P H of a Buffer - Chem 1128 lab report PDF

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Chem 1128 lab report...

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“pH Measurements – Buffers and Their Properties” Arushi Mathur Partners: Rachel Lese, Gabriella Perry 20 August 2019

2 Purpose: The purpose of this experiment is to study aspects of pH in different compounds. In Part A of this experiment we will qualitatively observe and approximate the pH of some solutions using various indicators. Then, we will use a pH meter in order to gauge the pH of solutions more accurately, and verify our results with the pH indicators. Next the properties of buffers and pH effects will be observed by physically creating one and calculating the Ka of the resulting solution. Finally, we will test to see the capacity of buffer solutions by adding base and acid and noting the pH change (or lack thereof).

Procedure: Procedure was followed as detailed in the lab handout pages 205- 210.

Data: Please refer to the included data pages.

Calculations: Please see the attached calculations page (Part C).

Results: In Part A, we estimated a pH range of 1.5- 6 for HCl, 3-6 for NaH2PO4, 2-4 for HC2H3O2, and 6-7 for ZnSO4. For Part B, we confirmed that the pH measured by the pH meters was within the expected color range for that given pH: NaCl was ~6.00 and turquoise, Na2CO3 was ~11.05 and blue, NaC2H3O2 was ~7.85 and blue, and NaHSO4 was ~1.65 and yellow. Using the Ammonia buffer system, our average pKa was 9.04. When we designed our own buffer, we wanted to maintain a pH of 8.75 or so, after creating it, our observed pH of the resulting solution was 8.95.

3 Discussion/Conclusion: In part A, we figured out how to look at multiple indicator colors and from that, determine the approximate pH of some solutions. This step turned out to be very helpful when we used a measuring device to test some other solutions, although it is not very accurate because it gives a range of pH rather than a definite value. Part B and C used the pH meters which gave more precise results, with increased accuracy as it measured the pH relative to an electrical current. In our creation of a buffer system using ammonia, we found our observed value (8.95) to be pretty close to what we chose for the buffer pH (8.75). That being said, the measurement still fluctuated a little because we had to re-standardize the pH meters and the measurements would not hold one consistent value. Some error sources could have been in the measurement of the solutions used to make the buffer, which may not have been as accurate as a pipette would be. A slight change in volume can affect the pH slightly, causing it to be more acidic or basic and directly affecting our calculated ka and volumes needed to make the buffer (and its resulting pH)....