All of AQA CHEMISTRY Paper 1 in 30 minutes - GCSE Science Revision

Summary

This 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

00:00

📚 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.

05:02

🔬 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.

10:03

🔬 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.

15:03

⚖️ 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.

20:04

⚛️ 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.

25:05

⚡ 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.

Keywords

💡Periodic Table

The Periodic Table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. It is a fundamental tool in chemistry, providing key information about elements such as atomic number and relative atomic mass. In the video, it is used to explain the properties of elements and how they are grouped based on shared characteristics.

💡Chemical Reaction

A chemical reaction involves the rearrangement of atoms during which chemical bonds between atoms are broken and new bonds are formed, resulting in a change in the substances initially involved. The video emphasizes that in a chemical reaction, atoms are neither created nor destroyed, highlighting the law of conservation of mass and the importance of balancing chemical equations.

💡Ionic Bonding

Ionic bonding is a type of chemical bond that involves the electrostatic attraction between oppositely charged ions. It typically occurs between a metal and a non-metal. In the context of the video, ionic bonding is explained through the transfer of electrons from a metal to a non-metal, resulting in the formation of positive and negative ions that are attracted to each other.

💡Covalent Bonding

Covalent bonding is a type of chemical bond where two atoms share one or more pairs of electrons. This bond is commonly found between non-metal atoms. The video illustrates covalent bonding with examples such as the sharing of electrons between chlorine atoms in Cl2 or the double bond between oxygen atoms in O2, emphasizing how such bonds contribute to the stability of molecules.

💡Mole

A mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as exactly 6.02×10^23 particles, which is the number of atoms in exactly 12 grams of carbon-12. In the video, moles are used to quantify the amount of a substance in a chemical reaction, allowing for the calculation of reactants and products based on their relative atomic or formula masses.

💡Limiting Reactant

The limiting reactant is the reactant that will be completely consumed if the reaction goes to completion, and it determines the maximum amount of product that can be formed from the reactants. In the video, the concept is discussed in the context of reactions where not all reactants are used up, and it is used to calculate the theoretical yield of a product.

💡pH Scale

The pH scale is a logarithmic scale ranging from 0 to 14, used to specify the acidity or basicity of an aqueous solution. A pH of 7 is neutral, values less than 7 indicate acidity, and values greater than 7 indicate basicity. The video explains the pH scale in the context of acid-base reactions and how it is used to measure the strength of acids and bases.

💡Electrolysis

Electrolysis is a chemical process that uses an electric current to drive a non-spontaneous chemical reaction. It involves the decomposition of a substance and the driving force is the electric current itself. In the video, electrolysis is discussed in the context of extracting metals from their compounds, such as the extraction of aluminum from aluminum oxide.

💡Energy Profile

An energy profile is a graphical representation that shows the potential energy changes that occur during a chemical reaction. It illustrates the energy required to break bonds in reactants and the energy released when new bonds are formed in products. The video uses energy profiles to explain exothermic and endothermic reactions, showing how the difference in energy levels before and after the reaction determines whether the reaction is energy-absorbing or energy-releasing.

💡Reactivity Series

The reactivity series is a list of metals arranged in order of decreasing reactivity. It is used to predict the outcomes of reactions involving metals. In the video, the series is mentioned when discussing how more reactive metals can displace less reactive metals from their compounds, a concept crucial for understanding metal extraction and reactivity in chemical reactions.

💡Isotopes

Isotopes are variants of a particular chemical element which differ in neutron number, and hence in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons. The video explains isotopes in the context of the periodic table, noting that the relative atomic mass of an element is often a weighted average that reflects the presence of different 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