Scientific theory for prediction
Basically, at higher concentrations, there are more molecules per litre, so there will be more collisions, so the reaction rate should be higher at the same temperature. Increasing the concentration should increase the reaction rate. However for some reactions, the rate may be proportional to the concentration squared. For some reactions it can even be proportional to the concentration to the power 1.5
The Kinetic Rate Law defines the relationship between concentration and reaction rates. According to the law, the rate is directly proportional to the molar concentrations of each reactant in the rate-determining step of the reaction mechanism; each raised to a power equal to their rate order. The Rate of a chemical reaction is equal to a rate constant multiplied by the molar concentration of each reactant raised to the power equal to the rate order. For example if we have a chemical process defined in the following manner:
A + B → C
According to the Rate Law:
Rate = k [A]m [B]n
where:
k = rate constant
m = rate order in respect to A
n = rate order in respect to B
()
Apparatus and Chemicals:
Apparatus to be used in the experiment are:
- 100m3 conical flask
- Measuring cylinder
- Delivery tube
- Stop watch
- Thermometer
- Container
- Pipette
- Clamp
Chemicals to be used in the experiment are:
- Hydrochloric acid (HCL) with certain concentration as indicated on the bottle
- Lime stone CaCO3
- Water
Diagram of the experiment:
Plan of experimental method:
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 say 30 cm³ (2 molar) of HCL using a pipette straight from the bottle to add it to CaCO3 in the conical flask.
I will then add the hydrochloric acid to the marble chips and immediately put the rubber cork back on top of the conical flask. My partner will then start the stopwatch. We will keep the stopwatch running for 5 minutes and we will check the volume of CO2 every thirty seconds and record the readings in a table as follows:
HCL CO2 Time Weight of CaCO3
Concentration volume (constant)
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. I will then pour 25cm³ of HCL and 5 cm³ of water (1.7 molar).
I will then add the hydrochloric acid to the marble chips and immediately put the rubber cork back on top of the conical flask. My partner will then start the stopwatch. We will keep the stopwatch running for 5 minutes and we will check the volume of CO2 every thirty seconds and record the readings in a table as above.
I will repeat step two a few times by decreasing the concentration level of HCL and increasing the level of H2O.
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
Safety considerations:
- Use goggles while conducting the experiment.
- Keep all bags and jackets under the table.
- Always stand up when carrying out the experiment so you can move away if in any danger.
- Keep lab table clean and clear and just keep necessary experiment equipment
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
Chemical Reaction:
The chemical reaction that is taking place while conducting above experiment is:
CaCO3 + HCL → CaCl2 + H2O + CO2