Experiment 14 part 1.pdf - Penn State CHEM 113 Experiment...

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Penn State CHEM 113 Experiment 14 Part 1: Acid-Base Equilibria Experiment Goal: To be able to interpret the conductivity experiments. To be able to identify strong and weak acids and bases by means of K a , K b , pK a , and pK b values. To investigate several aspects of acid-base equilibria by means of a colored dye called bromocresol green. To carry out a determination of the acid dissociation equilibrium constant of several colored, weak acid indicators. To use a solution of a combination of indicators (a universal indicator) as a color probe for sensing [H + ] and, therefore, pH. To investigate various quantitative aspects of acid-base chemistry by interpreting experimental titration curves and by comparing the data with computer-simulated titrations. To apply the principals of graphical interpretation of titration data to investigate polyprotic acid equilibria. Procedure: Thompson, S. PSU Chemtrek: Expt. 14 Acid Base Equilibria; Keiser, J., Hayden-McNeil Publishing: Plymouth, MI, 2020, pp 14-1 to 14-39. Section A. Conductimetry and the Strength of Acids and Bases Goal: (1) To be able to interpret the conductivity experiments. (2) To be able to identify strong and weak acids and bases by means of K a , K b , pK a , and pK b values. Data and Observations: Table 14-1 ~ Conductivity of Solutions Conductivity 0.1 M NH 3 /NH 4 OH 5/10 0.1 M acetic acid 4/10 0.1 M HCl 9/10 0.1 M NaOH 8/10 Tap water 5/10 Distilled water none Question 1: Arrange the six solutions tested from the lowest to the highest conductivity. Explain the order observed i.e., why do solutions of the same concentration have different conductivities? If you cannot differentiate between them, explain why not. Distilled water < 0.1 M acetic acid < Tap water < 0.1 M NH 3 /NH 4 OH < 0.1 M NaOH < 0.1 M HCl The reason for solutions with the same concentration having different conductivities has to do with their strength, whether they are an acid or a base. The most acidic in this order is HCl, it also has the highest level of conductivity. Question 2: The conductivity of an H 2 SO 4 solution was followed as it was titrated with the strong base Ba(OH) 2 . Predict the relative conductivities of: (a) the starting solution The H 2 SO 4 solution should have a 9/10 level of conductivity.
Penn State CHEM 113 (b) the solution at the equivalence point There will be no conductivity at the equivalence point, because the moles of acid would equal moles of the base.

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