For the 2 Molar solution, as the amount of acid added to the alkali increases the temperature of the solution begins to increase at a fairly steady rate until 22cm3 of acid is added to the 25cm3 of alkali and at this point the temperature increase almost comes to a complete stop. Between 22cm3 and 27cm3 of acid added to the alkali the temperature either didn’t change or went up by only 0.5oC. Then from 28cm3 to 30cm3 of acid added to the alkali the temperature dropped by 0.5oC. The graph of the acid added against amount of temperature shows a positive correlation up to 27cm3 of acid added and then also shows the signs of a negative correlation between 28cm3 and 30cm3 of acid added. I have found that for the thermometer method, the temperature was inversely proportional to the amount of acid that was added to the alkali. Also, before the neutral point, the temperature started to increase quickly and then slowed down as it got closer to the neutral point. This may have happened because at the start of the experiment there was less liquid in the beaker for the reaction to heat. As acid was added, this meant that there was more liquid for the reaction to heat, and so the rate of temperature increase would have started to slow down as you got closer to the neutral point, where the temperature started decreasing. Another reason for the slow increase in temperature was that the acid was cooler than the alkali when it was added.
Acid + Alkali→Salt + Water + HEAT
Hydrochloric Acid + Sodium Hydroxide→Sodium Chloride + Water + HEAT
HCl + NaOH→NaCl + H20 +HEAT
Both the indicator and the thermometer method gave similar results. When neutralisation took place it was at similar points in all of the experiments.
Evaluation
As I had first thought, the graph peaked at the point where neutralisation took place. The human error that occurred during the experiment was due to careless acid adding and thermometer reading. These mistakes led to slight inaccuracies in the results. It is slightly difficult to add the right amount of acid to the alkali by using a burette because it is very easy for a person to turn the handle of the burette too much and it will allow too much acid to be poured into the sodium hydroxide and indicator solution. It also takes some practice when measuring to see if the miniscus reaches the right calibration point on the burette.
As for improvements to the experiment: -
- The polystyrene cup should have had a lid on it to prevent heat loss so that temperature of solution is not affected. The lid can be also be made of polystyrene and a small hole should be made to insert the thermometer and allow the acid to be poured into it
- An alternative piece of equipment than a burette should be used to make sure that the correct amount of acid is poured into the beaker containing alkali. I suggest using a 2ml syringe to slowly pour the acid in as the results will be more accurate
- You could also keep adding more and more acid to the alkali and see how the temperature of the solution is affected and draw a graph to show your findings
- The main problem that was affecting the results of the thermometer method was that the room temperature was changing and never remained at a constant temperature. There was no way of controlling the temperature in this experiment unless it was done in a laboratory under controlled conditions
If I had had enough time, I would have repeated my experiment for each molar solution two times and take an average of the results so that I can get a more accurate result. I would have also taken more readings closer to the point of neutralisation to make sure that I got a more accurate result.
