Chemistry Revision Notes - Unit 2 (OCR B - salters chemistry)


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OCR B (Salters) AS level Chemistry
UNIT 2 ­ F332
Elements from the sea
Halogens and Halides (group 7 chemistry)
Halogen is the elemental molecule, eg/ Cl, Br
Halide is in a compound, eg/ KBr, KCl
Fluorine Chlorine Bromine Iodine
Appearance Pale yellow Green gas Dark red Shiny black
at room gas volatile liquid solid ­
temp sublimes to
purple gas
Halide Colour precipitate with silver nitrate
KCl White
KBr Cream
KI Pale Yellow
Redox reactions
`Reduction is gain of electrons, oxidation is loss of electrons'
Overall reaction = 2KBr + Cl 2KCl + Br
Halogens get more reactive going up the group, and in redox reactions the less
reactive element come out of the compound/solution, and is oxidised.
Half equations = 2Br Br + 2e
Cl + 2e 2Cl
This shows that Chlorine is reduced because it has gained electrons, and
Bromine is oxidised because it has lost electrons.
Oxidation states

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Element Oxidation number
Fluorine -1
Oxygen -2 (unless with Fluorine)
Chlorine -1 (unless with Fluorine or Oxygen, then +1)
Hydrogen +1
Working out oxidations states is really just simple maths.…read more

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Needs to be covalently bonded.
One element has to be more electronegative then the other.
Has to have a delta negative end and delta positive end according to
the shape of the molecule.…read more

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Nucleophillic substitution
`A nucleophile is a species which is strongly attracted to a region of positive
charge in another molecule, and can donate an electron pair'
SN2 mechanism
The Nu ion represents the attacking nucleophile
Curley arrows show the movement of electron pairs
The nucleophile is attracted to the carbon because it has become
delta positive due to its bond with the bromine
As the nucleophile gets closer to the carbon, the electrons in the
C-Br bond are pushed further towards to bromine, until…read more

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The first ionisation energy is the energy required to remove the most loosely
held electron from one mole of gaseous atoms to produce 1 mole of gaseous
ions each with a charge of 1+.
This is more easily seen in symbol terms.
It is the energy needed to carry out this change per mole of X.
`First ionisation energy shows periodicity.…read more

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Last calculations
Number of moles = Volume (dm³) x Molarity (mol dm³)
% uncertainty = (total error range) / (volume) x 100
7…read more



really helpful, thanks

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