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Chemistry Unit 3

AQA GCSE Chemistry Syllabus

C3.1.1 The early periodic table
C3.1.2 The modern periodic table
C3.1.3 Trends within the periodic table

The modern periodic table has been developed from work begun by Newlands and Mendeleev.
There are trends in chemical properties within the periodic table linked to how…

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Chemistry Unit 3

e) The elements in Group 7 of the periodic table (known as the halogens) react with metals to form
ionic compounds in which the halide ion carries a charge of ­1.
f) In Group 7, the further down the group an element is:
the less reactive the…

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Chemistry Unit 3

C3.2.1 Hard and soft water

a) Soft water readily forms lather with soap. Hard water reacts with soap to form scum and so more
soap is needed to form lather. Soapless detergents do not form scum.

b) Hard water contains dissolved compounds, usually of calcium or magnesium.…

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Chemistry Unit 3

However if calcium (Ca2+) or magnesium (Mg2+) ions which are positive cations are present then
their presence produces permanent hard water.

Temporary hard water is easy to treat, boiling the water is sufficient.

Permanent water requires more sophisticated water softening methods. There are two solutions the

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Chemistry Unit 3

When heated to 1000c, only the water boils, it turns into a gas, which is then cooled down so it
condenses back into a liquid. Any ion impurities remain in the original heating vessel.

Because this method involves heating up water this is a very expensive method…

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Chemistry Unit 3

f) In an exothermic reaction, the energy released from forming new bonds is greater than the energy
needed to break existing bonds.
g) In an endothermic reaction, the energy needed to break existing bonds is greater than the energy
released from forming new bonds.
h) Catalysts provide…

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Chemistry Unit 3

In an endothermic reaction the total bond energy of the reactants is less than the total bond energy
of the products, this extra energy. So in photosynthesis there is less energy in the reactants water
and carbon dioxide, than there is in the products glucose and oxygen…

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Chemistry Unit 3

e) Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute
nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.
f) Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence…

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Chemistry Unit 3

3) Work out the concentration of the unknown substance
Concentration = number of moles / volume
25cm of sodium hydroxide of concentration 0.1moles/dm3 is in the flask and it takes 30cm3 of

sulphuric acid to neutralise the sodium hydroxide. Work out the concentration of the acid…

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Chemistry Unit 3

Ammonia has the chemical formula NH3, The raw ingredients for its manufacture comes from:
Nitrogen - the air
Hydrogen - methane gas
The reaction between these two gases is neither simple nor easy to control, it is a reversible
reaction. Both the reactants and the products are…


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