John Yeager

AP Chemistry

October 12, 2014

#7 Kinetics: Rate of Reactions Lab

The purpose of preforming the Rate of Reactions lab is to observe the reaction and reaction rate of CaCO3 and HCl at several different concentrations, then also to change one variable of the lab to see if the results from the change test differs from previous tests. A reaction flask was set up to monitor the rate of reaction between calcium carbonate, and the highly acidic hydrochloric acid. The method of determining the rate of the reaction itself was to place the flask containing the progressive reaction on a sensitive scale and as the reaction progressed, the weight was recorded at an interval of every two minutes. The reason for the decreasing weight within the reaction was because as the balanced equation shows, CaCO3 + 2HCl ——> CaCl2 + H2O + CO2 , carbon dioxide is released in a gaseous state and thus moving away from the solution and out of the container. Therefore from the weight the reaction began, and the weight the reaction finished, there was a significant decrease in weight. This method was preformed multiple times, changing the molarity (concentration) of the HCl from 3M, 4M, 5M, and finally 6M to observe the change in rate of the reaction. Each concentration derived from a 6M solution and had to have been diluted to that specific molarity using the dilution equation ( M1 * V1 = M2 * V2 ). Finding the amount of water necessary to dilute the 3M solution appeared as ( 6M * V1 = 3M * .050L ). The missing variable, V1, mathematically solved to be 25 mL, thus half water, half 6 M HCl to a total of a 50 mL solution. This process was necessary for each solution (besides the 6M) and the amounts of HCl in each solution were: 3M = 25 mL HCL, 4M = 33.3 mL HCl, and 5M = 41.67 mL HCl. After all these amounts were measured into a 125 mL Erlenmeyer flask and after doing so, 1.3 grams of calcium carbonate was measured and then added into the solution for the reaction and measurement of decreasing weight to begin. Note: the flask containing the acidic solution was set onto a scale prior to the addition of the calcium carbonate. The following tables contain data relative to the specific test preformed with the specific molar concentration:

3 M HCl (1.335 g CaCO3)

Time (Minutes)
Mass of Flask Contents (grams)
Cumulative Mass Lost
0
155.7 g
0 g
2
155.65 g
.05 g
4
155.6 g
.1 g
6
155.54 g
.16 g
8
155.5 g
.2 g
10
155.46 g
.24 g

4 M HCl (1.363 g CaCO3)

Time (Minutes)
Mass of Flask Contents (grams)
Cumulative Mass Lost
0
155.720 g
0 g
2
155.583 g
.146 g
4
155.440 g
.289 g
6
155.364 g
.365 g
8
155.327 g
.402 g
10
155.3 g
.429 g

5 M HCl (unsure of exact weight of CaCO3)

Time (Minutes)
Mass of Flask Contents (grams)
Cumulative Mass Lost
0
53.01 g
0 g
2
52.9 g
.11 g
4
52.79 g
.22 g
6
52.75 g
.26 g
8
52.69 g
.32 g
10
52.66 g
.35 g

6 M HCl (unsure of exact weight of CaCO3)

Time (Minutes)
Mass of Flask Contents (grams)
Cumulative Mass Lost
0
55.98 g
0 g
2
55.42 g
.56 g
4
55.34 g
.64 g
6
55.28 g
.7 g
8
55.22 g
.76 g
10
55.16 g
.82 g

Note: Regarding the recorded weights for the flask contents for the 5M and 6M solution, the weigh of the flasks themselves were subtracted out of the weight total.

As each of the reactions took place, all tests differing in molarity, it was observed that upon contact of the calcium carbonate and hydrochloric acid, lots of bubbling occurred as well as a more homogeneous mixture took place off the pebbles of calcium carbonate into the solution. To explain the bubbling, carbon dioxide was being formed between the separation of the calcium atoms within the solution and water being also formed leaving carbon dioxide in its gaseous form to bubble out and escape the flask, resulting in a steady/exponential decrease in mass. Another method of measuring the rate at which the reaction took place would be to record the mass of the gas escaping the flask as the reaction progresses. The mass of the gas escaping quickly increases