- Hello my lovely kittens,
in this video we're going to
be covering everything
you need for your first
EDEXCEL Chemistry exam.
Now, if you wanna follow
along as we're going through
you can get the free revision
guide over on my website
where I've taken the
specifications and turned
it all into nice for you,
taken all the different bits
that you need to learn,
the formulas of compounds
and ions, the reactivity
series and I've put that all
in there for you.
All that's already done for free for you.
("Something Elated" by Broke for Free)
The model of atoms change
quite a lot over time.
You're going to know
all the details of this.
You need to know that
Rutherford was responsible
for discovering the nucleus and protons,
that Chadwick discovered neutrons,
and that Bohr developed our current model.
Here we have a structure of an atom.
We have electrons that
are on the shells around
the outside, protons
that are in the middle,
and neutrons that are in the middle.
And, this bit in the
middle here is collectively
called the nucleus.
Protons are in the nucleus.
They have a mass of one
and a charge of plus one.
Neutrons are also in the nucleus.
They have a mass of one
and a charge of zero.
Electrons are in the outer shells.
Their mass is 1/2000 and they
have a charge of minus one.
On the Periodic Table you will
see lots of boxes like this.
This tells you all about the elements.
This is the element's name, their symbol.
And, there are two numbers.
This is the atomic number.
And, this one is the mass number.
Now for these location doesn't matter.
Different textbooks,
different sheets are going
to put them in different locations.
The larger one is the mass number.
And, the smaller one is the atomic number.
The atomic number tells
us the number of protons
and the number of electrons in an atom.
The mass number is the number of protons
plus the number of neutrons.
So, here we have calcium.
The smaller number is the atomic number.
The large number is the mass number.
And, if you want to find
the number of protons
it's simply the atomic
number, so in this case 20.
The number of electrons,
still the atomic number
so again 20.
The neutrons is the mass
number, which is 40 minus
the atomic number, which
is 20, equaling 20.
Here we have two different
isotopes of carbon,
carbon 12 and carbon 14.
Working out the number of
protons is exactly the same,
it's the atomic number.
So, for both of those that is six.
The number of electrons
in an atom is the same
as the number of protons so that is six.
But, the neutrons here
is different because
for carbon 12 it is 12 minus
six giving us six neutrons.
And, for carbon 14 it is 14 minus six
giving us eight neutrons.
So, an isotope is something
that has the same number
of protons but a different
number of neutrons.
And, a proton is what identifies
the identity of an atom.
You may have noticed
from the Periodic Table
that some things have .5 mass.
So, Chlorine has 35.5 mass,
which is frankly ridiculous
because we can't have half
protons or half neutrons.
This is because the mass
is a relative abundance
of all of the isotopes.
There are two main isotopes of chlorine,
chlorine 35 and chlorine 37.
75% of naturally occurring
isotopes are chlorine 35
and 25% of naturally occurring
isotopes are chlorine 37.
To work out the mass this is what we do.
You take that MR 37 times it
by the relative abundance,
25%, do this for all of them.
35 times 75
and then divide that by 100.
37 times 25 is 925 plus 35 times 75
that's 2,625 over 100
giving us 3,550
over 100 making it 35.5.
Here we have our wonderful,
beautiful periodic table.
It is a list of all the elements
which are known to exist.
Elements are a single type of atom.
An atom's a very, very small thing.
The word atom is actually
Greek for un-cuttable.
And, when they names
them they thought it was
the smallest thing possible.
The Periodic Table tells
us loads and load and loads
of information about the
elements, the range of elements
that are known to exist.
There were still loads
yet to be discovered.
A compound is two or more elements that
are chemically bonded together.
That's the important thing:
chemically bonded together.
Our Periodic Table hasn't
always looked like this.
The first attempt at a Periodic Table
was by Newlands in the 1800s.
He tried to group things into octaves
and rate them by pattern
which is a really good idea
except we have oxygen and
iron in the same group
and they have very different properties.
He arranged them by mass but
he didn't leave any gaps.
And, he tried to force
things into having similar
patterns or properties as other things
and it didn't really work.
Mendeleev was the next
person to have a go.
He also arranged things by mass,
but the key thing is that he left the gaps
in his periodic table.
And, because he arranged
things so that they
were in groups with similar patterns
and he left gaps he could
predict the properties
of elements that have yet to be discovered
and he was correct in his predictions.
A few years after he
developed his Periodic Table
happily new elements were discovered
and they fitted in really, really neatly,
really nicely to his periodic table.
So, this table was accepted.
It was changed ever so slightly by then.
We now arrange things by
electronic arrangement.
But that is a very,
very subtle difference.
The Periodic Table gives us
loads and loads of information.
The first bit of information
it gives us are about groups.
Now, groups go down the periodic table.
Group one, group two, three, four, five,
six, seven, eight or group zero.
Groups tell us the number of
electrons on that outer shell.
So, things in group one
are going to have one
electron in the outer shell.
Things in group two are
going to have two electrons
in the outer shell.
Group six, six electrons
in the outer shell.
Groups seven, seven
electrons in the outer shell.
Periods go across the Periodic Table.
So, here is our first period, the one that
everyone always forgets
because it's only got
hydrogen and helium in.
Here is our second period.
Here is our third period.
And, periods relate to
the number of shells
that things have.
They also remind us how many electrons
are on or in each shell.
So, in the first period
there are two elements,
which means there are
going to be two electrons
in that shell.
In the second period there
are one, two, three, four,
five, six, seven, eight
elements which means there are
going to be eight electrons in that shell.
And, we can use this
information to tell us about
the electronic configuration.
Here we have magnesium.
Here is magnesium on the Periodic Table.
And, we can see that
the number of electrons
it has is 12.
It is in group two and
it is in period three.
So, that tells us it has
12 electrons in total.
It has two electrons on the outer shell
because it's in group number two.
And, it has three shells because it is in
period number three.
So, when we want to draw
the electronic configuration
of magnesium we know it's in period three,
it's gonna have three shells.
First thing we can do
is draw three shells.
Two, one, two, go on
the first shell.
One, two, three, four, five,
six, seven, eight go on the second shell.
That's the most that
can fit in that shell.
That brings us up to 10.
10, 11, 12, two electrons
on the outer shell.
From periods we know that the first shell
can hold a maximum of two electrons.
The second shell can hold a
maximum of eight electrons.
The third shell can hold a
maximum of eight electrons
and then you only need
to know up to calcium
so we're going to have
two for you to (mumbles).
Metals are going to lose electrons.
And, when we lose electrons
we get positive charges.
And, non-metals are going
to be gaining electrons.
And, when we gain electrons
we get negative charges.
Things in group one are
going to lose one electron,
so are going to be plus one ions.
Things in group two are
going to lose two electrons.
So, they're going to be plus two ions.
Things in group six here are going to gain
two electrons, so are
going to be minus two ions.
And, things in group
seven are going to gain
one electron, so are going
to be minus one ions.
Ionic bonding is the transfer
of electrons from a metal,
which is on this side
of the periodic table
to a non-metal on this
side of the periodic table.
Anything that is in group one
is gonna form a plus one ion,
group two a plus two ion,
group six a minus two ion,
group seven a minus one ion.
Here we're going to make magnesium oxide.
Magnesium is in group two
so it has two electrons
on its outer shell.
Oxygen is in group six,
it has six electrons
on it's outer shell.
In ionic bonding oxygen is
going to keep the electrons
that it's already had and
the electrons that were with
magnesium are going to
be transferred to oxygen.
We call these dot and
cross diagrams because
one element has a dot for
electrons and the other element
has cross for electrons.
We then draw square brackets around these
and indicate the charge.
So, magnesium has lost two
electrons so it's going
to have a plus two charge.
Oxygen has gained two
electrons so it is going
to have a minus two charge.
Here we have sodium and it
has an atomic number of 11,
which means it's going to
have 11 protons in the nucleus
and protons have a positive charge.
One, two, three, four, five, six, seven,
eight, nine, 10, 11.
Now, in the atom it has 11
electrons drawn on here.
Electrons have a negative charge.
One, two, three, four, five, six, seven,
eight, nine, 10, 11.
Now, in an atom the positive
charges and the negative
charges cancel each other
out so that all your charge
on an atom is going to be zero.
However, when sodium
makes an ion this electron
here goes away.
So, it still has the
same number of protons,
it's still sodium.
One, two, three, four, five, six, seven,
eight, nine, 10, 11.
But, it's lost an electron.
One, two, three, four, five, six, seven,
eight, nine, 10.
So, it has one more proton
that it has an electron
meaning this is going to have
an overall positive charge.
Here we have sodium chloride.
Sodium are the gray bits
you can see and chlorine
are the green bits you can see.
The blue lines are the
electrostatic interactions,
the electrostatic attractions.
Because the way we get
you to draw ionic bonding
is really false.
It's not just one sodium
combining with one chlorine,
it is this massive,
massive, massive lattice
of sodiums and chlorides or
whatever we're looking at
bonding with everything else.
So, one sodium, here, isn't
just going to be bonding
with a chlorine next
to it, or the chlorine
that is exchanged electrons to it.
It's going to be bonded
with all of the other ones
above it, next to it,
behind it, in front of it,
everything that it can reach.
So, this ionic bonding is
a massive, massive, massive
network, not just the
small things that we get
you to draw in class.
So for your ionic compounds
the structure is a giant
ionic lattice.
Properties: it is going to
have a high melting point,
high boiling point,
and it only going to conduct
when molten or dissolved.
This is because the ions
need to be free to move.
Covalent bonding is the
sharing of electrons
between two non-metals, these up here.
And, these are the common
ones you need to know
how to draw.
For each of these you need
to be able to give the name,
the formula, be able to draw it with lines
and be able to draw the
dot and cross diagram.
So, hydrochloric acid
or hydrogen chloride,
one element of hydrogen,
one element of chlorine.
Ammonia, NH3, nitrogen in the middle,
three hydrogens coming off round the side,
methane CH4, carbon in the middle,
four hydrogens branching
off it, hydrogen H2,
a very simple one there,
chlorine hydrogens
go around diatomic molecules, oxygen,
getting a bit tricky
now, has a double bond.
Each line is equal to a pair of electrons.
Here, we have two lines, so
that is two pairs of electrons,
we need four electrons
being shared in the middle.
And, nitrogen has a
triple bond, two, four,
six electrons being shared in the middle.
If in the exam they give you a picture
and ask you to make the formula of it
you simply need to list what we have.
So, in the first one we have
carbon and we have hydrogen
and then we need to count them.
One, two, three, four, five, carbon five.
Hydrogens, one, two, three, four, five,
six, seven, eight, nine, 10, 11, 12.
Last one carbon, hydrogen, oxygen.
We have one, two, three carbons.
One, two, three, four, five, six,
seven, eight hydrogens and one oxygen.
So, we don't need to
put a number after that.
It's really important
that you write things
in the right size and in the right place.
So, that is incorrect 'cause
your numbers are too big.
That is incorrect 'cause
your numbers are in
the wrong place.
I seriously recommend you
learn at least these formula.
Carbon dioxide is CO2, water H2O,
oxygen gas O2, hydrogen gas H2,
nitrogen gas N2, ammonia NH3,
hydrochloric acid HCL,
sulfuric acid is H2SO4.
For simple covalent
compounds such as water,
carbon dioxide, oxygen,
nitrogen, hydrogen gas,
hydrochloric acid, or
methane, oxygen gas, or water
as we have here they are
very, very small structures.
They have covalent bonding.
Their properties is that
they have low melting points
and boiling points.
They're generally going to
be gas at room temperature
or a liquid at room temperature.
They do not conduct
electricity.
For giant covalent compounds
ones we have carbon,
such a graphite, diamond,
or any fullerenes
or silicone dioxide they're going to have
a giant covalent structure.
Their properties are high
melting and boiling points,
and they do not conduct
and they do not dissolve.
Here we have diamond.
It is a giant covalent compound,
or a giant covalent lattice.
It is made of carbon, pure
carbon, nothing else in there.
And, each carbon makes four bonds.
So, in the video you
can see that the carbon
is the black bits, the covalent
bonds are the red bits.
And, each carbon is bonded
to four other carbons.
Obviously the one on the edge
aren't bonded to anything.
But, if you try and look
at the middle you can see
that they are bonded to four other things.
The properties of diamond
that make it really useful
is it is incredibly hard.
It's very rare, it's hard to find.
It's also very beautiful
which makes it very precious.
But, the main thing it is incredibly hard
so we can use it in drills.
Graphite is also a
giant covalent compound.
It is like diamond, pure carbon.
But, each carbon
make three bonds to other carbons
not four like in diamond.
The properties are that it is soft
and it conducts electricity.
Because it is in sheets and
there is a spare electron
floating around in between these,
that means it will conduct electricity.
Graphite is what you find in pencils,
graphene is just a single sheet.
If we were to compare diamond and graphite
they are both made of pure carbon.
Then graphite is made of
three carbon covalent bonds.
Diamond is made of four
carbon covalent bonds.
Graphite is soft, diamond is hard.
Fullerenes are either carbon nanotubules
or Buckminster fullerenes,
which are balls.
These are again all made of pure carbon.
They make three carbon carbon
bonds but unlike graphite
which is soft these are incredibly hard.
Buckminster fullerene
can be used as lubricant
in things that need lubricating
like electrical cycles
or some parts of machines.
It can be used for
reinforcement so where you need
a very, very strong, a
very, very light things
like aircrafts or bicycles.
They can also both be used
or in the future be used
for drug delivery.
And, fullerenes, carbon
nanotubules, Buckminster fullerenes
there are loads and loads
of potentials for these
but they haven't been realized yet.
With polymers whether
they have cross links
or not are going to determine
what their properties
are going to be like.
So, polymers that do have
cross links are very, very
fixed in place.
These are going to burn upon heating
whereas polymers without
cross links are going to
melt upon heating because these polymers
can slide across each other
whereas these ones cannot
slide across each other.
Metals are made up of
positive atoms in a sea
of delocalized electrons.
And, these electrons being
free to move is the reason
that metal can conduct electricity
and work so good at conducting heat.
An alloy looks slightly
different to a metal.
We still have our positive ions.
We still our delocalized electrons
but there's something
else in there as well.
This maybe another meta; it's alloyed with
or it may be something else like carbon
that it's alloyed with.
Pure metals have layers.
Layers can slide across each other.
Because they have layers and because
they can slide across
each other they are soft.
Alloys don't have layers or
they have distorted layers.
And, the distorted layers cannot slide.
And, because the distorted
layers cannot slide
it means they are hard.
The new style exams means
there are a lot of worded
questions that incorporate
a lot of skills all at once.
In this question you need
to first of all recall
the formula of things
then balance the equation.
So, hydrochloric acid is HCL,
magnesium is MG.
Now, we need to work out the products
and the formula of the salts.
A metal plus an acid is going to give us
salts plus hydrogen.
Hydrogen's the easy bits it is H and then
a two because it goes
around to diatomic molecule.
The salt is going to
be magnesium chloride,
but we need to know that
magnesium is a two plus ion
and chlorine is a one minus ion.
So, it needs to be MGCL2 so
that there are two negative
ions for each positive ion.
Now, these supports here a lot of skills,
recall of the formulas
and working out the salts,
the products so working out
what type of equation it is.
And then, after all that
we need to balance it.
So, to balance our equation we draw a line
down the middle, list what we have
hydrogen, chlorine, magnesium,
hydrogen, chlorine, magnesium.
It's really going to help
you if you keep things
in the right same order.
Circle the compounds that we have.
List the numbers of things.
So, we have one hydrogen,
one chlorine, one magnesium,
two hydrogens, two
chlorines, one magnesium.
So, you can see straight
away we need some more
hydrogens and some more chlorines.
The easiest way for us
to do that is to add
another HCL on there.
Then we do our numbers,
we have two hydrogens,
and two chlorines so it's balanced.
Writing out neatly for the examiners
because just leaving it like
this won't get you the marks.
We have two bubbles of
hydrochloric acid plus magnesium
turns into magnesium
chloride plus hydrogen.
You need to know how
to take a set of words
and turn it into a balanceable equation.
So, there is quite a
lot for you to do here
because you have to remember
the chemical symbols
for quite a large number of things.
Water is H2O that turns into hydrogen gas
which is going to be H2
plus oxygen gas which
is going to be O2.
And now, we need to balance
it, draw a line down
the middle, circle everything
and list what we have.
We have hydrogen, we have oxygen,
we have hydrogen, we have oxygen,
count the number of things.
Two hydrogens, one oxygen, two hydrogens,
one, two oxygens, sorry.
So, we need to increase
the number of oxygens
on this side 'cause it's
either aren't enough
then we have to add another H2O.
Put that in a circle, we do our numbers.
We now have two, four hydrogens
and two oxygens.
So, our oxygens are balanced
but now our hydrogens are
we have more on this side
than we do on this side.
So, we need to add more hydrogens here.
Again, the only thing we can do is to add
a whole nother bubble.
We now have two hydrogens
here, two hydrogens here
making four in total and two oxygens.
So, now we have four
hydrogens on this side
two oxygens, four
hydrogens, and two oxygens.
We need to rewrite that
neatly for the examiner.
So, we have one, two bubbles of H2O
turning into plus one, two bubbles
of H2 plus one of O2.
When you working out the
MR, which is the relative
formula mass you need to
take all of the ARs which
is the relative atomic
masses and add them together.
Now, the mass remember is
the larger number of the two,
doesn't matter where it's located.
It is the larger number of the two.
So, hydrogen has a mass of
one and we have two of them.
Sulfur has a mass of 32.
Oxygen has a mass of 16
and we have four oxygens.
So one times two is two plus 32
plus 16 times four which is 64.
Add these together we get 98.
The empirical formula is the lowest ratio
of all of the elements in a compound.
And, this is how we work it out.
We have a compound that is 75% carbon
and 25% hydrogen.
So, we're gonna list carbon, hydrogen.
Write down the number in the question
and units do not matter for this.
Not very often I say
that, more than likely
you need to learn your units.
But, whether it's percentage,
whether it's tons,
whether it's grams units do not matter.
Write down the mass
from the Periodic Table.
So, carbon has a mass of 12,
hydrogen has a mass of one.
You then need to divide
the number in the question
by the mass.
So, 75 divided by 12 is 6.25.
25 divided by one is 25.
You then need to divide both of these
by the smallest number.
6.25 is smaller than
25 so we need to divide
both of those by 6.25.
6.25 divided by 6.25 gives us one.
25 divided by 6.25 gives us four meaning
there is one carbon to
every four hydrogens
and that is the empirical formula.
There is loads and loads of maths in this.
And, the majority of the
content of this topic
and a few other bits
that come up elsewhere
you can get loads and loads
of practice of this in my book
Maths The Chemistry Bits.
It has 60 equations for
you practice balancing,
loads of titration calculations,
load to bond entropy
calculations, which come
up later in the course.
Lots and lots of things for you to do.
A mole is not a rather cute,
blind, black, furry thing
but it is the unit
for the amount
of a substance.
And, that is going to be six times 10
to 23 atoms,
ions, or molecules.
And, that is because that is
the number of carbon atoms
in 12 grams of carbon.
So, our equation for this is going to be
moles is equal to mass over MR.
This is an incredibly complicated question
which combines a lot of skills.
First of all we have to work
out the formula of things,
write out the equation,
balance the equation
and then finally work out the
amount of hydrogen peroxide.
We have hydrogen peroxide
decomposing into water,
H2O and oxygen gas.
Now, we need to balance the equation.
Hydrogen, oxygen, hydrogen,
oxygen two hydrogens,
two oxygens, two hydrogens, three oxygens,
so we can increase that
by putting more oxygens
over this side.
H2O2 giving us four
hydrogens, four oxygens,
now we need some more
hydrogens and oxygens
over the right hand side,
but another H2O in there.
And, we have four oxygens
and four hydrogens
giving us a final balanced equation of
two hydrogen peroxides making
two water and one oxygen.
Now, we need to have an
oxygen gas that's given
off from 40.8 grams of hydrogen peroxide.
The first thing we do is
to work out the masses
involved in the equation.
Hydrogen has a mass of one
and there are two of them.
Oxygen has a mass of 16
and there are two of them.
That is two plus 32 giving us 34.
And, because there are
two of them that gives us
a total of 68.
Hydrogen is two,
one times two equals two.
Oxygen is 16, two plus 16
gives us 18.
18 times two gives us 36.
And then, oxygen is 16 times two
giving us 32.
So, we can say that if we had
68 grams of hydrogen peroxide
it would decompose into
32 grams of oxygen.
But, we don't have 68
grams of hydrogen peroxide
we have 40.8 grams of hydrogen peroxide
and we need to find how much
oxygen that decomposes to.
This is now just a ratios
question from maths.
I'm going to put a one in there.
To get from 68 to one
we need to divide by 68.
So, that's what I need
to do on the other side
as well divide by 68
giving us 0.47.
To go from one to 40.8 we need to times it
by 40.8 which is exactly
what we need to have
this side times 40.8.
But, I don't want you to
clear your calculator.
I want you to keep the
number in your calculator.
So .47 or the long
number in the calculator
times 40.8 gives 19.2 grams.
If you had cleared your
calculator and just did
0.47 times 40.8
you'll have got an answer of 19.176
which is close but not the same answer.
What you've introduced
is a rounding error.
When we are working out concentration
that is going to be youR amount
divided by your volume.
Concentration is noted in
moles per decimeters cubed,
amount is in moles, and your
volume is in decimeter cubed.
When you have an equation
there's always going to be
a limiting reactant.
And, your reaction is going to continue
using up the limiting
reactant forming product
until you get to the point
where your limiting reactant
is used up.
At that point the
reaction is going to stop.
So, whatever you don't
want your limiting reactant
to be you always need to
make sure the other one
is in excess.
Solids have a very, very fixed structure.
The atoms may wiggle a
little bit, but it is round
a fixed point.
There is going to be some
movement and some vibration
but they're not flowing at all
and they can't be compressed.
Liquids have much more movement
around but they are not
in a fixed position.
They can flow but they
can't be compressed.
Gases are very, very free to move.
There's lots of movement going on in here.
It's not around a fixed bit
and they do a lot of moving.
They can flow and they can be compressed.
Go from a solid to a liquid is melting.
From a liquid to a gas is evaporating.
Going in this direction
we're putting energy in.
Going in the other direction
energy is coming out.
So, from gas to a liquid
you're actually condensing
from a liquid to a solid we are freezing.
A compound has a melting
point of 19 degrees,
a melting point and a boiling
point of 74, boiling point.
What is the state at room temperature?
Room temperature is about 25 to 27.
So, when it boils it turns from
a liquid into a gas, so above there it is
going to be a gas and below that
it is going to be a liquid.
Melting point were turning
from a solid so this way
is going to be a solid and above there
is going to be a liquid.
So, at room temperature
it's going to be liquid.
Now, the other important thing to remember
about boiling point and
melting point is that
the opposite is the same name.
So, boiling point is
equal to condensing point.
A melting point is
equal to freezing point.
We just took that boiling
point and melting point
instead of condensing
point and freezing point,
they're exactly the same number.
So, if the boiling point is
74 the condensing point is 74.
If the melting point is 19
the freezing point is 19.
State symbols tell us what
state something it is in.
So, a S is a solid.
L is liquid.
Aq is aqueous.
And G is gas.
If you see state symbols in an equation
the answer generally refers to them.
If you see something
that's liquid in liquid
or aqueous and aqueous going to a solid.
It is going to turn cloudy.
If you have a liquid in a
solid or a liquid in liquid
and a gas is produced
you're going to see bubbles
or a loss of mass,
bubbles or fizzing.
Elements, pure things,
compounds two or more
different things
chemically bonded together.
Mixture lots of different
things, some of them
chemically bonded, some of them not.
If you have a pure substance
it is going to melt
at its melting point.
If you have a mixture
it's going to bear out
on a range of melting points.
We can test this by getting
some crystals of the pure
solution into a very, very thin tube.
Putting it into a rather old fashioned
melting point apparatus.
You can see that's the ends
of the very, very thin tube
have the crystals in so
we can see that happening.
And then, they go in the top
of the melting point apparatus.
And, as the temperature rises
this is slowly heated up
we can have a look through
the little glass window
and see if the substance
melts at one temperature
or whether it melts slowly
over a range of temperatures.
We can use chromatography
to separate out compounds
and you're going to get
probably what you did in class
is beautiful, beautiful
separations by fo-hem.
We need to make sure
that the end of the paper
is just in the water and
that the you've drawn
your start line in pencil.
If you draw it in pen then your start line
is going to run as well
and that is going to
cause you problems.
We're gonna put a lid on here to stop
the solvent evaporating.
When we want to work RF
value it is distance moved
by the spot divided by the
distance moved by the solvent.
When you have mixtures and
you want to separate them
there are a number of
different things you can do.
Distillation where you're
going to separate things off
by boiling points, so
things that have a different
boiling point will distill
at different temperatures.
Evaporation where we are
going to remove the liquid
and leave solids that
have been dissolved in
the liquid in the dish.
Filtration where we have large particles
of solid in a liquid.
The particles of solid
puts down the filter paper
and the liquid will drip through.
And fractional distillation
where you can take
things off at different boiling points.
We would not survive
very long without water.
But, only a small percent
of the water on Earth
is suitable for us to drink.
So, we need to remove salts from it
which is desalination.
And, we need to make it safe to drink
or potable water.
To make water safe to
drink we need to remove
any dirt, mud, in there
so any large solids.
We need to remove the bacteria
and we need to remove any
nasty or unwanted bits
of too many mineral irons, like the salt
that would be in sea water.
We add in various
different things to water.
We add in chlorine to
kill things and we add in
fluoride for tooth protection
and bone protection.
On the pH scale things
that have a pH of one
are acidic, pH 7 is neutral,
and 14 is an alkali.
The iron's responsible for acidity.
Hydrogen ions, the ions
responsible for alkalinity
are hydroxide ions.
The neutralization equation
is incredibly important.
It comes up a lot.
And, that tells us that
hydrogen ions plus hydroxide
ions can be neutralized
to produced water.
There are two indicators
you can use for titrations,
phenolphthalein, which is
the one you're seeing here
which in an alkali will be bright pink
and in an acid will be clear or colorless.
Or methyl orange which
in an alkali you can see
it's going this yellowy color
and in an acid will be
bright red giving us
a neutralization point
where it is an orange color.
There is a big difference between
strength and concentration.
Strong acids are going
to freely disassociate
into hydrogen ions and other ions.
The strong acids are
hydrochloric acid, nitric acid,
sulphuric acid, hydrobromic
acid, hydroiodic acid,
and chloric acid.
I would expect you to know
that hydrochloric acid
is HCL, nitric acid is HNO3,
and sulfuric acid is H2SO4.
The other ones we don't have
to worry about too much.
Everything else is a weak acid which means
only partially dissociates.
Here we have strong and weak acids at high
and low concentrations.
So, for our strong acid we
can see our hydroxide ions
and our hydrogen ions
are fully dissociated,
they're not touching each other.
They are separated.
Here we have them at a high concentration
which means there are lots of
hydroxide and hydrogen ions
compared to very few water molecules.
Here we have our strong
acid again fully dissociated
but at a low concentration
meaning there aren't
very many hydrogen or hydroxide
ions in a lot of water.
For our weak acids they are
only partially dissociated.
So, some of the hydrogen and
hydroxide ions are separated
and some of them haven't
meaning that we are going
to get some which are
still together and some
that are separated.
At a higher concentration
there are going to be
lots of acid particles for a
very few particles of water.
Whereas at a low concentration
there aren't going
to be very many acid molecules
per molecule of water.
You need to remember all of the equations,
remember the ions, and be able to work out
what is going to come from a reaction.
So, if we have an acid
and a metal we are going
to get a salt plus hydrogen.
Acid and metal oxide is going to give us
a salt plus water.
Acid and metal hydroxide is
going to be a salt plus water.
Acid and metal base, salt plus water.
Acid plus metal carbonate
is going to give us a salt,
water and carbon dioxide.
To work out the formula
of the salts you need
to know the formula of all of your ions.
And, I've wrote flashcards
you help you with this.
You can watch the video,
I'm afraid you're going
to need to watch it over and over again
so that you learn it.
And then, you're going
to need to make sure
that you combine the ions in such a way
that they are neutral over all.
In an experiment when
you see bubbles coming up
something chance is
it's going to be one of
these four types of gases.
So hydrogen gas, oxygen
gas, carbon dioxide,
or chlorine gas.
To test for hydrogen
gas it is a squeaky pop.
To test for oxygen gas
it's going to relight
a glowing splint.
Carbon dioxide turns
lime water cloudy.
And, chlorine gas is going to bleach
damp litmus paper.
For making a pure salt we are going to be
making copper sulfate.
This is mixing sulfuric
acid and copper oxide
to make copper sulfate and water.
You're going to need to
heat the sulfuric acid,
stir in the copper oxide
which is a black powder
until it is excess, which
basically means you can't
dissolve it anymore.
Let it cool a bit and then
you can filter the solution
to remove the excess copper
oxide so that the black
copper oxide powder will
stay in the filter paper.
And then, the solution of
copper sulfate will come out
down the bottom.
Once you have your
solution of copper sulfate
you can evaporate away
the water to leave you
with the copper sulfate crystals.
Now this, the size of the
crystals will depend on
how quickly you do this.
You're going to be left
with blue crystals.
The blue crystals here
are the hydrated ones.
And, the white crystals around the edge
are the anhydrous ones.
To carry out titration
first of all you need to put
25 centimeter cubed in an alkali into
a conical flask.
Add a phenolphthalein
indicator or an indicator
like methyl orange.
Fill a burette with an acid
of a known concentration.
Take the initial reading on
the burette and record it.
And, while swirling fast
use the tap to slowly add
drop by drop the acid into the alkali.
When the first permanent
color change happens
pink to clear for phenolphthalein,
stop adding the acid.
Record the final volume
in the burette and repeat
titers until you get it
within 0.05 centimeters cubed.
A bit of a mental break here for you guys,
just a tiny pause.
You're doing so, so well.
Let's keep going, we are nearly there.
When we are working out solubility rules,
what is soluble, what is
not soluble it is really
going to help if you
know the formula for ions
and your salts equations.
All nitrates are soluble.
Most sulfates are soluble
apart from lead sulfates,
barium sulfate, and calcium sulfates.
Most halogen compounds so most chlorides,
bromides, and iodides are soluble except
when they're combined with silver or lead.
So, for example silver
chloride, silver bromide,
silver iodide are insoluble.
Lead chloride, lead bromide,
and lead iodide are insoluble.
Sodium carbonate, potassium carbonate,
and ammonium carbonate are soluble.
All other carbonates are insoluble.
Sodium hydroxide, potassium hydroxide,
and ammonium hydroxide are soluble.
All other hydroxides are insoluble.
Here we have sodium chloride.
Now, ionic compounds have
to be molten or dissolved
to be able to conduct electricity.
'Cause it's when it's in its solid state
you can see that these
sodium and these chlorines
are not going anywhere.
They are very, very fixed.
However, in a liquid or a
molten or a dissolved state
when these ions are free to move around,
that is when they're going
to be conducting electricity
and that's when you can do electrolysis.
The common set up for
electrolysis that you need to know
are sodium chloride, sodium
sulfate, copper chloride,
and copper sulfate.
For sodium chloride the
products you are going to get
are hydrogen gas, chlorine gas,
and sodium hydroxide.
For copper sodium sulfate
the products you're
going to get are going to be hydrogen
and oxygen gas.
For copper chloride
you're going to get copper
and chlorine gas.
And, for copper sulfate
you are going to get
copper and oxygen gas.
When we set up electrolysis
you need a positive
and a negative electrode.
The light bulb are there just to check
that electricity is flowing.
You can see bubbles
collecting around the positive
and negative electrode.
Sometimes this might be a metal collecting
as in the case of copper
collecting here and here
in coppers sulfate and copper chloride.
You can test for all
of the different gases
coming off, for example,
hydrogen, chlorine, and oxygen.
The test for hydrogen
gas is a squeaky pop.
The text for oxygen gas is relighting
a glowing splint.
And the test for chlorine
gas is that it bleaches
damp litmus paper.
When you have a reductive action oxidation
is loss of electrons.
Reduction is
gain of electrons.
A good way to remember what
the electrodes are called
is that the positive
electrode is the anode
and negative
is cathode.
At each electrode in
electrolysis we're going to have
oxidation and reduction taking place
and movement of electrons.
And, the half equations
need to reflect this
and they need to be balanced.
The first thing you need
to balance is the elements.
In the first one we
have copper and copper,
one on each side, that's fine.
But, here we have two plus charge we need
to make a neutral charge.
The only thing we can add in is electrons
which have a negative
charge because copper is
two plus we need to add in two electrons.
We are adding in electrons,
this is gain of electrons
so this is reduction.
And because copper is
positive it will go to
the negative electrode
which is the cathode.
The second one is a bit more complicated
'cause you can see fluorine ion will go to
a diatomic fluorine molecule.
First thing we need to do
is to balance the fluorines
to go in there.
Now, we need to balance
atoms, we have two negatives
that need to go to neutral.
So, we need to lose something.
The only thing that we can lose
are electrons and to balance
out the charges we need
to lose two electrons.
This is loss of electron
so it is oxidation.
Fluorine is negative so it will go
to the positive electrode.
And, the positive electrode is the anode.
We can list the metals
by how reactive they are
with the most reactive being at the top.
And the least reactive
being at the bottom.
Now, you need to remember these.
If you have any good
mnemonics remembering these
you can mark these in
the description below,
in the comments below,
that will really, really
help other people.
Things that are above
carbon need electrolysis
to be extracted whereas
things that are below carbon
can just be extracted by reduction.
However, things that are
really, really uncreative
like silver, gold, and
copper are generally found
in the earth as their pure
ores un-reacted with anything.
Everything else is generally
going to be reactive
with oxygen in the form of metal oxides.
You can also use this to predict
the products from electrolysis.
If the metal you are
using in the electrolysis
is more reactive than
hydrogen then you're going
to get hydrogen as a gas.
If it is less reactive than you're going
to get something else as a gas.
And, we can use this
to predict the products
for displacement reactions.
If we reacted magnesium
chloride with calcium
because calcium is more
reactive than the magnesium
the calcium is going to take the place.
So, we are going to get calcium
chloride plus magnesium
as our products.
However, if we reacted
magnesium chloride with aluminum
because magnesium is more
reactive aluminum cannot
take the place, it will not displace it.
So, no reaction is going to take place.
There are lots of very
important metals on Earth
and some of them are very, very rare.
So, we need to develop new
ways to get rare metals
out of low yield ores.
Low yield is where using
traditional mining methods
wouldn't be financially viable.
Two of these methods are
bioleaching and phytomining.
Bioleaching is when we have a large body
of water, say a lake, which
has metal in it such as
copper dissolved in it.
If we want to get the
copper out of the lake
out of the water we can add in bacteria.
These will take up the
copper from the water
and then they will leach out copper ions.
It's basically the bacteria's wee.
Another method is if
we have lots of copper
again in the soil but at
a very, very low yield,
so not enough for us to dig up the soil
and get the copper out say
by reduction or electrolysis.
We can put plants in, this
is generally, believe it
or not, broccoli.
The plants will then
absorb the copper ions
from the soil.
We can then cut them down and burn them.
And then, from the ash
we can do electrolysis.
The disadvantage to using phytomining
is that plants grow very slowly.
Aluminum electrolysis
is a slightly different
form of electrolysis.
We have one electrode up here, this is our
positive anode, and
another electrode down here
this is our negative cathode.
The molten aluminum and
cryolite, cryolite is just
a compound that is added
to reduce the melting
point of molten aluminum oxide.
It's added into this
reaction vessel and we get
one reaction taking place
down here and another
reaction taking place at the top.
At the bottom at the negative cathode
we are going to be attracting
the positive aluminum ions.
They are going to be picking up electrons
and turning into aluminum atoms.
This is three plus so we need
to pick up three electrons.
And then, at the top
at the carbon electrode
we are going to attract
the negative oxygens.
They're going to be loosing
electrons and turning
into oxygen gas 'cause
we have two on this side,
two oxygens on that side, we
need two oxygens on that side
which means we now have
four negative charge.
So, we need to lose
four electrons as well.
This is a carbon electrode
up here and we are
starting a reaction
which causes oxygen gas
to be evolved.
Eventually the oxygen gas
will react with the carbon
electrode and we are going
to lose the electrode
as carbon dioxide.
So, the carbon dioxide will
wear away the electrode
eventually so this will
need to be replaced.
The molten aluminum collects at the bottom
and can be taken off like that
and that is how we purify aluminum.
The Earth provides us
with many things including
warmth from the sun,
shelter from the trees,
food from plants and animals,
transport along rivers.
And, we can get all of
these from the rivers,
the seas, the atmosphere,
and the land.
When you're doing a life
cycle assessment of an object
you need to look at the
different stages of its life,
the manufacture, the use, and the disposal
and the environmental impacts
of each of these sections.
So, the environmental
impacts of the energy.
So, the energy needed
for production of this
bearing in mind that
this generally comes from
fossil fuels which have
been burnt, so electricity
based on fossil fuels
leading to carbon dioxide
being put into the atmosphere.
The materials used
whether they can be used
from natural resources
or whether something else
can be used, whether natural resources
have to be further processed.
The production of the product,
using the product and disposal
of the products.
Using the product does it
need electricity to use it?
Does anything come out of
it when it's being used?
Production of the product
we're talking about things
like atom economy, how
much of the reactants
are actually going to
end up in the product?
How much waste is there?
How much waste of the natural resources
that went into it when
you're making the product?
And, disposal of the
product, can it be recycled?
Can it be incinerated for another use?
Or, is it just going to
have to go to landfill?
This half arrow on top
of the other half arrow
going in the opposite
direction is a symbol
for a reversible reaction.
Ammonium chloride will
decompose into ammonia
and hydrogen chloride gas upon heating.
And, this is an endothermic reaction
because you need to put heat into it.
Cooling it is an
exothermic reaction because
energy will come out.
Hydrated copper sulfate,
which is a lovely blue color,
upon heating will lose the water turn into
anhydrous copper sulfate
which is a white color.
Adding water in will turn it back to
hydrated copper sulfate.
Le Chatelier's Principle
tells us that whatever you do
to a reversible reaction the
reaction would do the opposite.
So, in this reaction
this way is endothermic
and this way is exothermic.
So, if you heat up a reaction
the endothermic reaction
will increase to compensate
and the exothermic reaction
would decrease to compensate.
Whereas if you decrease the
temperature then the endothermic
reaction would decrease to
compensate and the exothermic
reaction would increase
to compensate so that
the overall temperature stays the same.
If you're going to
change the temperature of
the concentration the reaction would also
adjust itself to compensate.
If you're going to increase the pressure
or the concentration then
the reaction will shift
to the side that has
less moles to compensate.
If you're going to
decrease it it will shift
to the side that had
more moles to compensate.
The Haber process produces
ammonia from nitrogen
and hydrogen gas.
Our main source of nitrogen
and hydrogen gas is
getting them from the air.
We can also get hydrogen gas from
the electrolysis of water.
They are fed into the
reaction vessel where they'll
be turned into ammonia which is a liquid
so that can be taken off at the bottom.
And, any unreacted gases can go back round
into the reaction.
It is done at 450 degrees
C at 200 atmospheres
and using an iron catalyst.
The production of
ammonia is very important
because it is an important source of
nitrogen for fertilizers.
The conditions used in the Haber process
are actually a compromise.
The forward reaction is
exothermic so this tells us
using the the Le Chatelier's principle of
dynamic equilibrium
that we should be using
a low temperature if we want
to drive forward reaction.
But, at low temperature we
have a low rate of reaction.
So, even though using the high temperature
of 450 degrees drives
the backwards reaction
away from ammonia towards
a production of the gas
the rate of reaction is so
fast that it is constantly
cycling between the two.
So, 450 degrees is a
compromise temperature.
The ammonia comes off as
a liquid so that can be
taken off, that can be
removed which is also
going to drive the forward reaction.
They are less moles of
products than there are
moles of reactants.
There are four over this
side and two over this side.
So, high pressures of 200
atmospheres are going to
drive the forward reaction
'cause this is going to take up
less space, there are less moles of it.
A high pressure would increase the rate
of the forward reaction even more,
but it would be dangerous
because high pressure
leads to risk of explosion.
So, 200 atmospheres is used because it is
a relatively safe pressure to do it with.
As we increase the pressure the danger to
the workers increases, the
thickness of the wall increases
and also stuff like insurance
cost are going to increase.
The rest of the video is set
for chemistry students only
so if you have finished
well done, excellent work.
It was a bit of a slog this video.
You can go move on to the next video,
use your revision guide.
Or if you guys are in chemistry I'm afraid
you've got a bit more to go.
Transition metals are in the middle.
Their properties are that they are hard,
shiny, and are good conductors.
These are basically
your traditional metals.
So, any property of traditional
metal you can generally
associate it with a transition metal.
And, because of their
properties they can be used
in jewelry, in wires,
or in sauce pans.
And, because they get all
these different colors
they can be used for
things like stained glass
or for coating statues.
Here, the Statue of Liberty
has a copper coating.
Copper transition metal
compounds are generally
going to be blue or a bluey-green.
Iron two
is light green.
Iron three is an orangy brown,
a rust color.
And, cobalt is a really
lovely, deep, rich blue.
For rusting to take place
we need to have iron,
oxygen, and water and
that is going to result
in iron oxide.
You can see my experiment
here that the iron oxide
is this brown orangy red
stuff that is on the sides.
Rusting will actually lead to
an increase in mass because
you're taking the iron and
you're adding in the oxygen.
There are a couple of ways we
can stop this from happening.
We can galvanize things.
We can coat things. We can
use a sacrificial metal.
For titration calculations
we first need to calculate
the number of moles of acid used.
We can use to find the
number of hydrogen ions
involved in the reaction.
This is going to equal the
number of hydroxide ions
at the point of neutralization.
We can use this to calculate
the number of moles
of alkali used and calculate
the concentration of acid.
We have 25 centimeters cubed of alkali
was neutralized by 15 centimeters
cubed of .2 moles acid.
Find the concentration of the alkali.
First thing I'm going to do
is pull all the information
out of the question.
Concentration of the alkali
is what we're trying to find.
Volume of the alkali 25 centimeters cubed.
Concentration of the acid 0.2 moles
per decimeter cubed.
Volume of the acid 15 centimeters cubed.
So, the first thing to do is calculate
the number of moles of acid used.
So, the number of moles
of acid used we're gonna
use concentration of the acid
times volume of the acid.
That is 0.2 times the volume of the acid
which is 15 divided by 1,000
because we need it in decimeters cubed.
So, 0.2 times 0.015
giving us an answer of 0.003 moles.
If we look at our balanced
equation we can see that
acid and alkali are in a
one-to-one ratio in this equation.
So, there's going to be an
equal number of hydrogen
and hydroxide ions.
So, we know that our moles
of acid are .003 moles
which means our moles of
alkali must also be .003 moles.
Now, we know the number
of moles of alkali we can
concentration by volume again,
rearranging that because
we know the moles and we know the volume
to find the concentration.
We can use moles equals
concentration times volume again
and rearranging that
because we know our moles
and we know our volume.
So, moles divided by volume
will give us concentration.
So our moles from what we've
just worked out is 0.003.
Our concentration is 25
centimeters cubed divided that
by 1,000 to get it in decimeters cubed.
So, there's going to be 0.003
divided by 0.025
giving us 0.12 moles
per decimeter cubed as our
concentration of alkali.
To work out percentage yields
you need to take your actual yields
and divide it by your theoretical yields.
So, this is your actual yields.
And, your theoretical yields
is how much you thought
you were going to make.
To work out your atom economy
that is your MR of atoms
in the required products
over your MR of reactants
or the MR of stuff you wanted
over the MR of the stuff you actually got.
When you are dealing
with gases what you need
to remember is that one
mole is always going to
take up 24 decimeters cubed.
Aluminum sulfate can be
made from the reaction
of ammonia and sulfuric
acid or ammonium hydroxide
and sulfuric acid.
Fertilizer is good 'cause
they increase crop production
but they also lead to an
increase in eutrophication.
Here we have a simple cell
with two different metals
copper and zinc in their own solutions.
So, here is zinc in zinc sulfate solution
and copper in copper sulfate solution.
They are connected by a salt bridge
or an ion bridge and
because zinc is higher
in the electrochemical
series it is going to
push electrons this way towards copper.
A flow of electrons
means we're going to have
a potential difference.
So, the zinc is going to
be giving up electrons and
the copper is going to
be accepting electrons.
That thing that we
commonly refer as a battery
is actually a cell.
I know, I know it's really annoying.
A cell is one battery.
A battery is more than one cells.
So, this is a cell, and
then two or more of them
together would be a battery.
In non-rechargeable batteries
the chemical reaction
that produces electricity
once that is used up
the battery is dead.
Whereas in a rechargeable battery there is
a reversible reaction that goes on.
So, once the reactants
are used up you can pass
electricity through it which
will cause the reaction
to go in the opposite direction
recharging the battery.
In a hydrogen fuel cell we
just have a hydrogen gas
reacting with oxygen gas
and turning into water.
There is a large amount of energy released
which can be used to
power an electric car.
And, water is the only product
which means there are no carbon emissions.
There are a few problems with this,
predominantly with the
production of hydrogen.
At the moment this uses
fossil fuels because
hydrogen is made by
reacting steam with coal
or natural gas which
are both fossil fuels.
All hydrogen is made by
electrolysis of water,
but that involves electricity
which is generated
using fossil fuels.
The other problems are
it's quite hard to find.
The hydrogen needs to be compressed
which is a problem because
it will be explosive.
It also needs a very, very
large tank to store it in.
And, they don't work at low temperatures.
At the negative electrode
we are going to have
a hydrogen gas minus two electrons,
turning into hydrogen ions.
At the positive electrode
we are going to have
these hydrogen ions
reacting with the oxygen gas
and some electrons.
And they, are then going
to turn into the water.
Well done making it to
the end of this video.
You are all absolute superstars.
All the best in your exams.
I'm keeping all of my
fingers crossed for you.
("Something Elated" by Broke for Free)
