My dependent variable will be the mass of CO2 given off with time.
My independent variable will be the concentration of acid.
To change the concentration of hydrochloric acid I will used a total of 40 cm3 of hydrochloric acid/water solution. To vary the concentration of acid I will use 40 cm3 of acid and 0 cm3 of water, then I will use 30cm3 of acid and 10 cm 3 of water as shown in the table below.
To make sure that there are no weird answers we will repeat each experiment twice and take the average of each of the two results.
List of Apparatus
- Weighing Scale
- Measuring cylinder
- Beaker
- Safety Goggles
- Stopwatch
List of Chemicals
-
Hydrochloric Acid, HCl(aq) 2 mol/l
- Marble chips CaCO3
Safety Requirements
- Wear Safety glasses.
- Don’t crowd around sinks and weighing scales etc.
- Don’t run in the laboratory.
- Do not taste chemicals.
- Follow teacher’s instructions.
- Put unnecessary books and bags away so you do not trip over them.
Method
- Bring all necessary apparatus to your desk.
- Tare your scales so they read nothing.
- Put a beaker on the scales and tare it.
- Weigh out 30 grams of marble chips into the beaker.
- Take the beaker off and weigh out the concentration of hydrochloric acid/water into a measuring cylinder.
- Put the measuring cylinder with a total mass of 40 ml of solution in it on the scales along with the beaker with 30 grams of calcium carbonate in it.
- Tare the scales.
- Drop the Hydrochloric acid into the beaker and start the stopwatch, record how much carbon dioxide was given off in the first minute every 20.0 seconds then after that every 30.0 seconds. Record in the table shown below. (Remember to put the measuring cylinder back on the scales after you have added the acid).
- Repeat the experiment twice for each concentration.
- Take the average of all of the concentrations and plot them on the graphs below.
- Put away and clean all of your equipment after you have finished.
Displaying my Results
I will display my results in a table like this.
Concentration- __mls of HCl and __ mls of Water.
I will then put my results in graphs labelled like this.
Mass of CO2
Given off
Time
And,
Average rate
Of reaction
Concentration of acid.
Interpretation
I have done my experiments on the rate of reaction with hydrochloric acid and calcium carbonate. The results are shown in the tables below.
On the next four pages are the graphs of my results.
I am now going to work out the reaction rate for each of my results, the formula for this is;
Reaction Rate = Change in amount of a substance
Time Taken
The results for the reaction rates are as follows,
Average Reaction Rate for
40 cm3 Acid = 1.61 / 360 = 0.004472000
0 cm3 Water
Average Reaction Rate for
30 cm3 Acid = 1.20 / 360 = 0.003333333
10 cm3 Water
Average Reaction Rate for
20 cm3 Acid = 0.80 / 330 = 0.0024242424
20 cm3 Water
Average Reaction Rate for
10 cm3 Acid = 0.27 / 270 = 0.001
30 cm3 Water
A graph to show the average rates of reaction is shown on the next page.
This is what I have found out after doing my experiments on the rates of reaction between Calcium Carbonate (CaCO3) and Hydrochloric Acid (HCl). As the concentration of hydrochloric acid used to dissolve the calcium carbonate decreases the time taken for the hydrochloric acid to dissolve the calcium carbonate increases.
As you can see from the graphs I have drawn, all the graphs look quite like and are similar to a cumulative frequency curve. The dissolving of Calcium carbonate starts slowly then the gradient of the graph increases for a while which shows that the calcium carbonate is dissolving at a faster rate. Then the graph starts to flatten out (gradient decreases) which indicates a slowing down in the dissolving of the Calcium carbonate chips.
I conclude that following the evidence from my experiments that as the concentration of an acid increases, the time it takes for the acid to dissolve something decreases. My prediction stated, “as the concentration of hydrochloric acid used is increased, the rate of reaction will increase also,” so this then proved my prediction to be correct, i.e.
At the acid concentration of 2mol/l the reaction rate in the first minute was 0.52 g/min
At the acid concentration of 1.5 mol/l the reaction rate in the first minute was 0.43 g/min
At the acid concentration of 1 mol/l the reaction rate in the first minute was 0.27 g/min
At the acid concentration of 0.5 mol/l the reaction rate in the first minute was 0.07 g/min
These results indicate a large decrease in the rate of reaction as the acid concentration was decreased.
My experiment was unsuitable for carrying out this experiment accurately because of the inaccuracy of the results. The mass of calcium carbonate could not always be exactly 10 grams because you would have to break stones up to get the 10 grams, this would then lead to a different grade size of stone and a increased surface area so this could leave the results inaccurate. To improve this we could use a smaller calcium carbonate chip grade. Also at the times of the recording the reading on the scales changes sometimes on that second, therefore some readers could take the later results and some could take the earlier results, to improve the accuracy of this we could have a set standard, either use the later result all of the time or use the earlier result all of the time. Also we done the experiments on two different days with a week of difference in between the two dates of the experiments so there could have been a slight temperature difference on these two different days, if I had a longer time to do the experiments on the same day then we could conclude that temperature made no difference on my findings.
Although there is many factors which were not made constant that could influence the results of our findings, there is still significant evidence to prove that the results are accurate enough to say that, as the concentration of acid used will affect the rate of dissolving Calcium Carbonate. The higher the concentration of acid used the faster the CaCO3 will dissolve and the smaller the concentration of acid used the slower the CaCO3 will dissolve. This is because all our results have a trend, the higher the concentration of the acid the quicker the acid will dissolve the CaCO3, and all the graphs display that erosion happens slowly at first and then starts to speed up and finally slowing down, indicating that there is a link between all the graphs therefore I deem my results to be reliable.
