Rate of Reaction Lab Report

Equipments:

-thermometer

-white paper

-0.28mm black ball pen

-water

-Hydrochloric Acid (HCl)

2 moles, 1 mole, 0.5 moles, 0.25 moles (50ml each, 10ml spare)

- Sodium Thiosulphate(Na2S2O3) solution:

0.1 mole (around 200ml, 40ml spare)

-80 ml beaker

-two 100 ml measuring cylinders (one for HCl and the other for Na2S2O3)

-glass (to put the waste materials)

-stop watch

Procedure

1. All the upper mentioned equipments should be set up.
2. Measure the temperature of the hydrochloric acid and sodium thiosulphate solution: 20°C in our case.
3. Take the white piece of paper and use the 0.28 mm black ball pen to draw two perpendicular lines that are 3cm each. This should look like a cross in the end.
4. Put one of the 80ml beakers on top of it.
5. Use the 100ml measuring cylinder to measure 20ml of sodium thiosulphate solution.
6. Pour it into the 80ml beaker on top of the cross.
7. Measure 20ml of 2 mole hydrochloric acid with another 100ml measuring cylinder so that the solutions do not get mixed.
8. Get the timer ready.
9. Pour the hydrochloric acid into the sodium thiosulphate solution and start the stop watch.
10. One person determines when the reaction is over. This is when the cross cannot be seen anymore due to the color change of the acid.
11. Stop the time watch when the reaction is over and record the time.
12. Pour the waste solutions into the glass and rinse the beaker for the next experiment.
13. Repeat the step 4-12 should be repeated once more for the 2 mole hydrochloric acid.
14. The entire process (4-13) should be repeated for 1 mole, 0.5 moles and 0.25 moles hydrochloric acid. (Also, remember to rinse the 100ml measuring cylinder for the hydrochloric acid between each experiment when the concentration is changed)

Results

Calculations

First of all, the mean of the time of reaction for each hydrochloric acid should be found. The equation used is:

Then using the equation in the introduction, this should be changed into the rate of reaction. The results will be rounded off to 4 decimal point so that the results are more accurate but not too detailed.

The actual calulations:

-2 moles

Mean: ( 18.0 + 19.4 ) / 2 = 37.4 / 2 = 18.7

Rate of Reaction: 1 / 18.7 = 0.0535 (4 d.p)

-1 mole

Mean: ( 20.1 + 19.7 ) / 2 = 39.8 / 2 = 19.9

Rate of Reaction: 0.0503 (4 d.p)

-0.25 moles

Mean: ( 22.2 + 23.4) / 2 = 45.6 / 2 = 22.8

Rate of Reaction: 0.0439 (4 d.p)

-0.5 moles

Mean: (26.4 + 24.6 ) / 2 = 51.0 / 2 = 25.5

Rate of Reaction: 0.0392 (4 d.p)

Conclusion

Looking at my results, it seems that my hypothesis was supported since the line of best fit is showing a positive slope. As the concentration of hydrochloric acid increased, the time of reaction decreased. And when it was put into the equation of ‘1 / (time of reaction)’, the decrease in time of reaction meant the increase of the rate of reaction. According to the collision theory, if there are more collisions in a system, more successful combinations of molecules are likely to happen and the more substance there is in the system, the more collisions there will be. Therefore, as the graph on the right shows, the higher the concentration, the more collision there are and thus, the reaction rate is higher.

Evaluation

     I believe that our experiment was quite accurate but there were some places where changes could have been made.

Random Errors

Most of the random errors we had were related to the inaccuracy of measuring equipment. For example, the timer we used had 0.05s error range and the thermometer was ± 1 °C. Also, the 100ml measuring cylinder was ±0.5ml. It would have be hard to improve the equipment though because the measuring cylinder used was A class and the timer’s error is so minor that it does not have a big impact to the result. But what we could have done is to use the pipette, which has a less error range. Also, a digital thermometer could have been used as they are known to be more accurate.

Additionally, it would have been better if the experiment was done one more time for each concentration of hydrochloric acid. In this lab, the experiments were done only twice so I had to use all the data to find an average. However, if it was performed once more, the first record would have not been a part of the average. This would have made the lab more reliable since there is likelihood that the first experiment may be an anomalous data.

Systematic Errors

     One of the systematic errors we had was that we did not know, for sure, when the reaction was over. Although we did draw a cross below the beaker and a specific person to detect when the cross cannot be seen anymore, it did not seem that accurate enough. A better way of figuring this out would have been by sending light through the beaker with a detector on the other side. This way, we will be able to measure the amount of light passing through the beaker which tells how much the colour of the solution has changed.

Another systematic error was that the temperature might not have been constant throughout the experiment. We set the temperature as room temperature so there could have been some small fluctuations. A more accurate way would have been by using the water bath to arrange a constant temperature.

     

I think that our results were quite reliable in general since there were no anomalous data and we followed procedures orderly. But the results could have been improved with the methods suggested above.

Some other related possible experiments can be suggested by using one of the controlled variables as the independent variable. Since rate of reaction also depends on temperature and presence of catalyst, it would be nice to test them by using the same experiment. (The surface area is one of the factors affecting the reaction rate as well but it is more effective when one of the reactants is solid so it is not relevant in this case with liquid solutions) I would also remind the fact that for the following experiments the concentration of hydrochloric acid used should be the same all the time.

Other Possible Experiments

1. What is the relationship between the presence of catalyst and the rate of reaction?

-This can be done by putting different amount of catalyst in the hydrochloric acid and sodium thiosulphate and measuring the time of reaction.

2. What is the relationship between temperature and the rate of reaction?

-This can be done by putting the beaker of sodium thiosulphate in a hot bath with different temperature and measuring the time of reaction.

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