A Level Chemistry Bridging tasks 2021 - Ripley St Thomas
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A Level Chemistry Bridging tasks 2021
Write an essay on your chosen topic.
The essay should be no more than two sides of A4 and should include a reference list and
diagrams, if appropriate.
The essay should be written in an appropriate style and pay due care to spelling, punctuation,
grammar and the use of scientific conventions and notation where appropriate.
Essay Titles
1) The development of atomic theory
Describe the development of our understanding of atomic theory.
What were the major theories and discoveries that allowed the model to develop?
2) Combating Plastic Pollution.
Plastics and polymers have revolutionised the modern world. However, their overuse is
now causing a pollution crisis.
Describe what polymers are (include diagrams) and the different types. Explain why
polymers are causing a pollution problem. Research and describe some possible
solutions to the plastic pollution problem.
3) Water and bonding
Water has many unusual properties due to the nature of the bonding within it and
between its molecules.
Describe the nature of bonding in water.
Research and describe how and why the physical and chemical properties of water are
different to the other hydrides of group 6 (hydrogen sulphide, hydrogen selenide,
hydrogen telluride and hydrogen polonide) using data to support your comments.
Describe some of the unusual properties of water and the impact that this had had on
planet Earth.
Work is due to be submitted in the first week of the new term in September.The following pages contain reminders of the work you did at GCSE which is still relevant at AS level.
Page 1 - Atomic Structure
Page 2 - Calculations Try to complete as many
sections as you can.
Page 3 - Writing equations
Page 4 - Chemical Bonds As a minimum, you should
Page 5 - Properties of ionic and covalent compounds read the summaries and
attempt 1-2 questions per
Page 6 - The Periodic table section.
Page 7 - Energy and rates of reactions (kinetics)
If you are able, you can
Page 8 - Reversible reactions (Equilibria) complete more.
Page 9 - Reactivity and metals
Page 10-11 - Displacement and Redox reactions The aim is to remind
yourself of the core ideas
Page 12 - Crude oil and Organic chemistry and principles from GCSE.Atomic Structure – what is in an atom?
Energy levels always
Atoms contain fill up from the 7. Two isotopes of chlorine
Small dense nucleus comprised of positive bottom are chlorine-35 and
protons and neutral neutrons chlorine-37. How many
Negative electrons orbit the nucleus in energy protons, neutrons and
levels (shells) electrons are there in each
An atom is mostly empty space as most of the Questions isotope?
mass is concentrated in the nucleus
The size of the atom is governed by the numbers of 1. Complete the table 8. How many electrons are
orbiting electrons Particle Relative Charge there in Ca2+ ?
mass
Atoms on the Periodic Table Proton
Atomic number, Z – represents the number of Neutron
protons in an atom Electron
Relative atomic mass, A – represents the
number of protons and neutrons added together, 2. How many protons are
those particles with mass. there in fluorine?
Properties of atoms 3. How many neutrons are
Atoms are electrically neutral as they contain the there in manganese?
same number of electrons and protons
Atoms gain or lose electrons to become charged – 4. How many electrons are
IONS there in bromine?
Atoms containing the same numbers of protons but
different numbers of neutrons are called 5. What is the charge on
ISOTOPES an atom that loses 2
electrons?
Arranging electrons
Energy level 1 contains 2 electrons – called an s 6. What is the charge on
level an atom that gains 3
Energy level 2 contains 8 electrons – split into two electrons?
sub-levels, s and p
1Calculations Add up the masses h. (CH3CO)2O
of the elements from i. C6H5OH
Mass and moles the periodic table j. Fe2O3
raking into account k. K2Cr2O7
The mole is an amount of chemical. It stands for a fixed the numbers of l. Al2(SO4)3
number of particles. That number is 6.022x1023. The elements m. KMnO4
number is huge! Instead of counting out atoms for Where there are n. CaC2O4
reactions we use a rule to convert masses of substance brackets the small o. CH3COOH
into a number of moles and vice versa. number outside the
bracket multiplies
1 mole of a substance is the Mr of the substance weighed everything inside the
out in grams (g). bracket.
2) Calculate the number of
So 1g of H atoms contains 1 mole of H atoms. e.g. Al3(PO4)2 moles of particles in 0.1 kg
1g of H2 molecules contains 0.5 moles of Hydrogen of each substance in
molecules as the mass of a molecule of hydrogen is 2. Al = 3 x 27 = 81 questions a-g.
(PO4)2 = [31 + (4x16)] x 2 State if the type of particle
To convert mass in to moles you need to do mass (g)/Mr = 190 would be atoms or
of the substance. molecules or formula mass.
Be wary of questions giving mass in kg. You need to Total = 271
convert Kg to g first. (100g in 1kg so times the mass in kg
by 1000 first). Questions
Remember n= m . 1) Work out the relative
Mr molecular/ formula mass of
these elements and
Mr can be relative atomic mass for atoms/elements (Ar), compounds.
Molecular mass (Mr) for covalent substances or formula a. O2
mass for ionic substances. b. S
c. H2O
Relative molecular/ formula masses d. CO2
Only tool required is your periodic table e. SO3
f. CaCl2
g. C2H5NH2
2Writing Equations
Lastly you have to 4. Balance your equations
In order to write a correct equation you need a balance the equation
correct formula. This means you need to learn common Numbers go at the
formulae – such as acids - the charges of common ions front
and the formulae of polyatomic ions. Once you have Don’t change the
these charges the best method is the criss-cross. FORMULAE!
Questions
E.g. Aluminium nitrate
Identify the ions and charges 1. Work out the following
Al 3+ and NO3 1- formulae
Put a circle around the number on each charge a. magnesium hydroxide
b. lithium bromide
Al 3 + and NO3 1- c. aluminium oxide
Criss – cross your numbers d. potassium sulphate
e. calcium carbonate
Al3 + and NO31 -
2. Complete these word
equations
Al (NO3)3 a. sodium hydroxide +
Al(NO3)3 – you need brackets or it looks like you have hydrochloric acid
33 nitrogens! If the number is a 1 we don’t write it b. aluminium + nitric acid
down. =
c. magnesium carbonate +
With correct formulae you need to recall how sulphuric acid =
chemicals react. d. C2H6 + oxygen =
- ACID + BASE = SALT + WATER e. Iron + copper sulphate
- ACID + METAL = SALT + HYDROGEN =
- ACID + METAL CARBONATE = SALT + CARBON DIOXIDE + WATER f. magnesium sulphate +
- HYDROCARBON + OXYGEN = CARBON DIOXIDE + WATER barium chloride =
- X + YZ = XZ + Y (single replacement)
- AB + CD = AD + BD (double replacement) 3. Turn the word
Remember certain gases hang out in 2s – H2, N2, O2, equations in qu.2 into
halogens symbol equations
3Chemical Bonds
Questions
There are three types of chemical bond:-
Ionic bonding 1. Explain the formation of
Covalent bonding NaCl, MgO and MgCl2. Use
Metallic bonding diagrams to illustrate your
answers.
Ionic Bonding
Bond formed between oppositely charged ions 2. Draw dot and cross
held together by electrostatic forces of diagrams to show the
attraction formation of ammonia
Ionic bonds form between a metal and a non-metal (NH3), water (H2O),
The formula of a ionic compound denotes the nitrogen (N2), oxygen (O2)
smallest repeating unit and methane (CH4).
Each ionic crystal is a giant ionic lattice
3. Explain the difference in
Covalent bonding strength between the
Molecules formed between two atoms sharing a metallic bond in aluminium
pair of electrons and sodium. Use diagrams
Bonds usually formed between two non-metals to illustrate your answer.
The formula of a covalent compound is the
individual molecule 4. Draw a dot and cross
Covalently bonded substances can also be diagram to show how
MACROMOLECULAR – giant compounds ammonia (NH3) can form a
containing many covalent bonds co-ordinate covalent bond
with a hydrogen ion (H+).
Metallic bonding
Positive metal ions surrounded by a sea of 5. Predict the type of
electrons bonding formed between
The larger the ion the stronger the bond a. copper and chlorine
b. sulphur and fluorine
Co-ordinate or dative covalent bonds (new for A level)
Covalent bond formed between two atoms when
both electrons come from one atom
4 Macromolecules are polar liquids and covalently
Properties of ionic and covalent compounds not soluble in bonded substances don’t
water – you would dissolve.
Ionic Bonds have to break many
Forces between oppositely charged ions are very strong covalent 5. Which compound will
strong bonds have the higher melting
The bigger the charge on the ion the stronger the Covalent point?
bond macromolecules do a. C5H12
Ionic compounds have very high melting points not conduct b. C10H22
as a lot of energy is required to overcome the electricity – Explain your reasoning.
forces of attraction exception -
Ionic compounds are soluble in water because it is graphite 6. Which compound has
a polar molecule the higher melting point?
Ionic compounds do not conduct electricity unless a. NaCl
they are MOLTEN – this allows the ions freedom to Questions b. MgCl2
move Explain your reasoning
1. Explain how adding salt
Covalent Bonds to water allows it to
The covalent bond itself is very strong conduct electricity
The intra-molecular forces between molecules are
very weak and therefore not a lot of energy is 2. Draw the structure of
needed to overcome them – low melting points diamond and graphite.
Intra-molecular forces increase with mass Explain how graphite is
Covalent molecules are non-polar and not able to conduct electricity.
soluble in water – they are soluble in other non-
polar liquids 3. Explain how you could
Covalent molecules do not conduct electricity – distinguish between
there are no free electrons to carry the current identical looking crystals if
you knew that one crystal
Giant covalent molecules - Macromolecular was ionic and one
Made up of strong covalent bonds – a lot of energy macromolecular covalent.
is required to break these bonds – they have very
high melting points 4. Explain why ionic
compounds can dissolve in
5The Periodic Table If you learn this you will these elements? Kr,
always know the charge of Ne, F, Li, Cu, Zn, Mn
The periodic table will always be given out in an a common ion.
exam and it is full of useful information
Questions
Columns are known as GROUPS – they are families
of elements with similar chemical properties 1. Write down the
Rows are known as PERIODS – elements exhibit atomic number of
periodic behaviour these elements. Na,
The larger number on the table is the MASS B, At, W
number – the total number of protons and neutrons
added together 2. Write the down the
The smaller number on the periodic table is the mass number of
ATOMIC number – this is the number of protons these elements. Ca,
contained in that particular atom F, K, As
The periodic table also tells you the symbol of each
atom 3. Calculate the
number of neutrons
You can also use the periodic table to work out the in these elements.
electronic structure of the elements and the number of Ge, H, I, V
ions present
As you go from left to right on the periodic table you can 4. What period are
work out the charge of the most common ions these elements in?
F, Cs, Au, He
Miss out the middle
+ + + +/- -3 -2 - 0 5. What is the charge
1 2 3 4 1 on the following
ions?
Br, Sr, Rb, S, Xe, Ge, Sb
6. What is the
electronic
configuration of
6Energy, rates of reaction (kinetics)
Energy is transferred during chemical reactions. 1. In a reaction between
When energy is transferred into reactions limestone and hydrochloric
overall the reaction is said to be endothermic acid which form of
and the surroundings cools down (reaction feels limestone would you use
colder). for the fastest rate?
When energy is transferred to the surroundings Powdered, small chips,
from the reaction it is called exothermic and the large lumps.
surroundings heat up (reaction feels hotter).
Reaction rate is a measure of how fast the 2. When how would you
reaction takes place in a given amount of time. stop a reaction from going
You can measure changes in pH, colour, volume to fast because it produces
of gas produced, change in mass etc to give a excess heat.
rate.
4 factors affect the rate of reaction. 3. Sketch a graph of
Surface area, temperature, concentration of volume of gas made
reactants, addition of a catalyst. against time. Label the
You should be able to recall how these factors areas with the fastest and
can be used to increase or decrease rates of slowest rates of reaction.
reaction.
Yield is used a measure of a reactions success. 4. On the same graph
Theoretical yield is a calculation (using moles sketch two other lines to
theory) to calculate what the maximum possible show the same reaction
yield can be. happening at higher and
Actual yield is a measure of how much was lower temperatures than
actually made the original reaction. Label
Percentage yield is a calculation that expresses accordingly.
the actual yield compared to the theoretical
yield. 5. Why is it only necessary
High yield and fast reaction rates for the lowest to add a small amount of
cost are best for chemical industries. catalyst to a reaction?
Remember energy cost money!
7Reversible reactions and equilibria. ammonia (NH3). So in this SO3(g) + H2O(g) + H2SO4(g)
case raising the 2) In the reaction
Some reactions are reversible. The backwards reaction temperature to increase above what
can take place at the same time as the forwards reaction the rate of reaction conditions would
under the same reaction conditions. wouldn’t be a good idea. you use to increase
the yield of H2SO4
It is important to remember that the reactants and We would say “raising given that the
products are in a sealed container. All reactants and temperature moves the forward reaction
products will be at the same temperature and pressure. equilibrium to the left as exothermic.
this opposes the change
These reversible reactions eventually reach a point where (by favouring the 3) In practice in the
the RATE of the forwards and backwards reaction will endothermic direction). Haber process the
become equal. This means that the relative mixture of ammonia
concentrations of reactants and predicts remain Increasing pressure gas and unreacted
constant. The reaction has reached dynamic always favour the side of hydrogen is cooled
equilibrium. the reaction (equation) that so that the ammonia
has the least moles of gas condenses and
These reactions can be difficult to control as the ratio or gas. then removed.
reactants and products is controlled by picking the correct Explain how this
conditions of temperature and pressure. This is done 1) In the example helps the overall
according to Le chatalier’s principle which state the above explain the yield of ammonia
reaction system will always seek to oppose the change effect of raising increase.
applied to it. pressure and
lowering pressure on 2HI(g) H2(g) + I2(g)
N2(g)+ 3 H2(g) 2NH3(g) the position of 4) In this example
equilibrium. above pressure has
In the reaction above (the Haber process) the forwards no effect. Explain
reaction is known to be exothermic. Raising the why?
temperature forces the reaction to oppose that change.
This means that the endothermic direction is favoured,
this has the result of absorbing the extra heat energy and
favours the production of Nitrogen and hydrogen. This has
the knock on effect of reducing the concentration on
8Chemical reactions Part 1.
There are many different chemical reactions that can take Or in the case of
place. carbonates
Making salts. 2H+ + CO32- H2O + CO2
A salt is the by-product of when acids and bases
react together. Here the oxide ion is part
Acids are substances that release hydrogen ions (H+) into of the carbonate ion and as
solution. These substances dissolve in water to give it a you can see CO2 is
pH of less than 7. released.
Some acids are described as strong acids- these fully
ionise in solution. All of their molecules break up and 1) Write word and symbol
produce large numbers of hydrogen ions. E.g. Sulphuric equations for the
acid H2SO4 pH 1-2. reactions between
Nitric acid and iron (III)
Some are described as weak acids e.g. Ethanoic acid oxide
CH3COOH. Here only a relatively small number of acid Copper Carbonate and
molecules ionise. So the number of H+ ions made is a Sulphuric acid.
much smaller and the pH is higher (3-6) Potassium Hydroxide
and Hydrochloric acid.
Bases are chemicals that can neutralise acids.
Alkalis are soluble bases. They release Hydroxide ions 2) Suggest a reaction
(OH-) when they dissolve. E.g. Sodium Hydroxide. that will produce
A neutralisation reaction is always nickel sulphate.
H+ + OH- H2O
So what about Metal oxides and carbonates?
Metal oxides and metal carbonates are bases but are
insoluble in water.
Here the Oxide ion itself can react with hydrogen ions to
neutralise it.
2H+ + O2- H2O
9Chemical reaction part 2 Here Iron reduced Copper This will work as long as
Reduction/oxidation reactions Part A. oxide. the metal (element) is
Actually, we can say the more reactive than the
Redox reactions involve the transfer from one thing to Iron atoms reduce the metal already in the
another. Cooper ions in the copper compound.
oxide. This can be shown
Reduction – Gain of electrons by a substance (species) using electron ion 1) Write the chemical
Oxidation – Loss of electrons by a substance (species). equations (aka- half equation for the
equations, aka ionic displacement of
We use the word species at A-level because we want to equation) Silver from silver
say specifically what “thing” in a compound is being nitrate (AgNO3)
reduced or oxidise. Fe Fe3+ + 3e- using Copper.
The iron atoms loos 2) Explain why
Remember gain of oxygen is oxidation because oxygen is electrons and forms the Hydrogen gas can
good at gaining control of electrons in a compound. Iron (III) ions. be used to extract
copper from Copper
Displacement reactions are examples of redox reaction Cu2+ + 2e- Cu. oxide (CuO). Use
(metal displacement and halogen displacement are the The copper ions in the chemical equations
same type of reactions.) copper oxide gain those and half equations
electrons and form copper to support your
The reactivity of a metal depends on its ability to for a atoms (i.e. copper metal). answer.
positive ion. Na is very good, K is even better. Cu is pretty
rubbish at it. Fe and Zn sit somewhere in the middle. Notice the electrons appear
Carbon also appears in this list as carbon is pretty good at on opposite sides of the
reducing most metals. Even Hydrogen crops in the list too, reaction arrow. This is
somewhere near the bottom. important for developing
this idea further at A level.
Metal displacement reactions. The Fe reaction is the
oxidation half equation and
Iron + copper oxide Iron (III) Oxide + Copper. the Cu equation is the
reduction half equation.
2Fe + 3 CuO Fe2O3 + 3 Cu
10Cl2 + 2e- 2Cl- reaction does not
happen.
Displacement reactions part B Halogen/halide These displacement
redox. reactions will work as long
as the halogen (atom form
The halogens are very good oxidising agents. They are of the element) is higher
good at stealing electrons form other species and oxidising up the group (smaller
the species react with (whilst reducing themselves). atom) than the halide ion
(the ionic form).
The ability to gain electrons is related to the size of the
halogen atom F has only 2 shells, Cl has 3 Br has 4 and I You will see at A level that
has 5. As the outer electron shell gets further away from the halogen are used to
the nucleus the attraction to gain electrons gets weaker oxidise lots of different
and weaker. So F2 is a very strong “gainer of electrons” things (because they are
(at A level we would say it is a strong oxidising agent), very good at gaining
whilst I2 is much weaker (compared to F2). electrons). One of these is
chlorine in bleach.
We can study the displacement reactions of the halogens
like this. 1) Write the word and
symbol equations for
2 KBr + Cl2 Br2 + 2KCl the reaction
between Potassium
Chlorine is able to gain electrons from the bromide ions. iodide and Fluorine.
This means the bromide ions turn back into Bromine 2) Work out the half
atoms and pair up. equations involve.
3) Iodine is not able to
Again this can be broken down into two half equations displace Chloride
showing the movement of electrons. ions form Sodium
chloride. Using half
2Br- Br2 + 2e- equations and
referring to the sizes
Notice here how the number of ions and atoms has to of the atoms,
balance. explain why this
11Oil and hydrocarbons. Alkenes- have at least one cracking. Describe the two
C=C bond. This bond could processes and state the
Carbon compounds are very special numerous and varied. hold extra hydrogen (or differences in products
Hydrocarbons are the simplest and a natural source of other atoms, so it is an produced.
these is crude oil. unsaturated hydrocarbon.
3) Draw the first four
Homologous series- a family of related chemicals. Short chain alkanes are members of the
Organic molecule- molecule based on carbon (and useful as fuels. They are
usually hydrogen) volatile and burn well in air Alkane
Functional Group- the part of the molecules that is and give out useful Alkene
different between one family of molecules and another. amounts of energy. Alcohol
Molecular formula- shows the actual number and type Carboxylic acid
of atoms in a compound Long chain hydrocarbons, Homologous series.
Displayed formula- shows the position of atoms and whilst some are useful as State the family name and
bonds in a molecule. fuel such as diesel and highlight the functional
heavy fuel oil used in ships, group in each family of
A good skill for this area is to quickly recognise functional it doesn’t burn as easily molecules.
groups and structures of molecules. Is it an alkane, alkene and so these hydrocarbons
or something else? are much lower in demand.
Fractional Distillation separates Hydrocarbons in crude Cracking- A chemical
oil in to “fractions” which have similar chain lengths. This process that breaks long
is a physical process. chain hydrocarbons in to
shorter one and sometimes
Hydrocarbons produces Alkenes as well.
The chemicals found in crude oil are mainly hydrocarbons.
They are a family of molecules made form only hydrogen
and carbon. Examples of family members are methane 1) Find a diagram of a
ethane and propane. fractional distillation tower.
Alkanes- are saturated hydrocarbons, they hold as much Annotate it (labels and
hydrogen as possible as there are no double bonds only describe) how crude oil is
C-C bonds separated into fractions.
2) Research the use of Cat
cracking and thermal
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