Prediction:
Through moderate understanding I predict that the greatest concentration of either reactant should equate to a faster rate of reaction (i.e. a greater concentration of reactants should yield the yellow sulphur precipitate faster)
Variables: A B C
INDEPENDANT- Concentration (sodium thiosulphate) 0.15mol/cm³ 0.12mol/cm³ 0.09mol/cm³
D E
0.06mol/cm³ 0.03mol/cm³
DEPENDANT- Time for cross to disappear/substance to turn yellow (secs)
FIXED- Concentration of other reactant (hydrochloric acid) 5cm³
Apparatus:
- Conical Flask
- Measuring Cylinder (50cm³)
- Measuring Cylinder (10cm³)
- Paper
- Stop Watch
Method of Experimentation:
Safety note- the contents of the flask should be flushed down the fume cupboard sink after use.
- Stand the conical flask on a cross drawn on the paper.
- Pour 50cm³ sodium thiosulphate into the flask.
- Add 5cm³ dilute hydrochloric acid
- Swirl the contents of the flask and immediately start the stop watch
- Stop the stop watch as soon as the cross is completely obscured (the time take for this to occur is a measure of the rate of reaction)
-
Waste materials should be poured slowly down the fume cupboard sink with plenty of water. Wash out the flask thoroughly .
- Repeat the experiment using the volumes of sodium thiosulphate, hydrochloric acid and water outlined in the table below.
Diagram:
Before Reaction
After Reaction
Results:
CONCLUSION-
Analysis:
The graph primarily indicates that as the concentration of sodium thiosulphate increases, the time taken for the reactants to react reduces, i.e. a greater concentration equates to faster rate of reaction; thus my prediction was accurately composed. However theoretical analysis illustrates that the concentration of reactants should be indirectly proportional to the time taken for them to react i.e. concentration is linear to 1 .
time taken
My graph/results do not a show an absolute indirect proportionality between the concentration and the rate of reaction (which was indicated by the time taken for the cross to disappear). Therefore the accuracy of my experimentation and readings will be questioned later in my evaluation.
Primitively I have outlined that there was a clear relationship between the concentration and rate of reaction, despite some inaccuracies in my results.
This relationship may be defined according to the readings of the ‘collision theory’ which states:
‘For substances to react, their particles
- must collide
- and with enough energy to break the existing bonds’
Within our investigation, the concentration of sodium thiosulphate was variegated. So as the concentration of sodium thiosulphate increased, there were a greater number of particles. A greater number of particles of sodium thiosulphate equated to a greater number of collisions with the hydrochloric acid particles. Greater number collisions increased the likelihood of them reacting, i.e. ‘breaking the existing bonds’ and thus the time taken for all the reactant particles to react and yield this yellow precipitate reduced.
So therefore the rate of chemical reaction will increase if the concentration of the reactants increases.
Evaluation:
According to theoretical analysis, an increase in concentration should be indirectly proportional with the time taken for the reactants to react. However the results which were obtained show no absolute relationship. This was subsequently due to inaccuracies in the results.
Inaccuracies would have originated from the temperature of the sodium thiosulphate which was used. At the beginning of the investigation and through to obtaining the results for concentration 0.06mol/cm³, the sodium thiosulphate was at approximately room temperature. However the sodium thiosulphate used for obtaining the final concentration was taken out of the fridge and thus was at a much lower temperature. This would have had a huge impact in our results (which has been outlined on the graph).
The amount agitation which was given to the each conical flask as the reactants reacted may project slight inaccuracies in the results
In order to achieve more promising results, the readings should be obtained more accurately (e.g. time for cross to disappear) and set amount of trials should be initiated for each concentration which was investigated. The temperature of reactants should remain constant throughout experimentation.
Unfortunately from the inaccurate results which were obtained we could not draw an absolute firm conclusion. However we were able to equate on an elementary basis, that as the concentration of the reactants increases, the rate of chemical reaction increases.