Planning
I am going to investigate how the concentration of Hydrocholoric acid will effect the rate of the reaction of calcium carbonate (marble chips) . The word equation for the reaction is:
Calcium carbonate +Hydrochloric acid Calcium Chloride + Water + Carbon Dioxide
The chemical formula for this reaction is as follows:
Ca Co3 + 2HCl + H20 + C02
I will collect the carbon dioxide as a measure of the rate of reaction.
I plan to use 3 different concentrations of hydrochloric acid e.g quarter concentration, half concentration acid and 3 quarter concentraton. The total amount of acid and water in each concentration will add up to 50ml. I plan to measure the volume of carbon dioxide that is collected Cm cubed. I plan to run my experiment over a 6 minute period taking a reading every minute. I am going to do a preliminary experiment to see if the experiment runs well, and if not I will make alterations so my main experiment will run well.
Trial Run
Changes to final experiment
I will repeat each concentration of acid twice and average them to make sure it is a fair test. I will use safety glasses, for protection from the acid.
Method
I will first collect the apparatus and set it up as shown below. I will first put the safety goggles on then. I will collect 3 marble chips roughly the same size and then drop them into the conical flask. For my first concentration I will pour 12ml of hydrochloric acid into a measuring cylinder, and mix it with 38ml of water so it totals 50ml.I will then carefully pour the mixture, and immeditatly place the bung over the conical flask, and my partner will start the stopwatch, and I will take readings of the volume of carbon dioxide taken every minute over six minutes. I will repeat this process using 25ml water, 23ml of acid and 38ml acid , 12ml water. I will repeat each concentration twice so my results are fair. I will average the results to find the average reading for each concentration. In order to make the test as fair as possible I will try and keep the marble chips the same size, the room should stay at a constant temperature. There will be no catalyst in this reaction. The only variable that I am going to change throughout the experiment is the concentration of acid.
Apparatus:One bung, A piece of delivery tube ,One measuring cylinder ,Clamp stand, a conical flask, 9 pieces of marble chip(same size), altogether 75ml of hydrochloric and 75ml of water.
Diagram of apparatus set up
Prediction:
I predict that the “solution with the highest concentration of acid will have a much faster reaction than the weaker solution of acid.” I have predicted this from my knowledge my trail run experiment and scientific knowledge. I think that this happened because the more HCl in the solution the greater the concentration and there will be more particles colliding and more energy and therefore a faster rate of reaction. The reason I think that the rate of reaction will increase is that the experiment is exothermic, this means that it will give itself more energy and therefore more collisions and faster collisions. Therefore I predict that the rate of reaction will increase with the concentration of the HCl solutions.
Final results
Analyasis of Results
Evaluation
I feel that this was a successful experiment. My results seem to indicate a clear pattern from which I was able to confidently draw a conclusion. This conclusion confirmed my hypothesis. The method produced results accurately and quickly enough to finish the experiments in the time. My results were reliable, as the experiment was a fair test. I ensured that this was true by keeping all of the variables not involved in my experiment constant. These were the presence of catalysts and the starting temperature of the reactants. I could not control the temperature at any time in the reaction except for at 0 seconds. This is because the reaction released thermal energy. I can say that no other energy was deliberately put in or taken out of the contents of the conical flask during the experiment. I used roughly the same weight and four chips of roughly the same size throughout the whole experiment, this kept the surface area constant, but something unexpected happened. I had a problem with my method in that I had to drop the marble chips into the conical flask, place the bung into the top and start the stopwatch. This is such a long sequence of activities to do in the time it takes the marble chips to hit the surface of the solution. There is a potential for error. I think this is the reason for the abnormalities in my results as I did not start the watch at the correct time as I had trouble putting the bung into the conical flask. This means my results are higher than they should be. The truth of my conclusion is not undermined by this however, as the same effect happened to each concentration. I could overcome this problem and the one mentioned in the previous paragraph by only starting the timer when the gas starts to fill the measuring cylinder. This would not include the time taken to push the water down the delivery tube in my results, and I would not have to start the stopwatch at the same time as putting the marble chips in the flask. To provide more evidence for my investigation I could use a thermometer to measure the temperature during the experiment as then I could produce a fairer test as the temperature will differ throughout the whole experiment. Also, I could measure the mass loss of the reaction by having the conical flask on a top pan balance. I could take away the mass at regular intervals from the original and find out how quickly the reaction takes place.
