Temperature
The higher the temperature, the quicker the rate of reaction.
The particles of the reactants receive more thermal energy, which they can convert into kinetic energy. This means they are able to move faster and therefore collide faster.
Light
The more light there is the quicker the rate of reaction.
The particles of the reactants receive more light energy, which they can convert into kinetic energy. This means they are able to move faster and therefore collide faster.
Some reactions only take place on the presence of light.
Catalyst
A catalyst is a substance that can alter the rate of reaction without being chemically changed itself. It uses alternative energy, which is another path of reaction. As a result the activation energy is lower.
Concentration
The higher the concentration of a substance in a reaction the quicker the rate of reaction will be.
I will be using this factor to measure the speed of reaction in this investigation.
Reactions take place when the particles of the reactants collide. When the concentration of a reactant is increased, this means there are more particles of that substance. As there are more particles, there are more chances of collisions taking place. The more reactions that take place, the quicker the speed of reaction will be.
HYPOTHESIS:
I predict that the higher the concentration is, the quicker the rate of reaction will be.
This is because due to previous gained scientific knowledge, I know that the higher concentration of a substance means more particles of that substance. When there are more particles it increases the number of collisions therefore more reactions will take place. If the number of reactions increases it will consequently increase the rate of reaction.
In this case this means the sodium thiosulphate solution particles will have more hydrochloric acid particles to react with.
My results should be similar to the following:
0.5: 4min
0.75: 3 min
1 mole: 2 min
1.5 moles: 1.30 min
2 moles: 1 min
Apparatus:
- 1 conical flask
- 2 test tubes
- Sodium thiosulphate solution Na S O (aq)
- Hydrochloric acid in concentration of 0.5, 0.75, 1, 1.5, 2 moles HCl (aq)
- Paper
- Pen
- Stop clock
Method:
- Collect all apparatus and make sure all bags and books are removed from experimenting area.
- On a white piece of paper draw a clear cross in black pen.
- Place the conical flask on top of the cross.
- In the flask place 20ml of sodium thiosulphate solution and 20ml of hydrochloric acid of 0.5 moles.
- Start the stop-clock and time how long it takes till the cross completely disappears.
- Wash out the conical flask and repeat this with all other concentrations of acid.
- Results should show that the higher the concentration becomes, the quicker the cross will disappear.
Fair Test:
It is essential that this experiment is carries out fairly to give the most accurate results.
- The same cross should be used all the time. – This makes sure that each time the same amount of area needs to disappear every time.
- The same person should do the experiment. – This makes sure the speed is judged equally.
- The person should see from right above. – This gives the best view and makes sure the whole cross is covered.
- The same amount of sodium solution and hydrochloric acid should be used.
- The flask should not be stirred to increase rate of reaction. – This will disrupt the true results.
- The stop-clock should be stopped when the cross is COMPLTELY out of sight.
- The conical flask should be washed out thoroughly after each experiment. – This ensures the sulphur form the previous experiment is gone.
- Must carry out two other tests to improve accuracy of my results.
Safety Test:
This experiment is potential to be hazardous as it involves corrosive chemicals.
- Goggles must be worn during the experiment, as sulphur dioxide will be released.
- Overalls should be worn in case the acid falls on the clothes.
- Hair should be tied back.
- The windows should be kept open to let out the sulphur dioxide.
- All books, coats, bags etc should be kept out the way in case the chemicals fall on them.
Obtaining evidence
RESULTS
Results Table
This table shows the results of my three tests with the averages. As a back up, I have used secondary data along with averages using the same experiment
Analysing Evidence and Drawing Conclusions
The line graph above shows the average times taken for the reaction with different concentrations of HCl.
As can be seen, when the concentration increases, the time taken for the reaction decreases.
The above line graph shows the proportionality between the time of reaction and concentration. It shows roughly the speed of reaction is inversely proportional to the concentration.
CONCLUSION
My results were quite accurate and complied with my prediction.
As expected my results showed that the Hydrochloric acid at 2 moles was the fastest to react and the Hydrochloric acid at 0.5 moles was the slowest to react. It shows the rule of when:
Conc. Rate of Reaction
This is what I predicted in my hypothesis when I said ‘the higher the concentration is, the quicker the rate of reaction will be’.
The explanation of this is because the increase of particles has more active energy; therefore collide easily with the sodium thiosulphate particles. The more particles there are to react with, the quicker the reaction will be.
Evaluating Evidence
I find this method of seeing how concentrations in a reaction affect the rate of reaction is quite a good way. We did not need much equipment as we just needed to use the human eye. Nevertheless, the downside was, it was not a very accurate method. It was difficult to tell when exactly to stop the clock because even after a long time a faint outline of a cross could be made out. Situations such as these do not make the method so accurate.
If I were to repeat the experiment I would repeat all readings again with improved accuracy. I still felt we were not sure about when exactly to stop the cross and I felt we stopped it too early. Each of our results was lower than the expected.
For example, for hydrochloric acid with concentration 0.5 moles took 3.01mins, which should ideally be 4mins.
ANOMALIES
The main anomalies were during the first test, where we stopped the stop-clock too early. We ended up with 2 minutes for the hydrochloric acid with 0.5 moles. As can be seen this affected the averages.
OTHER EXPERIMENTS
To see what else affects the rate of reaction, I could do experiments investigating the other factors like, temperature and surface area. I could do an experiment between hydrochloric acid and limestone to test the surface area factor. This is a more accurate experiment because to measure how quickly a reaction occurred you could measure:
- The volume of the carbon dioxide gas which is a product
- The loss in mass of the reaction in a set time with weighing scales.
