In preparation, I carried my experiment out a few times to help me decide what strengths of acid, time intervals to record data and the amount of chippings I would use in my experiment.
On my first attempt I used 25cm² of 2 molar, hydrochloric acid and 4 grams of marble chippings. I found that this produced carbon dioxide gas at too quick a rate. I then decided to reduce the amount of marble chippings to 3 grams and keep the volume of acid at 25cm². This produced carbon dioxide at a steady rate. I decided to use 2 molar, 1.5 molar, 1 molar and 0.5 molar acid strengths. Now that I had found the amount and strength of hydrochloric acid and the amount of marble chippings, I set out to find a practical time interval to record the amount of gas given off by the reaction.
I tried recording the data every 5 second but I found that it was very difficult to look at the syringe, record the volume and look back up to see the next reading. I then tried measuring the volume of gas every 30 seconds, this worked okay but it wasn’t producing enough readings. For my last attempt I wrote down the volume of gas every 10 seconds. This was perfect, I could read the data, record, and look up in perfect time for the next reading and it also produced a lot of results, benefiting the appearance of my graph.
I decided I would use 25cm² of hydrochloric acid, 3 grams of marble chips and would record the volume of carbon dioxide gas given off every 10 seconds.
I will carry out my experiment 3 times as this is more reliable as the experiment could produce extreme results one time but the next could be different, I will average off my results and use these for my final graph.
Apparatus:
- Bung
- Conical flask
- Retort stand
- Clamp
- Gas syringe
- Calcium carbonate (marble chips)
- Hydrochloric acid
- Stop Clock
Results:
Conclusion: This experiment shows that as I decreased the concentration of the hydrochloric acid, the volume of carbon dioxide gas given off also decreases. The table shows that the 2 molar acid gave off more gas than the 1.5 molar acid, this gave off more than the one molar and so on.
I also discovered that the stronger the acid the quicker the rate of reaction between the calcium carbonate and the hydrochloric was. The graph shows that the more concentrated the acid is, the faster the reaction occurs, this is shown in the graph by the steepness of the line, the 2 molar line is steeper than the 1.5 molar line and so on.
My results agree with the collision theory. There are more ions in the 2 molar acid than the 1.5 molar acid, this means there are more particles for the calcium carbonate to collide with, therefore a quicker reaction and more gas will be given off.
When the concentration of acid was doubled, as was the acid particles, this meant that there were more acid particles and that meant more collision took place
Error and improvement: My results were inconsistent throughout all three experiments. One result could be 100 cm²
And the next one could be 150cm².
E.g.
In some cases in my investigation my results were very inconsistent. One way that I could improve my results would be to use a better gas syringe; I think that after many uses they would begin to stick, which could manipulate the results.
Another improvement I would make would be to carry out all three experiments in the same day using the very same bottle of acid. I think that using different bottles of acid, although they are marked as the same strength, could be slightly more concentrated than other ones as they are mixed in school, this would affect the results.
Craig Lamont
