I have based this on my knowledge that calcium carbonate does not react in water. Therefore in solutions with little acid and more water, the calcium carbonate will not react as much as it would in pure acid for example. To make each of the different strengths of the acid, water is added to a solution of 2M hydrochloric acid. Therefore in the 0.2 value, there will be a lot of water, and so it is not expected that much gas will be produced.
Increasing the molarity of the acid, will result in more gas being produced simply because there is a higher concentration of acid, thus more acid molecules within the solution. This will mean that the acid molecules with react with the calcium carbonate more often than a lower molarity solution. With more collisions, the chance of a reaction occurring also increases, and so with more reactions, more gas will be produced. However, it is only the chance of reacting that is increased, and therefore it is not definite that a reaction will take place, which is likely to be responsible for any anomalous results.
Variables:
Equipment List:
(although simulated apparatus is being used, should the experiment be physically conducted, the following would be needed)
200ml Flask with air tight cork
Gas syringe
Measuring cylinder
Gas flow tube (from flask to syringe)
Hydrochloric Acid
Calcium Carbonate (medium pieces)
Thermometer
Water Bath
Stopwatch
Plan: The below apparatus will be simulated for use in the experiment:
Plan (continued):
50 cc of hydrochloric acid with a molarity of 0.2M will be placed into the flask. Ensuring that its temperature is 20°C (using a water bath) the 20g calcium carbonate in medium pieces will be added, the cork tightened to prevent any gas loss, and the stopwatch started. After 10 seconds the measurement on the syringe should be noted. This will then be repeated a further 2 times to get a set of data. This is to ensure that a reliable average is made. Should any anomalous results occur, the test should be repeated to get another result which can be used.
The above should then be repeated for each of the following values, ensuring that each is done 3 to get 3 reliable results: 0.4M 0.6M 0.8M 1.0M 1.2M 1.4M
Method:
As a computer simulation was used, the safety of reading the results needs not be questioned as it was reading from a computer screen.
Results:
The results in bold are those which were identified as anomalies and so were not counted. Instead the test was repeated, and its result written within brackets. If the 2nd result was also anomalous, it was written in bold, and a test done again. For the 1M test, the results were inconclusive with too many anomalies and therefore the average was not found, and it was not counted towards the final total.
It was necessary to get at least 3 good results and so the test was done so until this was achieved at each molarity.
The results can be classified as reliable as they were obtained and then repeated. The computer performed the experiment, to a level of human error, and this was unalterable by the experimenter.
Conclusion:
The results unanimously show a clear trend that as the molarity of the acid increases, the volume of carbon dioxide will also do the same. There is an even trend going up, with a straight line to fit as the line of best fit.
The reason for this pattern is the same as that that was made in the prediction. As the concentration of the acid increases, there are more HCl molecules and so there is more chance of the calcium carbonate molecules colliding with these and so reacting to form calcium chloride. With the reaction occurring more often, the products will form in a greater quantity and so more carbon dioxide is produced. This reflects the rate of the reaction on the graph and proves my prediction and its theory correct.
Evaluation:
As the experiment was computer generated, it simulated how the experiment would have been conducted. It accounted for human errors in all aspects of the expriment.
