Set up the equipment as shown:
Preliminary results:
With this mass of chips the experiment far too slowly, and the lower concentrations would take far too long. I think that it would make the experiment go faster if I had more chips with a higher mass. This would make the experiment run faster, especially at the lower concentrations.
With this mass and number of chips it makes the experiment run in a reasonable amount of time. I have decided to use the following values for my main experiment:
- Number of limestone chips – 10
- Mass of limestone chips – ≈2.5g
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Volume of Hydrochloric acid – 20cm3
- Temperature – Room Temp
I will also make some changes to my experiment to improve the quality of my results:
- I will use an inverted burette for my main experiment so I can get more accurate results.
- I will record the progress of the experiment every 10 seconds so I can make a “progress curve” graph so it is easier to compare the different reactions and calculate the rate of reaction.
Main results:
Set 1:
Set 2:
Set 3:
Average rates:
I can work the rate of the reaction out by finding the initial gradient of the lines on my volume/time graphs:
Gradient=Rise/Step so Volume/time=average rate.
I will use the initial gradient because this shows the reaction at the start, so there will be more unused reactants and more products. This will make my rate values more accurate.
Set 1:
Set 2:
Set 3:
Conclusion:
My volume/time graphs show that the 2.0 mol/dm3 concentration was the fastest, and the 0.4 mol/dm3 concentration was the slowest. Also on the volume/time graphs, there is a gap between the y-axis and where the lines-of-best-fit start – a time lag. This is because it takes a few seconds for any CO2 produced to reach the top of the inverted burette.
The volume/time graphs also show a curve. This is because the reactants (limestone and hydrochloric acid) are being used up so there are less particles so a lower probability of collisions. This would result in less products.
Using the gradient from my volume/time graphs I could then work out the rate of reaction. On my rate/concentration graphs it showed that as the concentration increases, the rate increases. This is because of the collision theory – there are more particles in a the same space so there is a higher probability of collisions.
This proves my prediction correct.
Evaluation:
Of Method:
My method allowed me to complete the investigation successfully because I could get a large amount of results so I could identify anomalies and get more reliable sets of results.
My method was not perfect however, as I used a different set of limestone chips each time, making the surface area would be different.
This would affect my results because if there is a larger surface area, then there is a higher probability of a collision , so the reaction would happen faster (collision theory).
To solve this problem I could use cubes of limestone, as this would make it a lot easier to keep the surface area the same, so the results would be more accurate. This is because roughly the same amount of limestone particles are able to collide with the hydrochloric acid so the only factor affecting the rate of the reaction would be the concentration.
I could improve my method by using a wider range of concentrations, e.g. 2.4 mol/dm3 or 0.6 mol/dm3. This would make my method better because I could get a wider range of results so they would be more reliable. This would also help support my conclusion.
I could extend my investigation by controlling the temperature of the reaction by using a water bath. This would able me to investigate how temperature affects the rate of reaction.
If I didn’t want to change the temperature then I could use a water bath to keep the temperature the same every time, because if the temperature is different then this would affect the rate because the particles would speed up (if hotter) or slow down (if cooler) – faster particles = a higher probability of collisions = a faster rate.
This would also allow me to write a value for temperature in my results instead of “room temp”.
Of Results:
My results betweens the sets are consistent with each other, showing the same pattern in each set. They are reliable and accurate enough to support my conclusion and prove my prediction correct.
My predication told me that I should have expected fastest rate for the 2.0 mol/dm3 than the rest, and the 0.4 mol/dm3 would be the slowest. This is what I have observed in my volume/time graphs.
Also, when I compared the rates for all three sets, the rates were very similar and followed the same pattern.
The few anomalies that I did have I think these were called by a build up of CO2 in the tube. I think this because the next result (10 seconds later) was higher than I would have expected, because more CO2 gas had reached the top of the inverted burette.
Examples of this are:
- Set 2, 0.4 mol/dm3, 150-160 seconds.
- Set 3, 0.4 mol/dm3, 140-150 seconds.
The 0.4 mol/dm3 in set 1 took a lot less time to produce 50cm3 of CO2 than sets 2 and 3. Set 1 took 293 seconds, set 2 415 seconds and set 3 392seconds. I think that these results are different because of the surface area.
E.g. the chips I used in set 1 could have had a surface area that was larger than the other sets. This would mean that there were more particles so a higher probability of collisions so a higher rate, so less time taken to produce 50cm3of CO2.
