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AQA UNIT 3 GCSE REVISION NOTES
(Higher only in italics)

The Periodic Table
History
At the start of the 1800s quite a lot of elements had been discovered, but there had been
no real attempt to organize them.

Newlands, an English chemist and Mendeleev, a Russian chemist both worked on…

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4) They have similar chemical properties. In particular they react vigorously with water
giving hydrogen and an alkaline solution of the hydroxide.
(e.g. 2Na + 2H2O = 2NaOH + H2)
For this reason, they are called alkali metals
Because of the violence of this reaction with water, alkali metals are…

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REACTIONS
1. They react readily with metals to form salts (chlorine does this most readily, then
bromine, then iodine)
e.g. Mg + Cl2 = MgCl2
2Na + I2 = 2NaI
2. Like metals, a more reactive halogen will displace a less reactive one:
e.g. chlorine + potassium bromide = bromine…

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Acids, Alkalis and Bases

Definitions

In 1887, the Swedish Chemist Arrhenius came up with the idea that all acids produced
hydrogen ions (H+) in water, while all alkalis produce OH ions.

However, these ideas were not readily accepted because

a) It did not explain why ammonia (NH3) behaved as an…

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Note that weak acids (like ethanoic acid in vinegar, citric acid in lemons or carbonic acid in
fizzy water) do not completely split up into hydrogen ions. The low concentration of H+ ions
makes them weak.

When a strong alkali such as NaOH or KOH is dissolved in water, it…

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Concentration is measured in mol/dm3 and volume is measured in dm3

1000cm3 = 1 dm3, so always divide cm3 by 1000 before using this relationship.

e.g.
a) What is the molar concentration if 0.2 moles are dissolved in 250cm3 of water?
volume = 250/1000 = 0.25 dm3
concentration = 0.2/0.25…

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a) 250 cm3 of a solution of NaOH of concentration 0.1 moles dm3 reacts with
hydrochloric acid. How much acid is used?
2NaOH + H2S04 = Na2SO4 + 2H2O
Moles = Concentration x Volume
Conc = 0.1M Vol = 250/1000 = 0.25 dm3
So Moles of NaOH = 0.1 x…

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3) Lime scale forms in kettles, pipes etc.
Hard water contains Ca2+ or Mg2+ ions in solution. These ions react with soap to form
scum.
This is because soap is sodium stearate, which reacts with calcium ions to form insoluble
calcium stearate which is scum.

Calcium is usually dissolved in…

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A solubility curve shows how much of a substance can be dissolved in a certain amount of
water at different temperatures. Usually more can be dissolved at higher temperatures.
By reading off the amounts which can be dissolved at different temperatures, you can work
out how much will crystallise out…

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Katie789

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thanks, this is a really useful resource. it sometimes has more info than needed, but i find that helps me understand it better.

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