All of AQA CHEMISTRY Paper 1 in 30 minutes - GCSE Science Revision
Summary
TLDRThis comprehensive video script offers an insightful overview of key topics for AQA GCSE Chemistry Paper 1, tailored for both Higher and Foundation Tier students. It covers a range of fundamental chemistry concepts, starting with the basics of atoms, elements, and compounds, and progressing through chemical reactions, including the importance of balancing equations. The script delves into the states of matter, the development of atomic models, and the significance of the periodic table in understanding atomic structure. It further explores chemical bonding, with a focus on ionic and covalent bonds, and explains the formation of ions and their charges. The periodic table's role in predicting an element's properties is highlighted, with a discussion on electron configurations and the reactivity series of metals. The script also covers quantitative chemistry, explaining moles, molar mass, and the calculation of mass in chemical reactions. It touches on energy changes in chemical reactions, including exothermic and endothermic processes, and introduces the concept of electrolysis. The summary concludes with an overview of energy profiles and their use in understanding reaction energetics, making it an invaluable resource for students preparing for their exams.
Takeaways
- 🔬 **Atoms and Elements**: Atoms are the basic units of elements, represented by symbols in the periodic table, and compounds are formed when atoms of different elements are chemically bonded together.
- 🧬 **Chemical Reactions**: Chemical reactions involve the rearrangement of atoms through bonding without creating or destroying atoms, often requiring the balancing of chemical equations.
- 🌊 **Mixtures and Solutions**: Mixtures consist of different types of elements and compounds not chemically bonded, like air, while solutions are homogeneous mixtures, such as saltwater.
- 💧 **Physical and Chemical Changes**: Physical changes, like melting or evaporation, involve a change in state and do not result in new substances, whereas chemical changes involve the formation of new substances.
- ⚛️ **Atomic Structure**: Atoms consist of a nucleus with protons and neutrons, and electrons orbiting in shells or orbitals, with the discovery of atomic structure evolving through models by JJ Thompson, Ernest Rutherford, and James Chadwick.
- 📊 **Periodic Table**: The periodic table organizes elements by atomic number and provides information on an element's properties, with elements arranged to reflect their similarities and differences.
- 🔋 **Reactivity and Ions**: Metals tend to lose electrons to form positive ions, while non-metals gain electrons to form negative ions, with the reactivity series dictating how metals will react with other substances.
- 🔗 **Bonding**: There are different types of bonding, including ionic, where electrons are transferred, and covalent, where electrons are shared between atoms to create molecules.
- 🧪 **Quantitative Chemistry**: Calculations in chemistry involve understanding moles, relative atomic masses, and the stoichiometry of chemical reactions to determine amounts of reactants and products.
- 🔥 **Chemical Reactions and Energy**: Reactions can be exothermic (releasing energy) or endothermic (absorbing energy), with energy profiles illustrating the energy changes during reactions.
- 🔋 **Electrochemistry**: Electrolysis uses electricity to drive non-spontaneous chemical reactions, and cells or batteries rely on chemical reactions to produce electrical energy.
Q & A
What is a compound and how is it represented in chemistry?
-A compound is a substance that contains two or more different types of atoms chemically bonded together. It is represented by a chemical formula, such as H2O for water, which is made up of two hydrogen atoms and one oxygen atom.
How do you balance a chemical equation?
-To balance a chemical equation, you ensure that the number of each type of atom is the same on both sides of the equation. You can balance it by putting numbers in front of elements or compounds to multiply them up without changing the compound's identity.
What are the three main states of matter?
-The three main states of matter are solid, liquid, and gas. In solids, particles are close together and vibrate but do not move past each other. In liquids, particles are still close but can move past each other. In gases, particles are far apart and move randomly with more energy.
How did the modern understanding of the atom come about?
-The modern understanding of the atom came about gradually through the work of several scientists. J.J. Thomson discovered that atoms are made up of positive and negative charges, leading to the plum pudding model. Ernest Rutherford found that the positive charge must be incredibly small, which we now call the nucleus. James Chadwick discovered neutral charges called neutrons, and Niels Bohr discovered that electrons exist in shells or orbitals.
What is the significance of the atomic number and mass number in the periodic table?
-The atomic number, found at the bottom of the periodic table, is the number of protons in the nucleus and determines the element. The mass number, or relative atomic mass (RAM), found at the top, tells you the total number of protons and neutrons in the nucleus.
How do metals and non-metals typically bond with each other?
-Metals and non-metals typically bond through ionic bonding. Metals, which tend to lose electrons, form positive ions, while non-metals, which tend to gain electrons, form negative ions. The opposite charges attract and form ionic bonds.
What is a mole and how is it used in chemistry?
-A mole is a specific number of atoms or molecules, often used as a way of comparing amounts of substances. It is used to calculate the number of moles of a substance, which is the mass of the substance divided by its relative atomic or formula mass.
How do you calculate the percentage yield of a chemical reaction?
-The percentage yield is calculated by taking the actual mass of product produced and dividing it by the theoretical mass of product that could have been produced if all reactants had reacted completely. This is then multiplied by 100 to get a percentage.
What is the difference between endothermic and exothermic reactions?
-Endothermic reactions require an input of energy to proceed, causing the surroundings to become colder as energy is absorbed. Exothermic reactions release energy, often observed as an increase in temperature, such as in combustion reactions.
How does the reactivity series of metals influence chemical reactions?
-The reactivity series predicts how metals will react with other substances. A more reactive metal can displace a less reactive metal from its compound. This is used in metal extraction processes, such as smelting, where a more reactive metal like carbon can displace a less reactive metal from its oxide.
What is the role of the pH scale in chemistry?
-The pH scale is a logarithmic scale that measures the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. A pH below 7 indicates an acidic solution, while a pH above 7 indicates an alkaline solution. The pH scale is crucial in understanding the properties and reactivity of substances in chemistry.
How are electrolysis and the extraction of metals related?
-Electrolysis is a process that uses an electric current to drive a non-spontaneous chemical reaction. In the context of metal extraction, electrolysis is used to reduce metal compounds to pure metals. For example, aluminum is obtained by electrolyzing aluminum oxide dissolved in molten cryolite.
Outlines
📚 Introduction to AQA Chemistry Paper 1
This paragraph introduces the AQA General Certificate of Secondary Education (GCSE) Chemistry Paper 1, covering topics suitable for both higher and foundation tiers. It discusses the syllabus, including atoms, bonding, quantitative chemistry, and energy changes, and notes that certain topics are exclusive to the triple science curriculum or higher tier. The paragraph also emphasizes the importance of understanding chemical reactions, balancing equations, and the concept of mixtures and their separation methods, such as filtration and distillation. It touches on the states of matter and the historical development of atomic theory, concluding with an overview of the periodic table and atomic structure.
🔬 Atomic Structure and the Periodic Table
The second paragraph delves into the specifics of atomic structure, including isotopes, relative atomic mass, and the significance of the periodic table's organization. It explains how the periodic table categorizes elements by their atomic number and mass number, and how it was historically developed. The paragraph also covers electron configurations, the concept of groups and periods, and the properties of metals, non-metals, and noble gases. It concludes with a discussion on ionic charges and how different groups in the periodic table form ions with distinct charges.
🔬 Chemical Bonding and Compounds
This paragraph explores various types of chemical bonding, including ionic, covalent, and metallic bonds. It explains how ionic compounds form lattice structures with high melting and boiling points and their ability to conduct electricity in certain states. Covalent bonding is described through the sharing of electrons to achieve stable electron configurations, with examples provided for simple molecular structures and giant covalent structures like diamond and graphite. The paragraph also discusses allotropes of carbon, such as graphene and fullerenes, and concludes with an introduction to quantitative chemistry and the conservation of mass in chemical reactions.
⚖️ Quantitative Chemistry and Stoichiometry
The fourth paragraph focuses on quantitative chemistry, explaining the concept of moles and how it is used to compare amounts of substances. It covers the calculation of relative formula mass and the use of moles in chemical equations to determine the mass of reactants and products. The paragraph also discusses the concentration of solutions, percentage yield, atom economy, and the importance of understanding these concepts for predicting reaction outcomes and efficiency. It concludes with a brief mention of the ideal gas law and the concept of surface to volume ratio in nanotechnology.
⚛️ Reactivity Series and Energy Changes
This paragraph discusses the reactivity series of metals and how it is used to predict the outcomes of reactions. It covers the principles of smelting, reduction, and oxidation, and how these relate to the reactivity of metals. The paragraph also explains the concept of pH, the difference between strong and weak acids and bases, and the process of titration to determine the concentration of an unknown solution. It concludes with an overview of electrolysis, including the principles behind the extraction and purification of metals, and the role of electrolysis in the production of chlorine gas and the refining of aluminum.
⚡ Energy Transfers in Chemical Reactions
The final paragraph examines the energy transfers that occur during chemical reactions, distinguishing between exothermic and endothermic reactions. It explains the concept of activation energy and how energy profiles can be used to visualize the energy changes in a reaction. The paragraph also discusses the practical aspects of measuring energy changes through neutralization reactions and the use of energy profiles to understand the relationship between potential energy, kinetic energy, and temperature changes. It concludes with a brief mention of cells and batteries, highlighting the importance of understanding energy transfers in various chemical processes.
Mindmap
Keywords
💡Periodic Table
💡Chemical Reaction
💡Ionic Bonding
💡Covalent Bonding
💡Mole
💡Limiting Reactant
💡pH Scale
💡Electrolysis
💡Energy Profile
💡Reactivity Series
💡Isotopes
Highlights
Introduction to AQA GCC chemistry paper 1, covering topics 1 to 5.
Explanation of atoms, elements, and compounds, including the chemical formula for water (H2O).
Guidelines on balancing chemical equations by starting with atoms only in compounds.
Discussion on mixtures, such as air and saltwater, and methods of separating components like filtration and distillation.
Description of the three main states of matter and the physical processes involved in phase changes.
Historical development of atomic models, from the plum pudding model to the discovery of neutrons.
Use of the periodic table to determine atomic properties and the concept of isotopes.
Electron configurations and the significance of electron shells in understanding atomic structure.
Differentiating between metals and non-metals based on their electron shells and reactivity.
Explanation of ionic and covalent bonding, including the formation of ions and the rules governing their charges.
Properties of ionic compounds, including their high melting and boiling points, and ability to conduct electricity in certain states.
Covalent bonding and the formation of molecular compounds, with examples of simple molecular structures.
Quantitative chemistry concepts, including moles, molar mass, and stoichiometry in chemical reactions.
Calculating percentage yield and atom economy to assess the efficiency of chemical reactions.
Reactivity series of metals and their applications in displacement reactions and extraction from ores.
Explanation of oxidation and reduction, and their relationship to changes in oxidation states during reactions.
Use of pH and titrations to determine the concentration of acids and alkalis, and the concept of strong and weak acids.
Electrolysis of ionic compounds and its applications in metal extraction and purification.
Energy changes in chemical reactions, including exothermic and endothermic processes, and their practical observations.
Construction and function of chemical cells and batteries, including renewable and rechargeable systems.
Transcripts
let's see how quickly we can cover
everything you need to know for AQA GCC
chemistry paper 1 this is good for
higher and Foundation Tier double
combined Trilogy and triple separate
chemistry that's topics 1 to five atoms
bonding quantitative chemistry and
chemical and energy changes I'll tell
you when something is just for triple
and when some of the bigger concepts are
just for higher tier we're going to have
to be moving it quite a right here you
can pause the video if you need a bit
more time to get your head around
something you see let's go substances
stuff are made of atom the different
types or elements of atoms there are are
represented in the periodic table by a
symbol a compound is a substance that
contains two or more different types of
atoms chemically bonded together for
example the chemical formula for water
is H2O it's made up of hydrogen and
oxygen atoms for every one oxygen atom
there are two hydrogen atoms if there's
no number after a symbol there's an
invisible one there these atoms change
what they're bonded to and how they're
bonded through chemical reactions we can
represent a reaction with a word
equation and a chemical equation using
symbols as atoms are not created or
destroyed in any chemical reaction there
must be the same number of each type of
atom on both sides so sometimes we must
balance equations Pro tip start
balancing atoms that are only in
compounds so with this one let's go with
the carbons first there's one on the
left one on the right so that's all good
hydrogens there are four on the left
only two on the right now we can't
change the small numbers because that
would change what the compound is so
what we can do is put numbers in front
of elements or compounds to multiply
them up sticker two in front of the H2O
we now have 2 * 2 hydrogens so that's
four that's also double the oxygen in it
however so now we have four Oxygen's on
the right still only two on the left so
doubling this O2 on the left takes care
of that if there's an element in a
reaction Like Oxygen here we always
finish balancing that as there's no
KnockOn effect a mixture is any
combination of any different types of
elements and compounds that aren't
chemically bonded together for example
air is a mixture of oxygen nitrogen and
more solutions are mixtures to like salt
water a mixture of water and sodium
chloride you can separate large
insoluble particles from a liquid using
filtration like sand from water as sand
can't dissolve crystallization can leave
a solute that's the solid dissolved in a
liquid behind after you evaporate the
solvent from a solution like salt from
water similarly distillation involves
heating the solution as well but this
time the gas is cooled so it condenses
back into a liquid you can also do this
at different temperatures to separate
the different liquids of a mixture as
they will have different boiling points
this is called fractional distillation
these are all physical processes though
and not chemical reactions because no
new substances are being made solid
liquid and gas are the three main states
of matter for example water can be ice a
solid where the particles or molecules
in this case vibrate around fixed
positions it can also be liquid water
where the molecules are still touching
but are free to move past each other and
it can also be a gas water vapor we call
it when it's water where the particles
are far apart and move randomly and they
also have the most energy and so move
quickly as molecules in a gas are far
apart gases can be compressed while
solids and liquids cannot to melt or
evaporate a substance you must supply
energy usually in the form of heat to
overcome the electrostatic forces of
attraction between the particles we
don't say we're breaking Bonds in this
case note that none of these make a new
substance so these have to be physical
changes again not chemical reactions
we're not breaking any chemical bonds in
chemical reaction equations we indicate
what state of substance es in with state
symbols brackets s for solid L for
liquid G for gas and also AQ for aquous
that means dissolved or in solution
again like salt in water the idea of
what atoms are like came about gradually
JJ Thompson discovered that atoms are
made up of positive and negative charges
he came up with the plum pudding model
of the atom a positive charge with lots
of little electrons dotted around it it
was Ernest Rutherford who found that the
positive charge must actually be
incredibly small We Now call this the
nucleus and the electon must orbit
relatively far away from it he
discovered this by finding that most
alpha particles fired at a thin Leaf of
gold atoms went straight through proving
that atoms must be mostly empty space
Neil's B later discovered that electrons
exist in shells or orbitals then James
Chadwick discovered that the nucleus
must also contain some neutral charges
he called them neutrons while the
positive charges are called protons
protons and electrons have equal and
opposite charges so we just say they're
plus one and minus one relatively
speaking neutrons have a charge of zero
protons and neutrons have essentially
the same mass so we say they have a
relative mass of one electrons are very
light in comparison so we say they have
a mass of zero or just very small
depending on the situation the periodic
table tells us everything we need to
know about an atom the bottom number is
the atomic number that's the number of
protons in the nucleus this is what
determines what element you have every
atom has an overall neutral charge so
that means they must have the same
number of electrons as protons if an
atom gains or loses electrons it's now
called an ion not an atom the top number
is the mass number or relative atomic
mass or RAM for short it tells you how
many protons and neutrons are in the
nucleus so that must mean that this
carbon atom carbon 12 has six neutrons
on top of its six protons to make that
12 however you can get a carbon atom
with seven neutrons instead so its
relative mass is 13 these are what we
call Isotopes atoms of the same element
but different numbers of neutrons you
might see a number that isn't a whole
number for the mass this is because
periodic tables sometimes show the
average mass for all of the Isotopes of
that element found in the world for
example if you have some chlorine gas it
turns out that 75% of the atoms will
have a mass of 35 while 25% of the atoms
will be 37 these are what we call their
relative abundance to find the average
we just pretend that we have 100 atoms
we add up the total masses of all the
Isotopes then just divide by 100 that's
why chlorine average relative atomic
mass is 35.5 the periodic table is
incredibly useful but how was was it
made before it scientists just put
elements in order of their atomic
weights some were then grouped together
if they were seen to have similar
properties but still using the atomic
weight order Dimitri Mev then came along
and grouped elements together based on
their properties even if the order
didn't follow atomic weight using this
method he found there were gaps in his
table he asserted that these elements
were yet to be discovered in time he was
proven correct showing that his table
was indeed correct like we said
electrons exist in shells around the
nucleus the shells fill up from the
inside with a Max maximum of two on the
first shell eight on the second and
third shells then we only go to two on
the fourth shell that's 20 electrons Al
together which brings us to a calcium
atom after this we get into the
transition metals where things get a
little bit crazy so we leave that until
a level chemistry so we only care about
the electron configuration going up to
2882 magnesium has 12 electrons so its
electron configuration for example would
be 2 82 the modern periodic table can be
split up into different sections for
example everything to the left of this
staircase is called a metal metal atoms
always donate electrons to gain an empty
outer shell of electrons again slightly
weird with transition metals but we
don't think about their shells to the
right of the stair case non-metals they
always accept electrons to gain a full
outer shell the column an atom is in is
called the group it tells you how many
electrons an atom has in its outer shell
again the transition metals work in a
really weird way so they don't get their
own group if fact it turns out this is
because they can donate a different
number of electrons when they bond to
different things the at atoms in group
one are called the alkal metals they all
have one electron in their outer shell
which they give away donate when they
bond to something so they have similar
properties like when they react with
water the further down the group you go
though the further that outer electron
is from the nucleus so the electrostatic
attraction is weaker between the
negative electron and the positive
nucleus this means that the electron is
more readily donated this means the
metals get more reactive as you go down
the group group seven are what we call
the halogens they're essentially the
opposite they have seven electrons in
their outer shell so they need one more
to gain a full outer shell the further
down the group you go the less readily
an electron is accepted onto that shell
that's further away from the nucleus so
they get less reactive down the group
their boiling points also increase down
the group too group zero sometimes
referred to as group eight are called
the noble gases they already have an
empty or full outer shell just depends
on your perspective so they don't react
in reality they can react under special
conditions so we just say they're very
unreactive we don't really say group
eight anymore though because some people
thought that helium might feel a little
left out as it only has two electrons in
it out shell as electrons are negative
themselves Metals become positively
charged when they lose them they always
form positive ions all of group one lose
one electron when they turn into an ion
so all of their ions are one plus but
again we don't write the one we just put
plus group two lose two electrons to get
an empty out of shell so their ions are
all two plus group seven gain one
electron each so all their ions are
minus group six is ions are all two
minus the atoms in group 3 4 and 5 don't
really form ions except for aluminium
which is 3+ like we said transition
metals can donate different numbers of
electrons for example an ion ion can be
fe2+ or fe3+ it can donate two or three
electrons so we give them the names Ion
2 and ion 3 to distinguish between them
transition metals are generally harder
and less reactive than the alkaline
metals they also form colored compounds
bonding next metal atoms bond to each
other through metallic bonding
essentially a lattice or grid of ions is
formed with a CA of delocalized
electrons around them delocalized just
means they're not exactly on the atom as
these electrons are free to move Metals
make good conductors of electricity and
heat Metals bond to non-metals through
ionic bonding like we said a group one
metal needs to lose an electron while a
group seven atom needs to gain one it's
a match made in heaven for example a
lithium atom donate or loans its outer
electron to the chlorine we can draw a
DOT and cross diagram to show where the
electrons end up you can choose which
one belongs to which we only need to
draw the outer shell for each don't
forget to put brackets and the charge of
the ions when it comes to ionic bonding
the charges of all ions in an ionic
compound must add up to zero so l+ and
cl minus is all good so this is the
chemical formula for it same with burum
oxide be2 plus and O2 minus burum
chloride on the other hand well the the
burum needs to lose two electrons while
a chlorine only needs one so that means
there must be two chlorines or chloride
ions for every burum so be2 plus and two
lots of Cl minus adds up to zero so that
means the chemical formula is be cl2
sorted ionic compounds consist of lots
of repeating units of these ions in a
latice to form a crystal they have high
melting points and boiling points due to
the strong electrostatic forces that
need to be overcome and they can conduct
electricity but only in liquid form that
is molten or when dissolved in Solution
that's because the ions are free to move
in both cases and they carry charge you
can also get molecular ions for example
oh minus is a hydroxide ion and consists
of a hydrogen atom and an oxygen atom so
magnesium would need two of these to
make magnesium hydroxide here are a few
other examples by the way I spell
sulfate with a pH instead of an F
because I'm stubborn and refuse to adopt
the American spelling you'll get the
mark either way any ionic compound can
be called a salt not only sodium
chloride you table salt the name is
always the metal ion positive ion or cat
we can call it followed by the non-metal
ion or annion annion names are different
from their normal names like we've just
seen it's not sodium chlorine but sodium
chloride some people remember which way
around cat ions and annion are by liking
cats and they say cat ions are positive
non-metals bond to each other with Cove
valent bonding to form molecules they do
this by sh sharing electrons to gain
full out of shells for example chlorine
gas is cl2 each chlorine atom shares an
electron with the other so they're both
happy never write down happy in the exam
though here's the dot and cross diagram
we can also draw the structural formula
for molecules with just symbols and
lines we could also say that every one
of these represents a DOT cross electron
pair each oxygen needs two extra
electrons so O2 is a result of each
oxygen atom sharing two electrons each
as such this is a double calent Bond
nitrogen N2 is one of the few molecules
with a triple bond in in calent bonding
the number of electrons an atom knes is
the same as the number of bonds it must
make hydrogen can only ever make one
Bond carbon makes four bonds Etc here's
a few more if you're not in a rush pause
the video and have a go with
them and here are the answers these
above are what we call Simple molecular
or simple calent structures individual
molecules that can all mix together
these have relatively low boiling points
as there are only weak intermolecular
forces between them that need to be
overcome with heating be careful though
there not Cove valent bonds being broken
like we said and unlike ionic compounds
these can't conduct electricity even as
liquids giant calent bonding is similar
to the ltis nature of ionic compounds
atoms form calent bonds to other atoms
which form bonds to other atoms and so
on until what we have in effect is one
giant molecule diamond is an example of
this it's a crystal of carbon atoms
bonded to each other that's why it's so
hard hard and has such a high melting
point you would have to break the Cove
valent Bonds in order to do that and
they're incredibly strong graphite is
only made of carbon as well but it's not
Diamond so it's an allotrope of carbon
made out of the same atoms bonded
together in a different way graphite
consists of layers of carbons with three
bonds each in a hexagonal structure
where's the fourth Bond though well the
spare delocalized electrons form special
weak bonds between the layers which
means that it can conduct electricity
because the electrons can move between
the lers as well and it also means the
layers can slide over each other easily
which is why it's used in pencils as a
side note metal alloys are stronger than
pure Metals having mixtures of metals
means that we have different size atoms
and that disrupts the regular lattice so
layers can't slide over each other as
easily back to carbon allotropes
graphine is just a single layer of
graphite ferin are 3D structures of
carbon atoms for example Buckminster
ferine is a spherical football-like
structure consisting of 60 carbon atoms
each ferin that have a tube shape are
called nanot tubes just for triple real
quick surface to volume ratio is just
one divided by the other if the length
of a side of a cube doubles that means
this ratio halves as nanop particles are
tiny this ratio is huge for them which
means that fewer could be needed to
fulfill a purpose compared to larger
ones quantitative chemistry next some
tricky stuff coming up total mass of all
substances is conserved in a chemical
reaction like we said earlier that must
mean the atoms that go in must come out
so we must balance equations to that end
we already know about relative atomic
mass but if it's a compound we can add
these up to give the relative formula
mass we just add up the individual Rams
so CO2 is 12 plus 2 lots of 16 so that's
44 some reactions produce a gas product
which if it leaves the reaction vessel
will result in a seeming decrease in
mass of the reactants a mole is just a
specific number of atoms or molecules
but we don't really need to know the
number it's just a way of comparing
amounts of substance Es as we can't deal
in individual numbers of atoms or
molecules if your foundation you don't
need to deal in moles by the way if you
have as many grams of a substance as its
relative atomic or formula mass you have
one mole so one mole of carbon has a
mass of 12 G that means we calculate the
number of moles of something we have
like this moles equals g over Rams where
Rams is short for relative atomic mass
but it also could be relative formula
mass this is an equation worth
remembering let's take our methane
combustion reaction from earlier like we
said in order to balance this we'd need
two oxygen molecules per one molecule of
methane this is also true for moles too
then we'd need double the moles of
oxygen to methane so here's how a
question could go how many grams of
water would be made if 64 G of methane
reacted completely with oxygen we need
to get from the mass of one thing to the
mass of another so we use moles as the
middleman the process is this Mass moles
moles Mass we switch from one to the
other at the halfway mark So a mass of
64 G of methane how many moles is that
moles equals g over R so that's 64
divided by 16 that's four moles of
methane but look there's no number in
front of the methane but there is a two
in front of the water which means we
must have double the moles of water so
that's 8 moles by the way we can say
that the stochiometry is 1 to2 that just
means the ratio of moles of one
substance to another in a reaction so
what we have to do then is turn that
back into Mass using our equation by
rearranging it put it into a triangle if
you have to and cover up Mass g equals
moles time Rams so that's 8 moles *
water's Ram of 18 that's 144 G of water
made you could also be given the mass in
kilograms or even tons the great thing
is is that because this is all relative
we can just put those masses into our
equation instead of grams and so long as
you stick with that unit for the whole
question you'll still end up with the
right answer of course we can also use
moles to predict how much of a reactant
we would need in a reaction
as you can see we need two moles of
oxygen to every one mole of methane if
we had that one mole of methane but only
one mole of oxygen that means that not
all of the methane would react some
would be left behind we say that the
oxygen is the limiting reactant in this
case it ran out first the concentration
of solutions can be given in G per decim
cubed where a decimeter cubed is 1,000
cm cubed but it's often useful to
convert this into moles per decim cubed
instead if one mole of H CL is dissolved
in 1 decim cubed of water we've made
hydrochloric acid at a concentration of
1 mole per decim cubed sometimes we
shorten this to just one Moler triple
only now until the next topic chemical
changes in many reactions we want to
make as much product as possible more
often than not though there will be some
reactants Left Behind over at the end
like we know for example if a reaction
is reversible like the harbor process to
make amonia more about that in paper too
you'll always end up with hydrogen and
nitrogen at the end in this case when
it's reached equilibrium percentage
yield merely tells you how much product
is actually made compared to how much
you could have made in theory had all
the reactants reacted for example if you
start with 20 G of reactants here but
only end up with 10 G of ammonia the
percentage yield is 50% you must be
given the actual masses involved in
questions on this so you can't predict
what the yield would be just from the
equation atom economy on the other hand
tells you how much of a desired product
you get out of a reaction compared to
the mass of the reactants that went in
you use relative Atomic or formula
masses to do this I like to think of
atom economy as efficiency of mass we
calculate it like this the ram of
desired product divided by the total Ram
of reactants Times by 100 back to the
methane reaction sometimes this is done
in green houses to make CO2 for the
plants it's an incredibly important gas
necessary for life to thrive you see the
ram of CO2 is 44 so that goes on top of
our equation now we could calculate the
ram of the reactants but there's a Nifty
shortcut we can take here because this
is also the same as the ram of all of
the products due to conservation of mass
as we know so we might as well use that
seeing that we've already got the RAM
for one product add on two lots of 18 so
that's 44 divided by the total of 80 *
100 that's
55% one mole of any gas takes up a
volume of 24 DM cubed regardless of its
relative mass this is true for RTP room
temperature and pressure that's 20° C
and a pressure of one atmosphere you
must be able to convert moles to volume
and back by multiplying or dividing by
24 double people wake up this is
chemical changes we saw briefly earlier
that Metals vary in their reactivity as
some donate their electrons more readily
than others here's the reactivity series
for the most common Metals we consider
you can see that hydrogen and carbon
have also snuck in there that's because
it's often necessary to compare the
reactivity of metals to those in order
to predict what will happen in a
reaction a more reactive metal will
displace a less reactive metal from a
compound that is kick it out for example
if you place zinc in Copper sulfate
solution you'll see copper forming on
the lump of zinc the zinc displaces the
copper to form zinc sulfate kicking the
copper out of the compound we know that
alkal metals react with water the
reaction happens because for example
potassium is more reactive than hydrogen
so in essence it displaces it from the
water leaving potassium hydroxide and
hydrogen gas is produced we can use this
when it comes to extracting metals from
their ores found in the ground any metal
less reactive than carbon can be
displaced by it for example ion can be
displaced from ion oxide with carbon
this is called smelting we can also say
that the ion oxide has been reduced it's
the opposite of oxidation because oxygen
is lost even if oxygen is not involved
in a reaction we can still say that
reduction and oxidation happen depending
on whether a reactant loses or gains
electrons the pneumonic is oil rig
oxidation is loss reduction is gain of
electrons that is the ion ions in the
ion oxide are positive of course because
they're metals and they gain electrons
to turn back into atoms they become
neutral they've been reduced here's the
half or ionic equation for this we
should never really have a minus in any
half equations so think carefully about
which side the electron should go on
depending on whether it's oxidation or
reduction Metals more reactive than
hydrogen can displace it from an acid so
most metals react with hydrochloric acid
and sulfuric acid for example this
produces a salt alkalis they have a pH
greater than seven react with acids less
than seven to produce say salt and water
if the quantities used are correct
according to this deometry they will
neutralize each other completely to
leave no unused reactants here's an
example sodium hydroxide and
hydrochloric acid makes sodium chloride
in water neutral pH of 7 if sulfuric
acid is used a metal sulfate is made
nitric acid metal nitrate these salts
are left in solution that is disol in
water when any substance dissolves its
ions partially dissociate as does the
water actually into H+ and O minus ions
we can obtain solid crystals of a
dissolved salt by warming gently so the
water evaporates the pH scale is a
logarithmic scale base 10 it's not
linear what does that mean well an acid
contains H+ ions and an acid that has a
pH of three will have 10 times the
concentration of these compared to an
acid of ph4 ph3 would have a 100 times
the concentration of H+ ions compared to
an acid of ph5 and so on alkal work in a
similar way but with oh minus ions
instead the higher you go the greater
the concentration a strong acid is one
that dissociates or ionizes completely
when in solution like Hydrochloric
Nitric and sulfuric acids weak acids on
the other hand only partially dissociate
like ethanoic citric and Carbonic acids
the pH of an acid depends on both its
strength and concentration if
hydrochloric acid and ethanoic acid have
the same concentration the hydrochloric
acid will have the lower pH as it's
stronger titrations are only for triple
this is how we deduce the concentration
of an acid or an alkaline we use a glass
pipet to measure out a known volume of
alkal and put it in a conical flask with
a few drops of an indicator like methyl
orange we put the acid of unknown
concentration in a buet above the flask
we open the tap and let it drip into the
flask slowly while we swirl it when it
turns pink we close the tap and if it
stays pink after we swirl it that shows
that neutralization has occurred you can
also Al do a rough titration to get a
rough value for the volume needed to do
this then do another and then add a drop
at a time near the end point to get a
more accurate value let's say that it's
sodium hydroxide and sulfuric acid
here's the balanced equation so let's
say that we have 50 cm cubed of 0.2
moles per decim Cub sodium hydroxide
first we need to turn that volume into
decim cubed so we divide by 1,000 so
that's 0.05 DM cubed of the alkaline
multiply that by the concentration and
we get 0.01 moles from the stock
geometry of 1 to two for the acid and
Alkali we can see that we need half the
number of moles of acid to neutralize it
so that's
0.005 moles of acid needed now we can
use our actual volume of acid measured
finally we just calculate the
concentration by doing moles ided by
volume that's
0.005 ID 0.125 DM Cub that's that's we
converted it which gives us a
concentration of 0.4 moles per decim
cubed don't forget that units are your
friends if you forget what calculation
you're supposed to do electrolysis is
for everyone if you melt an ionic
compound let's say aluminium oxide it
can conduct electricity as the ions can
move we know that from earlier by
passing a current through it using inert
electrodes that means they won't react
like carbon the positive metal ions or
cations al3+ in this case they move to
the negatively charged electrode we call
that the cathode where they receive
electrons and turn into atoms cations
are always reduced at the cathode so in
this case solid aluminium is formed on
the cathode the negative ions or anion
O2 minus in this case move to the
positive electrode the anode where a
lose electrons in this case oxygen gas
O2 is formed annion are always oxidized
at the anode this is one way of
purifying metals or extracting them from
compounds say if displacing with carbon
isn't an option due to their reactivity
in this case of aluminium oxide the
oxygen produced of the graphite carbon
anode reacts with the anode itself so
these need to be replaced every often
again specifically for this case
aluminium oxide is mixed with cryolite
to reduce its melting point making it
cheaper to extract the aluminum we can
also do electrolysis with ionic
substances in solution say sodium
chloride solution we know that the
solution is a mixture of na+ Cl minus H+
and O minus ions as they're all
partially dissociated but what will be
attracted to and reduced at the cathode
the na Plus or the H+ well it comes back
to reactivity the more reactive ion
stays in solution while the less
reactive one moves to the electrod
that's the H+ in this case that's why
hydrogen gas is made at the cathode here
if the metal is less reactive than
hydrogen say copper in copper sulfate
solution it forms on the cathode instead
and the H+ ion stay in solution that
actually makes an acid if there is a
haly ion present like the CL minus here
it is oxidized at the anode if there's
no halide ion in solution the oxygen
from the O minus is oxidized instead and
oxygen gas is produced finally energy
Chang hopefully a short one to finish
off any chemical reaction involves
energy transfers as energy is needed to
break chemical bonds while energy is
released when chemical bonds form both
of these happen in any reaction if there
is more energy released from bonds made
than energy needed to break bonds we say
this is a net energy released and we
should observe an increase in
temperature as a result this is an
exothermic reaction for example
combustion the way I think about it is
explosions are exothermic I mean the X
just means out if it's the other way
around there is net energy input into
the reaction so the reaction should get
colder this is an endothermic reaction
the Practical on this goes as follows we
carry out a neutralization reaction
between an acid and Alkali in a poyin
cup which is well insulated and a
thermometer poke through a lid that sits
on top we measure the maximum
temperature the reaction reaches then
increase the volume of alkal used and
repeat eventually the maximum
temperature will not get any higher due
to all of the acid reacting and the same
amount of energy released is being
shared across a larger volume of liquid
we can draw two lines of best fit for
the rise and fall in these Max
temperatures where they meet tells us
how much of the Alkali was needed to
neutralize the acid we can use an energy
profile to help us visualize the
difference in energies between the
reactants and the products now this is
something that people get confused with
the Y AIS is potential energy and you
should know that usually in science
potential energy and kinetic energy do a
balancing act if one goes down the other
one goes up so if the potential energy
of the products is less than the
reactants they must have gained kinetic
energy and that always means a hotter
temperature this is an exothermic
reaction it might seem like the energy
has gone down but kinetic energy has
increased of course fuel must need a
spark to start it burning which is why
we draw this bump to represent the
activation energy The energy needed to
get the reaction started here's an
energy profile for an endothermic
reaction too every Bond needs a very
specific amount of energy to break for
example a carbon hydrogen Cove valent
Bond needs 413 kles for every mole of
these break them if a mole of these are
made it's the same amount of energy
released so let's take our combustion of
methane equation one last time and draw
the structures so we can see all the
bonds we need to break all of the bonds
in the reactants first so that's four
lots of 4113 and two lots of 495 for the
two lots of oxygen double bonds so
that's 2,642 K per mole needed to break
all of the bonds the unit isn't that
important by the way we're more
interested in the numbers making Bonds
on the other side 2 * 799 is releas when
the CO2 double bonds are made plus four
lots of 467 for the two water molecules
that's
3,466 K per mole released by the way
you'll always be given these numbers you
don't need to remember them more energy
is released than goes in in this case so
it's exothermic that checks out doesn't
it one minus the other gives us the net
energy released and in this case that's
824 kils per mole finally just for
triple cells or batteries they contain
chemicals that can produce a potential
difference of voltage to power
electrical appliances the basic
composition is two different Metals in
contact with an electrolyte
non-renewable batteries stop working
when the reactants are used up
rechargeable batteries can be recharged
when a supplied current causes the
reverse reaction to occur hydrogen fuel
cells work in a similar way water is
split up into hydrogen and oxygen by
electrolysis when they recombine a
voltage is produced phew that was a bit
of a SLO but we made it hopefully this
has been useful please leave a like if
it has been and leave any comments or
questions you have below and hey come
back here after the exam to let us know
how you got on we'd all love to know
click on the card to go to the playlist
for all six papers and I'll see you next
time
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