GCSE Chemistry 3B - AQA
- Created by: Han2812
- 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 cm3 of 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
Energy
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
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
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
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
Test for Negative Ions
Sos, cant delete this card :/
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