Ethanoic Acid:
Na2CO3 + 2CH3COOH → 2CH3COO-Na+ + H2O + CO2
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Pour 50cm3 of CH3COOH into the copper cup and place the copper cup in the Styrofoam cup
- Measure the initial temperature of the acid
- Hold the weighing boat with sodium carbonate (2.65g) in one hand and the lid to the copper cup in the other. At once quickly put the sodium carbonate in the acid and place the lid on immediately.
- Stir and keep an eye on the thermometer until the temperature has reached the peak and measure that temperature
- Clean the copper cup and repeat steps 1 through 4 two more times, resulting in a total of three trials
Results:
Table 1: Initial and Final Temperatures of Reaction for Different Acids
Table 2: Change in Temperature of Reaction for Different Acids
As seen here the stronger acids, hydrochloric and sulfuric, had a greater rise in temperature, than the weaker acid, ethanoic acid.
Calculations:
One example of calculating the mean will be shown below:
Change in Temperature: Trial 1 = 6.5 ± 0.5°C
Trial 2 = 7.0 ± 0.5°C
Trial 3 = 6.0 ± 0.5°C
6.5 + 7.0 + 6.0 = 19.5
19.5 / 3 = 16.5
Therefore, the average change in temperature of this example is 6.5 ± 0.5°C.
How much Sodium Carbonate needs to be used?
Hydrochloric Acid:
1 = (x * 50) / 1000
x = 50 / 1000
x = 0.05
There are 2 moles of Hydrochloric Acid
0.05 / 2 = 0.025
0.025 x 106 = 2.65g
Ethanoic Acid:
There are also two moles, therefore its also 2.65g
Sulfuric Acid:
There was only one mole of sulfuric acid, therefore the amount of sodium carbonate is 5.30g
Hydrochloric: Na2CO3 + 2HCl → 2NaCl + H2O + CO2
How much heat was evolved?
q = mC∆T
q = (52.65)(4.18)(3.3)
q = 726.3J = 0.73kJ
How many moles of H+?
1mol HCl = 1 mol H+
? mol H+ = 1.00 x 0.0500 = 0.0500 mol H+
How much heat/mol H+?
∆H (neutralization) = 0.73/0.0500 = -14.6 kJ/mol
% Error
((-14.6 – -57.1)/-57.1 ) x 100% = 74.4%
Sulfuric: Na2CO3 + H2SO4 → Na2SO4 + H2O + CO2
How much heat was evolved?
q = mC∆T
q = (55.30)(4.18)(6.5)
q = 726.3J = 1.5 kJ
How many moles of H+?
1mol H2SO4 = 2 mol H+
? mol H+ = (1.00 x 0.0500)/2 = 0.025 mol H+
How much heat/mol H+?
∆H (neutralization) = 1.5/0.025 = -60.0kJ/mol
% Error
((-60 – -57.1)/-57.1 ) x 100% = 5.08%
Ethanoic: Na2CO3 + 2CH3COOH → 2CH3COO-Na+ + H2O + CO2
How much heat was evolved?
q = mC∆T
q = (52.65)(4.18)(1.0)
q = 220J = 0.22 kJ
How many moles of H+?
1mol H2SO4 = 3 mol H+
? mol H+ = (1.00 x 0.0500)/3 = 0.017 mol H+
How much heat/mol H+?
∆H (neutralization) = 0.22/0.017 = -13.0 kJ/mol
% Error
((-13 – -54.9)/-54.9 ) x 100% = 76.3%
Percentage Uncertainty:
Hydrochloric Acid:
Scale: (0.005/2.65) x 100% = 0.189%
Delta Temperature: (0.5/3.3) x 100% = 15.2%
q = %unc(m) %unc(T) = 15.4%
M(acid) = (0.005/1.00) = 0.50%
V(acid) = (2/50) = 4.00%
Moles(acid) = 4.50%
Delta H (neutralization) = 19.9%
Total: 59.7%
Sulfuric Acid:
Scale: (0.005/5.3) x 100% = 0.094%
Delta Temperature: (0.5/6.5) x 100% = 7.69%
q = %unc(m) %unc(T) = 7.78%
M(acid) = (0.005/1.00) = 0.50%
V(acid) = (2/50) = 4.00%
Moles(acid) = 4.50%
Delta H (neutralization) = 12.3%
Total: 36.8%
Qualitative Results:
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The reaction immediately started as soon as the sodium carbonate was dropped into any of the acids; however, specifically for the sulfuric acid there was a much louder fizzing noise and the temperature increased much faster.
- For some cases not all the sodium carbonate reacted fully.
- There was some smoke which escaped from the holes on the lid. This shows how the experiment was not perfect as there was some heat loss.
Graph:
Conclusion:
Overall, the hypothesis held correct. Clearly shown from the results, the temperature of the stronger acids increased more when reacted with sodium carbonate. As the strength of an acid increases than the change in temperature will also increase when reacting with a base. For example, when using hydrochloric acid the average change in temperature was 3.3 degrees Celsius; however, when using ethanoic acid, the average change in temperature was 1.0 degrees Celsius.
Looking at the theoretical value of the delta H of neutralization, it is more negative for strong acids than weak acids. This is due to the fact that sulfuric acid and hydrochloric acid are completely ionized in solutions. In comparison, ethanoic acid is not fully ionized.
Evaluation:
Overall, this experiment went very well; however, there were numerous limitations which affected the results. One very clear and important limitation is the heat loss. Heat loss was a huge factor which affected the results. Heat was lost to the environment through the copper cup, the holes in the lid, the time of the reaction when the lid was not on, etc. These limitations affect the results dramatically because the change in temperature is reasonably lower than what the actual change in temperature should be. This limitation cannot be fully avoided but can be easily improved. Realistic improvements to this limitation include:
- Doing the reaction straight in a Styrofoam cup and not in the copper cup which was placed in the Styrofoam cup. Due to the fact that copper is an extremely bad insulator, a lot of heat is lost to the copper cup itself.
- Designing a lid with air tight holes. The lid which was used was not air tight. Designing a lid with air tight holes would help because heat would not be lost to the environment through the holes.
- Designing an air tight hole on the lid which can easily be manipulated for the sodium carbonate to be dropped in. This would limit the heat loss of the reaction from the delay of putting the lid on after dropping the copper in.
Another limitation to this experiment is the fact that only one weak acid was used, as compared to two strong acids. Due to the fact that the school did not supply phosphoric acid, only one weak acid was available. This affects the results because the comparisons of weak acids and strong acids become limited to only two comparisons. If phosphoric acid was used than the comparisons between strong acids and weak acids would have been increased to four. All in all, this results in a more accurate conclusion.
Looking at the percentage error in these experiments:
Hydrochloric Acid:
For hydrochloric acid, the percentage error was 77.4% however for the percentage uncertainty it is 59.7%. The percentage error was greater than the percentage uncertainty meaning this is a random error which I made in the experiment. This is most likely due to the heat loss in the experiment.
Sulfuric Acid:
For sulfuric acid, the percentage error 5.08%, and the percentage uncertainty was 36.8%. This means that the error was a systematic error. The value to of delta H for sulfuric acid in the experiment was very close to the theoretical value of delta H for sulfuric acid.
Overall, the percentage errors for these acids were relatively very high. This could be due to the fact that calcium carbonate is a gas releasing base. Therefore, CO2 is released into the environment and a lot of heat is lost.
Bibliography:
- http://www.intute.ac.uk/sciences/reference/chemdata/3.html
