acid and base titration
...ured by using a “pH meter”, which is an electronic device with a probe that can be submerged into the solution of unknown pH. The probe is connected to a digital read out. Look at the examples of titration curves you received in class. Notice: · all these curves have a similar shape · pH changes very gradually at first (when the volume of titrant is small) · when the titration gets closer to the equivalence point, a dramatic change occurs. This behavior is due to the fact that early in the titration there is a relatively large amount of acid in the solution (in the Erlenmeyer Flask) and the addition of a small amount of base (or titrant from the buret) produces a small change in pH. However, near the equivalence point, the amount of acid left is relatively small and the addition of a small amount of base produces a large change in pH. Compare this with the dramatic color change you will experience in the lab today at the equivalence point of your titration. Determination of the equivalence point from a titration curve: The mid-point of the “vertical section” of the titration curve is the equivalence point. Therefore, one can use the titration curve to determine: · volume of the titrant at the equivalence point · pH of the solution at the equivalence point Pre-Lab Assignment: 1. A student conducted the following experiment in the lab. Pipet 50.00mL of nitric acid (of unknown strength) into a 150mL Erlenmeyer flask. Record the pH of this solution. While the probe of the pH meter is submerged in the acid solution, add 0.1M NaOH to the Erlenmeyer flask from a buret. Stir the contents of the flask continuously and record the pH periodically. Data collected: Volume of NaOH added (ml) pH 0.0 1.00 10.0 1.18 20.0 1.37 40.0 1.95 45.0 2.28 48.0 2.69 49.0 3.00 50.0 7.00 51.0 11.00 55.0 11.68 60.0 11.96 80.0 12.36 100.0 12.52 a) Using Microsoft Excel, draw a titration curve for the above titration (be sure to use the correct axes). · This should be a scatter plot, with a line going through the points. · Print graph on a separate sheet. Be sure to follow all guidelines to draw a good quality graph (title, name, date, etc.) b) Use this graph to determine the equivalence point. Clearly mark and label this point on your graph. c) What is the volume of NaOH at the equivalence point? d) What is the pH at the equivalence point? 2. Another student conducted the following experiment in the lab. 50.00mL of acetic acid of unknown strength was pipetted into an Erlenmeyer flask. The pH of this solution was recorded. 0.10 M NaOH was added to the flask using a buret. The contents of the flask were continuously stirred and the pH was recorded periodically using a pH meter. Data Collected: Volume of NaOH added (ml) pH 0.0 2.87 10.0 4.14 25.0 4.74 40.0 5.35 50.0 8.72 60.0 11.96 75.0 12.30 a) Using Microsoft Excel, draw a titration curve for the above titration (be sure to use the correct axes). · This should be a scatter plot, with a line going through the points. · Print graph on a separate sheet. Be sure to follow all guidelines to draw a good quality graph (title, name, date, etc.) b) Use this graph to determine the equivalence point. Clearly mark and label this point on your graph. c) What is the volume of titrant ...