AQA unit 3 GCSE revision notes

They might be slightly oudated but i hope they help!!

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  • Created on: 05-06-12 21:29
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(Higher only in italics)
The Periodic Table
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 the
problem by arranging the elements or order of their atomic weight (mass) and looking for
patterns in their properties.
Both were successful to some extent, but Mendeleev was much more successful because.
a) He recognized that there were some elements still to be discovered, so he left
gaps in his table
b) He was not afraid to change the order of some elements in the table where it
seemed to make sense.
c) He was able use the table to successfully predict the properties of some
elements which had not yet been discovered.
Later when more elements had been discovered and chemists realized that the elements
should be in order of atomic number rather than atomic mass, Mendeleev's Table was
shown to be extremely successful.
The Modern Table
The periodic tables patterns are now known to be based on the structure of the atom.
Elements in the periodic table are arranged in order of atomic number (number of protons
in the nucleus)
The group number of an element shows the number of electrons in the outer shell.
The period number shows the number of shells of electrons
e.g. Sodium is element number 11 and has the structure 2.8.1 It therefore has 11 protons, it
is in Group1, period 3 of the periodic table.
GROUP 1 , The Alkali Metals.(Li, Na, K, Rb, Cs, Fr)
1) All elements have 1 electron in the outer shell:
Li: 2.1 Na: 2.8.1 K: etc.
2) For this reason they all form 1+ ions when they react:
Ions are Li+, Na+, K+ etc.
3) They have similar physical properties. All are very light, soft metals which are shiny when

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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 stored under oil, and
only very small amounts should ever be reacted with water using safety screen, goggles
etc.…read more

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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.…read more

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Acids, Alkalis and Bases
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 alkali, nor how insoluble bases
such as magnesium oxide (MgO) behaved.…read more

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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 produces dissolved
OH ions.
e.g. NaOH = Na+(aq) + OH(aq)
A weak alkali is only partly ionised, e.g.…read more

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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.
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 = 0.8 mol/dm3
Find the number of moles of
a) NaCl in 3 dm3 of a 0.1M solution.
b) CuSO4 in 200cm3 of a 0.2M solution.
c) HCl in 50cm3 of a 0.5M solution.…read more

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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 0.25 = 0.025
From the equation, the moles of H2SO4 is half this: 0.025/2 = 0.0125
b) 50 cm3 of a solution of sodium carbonate of concentration 0.2 moles dm3 reacts with
hydrochloric acid.…read more

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Lime scale forms in kettles, pipes etc.
Hard water contains Ca2+ or Mg2+ ions in solution. These ions react with soap to form
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 the form of calcium sulphate or calcium hydrogen
If calcium hydrogen carbonate is present, it can be removed by boiling. This decomposes
the calcium hydrogen carbonate to calcium carbonate, which forms scale.…read more

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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 of solution when the temperature changes.…read more



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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