Apparatus:
Method:
- Firstly I will attach the gas syringe to the clamp and stand so that the syringe is at a horizontal angle. Next I will place the conical flask next to the gas syringe and join them up by a piece of rubber tubing. Next place the dish on to the scales and set the analogue reading to zero so that it only weighs the crystals. I will weigh the crystals equal to 3 grams.
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Now, I need to measure out 10 cm 3 of HCL. I will firstly test 0.5 mole.
- Take 1 gram of the medium calcium carbonate crystals and place them in the conical flask attached to the gas syringe. Now take the HCL and pour it into the conical flask making sure that all the crystals are being covered. As soon as the liquid is poured into the conical flask, add the rubber lid to stop the gases escaping, and start timing using the stopwatch.
- After 240 seconds (3 minutes), measure the amount carbon dioxide being given off. To measure, see how far the gas syringe has moved and take a reading in ml.
- Carry out the experiment for the different concentrations of HCL (0.125, 0.25, 1, 1.5 and 2mol).
- Repeat this twice to get three sets of results.
Fair test:
To ensure that my experiment is fair there are many aspects for me to consider. Firstly the apparatus will not be the exact same, for example I will use a different gas syringe in the first lesson from the second. Also we must remember that we will be using a different sample of Hydrochloric acid and calcium carbonate crystals. The surface area of the crystals cannot be measured, and so cannot be kept the same. I am able to ensure the crystals are approximately the same by using crystals of similar size and which share the same mass.
Another important factor which may not be kept constant is temperature difference due to different days and environments. If the temperature is different outside as the experiment is on different days it could affect our experiment, for example if it is hotter on different days the rate of reaction could increase. If a change in temperature causes a change in the rate of the reaction, the experiment would be unfair. To prevent this I am going to measure the starting temperature for all the experiments and ensure they are the same.
Preliminary Results:
With small marble chips
With medium marble chips
Results:
With medium sized marble chips
00= anomalous result
Analysis:
I have recorded my results in the table shown on page 3. There are 2 repeats for each concentration of hydrochloric acid, apart from the 2 mole concentration, where I attained an anomalous result. This was then repeated again and excluded from my averages and graph results. If there had been enough time I would have repeated each concentration 3 times and taken an average from these. This would make my results more accurate as it would be easier to spot any anomalous results because there are two other readings to compare it with.
The line graph of my results shows that the relationship between the rate of carbon dioxide produced and the concentration of hydrochloric acid is proportional. I have drawn in a line of best fit which starts at zero, and reaches 100 cm3 at 2 moles.
Conclusion:
From my results and the line graph, I can see that as I increased the concentration of hydrochloric acid, the rate also increased as there were more particles to collide with the marble, making the reaction quicker. The stronger the concentration of Hydrochloric Acid, the more gas produced. In a diluted concentration of hydrochloric acid, the chance of an acid particle hitting a calcium carbonate particle is less. But if a more concentrated solution is used, there are more particles and there is a greater chance of the particle colliding with another calcium carbonate particle. When the concentration was doubled, I expected the amount of particles to be doubled, and the amount of collisions to be doubled also. In actual fact this is not always the case, for example the average reading for 0.5 moles was 27cm3 and for 1 mole it was 61.5cm3. This is slightly more than double the amount, however this could be due to the accuracy of the results. The reading for 2 moles was 100cm3 which is less than double the amount of carbon dioxide produced than at 1 mole. This again could be due to the accuracy of results, or may be an indication that the rate of reaction was beginning to slow down as the concentration was increased. My results mostly agree with my prediction, however to determine whether the concentration is directly proportional to the rate I would have to do more repeats of the experiment.
Evaluation:
Overall I am pleased with my results and the way the experiment was carried out. I think my results were fairly accurate and proved my hypothesis. To make the overall experiment results more accurate we repeated it twice, and then took the average. If there had been time we would have repeated it three times, however this was not possible.
I had only one anomalous result due to the simplicity of the experiment. The only odd result that I had was the second time I repeated the experiment on the 2 mole solution, the reaction took place a lot faster then the previous two. I think this was due to the marble chips that we were using. At first there was a large selection of marble chips available, so finding three to match the weight that I had set was pretty easy, by the time I had to repeat the experiment for the third time it was a lot harder, so in that instance instead of three chips being used I had to use five to make up the weight, this altered the surface area giving a larger area for it to react, which is why I think the reaction went a lot faster then expected. This is also why I’m interested into investigating further the effect of surface area on the rate of reaction.
Also other things that I would like to investigate would be the experiment of time against amount of gas produced to show at which points the rate of reaction was at best and the curve/line of reaction. I would like to also investigate other factors, which affect the rate of a reaction like temperature and surface area to see what effect they have on the rate of the reaction.
Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch. There is lots of room for human error here. But the inaccuracies due to them were negligible because I paid close attention to these during the experiment.