Equivalence Point for Titration #1: 24.96 mL

Equivalence Point for Titration #2: 25.40 mL

Equivalence point for Titration #3: 25.20 mL; midpoint pH Titration #3: 9.80

QUESTIONS – Please answer using complete sentences and calculations where appropriate.

Why doesn’t the KHP concentration have to be exactly 0.100M? Explain using complete sentences.

Why is it important that you exactly know the concentration of KHP? Explain using complete sentences.

Why can’t you exactly know the concentration of NaOH by weighing some and adding water? Explain using complete sentences.

Set up the calculation required to determine the concentration of the NaOH solution via titration of a given amount of KHP. Include all numbers except the given mass of KHP.

Set up the calculation required to determine the concentration of the unknown strong acid via titration with a known volume of NaOH of known concentration. Include all numbers except the volume and concentration of NaOH.

Set up the calculation required to determine the concentration of the unknown weak base via titration with the unknown strong acid of known concentration and volume. Include all numbers except the volume and concentration of the unknown acid.

Error analysis – EXPLAIN what effect each of the following would have on the result listed:

a. The pipet you used to measure out exactly 25.00mL of KHP was rinsed only in distilled water but not rinsed in acid solution. What is the effect on the calculated concentration of NaOH? (remember: concentration is a number – increase, decrease, or no change). Explain your answer.

b. The beaker into which the 25.00mL of KHP was added was not dry. What is the effect on the calculated concentration of NaOH – increase, decrease, or no change? Explain your answer.

c. An air bubble of some size was present in the liquid in the buret at the end of the first titration but not at the beginning. What is the effect on the calculated concentration of NaOH – increase, decrease, or no change? Explain your answer.

d. After you correctly determine the concentration of NaOH, the NaOH is left open overnight, so that some CO2 is dissolved in it. What is the effect on the calculated concentration of strong acid – increase, decrease, or no change? Explain your answer. Include a balanced chemical equation involving NaOH and CO2.

e. Why would it be OK to use phenolphthalein during the second titration, but not the first and the third?

f. Suppose the KHP is contaminated and is only 95% pure. What is the effect on the calculated concentration of the weak base? Explain your answer.

8) What is the Kb of the unknown base? Describe how you arrived at your answer. Include calculations.

9) Using a chart of Kb, what is the unknown weak base? (Kb table.png)

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