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
                                                            1
Calculations                                      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

                                                               2
Writing 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

                                                              3
Chemical 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

                                                            5
The 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

                                                                    6
Energy, 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!

                                                            7
Reversible 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

                                                               8
Chemical 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

                                                              9
Chemical 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

                                                                10
Cl2 + 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

                                                              11
Oil 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

                                                                    12
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