Results & Observations
Raw Data » Table of results showing the initial and final temperatures of reactions between several group one metals with hydrochloric acid
Lithium -
Average initial temperature: 21.4 + 21.4 + 22.0 = 21.6
3
Average final temperature: 24.6 + 26.9 + 25.1 = 25.5
3
Average change in temperature: 25.5 – 21.6 = 3.9
Sodium -
Average initial temperature: 21.4 + 21.6 + 22.0 = 21.7
3
Average final temperature: 22.2 + 23.3 + 22.6 = 22.7
3
Average change in temperature: 22.7 – 21.7 = 1
Potassium -
Average initial temperature: 21.1 + 21.8 + 22.0 = 21.6
3
Average final temperature: 22.1 + 22.5 + 22.8 = 22.5
3
Average change in temperature: 22.5 – 21.6 = 0.9
Processed data » Table of results showing the average change in temperature of reactions between several group one metals and hydrochloric acid
Raw & Processed data » Table of results showing qualitative data before reactions between several group one metals with hydrochloric acid
Raw & Processed data » Table of results showing qualitative data during and after reactions between several group one metals with hydrochloric acid
Data Analysis
Lithium & Hydrochloric acid -
Balanced equation: 2Li(s) + 2HCl(aq) = H2(g) + 2LiCl(aq)
Total ionic equation: 2Li(s) + 2H+1(aq) + 2Cl-1(aq) = H2(g) + 2Li+1(aq) + 2Cl-1(aq)
Net ionic equation: 2Li(s) + 2H+1(aq) = H2(g) + 2Li+1(aq)
Oxidation: 2Li(s) = 2Li+1(aq) + 2e-
Reduction: 2H+1 + 2e- = H2(g)
Sodium & Hydrochloric acid -
Balanced equation: 2Na(s) + 2HCl(aq) = H2(g) + 2NaCl(aq)
Total ionic equation: 2Na(s) + 2H+1(aq) + 2Cl-1(aq) = H2(g) + 2Na+1(aq) + 2Cl-1(aq)
Net ionic equation: 2Na(s) + 2H+1(aq) = H2(g) + 2Na+1(aq)
Oxidation: 2Na(s) = 2Na+1(aq) + 2e-
Reduction: 2H+1 + 2e- = H2(g)
Potassium & Hydrochloric acid -
Balanced equation: 2K(s) + 2HCl(aq) = H2(g) + 2KCl(aq)
Total ionic equation: 2K(s) + 2H+1(aq) + 2Cl-1(aq) = H2(g) + 2K+1(aq) + 2Cl-1(aq)
Net ionic equation: 2K(s) + 2H+1(aq) = H2(g) + 2K+1(aq)
Oxidation: 2K(s) = 2K+1(aq) + 2e-
Reduction: 2H+1 + 2e- = H2(g)
For more accurate analysis, we should convert the amount of metal used from grams to moles. In order to do so, we must divide the weight, in grams, by the atomic mass:
Lithium: 0.03 / 6.94 = 0.004
Sodium: 0.03 / 22.99 = 0.001
Potassium: 0.03 / 39.10 = 0.0007
Conclusion
My aim was to find the change in energy by reacting lithium, sodium and potassium with hydrochloric acid. I was able to do this successfully by first measuring the temperature of the solution right before and after the reaction, then finding the change in temperature, and from there finding the energy produced for each metal. As you can see from the tables and graph above, we managed to gather fairly good results. We can see that our results were quite accurate because all three trials gave us around the same figures, for example, for Lithium, the temperature was 24.6ºC on the first trial, 26.9ºC on the second trial, and 25.1ºC on the third trial.
Also, we can see that while the basis of my hypothesis was correct « the further away the outer electrons are from the nucleus, the less of a pull the nucleus will exert to hold the outer electron. », the application of my information onto how this experiment was planned was not. While all metals did react violently with the hydrochloric acid, they did not react according to my expectations. Lithium was expected to have the lowest energy production, and Potassium the highest, but in fact, the complete opposite occurred: lithium had the highest (0.5 joules), and potassium had the lowest energy production (0.1 joules). Same with the average change in temperature; Lithium had the highest temperature change (3.9ºC), followed by Sodium (1ºC), and then Potassium, which had the lowest temperature change (0.9ºC).
When looking at the qualitative data however, we can see that my hypothesis was correct « I predict that all three metals, Lithium, Sodium and Potassium, will react violently with hydrochloric acid… Potassium, atomic number 19, will be the most reactive». My observations show that potassium was the most reactive, as there was popping, fizzing, bubbling, and sparks, and also it was the only metal which actually caught on fire during the reaction. We can see that Sodium responded more violently to the hydrochloric acid than lithium, but less than potassium, just as I predicted.
I now realise that the reason for why my hypothesis was partly incorrect is because I did not see that elements are measured in moles, and not grams. This means that measuring the mass in grams means nothing; although we used 0.03g of each element, we really used 0.004moles of lithium, 0.001moles of sodium, and 0.0007moles of potassium, showing that we did not use equal values – more lithium, than sodium, and least potassium. If I had done my experiment according to a certain amount of moles for each metal instead of a certain amount of grams, then I would be able to apply my hypothesis and expect corresponding results, even when bearing in mind the errors of uncertainty, in terms of temperature (±1ºC) and in terms of precise measurements (±1ml). For example, if I had used 0.16g of potassium instead of only 0.03g, then I would be using 0.004 moles (equal to the amount of moles for lithium). With 0.16g of potassium, the amount of energy produced would be 0.6 joules, which is higher than the amount of energy lithium produced (0.5 joules). Same for sodium, if I had used 0.10g of sodium instead of 0.03 grams, then the energy produced would be 5.2 joules, which is also higher than lithium, but less than potassium. This supports my hypothesis, as I had predicted that Lithium would have the least energy production, followed by Sodium, and finally, Potassium would have the highest energy production.
Evaluation
Overall, the experiment went reasonably well and the method was carefully carried out. However, I now realise that there is quite a big problem regarding my method: it requires two people for it to be accurate. Because this is experiment is one where there is a lot to set up, I found it hard to come up with a methodology where things can be done practically, and thus, had several mistakes during the procedure, such as spills. This experiment can be setup in two parts: one where we gather the metals and the other where we gather the hydrochloric acid. If we don’t have two people, then one or the other will have to be left outside for a while. For example, in the method my group used, we chose to pour out the hydrochloric acid before the metal, simply because the metals were highly reactive and therefore had high chances of reacting with air. To improve my method, I should find a way of simplifying it.
These sorts of problems may also interfere in our results, as can be seen in the table of results; generally, the hydrochloric acid had a temperature of about 21.4ºC, but by the last trials of each metal it had a temperature of 22ºC. Not only that, but we can see that, in general, the initial temperature keeps increasing from trial to trial. This shows that there may have been a contamination, as we had chosen to take the acid out first, so it was left in open air for longer than the metals. This could also make our results less reliable, as the original temperature for the hydrochloric acid may have been lower, and if this was the case, then we would have had a larger change in temperature. Also, we could look at the smaller things, like the uncontrolled variables, which can sometimes have a very big effect on results, such as air pressure and room temperature. Another problem, as I have mentioned earlier, is how we used grams to measure the weight of the metals instead of moles. This directly interfered with our results as it gave us the complete opposite figures, which can also be seen as one of the factors which makes our results unreliable. This can also be used as an improvement or something to bear in mind in case I ever repeat a similar experiment, because if I use moles instead of grams, then I am able to truly test my hypothesis.
Another improvement, or a way to take my experiment further, would be by using the same elements, but in different solvents; for example, in sulphuric and nitric acid, as well as water. Also, I could work with all the group one elements, using moles, so I could fully test the theory that metals become more reactive as we descend. Also, I could experiment across the periodic table of elements, or only test the transition metals in acid, to see what happens, and hopefully, find some successful patterns and comparisons. Furthermore, I could try measure the energy change with pH, to see if there was any difference.
Scientific information from hypothesis obtained from : http://richardbowles.tripod.com/chemistry/reactivity/reactivity.htm