACID    B = BASE    Vb and Va = VOLUME cm3    Cb and Ca = CONCENTRATION mol/dm3

Step 1: Write down the balanced equation of what you are working out

Step 2: Add in the values

Step 3: Use the formula to calculate the missing values

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Reactions are either EXOTHERMIC or ENDOTHERMIC

EXOTHERMIC: GIVES OUT ENERGY (eg.heat) to the surroundings, can tell by rise in temperature

ENDOTHERMIC: TAKES IN ENERGY (eg.heat) from the surroundings, can tell by fall in temp

Energy most always be SUPPLIED to BREAK BONDS and energy is always RELEASED when BONDS FORM

BOND BREAKING = ENDOTHERMIC - energy needs to be supplied to break the strong bond

BONDS FORMING = EXOTHERMIC - energy is released when the strong bond is formed

Bond energy can be worked out - the energies are given in the exam :)

Activation energy is lowered when using a catalyst

The activation energy is the minimum energy used to break the bonds. A catalyst provides a different pathway for the reaction so that it has a lower activation energy so the reation happens quicker and more easily.

This is represented by a lower curve on the diagram so lower activation energy, but the overall energy change still remans the same

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Hydrogen Energy

Petrol is the most common type of fuel for cars. Problem is that it produces damaging exhaust products such as CO2 which help global warming. Oil will run out but there is another fuel, hydroge

When hydrogen and oxygen react, they give out energy to produce water - non polluting. This reaction is exothermic - so it releases energy. This means that this can be used as a clean fuel.

Two types of hydrogen fuel cell: Burn in internal combustion engine or use hydrogen fuel cells

  • Hydrogen gas is burnt in oxygen as a fuel in cars
  • But to do this, you need a special and very expensive engine, as you need to store it safely and use energy from another source to make it
  • Hydrogen can be used in a hydrogen-oxygen fuel cells which use fuel with oxygen to produce electricity to run the cars

Hydrogen needs to be manufactured as there is no natural hydrogen sources on earth. This is done by methane + water ---> hydrogen + carbon monoxide

Carbon monoxide is poisonous, so its reacting with oxygen to make carbon dioxide


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Test for Positive Ions

Flames Test - This identifies ions

  • Lithium, Li+, gives a crimson flame
  • Sodium, Na+, gives a yellow flame
  • Potassium, K+, gives a lilac flame
  • Calcium, Ca2+, gives a red flame
  • Barium, Ba2+, gives a green flame

Coloured Precipitate - metal ions form this with NaOH (sodium hydroxide)

  • Calcium, Ca2+, White
  • Copper (II), Cu2+, Blue
  • Iron (II) Fe2+, Green
  • Iron (III) Fe3+, Brown
  • Aluminium, Al3+, White at first. But then redissolves in excess NaOH to form a colourless solutio
  • Magnesium, Mg2+, White
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Test for Negative Ions

Testing for Carbonates - check CO2

  • You can test for carbon dioxide by bubbling it through limewater. If its carbon dioxide the limewater turns cloudy
  • You can use this to test for carbonate ions since carbonates react with dilute acids to for CO2

Acid + Carbondate ----> Salt + Water + Carbon Dioxide

Tests For Halides:

To test for chloride, bromide or iodide, add dilute nitric acid followed by silver nitrate solution

A chloride gives a white precipitate of silver chloride  

A bromide gives a cream precipitate of silver bromide

An iodide gives a yellow precipitate of silver iodide

Test for Sulfate Ions:

Add dilute HCl, followed by barium chloride solution. A white precipitate of barium sulfate means the origional compound was a sulfate

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Test for Negative Ions

Sos, cant delete this card :/

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