As you increase the concentration of hydrochloric acid, there are more acid particles in the same volume of liquid. Therefore there is a greater chance of acid particles colliding effectively with the particles on the surface of the calcium carbonate chips. This means that as we increase the concentration of the hydrochloric acid the rate of reaction should increase. I predict that a graph of the results should look like this:
PLAN
In order to take accurate measurements of the rate of reaction between calcium carbonate and hydrochloric acid I will need the following apparatus:
?Conical flask (large enough to prevent spillage) ga!
?Delivery tube (for connection to the measuring cylinder)
?Bee hive (to support the measuring cylinder for delivery tube access and prevent gas escaping)
?Bowl (to hold the water)
?Measuring cylinder (in order to collect the carbon dioxide given off) Heidegger
?Calcium carbonate (reactant) idea.
?Hydrochloric acid (reactant- different molaraties are needed)
?Water (in order for you to trap the gas produced)
?Stop watch (to time the reaction)
When doing my experiments I will use the same procedure throughout. I will set out my equipment as shown in the diagram below:
To measure the rate of reaction between the calcium carbonate and hydrochloric acid I will time how long it takes for the reaction to produce 10cm3 of carbon dioxide. Once I have set up the apparatus I will measure out 10cm3 of hydrochloric acid and 1g of small calcium carbonate chips. I then pour the acid into the conical flask and then put the calcium carbonate in also. As quickly as possible I must push the rubber bung into the conical flask and start the stopwatch as soon as this motion is completed. I must then observe the amount of gas being collected and stop the watch as soon as 10cm3 of gas is collected. It is inevitable that there will be slight discrepancies in the amount of time it takes for the bung to be placed into the flask, the surface area of the calcium carbonate, the strength of the acid, the time it takes for the stopwatch to be started and the amount and temperature of calcium carbonate and hydrochloric acid. In order to try and keep these factors constant I will repeat this experiment 3 times for each of the 5 different strengths of acid and use the average result. If any anomalous results occur I must repeat the experiment for that result. As with any investigations great care should be taken and the experiment should be undertaken in a sensible manner.
?I will wear safety goggles throughout the investigation.
?I will be careful so as not to spill any acid, but would ensure there was nothing near the experiment that could cause an accident or be damaged if an accident did occur.
?In this experiment I will have to make sure I am careful with all glassware in case it breaks and if it does to make sure it is immediately cleaned up. As I will be using a conical flask its wide bottom gives a more secure base.
? I must be careful especially with the stronger molarity acid because it will be corrosive so I must make sure I do not spill it on my hands or more especially in my eyes, however proper use of goggles should avoid this.
RESULTS *RED TEXT = ANOMALOUS RESULT Heidegger oppressed
CONCLUSION
My results prove that the concentration of hydrochloric acid does affect the rate of reaction between hydrochloric acid and calcium carbonate. This is exactly what I predicted using the collision theory. The shape of the curve indicates an inverse proportionality between the strength of the acid and the time taken to produce a fixed volume of gas. The higher the concentration of acid the quicker the reaction. However the strength of the acid is not directly proportional to the time it takes to produce 10 cm3 of hydrogen, this causes a curve in the graph, which is asymptotic to both axis'. It would be useful to plot a graph showing if the amount of gas produced per second with different strength acids shows a directly proportional straight line. This would enable me to predict how long it would take for different acid to produce a set amount of carbon dioxide.
To calculate the average amount of carbon dioxide produced per second I must use my previous results. If I take the amount of carbon dioxide I was timing for (10cm3) and divide this by the average time, I will work out how much carbon dioxide was produced on average per second.
I will then plot my calculations onto a graph.
This graph seems to show that at the beginning when the acid is fairly weak, the line is straight showing that as you increase the strength of the acid the amount of acid produced per second is directly proportional to the strength of the acid. The line then begins to curve when the acid strength reaches around 1.25 molars. This could mean that there is a limit to how fast the reaction can take place or that my results for 1.5 and 2 molar acid are incorrect. The rate of reaction could be limited by the surface area of the Calcium carbonate (i.e. all the particles are reacting on the surface of the calcium carbonate, so how ever strong the acid is the reaction rate will not speed up). I could see if this was causing the limitation by undergoing the same experiment with an enlarged surface area and see if the rate of reaction is still limited. To rule out that my results were anomalous we could repeat the experiment again and compare the results.
EVALUATION
Are experiment did produce 1 anomalous result which occurred when using 0.75 molar acid in time 2. This differed from the other 2 times for that particular strength acid by 11 seconds, around 20% of the other two times. I believe that this result occurred due to the bung in the conical flask not being placed into the conical flask in the correct manner, thus not causing a completely air tight seal, letting some of the gas which was being produced escape. However there could have been other less likely reasons why this anomalous result occured. The time in which the bung was placed into the conical flask could have been prolonged causing gas to escape, the surface area of the calcium carbonate chips could have been smaller than otherwise used, we may have mixed the acid wrongly causing the strength of the acid to be too high, the amount of reactants could have been inaccurate or the stopwatch may have not been used accurately. As soon as this result was analysed I realised it did not fit the pattern and repeated the experiment for that particular acid in order that the anomalous result did not affect are final data.
On the whole I believe that I worked extremely accurately and safely completing the experiment to the best of my ability. All my readings were as accurate as the apparatus allowed, however are resources did limit how accurate we could make are results. We did take enough readings to show the affect which concentration has on the rate of reaction, but with more time and sophisticated equipment we would have been able to see the pattern more clearly and accurately, as I would have preferred to collect more data had time allowed so. I did not change my plan in any way from my original method but if we possessed the correct equipment I could have changed my plan in order to eliminate the highest possibility of causing an anomalous result, which was the inconstant time it took for the bung to be placed on the conical flask after the reactants were placed in.
I would use a bung with two holes, in the top of the conical flask. One for the delivery tube going to the gas collection area, and one for a dropping funnel, which would enable the acid to be dropped into the conical flask where the calcium carbonate had been placed earlier. The valve on the dropping funnel is then closed to prevent carbon dioxide escaping.
This would eliminate gas escaping before the bung is placed into the conical flask producing more accurate results.
Another way of improving the experiment would be to use calcium carbonate powder instead of using fine chips. This would keep the surface area of the calcium carbonate at a constant, improving the accuracy of my results. The only problem with this improvement is that when using powder instead of chips, the surface area although staying at a constant with the same mass of calcium carbonate. If you were to use the same mass of calcium carbonate chips and calcium carbonate powder the surface area is vastly larger with powder. This would mean that if powder was to be used the rate of reaction would increase tremendously and the experiment would be over in a few seconds. To overcome this problem there are various ways of adapting the experiment. You could use less calcium carbonate, increase the amount of carbon dioxide you are timing for or use a lower strength or less acid to try any compensate for the dramatic increase in surface area.
In order to try and keep the temperature constant through out the whole experiment, the experiment could be undertaken in a controlled environment, however this is impossible without sophisticated equipment which we do not posses.
In order to gain further information for my conclusion I could repeat the experiment with a higher range of acid to gain more results. In order to extend my investigation I could undergo experiments in order to find out how the other variables affect the rate of reaction, such as:
?Surface area
?Temperature
?Catalysts
or I could conduct an experiment to see how the concentration affects another reaction e.g. Magnesium and Hydrochloric Acid, and compare my results against this experiment
