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Rates of Reaction

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Rates of Reaction Coursework.

Introduction.

In this piece of science coursework I will be experimenting how the
rate of reaction between Sodium thiosulphate and hydrochloric acid is
affected by the concentration of Sodium thiosulphate. I will measure
the rate of reaction by mixing the different quantities of Sodium
thiosulphate (50 - 10cm³) with a fixed quantity (5cm³) of hydrochloric
acid in a Conical flask and placing the flask on top of a white sheet
of paper with a cross clearly marked on it. I will then measure how
long it takes for a chemical reaction to take place. The time might
vary depending on the concentration of Sodium thiosulphate. I will do
this by timing how long it takes for the cross to disappear. I will be
measuring the quantity of sodium thiosulphate and hydrochloric acid I
use, by using a ‘pipette’ and a measuring cylinder, which will allow
me to precisely conduct my measurements.

I will make sure that my experiment is fair by using a different
measuring tube and pipette for each chemical.

Prediction.

I think that the rate of reaction between sodium thiosulphate and
hydrochloric acid will increase as the concentration of the sodium
thiosulphate solution increases. I state this because by increasing
the concentration you’re also increasing the amount of particles in
the solution. If there are greater amount particles then there will
be greater number collisions taking place and so the rate of reaction
increases as well as the temperature. The collision theory explains us
that if a chemical reaction is to take place, the particles in a
substance have to collide into each other with enough energy to break
bonds and hence to form new bonds. In a successful reaction particles
need to collide with enough energy to form new bonds and this releases
energy, this is known as exothermic because energy is being released
into the surroundings.

Scientific Information.

The rate of a reaction is affected by four factors. The four factors
are:

Catalysts, Concentration, Surface Area and Temperature

· Temperature raises the amount of collisions between particles
because it causes the particles to move around more rapidly , and if
they’re moving around more quickly they will collide more often.

· Surface area raises the amount of collisions because if you split a
reactant up into smaller pieces then you will be expanding its surface
area. This means that the particles which are around the reactant will
have more surface area to work on, and this means that there will be
greater amount of successful collisions per second.

· An increase in concentration increases the amount of collisions
between particles because it means that there are greater amount of

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Rates Of Reaction         Taking Place         Rate Of Reaction         Thiosulphate Solution         Chemical Reaction         Collide         Quantity         Sure         Releases        




particles, and there for they will be packed together. This will
result with an increase in collisions because it will be easier for
particles to collide because there are more of them in a smaller area.

· Catalysts also increase the amount of collisions per second because
a catalyst gives particles a surface to attach to, this makes it
easier for them to collide into each other.

The following theories proves to us that temperature, concentration,
and surface area affect the rate of a reaction because.

· Rates of reaction are clearly explained through the collision
theory. It explains to us that the rate of reaction depends on the
amount of times the reacting particles collide with each other and how
hard they collide into. We’re told that particles have to collide with
enough energy for a reaction to take place.

The kinetic theory explains to us that heat energy causes the
particles in a liquid and gas to move around more rapidly, therefore
creating more energy will result in this energy being used to break
old bonds and to form new bonds. We’re told that heat energy causes
the particles in a solid to vibrate extremely quick, this causes the
heat energy to be spreaded out among it’s surroundings, this causes
the heat energy to be transferred in between each particles.

· The particle theory also explains to us that the more particles that
there is present in the same amount of volume the more closer the
particles will be to each other. This means that the particles will
collide more frequently into each other and the rate of the reaction
will increase because there are more reactions per second.

Fair test.

In order for my test to be a fair test I will have look out for the
following things:

· When the cross has disappeared completely out of sight then we know
that a chemical reaction has taken place because when Sodium
thiosulphate reacts with an hydrochloric acid, a yellow precipitate of
sulphur is created. And this yellow substance of sulphur will
eventually make the cross disappear. I should only stop the stopwatch
when the cross has completely disappeared out of sight because that is
when we know that the reaction is complete.

· I will have to be sure of that I use the same size conical flask I
used to measure out the chemicals.

· I will have to be sure of that I use the same cross through out the
entire experiment.

· I will have to be sure of that the measuring cylinders and pipette
that I use for the sodium thiosulphate and hydrochloric acid don’t get
mixed up. If I fail to do this, this will result in that I don’t get
the accurate sets results that i wanted because their will still be
remaining of other chemical particles in the cylinders.

· In order for my results to be valid the experiment must be a fair. I
will use the same standard of procedure each time for judging when
the cross has disappeared. This is judging whether the cross has
disappeared completely our of sight by looking down directly from the
top of the conical flask and immediately stopping the stopwatch when I
am unable to see the cross completely. I will make sure that the
measuring cylinders for the hydrochloric acid (2HCl) and the sodium
thiosulphate (Na2S2O3) do not get mixed up. The amount of hydrochloric
(2HCl) will be 5cm³ each time and the amount of Sodium
thiosulphate(Na2S2O3) will start of with 50cm3 and will be reduce at
each stage by 10cm3 and the amount of distilled water (H2O) will start
of at 0cm3 and will increase by 10cm3 each stage.

· By using the exact Conical flask and paper with a cross marked on it
I will be able to discover a relative measure of the speed of the
reaction in forming the same amount of sulphur.

· I have to make sure that the hydrochloric acid I use remains at a
fixed amount of 5cm³ through out the whole experiment because I am
going to be investigating how the concentration of sodium thiosulphate
affects a chemical reaction and this means that I must only change the
concentration of the sodium thiosulphate.

Safety Precautions.

During my investigation I am going to take the following safety
precautions:

· We should not eat or taste any form of substance. If we have any
contact with a chemical, the part that has made contact should be
washed immediately. Following those rules will prevent us from being
poisoning or have any harm done to us.

· It is vital to keep a certain distance from the chemicals whilst a
reaction takes place, as the outcome is Sulphur Dioxide, which is a
poisonous gas and can be dangerous to us living organism. We should
handle this experiment with great amount of care.

· A pair of goggles will have to be worn during the experiment in
order to protect my eyes from any harm.

· I would strongly advice people to wear an apron to protect their
skin and clothing because it prevents the acid making any sort of
contact with your skin and clothing.

· If you have long hair you will have to tie it back, because it could
be hazardous towards your safety.

· You mustn’t run in the laboratory because it is an extremely
dangerous environment because it has a whole variety of chemical and
if you do run then you might knock chemical or run into another pupil
which can cause a deadly accident or injury to you or other around
you.

· You should never play or mess about with water or squirt chemicals
at other students, as it may make contact with their eyes and skin and
cause irritation or may cause something worse.

· You should always wash your hands after coming in with chemicals for
health, safety and hygiene reasons, so that no chemicals are left on
your skin. Because if there is remains of chemicals on your hands and
you touch your eyes with your hands it may cause temporary blind and
irritation which may lead to a long term effect.

Tools that I have used.

During my experiment I used the following equipments through out the
entire procedure of my experiment, which are:

Tap where we get water from.

Digital stop watch to see how long a chemical reaction takes place.

Goggles for eye protection.

Conical flasks where all the experiment will happen.

Pipette to measure the chemical that we will use.

To measure fluids in cm3.

Pen to use it to record my results on a piece of paper.

Piece of paper with a cross marked on it that I used for my
experiment.

Method.

In order for me to do my experiment I will successfully I will go
through the following steps:

1) I will wear a pair of safety goggles to protect my eyes from any
harm.

2) I will clearly mark a black cross on the middle of a white piece of
paper.

3) I will then place a 500ml conical flask exactly on top of the paper
that has a cross clearly marked on it.

4) I will now measure 50cm3 of sodium thiosulphate using a 100cm3
measuring cylinder and leave it a side.

5) I will now measure 5cm3 of hydrochloric acid using a
10cm3-measuring cylinder and pour it into the conical flask.

6) I shall now have to prepare a stopwatch to measure the time for a
chemical reaction to take place.

7) I will now pour the Sodium thiosulphate into the conical flask and
at the same time start my stopwatch to record how long it takes for a
reaction to take place. When Sodium thiosulphate reacts with an acid,
a yellowish cloudy solution of sulphur is formed.

8) The sulphur solution that is formed eventually blocks the cross and
I then stop the stopwatch.

9) The time taken for the cross to be blocked by the sulphur must now
be written down on my chart.

10) These steps must now be repeated three times using 10cm3, 20cm3,
30cm3 and 40cm3of water and by lowering the volume of Sodium
thiosulphate by 10cm³ each time. However the volume of hydrochloric
acid must stay the same fixed rate of 5cm3 throughout the entire
experiment.

11) Once you have both the preliminary results and the repeat results
in hand, you will need to record them in a table showing how much of
each substance was used and how it affected the rate of reaction
between the sodium thiosulphate and the hydrochloric acid. Then you
must work out the average time for each one.

Diagram steps of how I did the experiment.

Here is what the chemicals look like at the first stage of the
experiment

At this point of the experiment a chemical reaction has taken place.

This is the final stage where the cross has been completely blocked by
the new solution.

Results.

Here is a chart that I have recorded during my experiment.

Sodium thiosulphate
50 40
30
20 10

Distilled water
0 10
20
30 40

Hydrochloric acid
5 5 5 5 5

Time taken for cross to disappear (sec)
57 74
83
110 364

Time 1st repeat
57 75
82
109 363

Time 2nd repeat
56 74
82
109 364

Time 3rd repeat
57 75
83
110 362

Average time
57 75
82
109 363

Analysis.

My results in the table above show the volume of substances, which I
used in my experiment and the time taken for these substances to react
with each other. I have also shown the average time. I repeated the
experiment three times so that my experiment and my results would be
more accurate. My results in the table above proves to us that my
prediction was correct, because I predicted that by increasing the
concentration of sodium thiosulphate it would also result in an
increase of the rate of reaction. The collision theory also proves
that my prediction is correct because it tells us that the rate of
reaction is the amount of collisions between reacting particles in the
particles per second. We already know that by mounting the
concentration there will be greater amount of particles and this means
that they are squashed up more, this will result with more collisions
taking place because of the fact that there are more particles in a
certain amount of area it will be easier for particles to collide with
each other. I have also presented my results in the form of graphs, in
order to make my results more understanding. This will also allow me
to show that my results are similar to each other in a clear way. In
conclusion my prediction was right because my results from the
experiment agree with it.

Evaluation.

My evidence is extremely reliable, I state this because the experiment
was repeated three times and this made the results even more accurate.
For example I know that my evidence was very reliable because as you
can see in the table above, my results were extremely similar to each
other. My evidences were also supported by theories such as the
collision theory and the kinetic theory. There were no irregular
results in my experiment, because they were very similar as you can
see in my graphs.

If I was to do this experiment again I would make sure I repeat my
experiment more times then I did to this one, so that I would have a
higher level of accuracy, and this would be clearly displayed in the
results.



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 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 - 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 pagesbut 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?????????
    153???
    2119???
      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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  • This page should help with rates of reaction coursework projects or assignments investigations


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