Volume of acid- this will be the amount of hydrochloric acid that will be reacted with the marble chips.
Mass of marble chips- the mass of the marble chips is a way of measuring the quantity of chips being used.
Temperature- the temperature adds energy to the reaction an affects how quickly the particles move. By doing this temperature affects the number of effective collisions
Light intensity- the light intensity has a very small affect on the experiment so will not be measured in this experiment.
Method:
The equipment and materials I used were a: cornical flask, capillary tube, stopwatch, water, hydrochloric acid, bowl, holder (to keep tube in place), measuring cylinder which is used to collect marble chips.
First I filled the bowl with tap water to about half way up and filled the measuring cylinder with water and then turned it upside down into the bowl of water so the cylinder was still filled with water. By doing this I did create a slight margin of error because some of the water was displaced when doing this although it was very little. Then I held the measuring cylinder in place with the metal holder in the bowl. I then put the capillary (delivery) tube under the cylinder so the air from the experiment could displace the water. The capillary tube was connected to the cornical flask via a cork that was shut tight on top of the flask. To make sure the volumes of acid and water were right we now measured the volumes of each in a measuring cylinder to be accurate. To make sure the mass of marble chips were right I measured them on a scale so I knew that I had exactly the amount that was needed. Then we put the chips and the acid in the conical flask and started the stopwatch to time the reaction rate.
As the experiment had now started I recorded the results every 15 sec. I did this for however long each of the molar tests took as they varied. I then changed the mass of the chips and the concentration of acid until I had all the data that was required.
The experiment would be set up as shown above.
PRELIMINARY RESULTS:
(Result on table on next sheet)
Preliminary description
For my preliminary results I tested each molarity experiment twice to get a broader reading database and to compare results to and see if any errors had been made.
For test one and the repeat the molarity was 2 (20ml hydrochloric acid) and so the results were very fast in both. 100ml of gas was collected in exactly 2minutes.
Test two had no results as the molarity was 0 and there was no acid for the reaction to take place. In test 3 the acid and water concentrations are equal (1oml each) 1molar. I took longer to collect 100ml of gas than test 1 because I changed half of the concentration. I thought that it would take twice as long but it didn’t because the surface area varies and so changes the speed that it dissolves in.
In test 4 the results were fairly in between and nearer to 2molar readings but slower. In test 5 I predicted that this would take long but turned out that it was longer than I expected. The experiment stopped at 255secs because only 47ml had gone.
MAIN RESULTS:
(On next sheet)
EVERY MOLAR TEST IS REPEATED AND THEN AN AVERAGE IS TAKEN.
ANALYSIS:
From looking at my results and graph I am able to conclude that the more concentrated the acid the quicker the reaction happened and the more gas was produced. As we look at the graph we can clearly see that in all five results at the beginning the reaction happened more quickly than at the end where we can see that it started to slow down.
After looking at my tables and results I can tell that the stronger the concentration of acid, then the faster the reaction will be apart from looking a my graphs as above. This was my prediction at the beginning and my results show this. E.G- test 1 had 20ml of hydrochloric acid in it and 1.5g of marble chips (1.5g was used in all tests), the 100ml of gas was collected at exactly 2mins (12o seconds). However test 3 had 10ml of acid and 10ml of water and took exactly 3:23mins to finish. There was 10ml of waster mixed in with 10ml of hydrochloric acid which effectively doubles the time it takes to finish compared to test 1 and also lowers the energy released by the acid.
For a quicker reaction the tests have to have more activation energy, which will in turn cause more molecular collisions. A higher molar acid is needed for a faster reaction. If the test is heated up it can also cause the activation energy to rise however temperature was not a major factor to consider to seriously in my tests as they were conducted under general room temperature and there was no anomalous results.
Evaluation:
I find that my results give me a varied but accurate answer to my prediction. The results vary a lot in the time taken to complete them i.e.- tests 1 and 6 (the repeat test) average was 98ml at 105 seconds but tests 3and 8’s average was also 98ml but at 270 seconds.
There are some things that may affect the speed or way the bubbles move or how the gas is collected e.g.- While most of the tests gave small bubbles through the tube at a small and steady rate some of the tests (5 and 10) gave very large bubbles that only came up every 30-40 seconds. I think this is because air/gas is trapped underneath the delivery tube holder and is occasionally released after pressure builds up and so the bubble takes all of the water in one go giving a sudden surge in present readings at the time.
Another way in which the tests could be made fairer is by changing the shape of the marble chips. Instead of having separate lumps/pieces off the calcium carbonate which all vary in surface area, shape and size, I think that the chips should be crushed into smaller segments which will solve the problem of one being bigger than the other.
During setting up my equipment and replacing the solutions the measuring cylinder had to be turned upside down quickly into the water bowl. By doing this I believe that some water was displaced, as it cannot be possibly done accurately by hand.
Overall I think that with the equipment and time given I was able to obtain enough evidence to back up my prediction.
