Materials required
- HCl, 50mL (1.00M, 1.50M, 2.00M, 2.50M, 3.00M)
-
Marble (CaCO3), powder, 2.00g ± 0.01g (per trial)
- Electronic balance (± 0.01g)
- Beaker, 500mL ± 50mL
- Stop watch (±0.01s)
- Rubber gloves
- Apron
- Safety Goggles
Method
Method to prepare HCl:
Total volume of HCl required (for 1 trial): 50mL
Concentration required: 1.0M
Concentration in-hand: 3.0M
C1V1=C2V2
(3.00)(x) = (1.00)(50)
x = 16.7mL of 3.0M of HCL
and 33.3mL (50 - 16.7) of distilled water.
1.00M of HCl= 16.7mL of 3.0M of HCL + 33.3mL of distilled water
This prepares 1.00M of HCl
Similarly, prepare 1.50M, 2.00M, 2.50M and 3.00M of HCl
1.50M of HCl= 25.0mL of 3.0M of HCL + 25.0mL of distilled water
2.00M of HCl= 33.0mL of 3.0M of HCl + 16.7mL of distilled water
2.50M of HCl= 41.7mL of 3.0M of HCl + 8.3mL of distilled water
And simply use 50mL of 3.0M of HCl
Method for Investigation:
- Before starting the experiments, all the materials should be acquired with all safety precautions
-
Accurately weigh out 2.00g of CaCO3 using the weighing boat on the electronic balance.
-
Accurately measure about 50mL of 1.00M (± 0.01M) of HCl.
- Put the beaker on the electronic balance and pour in the 50mL of HCl (1.00M).
- Put the 2.00g of marble powder besides the beaker but on the electronic balance (this will measure the mass of the acid, the beaker and the marble powder without the reaction)
- Put the reading values on the electronic balance to zero.
- Now use the measured out marble powder and put it in the beaker and start the stop watch immediately.
-
After 2 minutes, record the value on the electronic balance. This is the mass of CO2 evolved in the reaction. (the value will be negative because mass is being lost as CO2)
- Carefully clean out the beaker completely using tap water.
- Repeat steps 2-9, but use the other concentrations of 1.50M, 2.00M, 2.50M and 3.00M respectively and repeat 3 trials for each concentration.
- After the experiment has been completed, put the cleaned materials back to their original place.
Data Processing
Note: For the sample calculation below, data point 1 has been used (1.00M ± 0.01M).
Average mass of CO2 = Trial 1 + Trial 2 + Trial 3
3
= (0.41 + 0.45 + 0.47)
3
= 0.44 g
Uncertainty: (Highest value – Lowest value)
2
= (0.47 – 0.41)
2
= ±0.03g
Therefore, 0.44g ±0.03g
Average rate of reaction: Mass of CO2(g)
Time for reaction(s)
= 0.44
2 min
= 0.44 g
120 s
= 0.004 g s -1
Uncertainty = (Uncertainty 1) + (Uncertainty 2) X 100
(Value 1) (Value 2)
= (0.03) + (0.01) X 100
(0.44) (120)
= ±6.80 %
6.80 X 0.004
100
= ±0.0003
Therefore, 0.004 g s -1 ± 0.0003 g s -1
Conclusion
As it can be seen from the calculations and the graph, as the concentration of HCl increases, the mass of Carbon dioxide evolved increases. The relation between the concentration of acid and mass of CO2 is directly proportional. This is because, as the concentration of acid increases there are more H+ ions in the system. This gives the CaCO3 atoms to combine with the extra H+ ions and then produce more of the reactants, which includes CO2 atoms. As these CO2 atoms increase, obviously the mass of CO2 also increases. Hence, when the concentration was doubled, the mass of CO2 also gets doubled.
Along with the calculated data, the relation can be seen in the graph as well. The graph has a straight line which again favors the direct proportionality between the concentration of acid and mass of CO2. It can be concluded that the order of the reaction is first order since the graph has a straight line.
Evaluation and Improvements
Although the relation between the two variables was successfully determined, there were numerous flaws/errors in the experiment.
For example, the graduated cylinder that was used to measure the acid was not clean for each trial. To be precise, the cylinder had some water droplets before the acid was measured. These droplets had combined with the added acid and hence the volume of acid increased. This means that the volume of acid was not kept constant and hence the marble powder reacted with more acid than required. Another error was that when the marble powder was put in the beaker using the funnel, some of the power got stuck on the funnel. This means that the mass of the marble powder was not kept constant and the required amount didn’t react with the acid. This definitely affected the data and the graph and made the calculated rate decrease since more water reacted with the marble powder. This made the reaction slower hence decreasing the calculated rate of reaction.
Apart from that, there was another error. The experiment was performed over a period of 2 days. Hence, there was a difference in temperature for the reaction. Increase in temperature increases the rate of reaction since there is more kinetic energy that lets the H+ ions react faster with CaCO3 atoms. Hence this decreased the rate of reaction because the temperature increased the number of collisions in the system.
To eliminate these errors, a number of precautions can be taken. It should be made sure that the graduated cylinder is completely clean and dry before each trial. Though being time consuming, this can be done by using ethanol before every trial. Ethanol would mix with the water droplets and vaporize in seconds hence cleaning and drying the graduated cylinder. Also, it must be made sure that every time the mass of the marble powder should be used that is required. Instead of using a funnel, a weighing boat can be used to transfer it into the beaker. A weighing boat doesn’t let the particles stick to it, hence eliminating this error.
