 Doc Brown's
Chemistry KS4 science GCSE/IGCSE Revision Notes
A BRAINSTORM on "Rates of
Reaction" for chemistry coursework investigations-projects
Ideas for coursework
assignments or projects involving the rates or speed of chemical reactions and
is a companion page to see
All my
GCSE Chemistry Revision
notes
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This is a BIG
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also the
DETAILED GCSE Revision Notes on the Factors Affecting
the Rates
of Chemicals which also has brief
descriptions of experimental methods and equations, particle pictures and fully
explains all the factors affecting the rate of a chemical reaction
Advanced level chemistry theory pages for
GCE/AS/A2/IB and adventurous GCSE students!
and
A few health and safety
ideas on risk assessment
AIM for a high investigation-project mark
('lab' mark) - you have nothing
to lose for your assessment!
e.g. suppose you are investigating the effect of
hydrochloric acid concentration on the rate at which the acid dissolves limestone (calcium
carbonate)
- BUT you can use and extend these
'brain stormed'
ideas to most rates of reaction coursework assignments
e.g.
- The magnesium/zinc + acid
reaction, you can investigate acid concentration and amount of metal
and the zinc
reaction is catalysed by copper and other ions in the acid).
Decomposing hydrogen peroxide with a solid
catalyst or soluble transition metal compound.
Enzyme catalysed reactions e.g.
decomposition of hydrogen peroxide solution by catalase
(can
tricky at GCSE level).
The sodium
thiosulphate-hydrochloric acid reaction, you can investigate the effects
of temperature and concentration. (as
far as I know sulphur formation is only catalysed acid)
and these reactions get a
mention here and there and don't forget to pre-study the
rates
of reaction revision notes, lots of theory and
descriptions of experimental methods and graphs etc.
WARNING:
Your write-up must be
your
work produced from your study and your experiments.
- This web page
is
meant to teach you how to tackle an coursework e.g. on rates, it is not meant to be
copied and the details filled in! Your coursework write-up must expressed in your
language and expressed at 'your scientific level'.
- Your teacher will have a
good idea what to expect and you must be able to justify all your write-up. Use the
sources/references mentioned below and clearly indicate them in your write-up.
- More
marks are lost by not writing things down, than by not doing experiments!
Your write-up must be your
work produced from your study and your experiments.
This web page
is
meant to teach you how to tackle an coursework e.g.
on rates, it is not meant to be
copied and the details filled in!
- Your coursework write-up must expressed in your
language and expressed at 'your scientific level'. Your teacher will have a
good idea what to expect and you must be able to justify all your write-up.
- Use the
sources/references mentioned below and clearly indicate them in your write-up. More
marks are lost by not writing things down, than by not doing experiments!
-
EMAIL
a query or comment on the rates/coursework ideas pages but I do
NOT do students
coursework for them, neither do I replace your teacher supervisor!
however I sometimes get really interesting questions and learn something
new myself - and that's always a pleasure!
A BRAINSTORM outline of a whole
investigation is outlined below, it is not meant to be prescriptive, but can form the
basis of aiming for a high mark and hopefully give you plenty of ideas.
- For sources and references you should research 'rates of reaction' for theory,
experimental methods etc. using textbooks, the Internet, and of course your class work
and
exercise books and mention your research sources in your coursework report AND QUOTE YOUR
RESEARCH SOURCES and ANY PREVIOUS 'RATES' EXPERIENCES
- Any previous 'rates of reaction' experience is invaluable and can be used/quoted
in your write-up - particularly knowledge of experimental methods which can count as
preliminary work.
- Word process your work if you can and your results can be tabulated and
processed into graphs using software packages like Excel
-
Preliminary work usually involves doing a few trial runs of the
experiment to see how it goes and making modifications if necessary.
By writing up how, and why, you have changed the experimental conditions or
'recipes' you can gain more marks.
skill P: Planning - the theory and your experiment design!
First, you can start by describing the reaction
situation you are intending to investigate e.g. with the word and symbol equation,
short description about the reaction, and this sets the scene.
- If you are confident and chosen the VARIABLE you want to investigate you should try to
make a prediction and maybe justify it with some theory if you can.
- You can continue in a broader context by introducing some background theory and
descriptions of the factors or VARIABLES which may have an effect on the rate of
the reaction you are studying (include briefly factors which might not apply). In your
'method' description use the correct units or descriptors.
- The factors to discuss might be
... amount of limestone?, temperature of reactants?, acid
concentration?, volume
of acid?, size of limestone pieces? (relate to surface area?), stirring of the reacting
mixture, size of reaction vessel, volume of thiosulphate, any added water to
dilute etc.
- Is there any other factor for the reaction you are studying?, will
any of the reactants or products be affected by change in temperature or pressure?
e.g. there are several reasons why the same acid should be used if its a
reactant in the investigation, e.g. (1) its the hydrogen ion, H+(aq),
is the active ingredient that actually 'attacks' the metal or carbonate, and acids can ionise to
different extents, (2) 1 molar or 1 mol dm-3 (1M) H2SO4 is twice as acid as 1M HCl because each
H2SO4 provides 2 H+'s whereas each HCl just 1.
- If you have decided, for example, to investigate the effect of acid concentration on the
speed of a reaction, then everything else should be kept constant for a fair test, and
this should be obvious in your plan for the reasons discussed above!
- If you haven't already chosen the VARIABLE, do so now, and make a prediction and justify
it with some theory which you may have previously described and should refer to.
- Next you should describe initially, but briefly, some methods for following the
reaction = measuring the speed of the reaction. If a gas is formed, there are
at least two ways of collecting a gas e.g. initially empty gas syringe or a
measuring cylinder/burette full of water inverted over water with appropriate
tube connections and there is one other very different method
available for 'following' the reaction using a balance to record the mass
loss.
- The hydrochloric acid - sodium
thiosulphate reaction depends on the time for a certain amount of
sulphur precipitate to form and obscuring a marked black X on white
paper.
- Briefly
explain how
the method can be used to measure the speed - the
results of the first few minutes is usually the most crucial - you can
discuss (briefly) other methods, but perhaps better in evaluation as a means
of further evidence.
- When you have decided on the method, give a detailed
description of how you might carry it out. Include details of the amounts of chemicals you
might use mass, volumes, dilutions + UNITS etc. etc.
- Clearly indicate why the method would be expected to produce precise and reliable
evidence - the results!
- Include 'health and safety' points.
- If you are looking at changing the reaction
temperature, its not easy to accurately vary and control the temperature of
the reactants without a thermostated water bath to hold the reaction flask
in. Even with a thermostated water bath (normally only available to advanced
level students), all the reactant solutions should be pre-warmed in the bath
before mixing and start the timing and recoding of results.
- If you are varying temperature, you
need to heat up the reactant solutions separately and take their temperatures,
mix, start stopwatch. However, they will cool a little standing out in the
laboratory, so not completely satisfactory solution to the problem. In the
case of the sodium thiosulphate - acid reaction, you can leave the thermometer
in the flask and take the temperature at the end, then use an average for the
temperature of the reaction.
- If temperature isn't a variable, it
must be kept constant. The simplest solution here, is to make sure all the
chemicals have been standing in the laboratory prior to the lesson. Then, they
will all be at the same temperature, which should be recorded. If more
experiments are conducted at another the time, the temperature must again be
checked and recorded.
- Refer to any previous laboratory experience with 'rate of reaction' experiments which
may have helped you decide and design the experimental method.
- A clearly labelled diagram of the method with a brief outline of how you intend to carry
out the experiments - this cuts down on the writing and makes the scene clear!
- You must give details of how long you might time the experiment as well as the
time interval between experimental readings
- REMEMBER you can change your 'recipe' or way of doing the experiment. If you have to
change anything, describe and explain the changes you have made to the procedure (some of
this might count as valuable marks for the EVALUATION skill)
- AND
DON'T FORGET AT ALL TIMES QUOTE THE CORRECT UNITS in P, O, A or E.
skill O: Obtaining evidence - observations, measurements,
in other words the results! (possibly some data you might have been given)
These must be clearly recorded in neat tables
showing all the units e.g.
Run 3: acid concentration ?????,
temperature ???? |
Time ???? |
Gas volume ???? |
Gas volume ??? (repeat) |
corrected gas volume ??? |
0 |
??? |
??? |
??? |
1 |
5 |
3 |
??? |
2 |
11 |
9 |
??? |
You can produce a summary table with the
average/corrected (if necessary) gas volumes v time for all the different acid
concentrations or whatever variable
- For the hydrochloric acid - sodium
thiosulphate reaction you are recording just the reaction time for
different thiosulphate or acid concentrations or temperatures, so the data
gathering and subsequent processing is 'simpler'.
- All experiments should be repeated where time allows to check for accuracy and
consistency, this may become more necessary after you have done a preliminary analysis
- The 'bung effect'! - look up about dead volumes and its correction when dealing with gas volumes!
- Your recorded results should indicate the accuracy of the measuring equipment
e.g. 0- 2
decimal places.
- Some of the work done here in presenting the results,
e.g. working out averages etc.
actually counts towards the mark for analysing (described below).
- Have you got enough results, do they seem ok? Starting the analysis as soon as possible
will help you decide whether further, wider ranging or repeat experiments -
best decided after examining the graphs of results (see below) - difficult to decide just
looking at tables of data.
skill A: Analysing and considering the evidence - what do
the results mean in terms of your prediction and theory!
The results are initially processed into graphical
form ('graphing') for several reasons for both the analysis and evaluating the experimental ....
they can clearly show the general trend of the effect of changing that factor or variable,
highlighting experimental 'runs' that don't seem to fit the pattern of the other sets of
results for the other runs, individual points that don't seem the pattern of a particular
sets of results - BUT ITS UP TO YOU
- Ideally you should plot the average(*)
corrected gas volumes on the y axis and time on the x axis - what should the origin
be? (* May depend on the consistency of your results).
- For the hydrochloric acid - sodium
thiosulphate reaction you can plot either (i) reaction time, or (ii)
1/time versus a concentration or temperature (1/time = relative rate of
reaction).
- It is best, if possible, to have all the average results points plotted on the
same graph for easy comparison - take care because this may involve 4 or 5 lines for 4 or
5 different acid concentrations
- Make sure you use a clear KEY for the different line points and a clear title for the
graph AND clearly label the axis including the units or whatever ..
-
Use smooth 'best curves' for as many of the points as possible, though some parts of the
graph might be linear, watch out for the 'scatter' - the experiment is not that easy to
get good results.
-
From the graph you can then describe in words what the results mean, always refer to the
graph lines and gradients directly - don't make vague comments.
-
So what we are after is the main 'trend(s)' or 'pattern(s)' describing with reference to
the graphs.
-
Does the 'trend' of all the graph lines support you're your prediction, are all the
results consistent with your prediction AND theory?
-
For different the acid concentrations you can do a 2nd and more advanced
graphical analysis of the limestone results. This involves measuring from the graph, the speed of
the reaction at the start. Explain why best data at the start? (i.e. first 3-5
mins?).
- What graph could you then plot?...
where does the graph line start?, origin?, what is the 'shape' of the graph? is it
a better way of showing consistency (or inconsistency!) in your results?
- We are basically talking about plotting
the initial rate versus e.g. acid concentration.
- If you are doing something like the
hydrochloric acid - sodium thiosulphate reaction, your reaction
time measures the formation of a fixed amount of sulphur per
'time'. So the rate is 'x amount of sulphur per time', which means the
speed or rate is proportional to 1/time, then plot this 1/time against
the concentration of the acid.
- From this graph
re-discuss your findings in a more mathematical way and relate this to the particle
collision theory of reactions! It's all about chance! and explain why/why not the
results support your prediction.
skill E: Evaluating - and how good are your results then?
error sources? can we improve the existing method? are there other experimental methods?
Do your results seem consistent and accurate -
always refer directly to the graph or graphs in your analysis ... do any of the sets of
results not fit in with the others?, do most/all sets of results fit a pattern?, are there
any particular points that don't fit the pattern? (anomalies), can some results be ignored
in drawing your conclusion(s)? if so, which results and why? QUOTE DIRECTLY - WITH
REFERENCE TO YOUR GRAPH(s)
- Discuss possible sources of error which might lead to inconsistent results
i.e. points or
sets of results that don't fit the pattern AND how could the method be improved to
minimise these sources of error ... e.g. chip size? ,temperature or pressure checks for each
experiment? dead volume?, ? gas syringe operation? draughts? where these or any other
factor OK? in other words how suitable was the method overall? Do think the results are
reliable bearing in mind any anomalies?
- For the hydrochloric acid - sodium
thiosulphate reaction think about the precipitate, observing it etc.
- What further experiments, using the same method or another method, could be done to
support your prediction or conclusion? In other words give some detailed ideas on further
work that would provide additional relevant evidence.
- e.g. in the case of the sodium
thiosulphate - hydrochloric acid experiment , you can use a light gate
to detect the precipitate formation. The system consists of a light beam
emitter and sensor connected to computer and the reaction vessel is
placed between the emitter and sensor. The light reading falls as the
sulphur precipitate forms.
- Keeping the temperature constant is
really important for a 'fair test' if you are investigating speed of
reaction/rate of reaction factors such as concentration of a soluble
reactant or the particle size/surface area of a solid reactant. On the
advanced gas calculations page, temperature sources of error and their
correction are discussed in calculation
example Q4b.3, although the calculation is above GCSE level, the
ideas on sources of errors are legitimate for GCSE level.
- Note that if the temperature of a
rates experiment was too low compared to all the other experiments, the
'double error' would occur again, but this time the measured gas volume and
the calculated speed/rate of reaction would be lower than expected.
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