The whole of AQA Chemistry Paper 1 or C1 in only 72 minutes!! GCSE 9-1 Science Revision


Hey, guys. Here is a massive
summary of what you need to know for your
first chemistry paper. In here, we’re going
to go over everything but we’re only doing it quickly. If you’ll make sure that you
know absolutely everything, you want to get knowledge check
lists, thousands of questions, links to videos, equations
that you need to learn, formula you need to recall, then
you can get that all for free on my website in
my revision guide, or if you want to
one-click order it, you can get that from Amazon. 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 is a very,
very small thing. The word atom is actually
Greek for uncuttable. And when they named
them, they thought it was the smallest
thing possible. The periodic table tells
us loads, and loads, and loads of information
about the elements, the range of elements
that are known to exist. There are 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. 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 1
and a charge of plus 1. Neutrons are also
in the nucleus. They have a mass of 1
and a charge of zero. Electrons are in
the outer shells. Their mass is 1/2000 and they
have a charge of minus 1. 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, the 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 is simply the atomic
number, so in this case, 20. The number of electrons is also
the atomic number, so again, 20. The neutrons is the
mass number, which is 40, minus the atomic number,
which is 20, equaling 20. You need to be able
to take a set of words and turn it into a
balanced simple equation. So there is quite a
lot for you to do here, because you need 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. 2 hydrogens, 1 oxygen,
2 hydrogens, 1 ox– 2 oxygen, sorry. So we need to increase the
number of oxygens on this side because you see
there aren’t enough. So we have to add another H2O. Put that in a circle,
redo our numbers. We now have 2, 4
hydrogens, and 2 oxygens. So our oxygens
advance, but now our hydrogens 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 other bubble. We now have 2 hydrogens
here, 2 hydrogens here, making 4 in total and 2 oxygens. So now we have 4 hydrogens
on this side, 2 oxygens. 4 hydrogens and 2 oxygens. We need to rewrite that
neatly for the examiner. So we have one, two bubbles
of H2O turning into one, two bubbles of H2 plus 1 of O2. 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. 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. When you have mixtures and
you want to separate them, there are a number of
different things you can do. Distillation, where you
can separate things off by boiling points. The things that have a
different boiling point will just stay 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 that are solid
will stay on the folded paper and the liquid
will drip through. And fractional distillation
where you can take things off at different boiling points. We haven’t always
known that an atom had a nucleus and electrons
orbiting around the outside. We used to have a plum
pudding model where we had a large cloud
of positive charge with negative electrons
dotted throughout, a bit like a Christmas
pudding, which is why it’s called the plum pudding model. Rutherford and Marsden
did an experiment to test the plum pudding model. They took an alpha particle gun,
an alpha particle is positively charged, and they had a
sheet of very thin gold foil. And what they did is they fired
alpha particles at this sheet, and the majority of them
went straight through, which was weird. Some of them got deflected a
little bit, and some of them got deflected at
massive amounts. And they suggested
that there was a center which was positive, a
small part that was positive, and then a large section all
around which was negative. And this led to the development
by Bohr of the nuclear model that we use today. The model of atoms changed
quite a lot over time. You don’t need 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 is our current– or developed our current model. The periodic table gives us
loads and loads of information. The first bit of information
it gives us are about groups. And the groups go down
the periodic table. Group 1, group 2, 3, 4,
5, 6, 7, 8, or group zero. Groups tell us the number of
electrons on the outer shell. So things in group
1 are going to have 1 electron in the outer shell. Things in group 2
are going to have 2 electrons in the outer shell. Group 6, 6 electrons
in the outer shell, group 7, 7 electrons
in the outer shell. Periods go across
the periodic table. So here is our first
period, the one that everyone always forgets,
concerning hydrogen and helium. 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 the– in each shell. So in the first period,
there were 2 elements, which means there are going to
be 2 electrons in that shell. In the second period, there
are 1, 2, 3, 4, 5, 6, 7, 8 elements, which means
there are going to be 8 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 2, and
it is in period 3. So that tells us it has
12 electrons in total, it has 2 electrons
on the outer shell, because its in group number
2, and it has 3 shells because it is period number 3. So when we want to draw the
electronic configuration of magnesium, we know
it’s in period 3, It’s going to have 3 shells. The first thing we can
do is draw 3 shells. 2, 1, 2 go on the first shell. 1, 2, 3, 4, 5, 6, 7, 8
go on the second shell. That’s the most that
can fit in that shell. That brings us up to 10. 10, 11, 12. 2 electrons on the outer shell. From the period, we know
that the first shell can hold a maximum of 2 electrons,
the second shell can hold a maximum of 8
electrons, the third shell can hold a maximum of 8
electrons, and then you only need to know up
to calcium, so [INAUDIBLE].. 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 nuc protons have
a positive charge. 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11. Now in the atom, it has 11
electrons drawn on here. Electrons have a
negative charge. 1, 2, 3, 4, 5, 6,
7, 8, 9, 10 11. Now, in an atom, the positive
charges and the negative charges cancel each other
out, so the overall charge on the atom is going to be zero. However, when sodium
makes an iron, this electron here goes away. So it still has the
same number of protons. It’s still sodium. 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11. But it’s lost an electron. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. So it has one more proton
than it has an electron, meaning this is going to have
an overall positive charge. Metals are going
to lose electrons, and when we lose electrons,
we get positive charges. And nonmetals are going
to be gaining electrons, and when we gain electrons,
we get negative charges. Things in group 1 are
going to lose 1 electron, so are going to be plus 1 ions. Things in group 2 are
going to lose 2 electrons, so are going to be plus 2 ions. Things in group
6, here, are going to gain 2 electrons, so are
going to be minus 2 ions. And things in group 7 are going
to gain 1 electron, so are going to be minus 1 ions. This beautifully
colored periodic table is because there are lots
of different groups, lots of different categories,
on the periodic table. Group number 1, also known as
alkali metals, group number 2 are the alkali earth
metals, or alkaline metals, group 7 are the halogens, and
group 8 are the noble gases. The big chunk in the middle
are the transition metals. Our periodic table hasn’t
always looked like this. The first attempt
at periodic table was by Newland 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 grouped them– he
arranged them by mass, but he didn’t leave any gaps. And he tried to force things
in to have 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 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, a couple of the elements
were discovered, and they fitted in really,
really, neatly, really nicely, to his periodic table. So this table was accepted. It’s changed ever
so slightly by them. We now arrange things by
electronic arrangement. But that’s a very,
very subtle difference. The group right on the far right
side are group 8 or group zero. These are the noble gases. They have a full outer
shell and because they have a full outer shell,
they won’t gain or lose any electrons which means they
are really, really unreactive. And because they are
unreactive, they actually have quite a lot of uses. Helium we use in balloons,
and they are also used in neon lights,
as you can see here in the amazing city of Osaka. Moving over one group to
group 7, we have the halogens. We are still in the nonmetals. And these are going to go around
as diatomic molecules which means their formula is going
to be for chlorine gas, Cl2, fluorine gas, f2,
bromine gas, Br2. They’re going to go
around together in pairs. Because they only want
to gain 1 electron, a nice easy way
for them to do that is sharing an electron
with something else that is the same. So fluorine here can easily
gain an extra electron by sharing it with
another fluorine. They are highly reactive
because they only want to get one electron. And the most reactive ones
are going to be at the top. Boiling point is going to change
as we move down the group. So things that have a low
boiling point or a low melting point are going
to be at the top. High boiling points
or high melting points are going to be at the bottom. When they react they’re
going to gain an electron, meaning they’re going to 4 minus
1 ions and gaining an electron is a reduction. They’re going to react violently
and rapidly with group 1 metals because group 1 metals
want to lose 1 electrons. For example, sodium,
which is soft gray metal, will react very
violently very regularly with chlorine, which is a yellow
gas, to sodium chloride, which is a white powder of salt. A more reactive element will
displace a less reactive element. So here we have sodium
iodide reactive with bromine. Iodine is here, below bromine
on the periodic table, so bromine is more reactive. So we’ll displace iodine in
the compound, forming sodium bromide and iodine, whereas
if you try and react bromine gas with
sodium chloride, chlorine is higher than
bromine on the periodic table, so it’s more reactive. You are going to get no reaction
because bromine cannot displace chlorine out of this. These are commonly known
as displacement reactions. The halogens are mostly
sterilizing things. For example, chlorine,
your commonly going to know that as
from swimming pools. Halogens want to
gain 1 electron, so the most reactive
ones are the top. That’s where there’s
least shielding between the electron they
want to gain and the nucleus. Your alkali metals react
very violently with water, and this is where
you’re going to see some flames coming from– some
different colors coming from. This is one of
the things that we use to make the different
colors in fireworks. So the lovely, lovely
lilac flame from potassium, we can use in fireworks. If you’ve seen these in
school, these are soft, grey metals which
are easily cuttable. They need to be kept in
oil so it doesn’t react with oxygen or with
the water in the air because it’s a very,
very violent reaction. When the metal
reacts with oxygen, we’re going to get a
metal oxide, which, if you’ve seen these in school,
when it was cut, it was shiny, but [? it soon ?]
started to dull. The dullness is the metal oxide. The metal plus water is going
to form a metal hydroxide. This gives it its name,
it’s alkali metal, because the metal hydroxide
is going to be alkaline. And you can see that by
the change in indicator if that’s what your teacher did. And you will also notice this
is a very exothermic reaction. It released a lot of heat. It also released hydrogen gas. That’s what the fizzing was. The reactivity is most
reactive at the bottom, and least reactive at the top. Things at the bottom are
going to have a low melting point or boiling point,
and a higher melting point or boiling point at the top. Alkaline metals want
to lose an electron, and the ones at the
bottom are most reactive because there is more
shielding between the atom– the [INAUDIBLE] they want to
use and the positive nucleus in the middle. Solids have a very,
very thick structure. Their atoms may
wiggle a little bit, but it is around 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 float, but they
can’t be compressed. Gases are very,
very free to move. There’s lots of movement
going on in here. It is not around
a fixed position. They do a lot of moving. They can float and
they can be compressed. Going from a solid to
a liquid is melting. From a liquid to a
gas is evaporating. Going in this direction,
we are putting energy in. Going in the other direction,
energy is coming out. So from gas to a liquid,
we are condensing. From a liquid to a
solid, we are freezing. A compound has a melting point
of 19 degrees, melting point. And a boiling point
of 74, boiling point. What is the state
at room temperature? Room temperature is about
25 or 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 there, it is
going to be a liquid. Melting point we are
turning from a solid, so this way it is going to
be a solid, and above there it is going to be a liquid. So at room temperature it
is going to be a liquid. Now, the other important thing
to remember about boiling point and melting point is that the
opposite is the same number. So boiling point is equal
to condensing point. And melting point is
equal to freezing point. We just took that boiling
point and melting point instead of condensing
point and freezing point. They are 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 is in. So an 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 and liquid, or aqueous and aqueous
going to a solid, it is going to turn cloudy. If you have a liquid and a
solid, or a liquid and liquid, and a gas is
produced, you’re going to see bubbles, or a loss
of mass bubbles, or fizzing. Ionic bonding is a transfer of
electrons from a metal, which is on this side of
the periodic table to a nonmetal on this side
of the periodic table. Anything that is in group 1 is
going to form a plus one ion. Group 2 a plus 2 ion,
group 6 a minus 2 ion, group 7 a minus 1 ion. Here, we are going to
make magnesium oxide. Magnesium is in
group 2, so it has 2 electrons in its outer shell. Oxygen is in group 6. It has 6 electrons
on its 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
a cross for electrons. We then draw square
brackets around these and indicate the charge. So magnesium has
lost 2 electrons, so it’s going to
have a plus 2 charge. Oxygen has gained 2
electrons, so it’s going to have a minus 2 charge. Covalent bonding is the sharing
of electrons between two nonmetals, 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 and H3,
nitrogen in the middle. Three hydrogens coming
off around the side. Methane, CH4, carbon
in the middle, four hydrogens
branching off of it. Hydrogen, H2, very
simple one there. Chlorine halogens go around
to diatomic molecules. Oxygen, we’re getting a bit
tricky now, has a double bond. Each line is equal to
a pair of electrons. Here, we have two lines, 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 label
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. 1, 2, 3, 4, 5. Carbon, 5. Hydrogens, 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 11, 12. The last one, carbon,
hydrogen, oxygen, we have 1, 2, 3 carbons. 1, 2, 3, 4, 5 6, 7, 8
hydrogens and 1 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 because your
numbers are too big. That is incorrect because your
numbers are in the wrong place. 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 why it’s so good
at conducting heat. An alloy looks slightly
different to a metal. We still have our
positive ions, we still have our delocalized electrons,
but there’s something else in there as well. This may be another
metal is alloyed with, or maybe something
else like carbon that it is 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. Bit of a mental break here for
you guys, just a tiny pause. You are doing so, so well. Let’s keep going. We are nearly there. Here, we have sodium chloride. Sodium are the grey
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 chlorines, or
whatever we’re looking at, bonding with everything else. So one sodium, here,
isn’t just going to be bonded with the
chlorine and the [INAUDIBLE],, or the chlorine that it’s
exchanged electrons to. 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 ionic compounds,
the structure is a giant ionic lattice. Properties it is going
to have a high melting point, high boiling
point, and it is only going to conduct to a
molten or dissolved. This is because the ions
need to be free to move. 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 made of carbon, such as graphite, diamond,
or [INAUDIBLE] fullerenes, or silicon 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 4 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 4 other carbons. Obviously, the ones
on the [INAUDIBLE] aren’t bonded to anything,
but if you try and look in the middle, you
can see that they are bonded to 4 other things. The properties of diamond
that make it really useful is that it is incredibly hard. It is very rare, it’s hard to
find, it’s also very beautiful, which makes it very precious. But the main thing is that
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 makes the 3 bonds to other
carbons, not 4 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. Graphite is made of
3 carbon com bonds, diamond is made of
4 carbon com bonds. Graphite is soft,
diamond is hard. Fullerenes are
[? the carbon nanotubes ?] of buckminsterfullerenes,
which are balls. These are, again, all
made of pure carbon. They make 3 carbon bonds, but
unlike graphite which is soft, these are incredibly hard. Buckminsterfullerene can
be used as a 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, very, very light things, like
aircraft or bicycles. They can also both be
used, or in the future be used, for drug delivery. And fullerenes,
[? carbon nanotubes, ?] buckminsterfullerenes,
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. You can measure of the mass or
volume of a reactant or product by collecting the product,
say, in a gas syringe, or using a scale or balance,
to look at how the mass changes as a reaction progresses. Whenever you are
measuring something, there is going to be a
degree of uncertainty, whether it’s a
burette, a measuring cylinder, or a beaker. You need to look for the
bottom of the meniscus always, because
there is going to be this difference, this
dip between where it looks at the top and
where it is at the bottom. And you can say whether
it is on the line or in between the
line, but you can never say it that
accurately because it might be a quarter of
the way or three quarters of the way to the next line. So while you try measuring
things accurately as you can, there is always going to
be a degree of uncertainty. When we are working
out concentration, that is going to be your
amount divided by your volume. Concentration is measured in
moles per decimeter cubed, amount is in moles and your
volume is in decimeter cubed. The new style exams means
are a lot of wordy questions that incorporate a lot
of skills all at once. In this question,
you need to first, for 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. And metal plus an acid is going
to give us salts plus hydrogen. Hydrogen is the easy bits. It is H and then 2
because it goes around as a diatomic molecule. The salt is going to
be magnesium chloride, but we need to know that
magnesium is a 2 plus ion, and chlorine is a 1 minus ion. So it needs the MgCl2 so that
there are 2 negative ions for each positive ion. Now these support you in
a lot of skills, recall of the formulas and working
out the sort, the product, so working out what type
of equation it is, and then after all of 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 is really going
to help you if you keep things in the same order. Circle the compounds
that we have, list the numbers of things. So we have 1 hydrogen,
1 chlorine, 1 magnesium. 2 hydrogens, 2
chlorines, 1 magnesium. So you can see, straightaway
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 redoing our numbers. We have 2 hydrogens
and 2 chlorines. That is balanced, writing it
out neatly for the examiners, because just leaving it like
this won’t get you the marks. We have 2 bubbles of
hydrochloric acid, plus magnesium,
turns into magnesium chloride, plus hydrogen. When you are working out the
Mr, which is [INAUDIBLE],, you need to take all
of the Ars, which is [INAUDIBLE] 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 large
number of the two. So hydrogen has a mass of
1, and we have 2 of them. Silver has a mass of 32. Oxygen has a mass of 16,
and we have 4 oxygens. So 1 times 2 is 2, plus 32,
plus 16, times 4 which is 64, add those together, we get 98. Excellent work so far, guys. Well done. Only a little bit longer. Let’s keep going. Tiny mental break, and
then we can keep going. 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 6
times 10 to the 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, we will have to work
out the formula of things, work 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, 2 hydrogens, 2 oxygens, 2 hydrogens, 3 oxygens. So we can increase that
by putting more oxygens over this side, H2, O2, giving
us 4 hydrogens, 4 oxygens. Now we need some more hydrogens
and oxygens over the right hand side, pop another
H2 on there, and we have 4 oxygens and 4
hydrogens, giving us a final balanced equation
of 2 hydrogen peroxides, making 2 water, and 1 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 1,
and there are 2 of them. Oxygen has a mass of 16,
and there are 2 of them. That is 2 plus 32, giving us 34. And because there are 2 of them,
that gives us a total of 68. Hydrogen is 2, 1
times 2 equals 2. Oxygen is 16, 2
plus 16 gives us 18. 18 times 2 gives us 36. And then oxygen is 16
times 2, 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 for math. I’m going to put a 1 in there. To go from 68 to 1, 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 naught point 47. To go from 1 to 40.8,
we need to times it by 40.8, which is
exactly [INAUDIBLE] 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 0.47, or the long number
in the calculator and 40.8 gives us 19.2 grams. If you had cleared
your calculator, and just did 0.47
times 40.8, you’d have gotten an answer of
19.176, which is close, but not the same answer. What you’ve introduced
is a rounding error. When you have an
equation, there is always going to be a limiting reactant. And your action is
going to continue using that limiting
reaction forming product until you get to the point
where your limiting reactant is used up. And that point, the
reactant 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. There is loads and
loads of maths in this, and the majority of content of
this topic and a few other bits that come out elsewhere. You can get loads
and loads of practice of this in my book, Math
(The Chemistry Bits). It has 60 equations for you
to practice balancing, loads of titration calculations,
load [INAUDIBLE] calculations, which come up later in the
course, lots and lots of things for you to do. 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 pop those
in the description below and the comments below. That would 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 unreactive, like silver, gold, and
copper, are generally found in the earth as
their pure [INAUDIBLE],, unreacted with anything. Everything else
is generally going to be reacted 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, then 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 aluminium, because magnesium
is more reactive, aluminium cannot take the place. It will not displace
it, so no reaction is going to take place. And 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 cold is that the positive
electrode is the anode, and negative is cathode. At each electrode
in electrolysis, we’re going to have oxidation
or 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. Here we have a 2 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 2 plus, we
need to add in 2 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 because 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 [INAUDIBLE].. We have 2 negative and it
needs to go to a neutral, so we need to lose something. The only thing we can
lose are electrons, and to balance out the charges,
we need to lose 2 electrons. This is loss of electrons,
so it is oxidation. Fluorine is negative, so it will
go to the positive electrode, and the positive
electrode is the anode. 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 metal oxide is going to give
us a salt plus water. Acid metal hydroxide is going
to be a salt plus water. Acid 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. I’ve made flashcards
to 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 overall. For making a pure
salt, we are going to be making a 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 in 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, 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. On the pH scale, things
that have a pH 1 are acidic, pH 7 is neutral, and
14 is an alkaline. The ion is responsible
for acidity, a hydrogen ions, the ions
responsibility 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 produce water. 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 the acid
of a known concentration, take the initial
reading on the burette and record it, and while
swirling the flask, use the tap to slowly
add, drop by drop, the acid into the alkaline. 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 titres until you
get it within 0.05 centimeters cubed. 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 neutralization point
where it is an orange color. There is a big difference
between strength and concentration. Strong acids are going
to fully dissociate into hydrogen ions
and other ions. The strong acids are
hydrochloric acid, nitric acid, sulfuric 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 disassociates. 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 a strong acid,
again fully disassociated, 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 have 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 high
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. Here, we have sodium chloride. Now, ionic compounds have
to be molten or dissolved to be able to conduct
electricity because it’s when it’s in its
solid state you can see that this sodium
and these chlorines are not going anywhere. They’re 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 is when you
can do electrolysis. Aluminium 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 aluminium and
the cryolite– cryolite is just a compound that is added
to produce the melting point of molten aluminium 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 aluminium ions. They are going to be picking
up electrons and turning into aluminium atoms. This is 3 plus, so we need
to pick up 3 electrons. And then at the top, at
the carbon electrode, we are going to attract
the negative oxygens. They are going to be losing
electrons and turning into oxygen gas
because we have 2 on this side, 2
oxygens on that side, we need 2 on that side,
which means we now have 4 negative
charge, so we need to lose 4 electrons as well. This is a carbon electrode up
here, and we are causing a– 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 aluminium
collects at the bottom and can be taken off
like that, and that is how we purify aluminium. The common setups
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 are going to get are going to be
hydrogen and oxygen gas. For copper chloride,
you are 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 positive and negative electrode. [INAUDIBLE] 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 copper
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 test for oxygen gas is
relighting, glowing splint, and the test for chlorine gas
is that it bleaches damp litmus paper. An endothermic reaction
feels like it gets colder, whereas an exothermic reaction,
you can feel it gets hotter. Another way of saying gets
colder will be to take heat in. Another way to get hotter
would be to give heat out. Now, we can make these
slightly more sophisticated by replacing the word
heat with the word energy. So now a sophisticated answer
is that an endothermic reaction takes energy in, and
an exothermic reaction gives energy out. During an endothermic
reaction, energy is going to get taken in, so we
have our reactants down here. Energy gets taken in, so
our product’s up here. So we can say that the
energy of the products is higher than the
energy reactants. During an exothermic
reaction, energy reaction is given out, so our
reactants, energy is given out, so our products are going
to be down here, which means our products have lower
energy than the reactants. For example, an endothermic
reaction will be electrolysis. An exothermic reaction would
be burning or neutralization. You need to be able to
calculate the energy change when a reaction takes place,
remembering that bonds energy breaking takes energy in, and
bond making gives energy out. So burning hydrogen in
oxygen will give out water. Calculate the energy
change for this reaction. The first thing we need to do
is write the balanced equation. Hydrogen, plus
oxygen, gives water. We need to put a 2 there
to balance out the oxygens, and 2 there to balance
out the hydrogens. Draw everything we have. So we have hydrogen
and we have 2 of them, so I’m going to draw that twice,
plus oxygen, turns into water. And while the examiner
would probably expect you to be able to
work out formulas, balance the equation, and
draw them by yourself, they would not expect you
to record the bonds in it. The bond energies will be
given to you in the exam. Next, we’re going to list the
type of bonds that we have and the number. So we have a hydrogen,
hydrogen bonds, and we have 1, 2 of those. We have an oxygen,
oxygen double bond, and we just have 1
double bond in there. We have oxygen hydrogen
bonds, and we have 1, 2, 3, 4 of those. And now we need to take
that and multiply it by the bonds energies. So 2 bonds for hydrogen,
that is 2 times 436. 1 times 498. 4 times 464. We can do the maths
and work at how much is on each side adding those up. 872 plus 498 gives us 1370. There’s 1856 on that side. Now we need to do the energy of
the reactions minus the energy of the product. So, 1370 minus 1856, giving us
minus 486 kilojoules per mole. In this type of equation,
if you got the symbol wrong, you’d probably
only lose one mark. It having a negative
sign in front it tells us it is exothermic. So any reaction
that is burning you can check yourself, because it
should always be exothermic. We can pretty much guarantee
that a big calculation is going to come up on this
paper, so it is worth practicing these really well. To help you, I’ve
written a book. The rest of this video is to
separate 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. If you guys have chemistry,
I’m afraid you’ve got a bit more to go. 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 are going to have a potential difference. So zinc is going to be
giving up electrons, and the copper is going
to be accepting electrons. That thing that we commonly
refer to 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 more of them together would be a battery. In non-rechargeable batteries,
the chemical reaction that produces electricity,
once they’re used up, the battery is dead, whereas
in a rechargeable battery, there is a reversible
reaction that goes on. So once the reactions
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 hydrogen gas reacting
with oxygen gas and turning in to 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 [INAUDIBLE]
steam with coal or natural gas, which are both fossil
fuels, or 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 would 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 hydrogen
gas, minus 2 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 going to turn into the water. 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
a traditional metal, you can generally associate
it with a transition metal. And because they’re
properties, that can be used in jewelry,
in wires, or in saucepans, 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 transitioned
into compounds are generally going to
be blue or bluey green. Iron 2 is light green, iron 3 is
an orangey brown, a rust color. And cobalt is a really
lovely, deep, rich blue. Nanotechnology is
absolutely fascinating. It is taking atoms
and rearranging them into specific locations
or specific sizes so that we can use it. It is much, much
smaller than technology. It is very small, but it is made
up of lots of different atoms. Now, the potentials
for this are massive, because as we get small, we are
increasing the surface area, and when we get this small,
things have very, very different properties. Things look see-through,
things are flexible, things start to behave very
differently to they would if they were much, much larger. The potential for
this is massive, communications, drugs delivery,
personalized medicine, but people are wary about this
because it is a new technology. To work out
percentage yields, you need to take your actual
yields and divide it by your theoretical yields. So if this is your
actual yields, then 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. For titration
calculations, we first need to calculate the number
of moles of acid you used. We can use this to find
the number of hydrogen ions involved in the reaction. This is going to be equal
to number of hydroxide ions at the point of neutralization. You can use this to
calculate the number of moles of alkali use, and concentrate
the calculation of the acid. We have 25 centimeters
cubed of alkali, was neutralized by 15
centimeters cubed of 0.02 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, naught point 2 moles per decimeter cubed. Volume of the acid,
15 centimeters cubed. So the first thing you do
is calculate the number of moles of acid used. So for the number of
moles of acid used, we can use concentration of the
acid times volume of the acid. That is naught point
2, times the volume of the acid, which is
15, divided by 1,000, because we need it
in decimeters cubed. So naught point 2, times
naught point naught 1. Fine. Giving us an answer of naught
point naught, naught, 3 moles. If we look at our balanced
equation, we can see the acid and alkali are in a 1 to
1 ratio in this equation. So there’s going to be an
equal number of hydrogen and hydroxide ions. So we know there
are moles of an acid are 0.003 moles, which means
our moles alkali must also be 0.003 moles. Now we know the number
of moles of alkali, we can use concentration by
volume again, or rearranging that because we know the
moles and we know the volume to find the concentration. We can use moles
[? equals concentration ?] [INAUDIBLE] 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– we’ve
just worked out– is 0.003. Our concentration
is 25 centimeters cubed, dividing that by 1,000
to get it in decimeters cubed. So that is going to be
0.003, divided by 0.025, giving us 0.12 moles
per decimeter cubed as our concentration of alkali. When you are dealing with
gases, what you need to remember is that one mole is always going
to take up 24 decimeters cubed. Well done making it to the
end of 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.

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