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Redox Reactions

A resource i created as part of my chemistry homework for the year below.
by

Bekkie M

on 24 October 2013

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Transcript of Redox Reactions

Oxidation-Reduction Reactions
Most common oxidation-reduction (redox) reactions are combination, decomposition,
displacement, and combustion reactions

Here are some videos demonstrating some of them.
Decomposition
WARNING!
In the video you are about to watch, the presenter talks really, really fast, and even though it starts out simple, towards the end of the video it starts to get a little complicated! But don't worry if you can't catch all of it, I will summarise it afterwards :)

but try to pay attention anyway.
An Example
halogen displacement reaction
You will find redox reactions
EVERYWHERE
over the next two years! This presentation should give you a bit of an idea about how they work, along with examples of common redox reactions you will come across in AS and A2 chemistry. I have also included a few videos that i think might help you. It i s a lot to take in, so don't worry if you don't understand everything immediately.
for A Level Chemistry
Combustion reaction:
Methane bubbles!!!
And more!
Didn't quite catch that? Don't worry, here it is again:
to remember where the electrons are, use:
O
I
L
R
I
G
oxidation
is
loss
reduction
is
gain
Rules for Oxidation numbers:
#1 all elements by themselves have oxidation number of 0
#2 monatomic ions (ions of one element) have an oxidation number equal to their charge
#3 Oxygen almost always has oxidation number of -2
(except when it is in H2O2 of as O2)
#4 hydrogen always has ox. no. of +1
#5 fluorine always has ox. no. of -1 (so do the other halogens, most of the time, unless combined with oxygen or fluorine.
All oxidation numbers of individual atoms in a
Neutral
compound add up to 0
for example water:

there are to hydrogens each with +1 ox. no.
and there is an oxygen with ox. no. -2
2(+1) and -2 add to 0
in a Polyatomic ion, (more then one element),
the oxidation number is the same as its charge.
this can be used to work out unknown oxidation numbers
for example a sulfate ion:
its charge is
2-
it has four oxygens, adding to oxidation no. of 4x-2=
-8
it also has a sulfur atom, which has an unknown oxidation number
but we can work it out by noticing
S +
-8
=
-2
so S =
-6
redox reaction for
AMMONIA
N2 + H2 --> NH3

0
0
+1
-3
oxidation numbers:
unbalanced equation:
this is just a really easy example
using
Half Equations
to balance it:

N is reduced from ox.no 0 to -3
its half equation is:

N2 + 3e- --> 2N
because it gains 3 electrons
-3
0
H is oxidised from ox. no. of 0 to +1
its half equation is:

H2 --> 2H + e-
because it loses 1 electron
The oxidised half of the equation half of the equation releases 1 electron, but the reduced side needs to gain 3, so multiply the H side by three.
you get
N2 + 3H2 --> 2NH2
0
+1
You will come across a lot of problems like this, most of which will be more complicated, so make sure you get plenty of practice!
Hope you found this presentation helpful
Thank you for watching!!
Full transcript