Theory and Concept: When titrating a weak acid, HA, with a strong base the equilibrium between the weak acid and its ion is reestablished after every addition of base. The reaction in this titration is pushed towards the right after every addition of a base. At the beginning of a titration between a weak acid and a strong base, there is mostly HA in the solution with small amounts of HUH+ and A- because only a small amount of base has been added therefore a small amount of unionization has occurred.
As we added more base, more HA is unionized and more salt formation occurs meaning the concentration of HA will decrease while the concentration of A- will increase. The pH rises above the equivalence point because we are adding base to a solution with a relatively large volume. At the end of the titration the ratio of [A-V[HA] goes from low to high. This means that all of the HA will be neutralized, causing the pH to change. Because of the rapid pH change around the equivalence point, the iterant has to be added in lesser and lesser amounts s we approach the equivalence point.
Procedure: CHEM.. 1 13 Lab Manual, 2014, Determination of : Titration of a Weak Acid, pus. 89-96 Equations/Experimental Equipment and Apparatus: Logger, Labor, pH probe, drop counter, 60 ml reagent reservoir, stir station =p Data and Observations: Data: Original pH=3. 23 Equivalence volume = 50. 51 ml at pH of 8. 58 Drop rate: 1 drop every 2 seconds Observations: In the beginning of the titration the solution was made up of mostly acetic acid with a small amount of and because unionization was starting to occur. As the titration progressed, we watched the graph on the computer and saw the pH increase and then rise very slowly.
This slow rise continued for a long period of time. After this portion of the graph, the pH increased significantly. The pH kept increasing after the equivalence point and then started to level off again. Calculations: Equivalence volume = 50. 51 mammalian pH= 3. 23 Initial Volume= 20 ml [HAJJ original= 0. MM Aka from pH of original solution = ml = 25. Ml at pH=4. 8 =peak 4. 8=-egg(Aka) Aka = IOWA-4. 8 = 1. Xx Aka from pH of half-naturalization point = 1. Xx Discussion and Conclusion: Some possible sources of error could have been a drop rate that was faster or slower than one drop every two seconds.
Our drop rate at first was around 1 drop every 1 seconds at the start which was way to fast. We changed this to around 1 drop every 2 seconds to get better results. Another source of error could have been starting with more or less than 20 ml of the weak acid. The two values of Aka that were obtained through the two separate methods were similar. By using the method of the pH from the original solution, the Aka came out to ND when using the method of the pH of the half-naturalization point, the Aka came out to 1. Xx. This shows that there was only a slight amount of error that occurred in this experiment. As for the graph, the area where there was a sharp rise is known as the buffering region. This is because at this moment, up until around 50. 25 ml, the solution is being buffered by a presence of the weak acid and the weak acid’s salt. After the rapid rise in pH, the acid has been officially neutralized and the solution’s pH only has little change (seen around 55 ml where the graph begins to level off again)