Method of keeping other variables constant during the experiment:
- The experiment will be conducted at room temperature to ensure constant temperature during the investigation.
- Weighing the same amount of lime stone (CaCO3)
- Using the same type of lime stone (CaCO3)
- Using the same amount (volume) of HCL but changing its concentration
Procedure while conducting the experiment:
Step 1:
We weigh an exact amount of CaCO3 and place it in the conical flask. This weight is recorded and the same amount of CaCO3 will be used throughout the experiment. We then take a specific volume of HCL using a pipette straight from the bottle to add it to CaCO3 in the conical flask. We will read the concentration level of HCL as indicated on the bottle. If we assume it says 80% concentrate then this will be 80% concentrated HCL. When we add the acid to the conical flask we immediately start the stopwatch. After a specified time say two minutes we take a reading of the amount of CO2 collected in the measuring cylinder. We record the first set of readings in table as follows:
HCL CO2 Time Weight of CaCO3
Concentration volume (constant) (constant)
80% ---- 2 ------
Step 2:
Now that we have completed the first part of the experiment and recorded the first set of results, we then clean and dry the conical flask, pipette, container and measuring cylinder and start the experiment again. We weigh the same amount of CaCO3 as above and place it in the conical flask. We then take one measure of hydrochloric acid from same bottle as above, say 80%, and mix it with half a measure of water in a container. We then take the same volume as above from this mixture using a pipette and add it to the CaCO3 in the conical flask and immediately start the stopwatch. After the same time elapses as above, 2 minutes, we take another reading of the amount of CO2 collected in the measuring cylinder. We record the second set of readings in the same table as shown below:
HCL CO2 Time Weight of CaCO3
Concentration volume (constant) (constant)
80% ---- 2 ------
53.33% ---- 2 ------
Step 3:
Now that we have completed the second part of the experiment and recorded the second set of results, we again clean and dry the conical flask, pipette, container and measuring cylinder and start the experiment all over again. This time we weigh exactly the same amount of CaCO3 as above and place it in the conical flask. We then take one measure of hydrochloric acid of certain concentration and mix it with one measure of water in a container. We then take the same volume as above from this mixture using a pipette and add it to the CaCO3 in the conical flask and immediately start the stopwatch. After exactly the same time say two minutes as above we take a reading of the amount of CO2 collected in the measuring cylinder. We then record the third set of readings in the same table as shown below:
HCL CO2 Time Weight of CaCO3
Concentration volume (constant) (constant)
80% ---- 2 ------
53.33% ---- 2 ------
40% ---- 2 ------
Steps 4 to 9
This is then repeated several times as shown in measurement and calculation of HCL concentration section (steps 1 to 9) so we have enough data to plot a graph and analyse the results of the experiment. A graph is then plotted with CO2 volume on the y-axis and HCL concentration percentage on the X-axis.
In order to get more accurate and representative results we repeat the whole investigation two or three times and record fresh sets of results on new tables and take an average of the readings. This will ensure fair and accurate results.
Measurement and calculation of HCL concentration:
If we start with say 80% HCL concentration as indicated on the bottle then our steps are as follows:
Step 1: Use a specific volume of HCL using a pipette straight from the bottle
to add it to CaCO3 in the conical flask. This will be 80% concentrated
HCL
Step 2: Mix one measure of HCL from the bottle with half measure of water in
a container. Then use the same volume as step 1 using a pipette to add
it to CaCO3 in the conical flask. This will reduce concentration to 1/1.5 of its original concentration making it 53.33% concentrated HCL
Step 3: Mix one measure of HCL from the bottle with one measure of water in
a container. Then use the same volume as step 1 using a pipette to add
it to CaCO3 in the conical flask. This will reduce concentration to 1/2 of its original concentration making it 40% concentrated HCL
Step 4: Mix one measure of HCL with two measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/3 of its original concentration making it 26.67% concentrated HCL
Step 5: Mix one measure of HCL with three measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/4 of its original concentration making it 20% concentrated HCL
Step 6: Mix one measure of HCL with four measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/5 of its original concentration making it 16% concentrated HCL
Step 7: Mix one measure of HCL with five measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/6 of its original concentration making it 13.33% concentrated HCL
Step 8: Mix one measure of HCL with six measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/7 of its original concentration making it 11.43% concentrated HCL
Step 9: Mix one measure of HCL with seven measures of water. Then
use the same volume as step 1 using a pipette to add it to CaCO3 in the
conical flask. This will reduce concentration to 1/8 of its original concentration making it 10% concentrated HCL
Chemical Reaction:
The chemical reaction that is taking place while conducting above experiment is:
CaCO3 + HCL -------------- CaCl2 + H2O + CO2
Conclusion:
