Download AS Chemistry Transition Work

Getting Started in AS Chemistry
Chemistry is a fun subject. Now that you’ve chosen to study chemistry in more depth, you
may be feeling rather unsure about starting your AS chemistry course. This is
understandable – it’s a new beginning and we all feel a bit insecure about those! However,
you will be surprised at how much you already know from your GCSE studies, and it’s this
knowledge that is built upon during the AS course. So, it’s important that you remember
your GCSE work; it may be prudent to revise your GCSE studies before starting your AS
course – then you’ll be ready for your new and exciting course.
The following invaluable advice will show you how to work through the AS chemistry
course and, crucially, how to attain a rewarding grade.
What is the AS chemistry course like?
You may have glanced through the specification of your AS chemistry course and many
parts of it, particularly topic titles, may already seem familiar to you. The OCR AS
chemistry course has been outlined for you below. How many of the words and terms can
you recognise from your GCSE science courses?
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The enjoyment factor
Remember, you have chosen to study chemistry for a reason. You may be good at it, you
may like carrying out experiments or you may find the background theory interesting –
whatever your reasons, do enjoy your work. As with most things in life, you get out what
you put in!
What are the main differences between GCSE and AS chemistry?
As we have already discussed, many of the areas covered at AS level are similar, if not
the same, as those covered at GCSE. Furthermore, if you decide to study chemistry or
chemistry-based courses at University, you will find the same pattern. However, it is
essential that you realise that studying AS chemistry is more challenging than GCSE
chemistry; it is more testing in a variety of ways. The main difference is the way in which
you think – from studying chemistry to becoming a chemist!
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You will need to raise your thinking level
Many of the ideas covered at GCSE may have come quite easily to you and
consequently you did not need to work hard at trying to understand them. At AS
level you may find more areas that challenge you, so be prepared to work
harder at furthering your understanding. This will require patience, but will pay
dividends when you crack it and your marks start improving. Making sure you go
over concepts you’re not sure about, reworking notes or using other information
sources are all areas that may help you understand these new ideas.
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There will be more facts to recall
During your GCSE courses you were required to recall certain facts during
examinations and this number increases at AS level. Whether it be the formula
for sodium hydroxide or sulfuric(VI) acid, or knowing a particular use for chlorine,
you will be expected to know these facts and many more besides. This should
not come as a great surprise, since we know the AS course is more challenging
than a GCSE one. So, remembering your chemistry facts is a key area at this
level.
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The amount of chemistry increases
During your AS course you will become more involved in the chemistry
experience. Chemistry has its own language or codes, for example, chemical
formulae and equations. In order to develop a greater understanding of chemistry
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at this higher level, more of the serious ideas that chemists use in their work will
be explored during your AS course. Think of it as learning a new language –
chemists use concepts and ideas understood by other scientists. You will
become familiar with these throughout the course and it is important that you
become confident in using this language, especially chemical equations, since
this is how chemists represent chemical reactions. If you’re a bit rusty on these it
may be wise to revise some of your GCSE chemistry before you start your AS
course. Another area that may benefit from a revisit is chemical calculations, for
example the mole – find appropriate problems to see if you can do the
calculations.
Chemical structure and bonding is a topic also worth revisiting – even good AS
level students can find it difficult to explain why molten ionic compounds conduct
electricity! It’s important to use the appropriate words in the correct context. Is the
question referring to atoms, molecules, ions or electrons? Are you going to
discuss electrostatic forces between ions to explain your answer or
intermolecular forces between molecules? It is important to realise which terms
to use in which context. Of course, you may find, as many do, that things just
click into place once you start your new course.
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There will be a greater expectation of your advanced skills
For example, your skills in applying what you know to unfamiliar areas will be
assessed in examinations. This is an area that many students find daunting at
first. You may only have experienced examinations that test what you have
been taught and know. However, as you progress through higher educational
levels examinations will begin to test your ability in applying your understanding
to unfamiliar areas. In our case, for example, the chemistry of ant stings, sun
creams, poisons and pharmaceuticals.
You may find this difficult at the beginning, but as you practise questions you
will find it becomes easier and your marks will improve. As with anything we’re
unfamiliar with patience and dedication help us get it right in the end! It is also
important to be able to discuss areas from other modules throughout the AS
and A2 specification. You will need to apply AS ideas and contexts covered in
the first AS module to other modules both at AS and A2 levels. So try not to box
things up and forget them, because you will need to revise all key areas before
you sit the rest of your papers.
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There is a greater emphasis on practical skills
You will already have carried out chemistry experiments, often a part of the
course that many students enjoy. You may be used to being assessed in your
practical work during your GCSE course, and this may have counted towards
your final grade. It will be the same during your AS course. Again you will be
asked to carry out various experiments, but this time you will be expected to
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think about these experiments at a higher level than previously. As with GCSE,
you will have plenty of practice in this vital area and your practical skills will
improve as you gain in confidence. You can use the 'Build Your Practical Skills'
section of this CD to help you as well. Remember that the practical assessment
component is worth 20% of your total grade – this is worth a couple of grades,
so recognise the importance of your practical components!
To summarise:
Deeper THINKING regarding new concepts and proper PREPARATION in how
you work within your AS course – get these right and success should follow.
Using a different approach at AS level
This is probably the most important concept for success in your AS chemistry course.
Remember that you need to earn your success – it does not just happen! However you
decide to work throughout the course, the biggest challenge can be sticking to your work
routine for the whole academic year.
At GCSE you achieved success by revising and preparing well for tests and exams; the
same is true at AS. However, there is more to learn and there are more ideas to
understand, so it is important that you not only work hard for the tests but develop a work
routine that you stick to throughout the course.
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When can you work?
We all have days in which we are busy at certain times and free at others.
Whenever you are free, you must learn to work smart and make the most of
your free time. If you make sure that it becomes a regular occurrence, i.e. a
habit, you will develop a routine way of working. It is always easy to put off work
– everybody does it! However, if you timetable your AS chemistry work you will
find it easier to stick to a plan that works and thus continues. For example, you
may be free on Monday, Wednesday and Friday evenings from 7 to 9 o’clock, so
you timetable the AS chemistry work you’ve been set for this free time. But if you
have enough time you could also do extra work – the work that really makes a
difference. Successful students are those who develop a work routine in their
own time, so they are able to enhance their learning. This is independent
learning.
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How do you work throughout the course?
This may seem a strange question – surely the fact that you are working harder
will automatically make a difference? Well, this is not always the case; you may
have been unable to find a method that works or you could have improved the
way you worked. Many students revise by reading a textbook and assume that
they will magically get better results. Why not reflect on how you worked and
revised at GCSE – do you think that it is a method that is right for you? Was it an
interesting way to work? Did you feel engaged with the material? It isn’t easy to
sit on your own and work through the AS chemistry course without finding some
of the work difficult.
You must try to make your work routine as interesting as possible by engaging
with the work. How many times have you read a page from a textbook and after
a few minutes can’t remember anything you’ve just read? Don’t worry, this is
very common! However, you may find that when you go shopping, just by writing
a list of the required items is enough to remember them by – you often don’t
need to refer to your list at all! What does this everyday example reveal about
the way in which we learn?
You must make your learning as interactive as possible and do as much as you can
with the information that you are trying to remember
Most people learn about 10% of what they hear, about 20% of what they read,
about 60% of what they read and write and about 80% of what they read, write
and say! As a teacher myself, I discovered that I only understood something
when I had to explain it to someone else. It is easy to fall into the trap of thinking
that we understand something well once we’ve worked on it; however, try to
explain it to someone else and you may be unpleasantly surprised! If you have a
friend who is also studying AS chemistry try to pair up while revising and test
and explain concepts to each other. This approach works really well and can be
highly motivating.
So, work smart, don’t just work!
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How do you remember facts?
During your AS chemistry course you will come across many more facts and you
must find a way to remember them. Unfortunately, there is no single method for
remembering these facts that works for all students; you must find a method that
works for you. Remember, that the more you do with the information, the more
likely you are to remember it. For example, how to learn the AS organic
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reactions of alkenes? What reactions do you need to know? This is where your
AS specification will come in handy. Consult it to find out which reactions are
important, i.e. reactions with hydrogen, hydrogen bromide, bromine, steam and
polymerisation. Now, how to remember them:
(a) Writing and blanking out
This method works for some students, but not all. Firstly, copy the
reactions from your notes. Now cover them and see how many you
can rewrite correctly from memory. There may not be as many as you
first thought! Look at your notes again and repeat the process. You
will find that by practising this process you will start to remember more
of the reactions. It may seem hard work initially, but it will be worth it in
the long run. To reinforce your memory you should re-test yourself the
following day to see how much you can remember. Re-test again
three days later and again after seven days. Increasing the time
difference between the tests will aid your long-term recall.
(b) Using coloured pictures
When information is presented in sentence form it is not always easy
for the brain to process and remember. Presenting the information in
different and more interesting ways may aid you in remembering it.
For alkene reactions you could draw a spider diagram using a
different colour for each reaction. Sticking this coloured diagram on
your wall will also help you remember the information as you’ll see it
every day, rather than it being tucked away in a file. You may find that
the position of each reaction on the paper, along with its unique
colour, makes it easier for you to remember.
(c) Sharing your information
As mentioned earlier, it is also helpful if you can pair up with a fellow
AS chemistry student or a family member and test each other. For
instance you could test each other on:
(i)
the structure of a propene molecule;
(ii)
the structure of the product(s) formed when propene reacts
with hydrogen with a nickel catalyst; hydrogen bromide; or
bromine.
Try using flashcards and draw a molecule’s structure with its name on
the reverse, then try to work out the molecule’s name. Your aim is to
score more than 8 out of 10! Make it a challenge – aim for something
that may motivate you, for example, a personal best score on naming
alkenes or for working out reaction products.
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Why not use previous examination papers?
These are available from OCR or your teacher, as s/he will have access to
them. However, make sure that you are using papers that are appropriate for
your course since courses may vary in content, and if your course is new very
few appropriate papers may exist other than specimen papers. The Exam Cafe
CD has example questions and answers that you can practise on and that will
help improve your understanding of the chemical concepts. You can see how
you do by using the mark schemes provided. When you’re comfortable with your
AS chemistry knowledge, it is essential that you test your understanding by
trying some AS questions, just a few at a time. Don’t forget, your marks will
improve as you practise more questions. Try and ensure that you have access
to an examiners’ mark scheme – this shows what the examiner is looking for.
Sometimes mark schemes have their own unique criteria, for example, in the
definition for le Chatelier’s principle – different examination boards may expect
slightly different definitions. So ensure you know what OCR requires and don’t
just go by the definitions you find in general texts.
Hopefully you should now have surmised that it is important to practise – grades do not
just happen, they are earned. Successful students practise questions to see whether they
understand as well as know their chemistry – they are genuinely concerned with their
progress. Furthermore, the natural emphasis at AS level is more on the student than it was
at GCSE, so try and do some extra chemistry work each week – a type of drip-feed
approach which you routinely stick to throughout the course. The result will be a grade that
you can be proud of and, perhaps more importantly, help you progress to A2. However,
remember that whilst you are working hard you should also try to analyse how you are
working. Work as effectively as you can in the time available and ensure your extra work
makes a real difference.
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My action plan
What I need to do to make sure I am ready for my AS studies
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What do I already know?
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What are my strengths and weaknesses?
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What do I need to do before my AS course starts?
1. Make notes/ show evidence of the following:
Revise ionic/covalent/metallic bonding and structures
Revise writing and balancing chemical equations
Revise atomic structure and electron configuration
Revise mole calculations
2. Complete the following numeracy tasks
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AS Chemistry transition numeracy tasks
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a) Calculating Relative Masses
The relative atomic mass (Art) of an atom is shown in the periodic table, usually at the top,
it is the larger of the 2 numbers given (the other is the atomic number).
It is called relative because the mass does not have units, it is the mass compared to 12C
isotope.
Find the Ar of 1) Sodium, Na
2) Zinc, Zn
3)Carbon, C
4) Sulphur, S
The molecular or formula mass (Mr) is found by adding up the Ar values of the atoms
present
e.g. 1) O 2 (oxygen)
contains 2 O atoms.
Ar of O = 16,
Mr = 2x16 = 32
2) H 2 O (water)
contains 2 H and one O atoms.
Ar of H=1, Ar of O =16
Mr = 2x1 + 1x16 = 18
3) Na 2 SO 4 (sodium sulphate)
contains 2 Na, 1 S and 4 O atoms
Ar of Na = 23, Ar of S =32, Ar of O=16
Mr = 2x23 + 1x32 + 4x16 = 142
4) Mg(NO 3 ) 2 (magnesium nitrate)
contains 1 Mg, 2 N and 6 O (the 2 at the end of the bracket doubles the atoms inside)
Ar of Mg =24, N=14, O=16
Mr = 24 + 2x14 + 6x16 = 148
Find the Mr of
H2
C2H6
CO 2
CaCO 3
NaCl
NaNO 3
P2O3
Ca(OH) 2
H 2 SO 4
Pb(NO 3 ) 2
b) PERCENTAGE OF AN ELEMENT
To find the percentage of an element
1) Find the mass of all the atoms of the required element
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2) Find the relative mass of the whole compound (Mr)
3) Divide 1) by 2) and multiply by 100
% of Element = Mass of all atoms of Element x 100
Mr of Compound
Example
Find the % of iron in Fe 2 O 3 (Mr: Fe = 56, Fe 2 O 3 = 160)
Mass of 2 Fe atoms = 2x56 = 112
Mr of Fe 2 O 3 = 2x56 + 3x16 = 160
% of iron in Fe 2 O 3 = 112/160 x 100 = 70%
Or % of iron in Fe 2 O 3 = 2x56 x 100 = 70%
160
Find the % of C in CO 2
Find the % of H in H 2 O
Find the % of Zn in ZnCO 3
Find the % of Mg in MgCl 2
Find the % of Pb in PbO 2
Find the % of Cl in MgCl 2
Find the % of Pb in Pb 2 O 3
c)
PERCENTAGE YIELD.
When a substance is made by a chemical reaction, you do not always get as much as you
expected.
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This can be for a number of reasons:
1) Some of the material is lost in the experimental process.
2) An unwanted reaction takes place, giving you less of your product.
3) The reaction is reversible.
The percentage yield compares the mass you actually get with the amount you expected
to get under ideal conditions.
Percentage Yield = Mass obtained in Experiment x 100
Expected Mass
e.g. Ebenezer expects to get 4.6g of alcohol from his experiment. The actual mass
obtained was 3.5g. Find the % yield.
Answer = 3.5 x 100 = 76.1%
4.6
Priscilla is making some exclusive perfume. She expects to get a maximum of 10.6g from
her procedure, but only manages to get 7.1g. What is her percentage yield?
Answer = 7.1 x 100 = 67%
10.6
Complete the following
Mass obtained from
experiment
Expected Mass
10g
20g
2.5g
12.5g
1.7g
5.1g
25kg
18.5kg
Percentage Yield
d) FINDING THE EMPIRICAL FORMULA OF A COMPOUND
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The empirical formula of a compound shows the ratio of the atoms in it. If we can find the
mass of each element present, we can convert this to numbers of particles and find the
ratio. This will give us the empirical formula. Note that the empirical formula only gives us
the ratio of atoms, while the molecular formula tells us the actual number of atoms.
e.g
Molecular Formula
Empirical formula
H2O2
HO
C2H4
CH 2
C2H6
C 4 H 10
K2O2
C 6 H 12 O 6
Rules for Finding an Empirical Formula
a) Write the symbols for the elements present.
b) Find the mass (or %) of each element present in the compound.
c) Find the relative mass of each element from the Periodic Table
d) Divide the mass of each element by its relative atomic mass to give ratio or atoms.
e) Divide each number in the ratio by the smallest number to get a whole number ratio
f) This gives the empirical formula, i.e. the ratio of atoms in its simplest form.
Example
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20g of a compound of Silicon with hydrogen contains 17.5g of silicon. Find the empirical
formula.
Element
Si
H
17.5
20-17.5 = 2.5
28
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Mass ÷ Ar
17.5÷28 = 0.625
2.5÷1 = 2.5
Divide through by
smallest.
0.625 ÷ 0,625 = 1
2.5 ÷ 0.625 = 4
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Mass of element
present
Relative Mass (Ar)
Whole Number Ratio
Empirical Formula
SiH 4
Percentages can be used in place of masses
A compound contains Na 33.3%, N 20.3% and O 46.4%. Find its empirical formula:
Element
Na
N
O
33.3
20.3
46.4
23
14
16
Mass ÷ Ar
33.3÷23 = 1.447
20.3÷14 =1.45
46.4÷16 = 2.9
Divide through by
smallest.
1.447÷1.447 = 1
1.45÷1.447 = 1.002
2.9÷1.447 = 2.004
1
1
2
% of element
present
Relative Mass (Ar)
Whole Number
Ratio
Empirical Formula
Na NO 2
EXERCISES
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Find the empirical formulae of compounds containing:
(useful Ar values: S=32, O=16, Mg=12, Br=80, K=39, C=12, H=1)
a) 24g of sulphur and 36g of oxygen
b) 3g of magnesium with 40g of bromine.
c) 54.9% potassium with 45.1% oxygen
d) 6g of carbon with 2 g of hydrogen
e) 52.1% carbon, 13% hydrogen, 34.9% oxygen.
e) 1g of a compound of hydrogen and oxygen containing 0.0588g hydrogen.
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