GCSE AQA Chemistry 'Unit 3b' Revision Guide

Revision guide for the second half of the GCSE AQA Chemistry 'Unit 3' / 'C3' exam paper.

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GCSE Chemistry
`Unit 3b' written by Applequestria
Table of Contents
Table of Contents..................................................................................................................................... 1
Energy from reactions.............................................................................................................................. 2
Use of calorimetry method: ................................................................................................................ 2
Use of calorimetry results: .................................................................................................................. 2
Energy from reactions (continued)........................................................................................................... 3
Energy from reactions (continued)........................................................................................................... 4
Energy bond calculations: ................................................................................................................... 4
Fuel cells: ............................................................................................................................................. 4
Analysing substances ............................................................................................................................... 5
Tests for positive ions .......................................................................................................................... 5
Analysing substances (continued) ............................................................................................................ 6
Tests for negative ions......................................................................................................................... 6
Analysing substances (continued) ............................................................................................................ 7
Use of titration, to find concentrations of acids and bases method: .................................................. 7
Use of titration, to find concentrations of acids and bases results (mol/dm3): ................................... 7
Analysing substances (continued) ............................................................................................................ 8
Use of titration, to find concentrations of acids and bases results (g/dm3): ....................................... 8
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Energy from reactions
Different fuels produce different amounts of energy. The relative amounts of energy released when
substances burn can be measured by simple calorimetry, such as by heating water in a glass or metal
container (usually copper as copper is a good conductor of heat). This method can be used to
compare the amount of energy released by fuels and foods.
Use of calorimetry method:
Add 50g of water into a copper can.
Record the initial temperature of the water in the copper can.…read more

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Energy from reactions (continued)
The amount of energy released or absorbed by a chemical reaction in a solution can be calculated
from the measured temperature change of the solution when the reagents are mixed in an insulated
container. This method can be used for reactions of solids with water of for neutralisation reactions.…read more

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Energy from reactions (continued)
Energy bond calculations:
Different chemical bonds have different bond energies. You can use bond energies to work
out the overall energy change (H) of a reaction. For example, you can calculate the overall
energy change (H) when hydrogen and chlorine react to form hydrochloric acid.
Write down the balanced chemical equation of the reaction. Hydrogen-hydrogen
bonds have a bond energy of 436kJ/mol, chlorine-chlorine bonds have a bond energy
of 242kJ/mol and hydrogen-chlorine bonds have a bond energy of 431kJ/mol.…read more

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Analysing substances
Tests for positive ions
Ionic compounds contain positive ions and negative ions. Flame tests can be used to identify positive
metal ions. Lithium, sodium, potassium, calcium and barium compounds produce distinctive colours
in flame tests:
To carry out a flame test on an ionic compound, dip a clean wire loop (to clean a wire loop,
dip the wire loop in hydrochloric acid and rinse the wire loop with distilled water) in
compound sample, and put the wire loop in a Bunsen flame.…read more

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Analysing substances (continued)
Tests for negative ions
Ionic compounds contain positive ions and negative ions. To test for carbonate ions (CO32-), add a
dilute acid to the solution. Carbonate ions react with dilute acids to produce a salt, water and carbon
dioxide. Carbon dioxide reacts with limewater to produce calcium carbonate (which is a white
precipitate) and water. This turns limewater cloudy.…read more

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Analysing substances (continued)
Use of titration, to find concentrations of acids and bases method:
The more solute you dissolve in a given volume, the more crowded the solute molecules are
and the more concentrated the solution. Concentration is measured in mol/dm3 or g/dm3.
One mole of a substance is the mass of a substance that has the same number of particles as
there are atoms in twelve grams of carbon-twelve.…read more

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Analysing substances (continued)
Use of titration, to find concentrations of acids and bases results (g/dm3):
Find the relative formula mass of sulphuric acid, which is the total of the relative atomic
masses. This gives the relative formula mass of sulphuric acid as 98.
Number of moles is equal to mass over relative formula mass. Therefore concentration in
moles is equal to concentration in grams over relative formula mass. Therefore the
concentration sulphuric acid is 4.08g/dm3.…read more

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