Wednesday, May 14, 1997
Determining pH is important in various chemical experiments. This lab uses two methods, one with an electronic probe and the other, titration neutralization. Our results (2.339) contradicted the probe's reading of 2.76. Errors included the qualitative observation of pinkness.
Measuring pH using a neutralization reaction was one of the goals. We also learned how to properly titrate a solution. Other challenges included measurements to the 0.01 mL. An indicator was added to the solution so that we could see when it was neutralized. Our investigation used the H+ ion and OH- ion combination into H2O.
Trial Acid Level Base Level 1 21.96 3.835 25.18 42.015 2 15.85 1.79 18.95 36.75 3 18.95 0.88 21.82 33.59
Table 1: Readings
It should be noted that the burets were labeled with zero on the top and 50 mL on the bottom. It will not affect our readings because we can just subtract the readings to find out how much liquid actually came out.
Trial Change in acid (mL) Change in base (mL) Normality pH 1 3.22 38.18 1.857 2.236 2 3.1 34.96 1.128 2.394 3 2.87 32.7 1.39 2.307 Average 1.1509 2.339
Table 2: Calculated Data
The following equations were used:
Determining the color change became harder as the solution approached neutrality. The pink started appearing at first at the contact point between the stream of incoming base solution and the dilute vinegar solution. It would then spread and we would have to wait, shaking the flask to make the pink go away. We would wait about thirty seconds for the pink to leave. It could be possible that the pink dissipate after 30 seconds and thus our solution would not have been neutral. Carrying an increase through the equations shows that we would have generated a bigger pH number.
Our measurements gave us the correct pH within one pH of the actual reading. Qualitative errors of pinkness impeded a more accurate reading. Changing the indicator or using dual indicators would increase accuracy. A colorimeter coupled with a titration machine could quickly be able to determine pHs of various substances including those that are too dangerous to read using an electronic pH meter.