Experiment 6 Buffers and Potentiometric Analysis (32 points possible) Section (d

Question

Experiment 6 Buffers and Potentiometric Analysis (32 points possible) Section (daytime):- Instructor: Due date: Answer the following questions using complete sentences and support your answers with calculations, if desired. Attach additional pages as necessary. Handwritten or typed answers are acceptable Assuming that the unknown weak acid solution is vinegar (aqueous acetic acid, CHiCOH) with a density of 1.00 g/mL, calculate the mass percent of acetic acid in your unknown solution 1. 2. If the endpoints you reached during the standardization of your NaOH solution were very precise (relative average deviation of 0.03%) but were all overshot, is the reported molar concentration of the acid solution from this experiment greater than, less than, or equal to the true concentration? Explain your answer. 3. If your absent-minded lab partner spilled deionized water into your NaOH titrant, dilutingt, would the K, value you determined for the weak acid be greater than, less than, or equal to the true K, for the acid? Explain your answer. while the other two are not very good buffers. The two poor buffers are ineffective buffers for different reasons. Explain why the buffers are not good at resisting pH changes. Write a conclusion for the Potentiometric Analysis and Buffers lab. (Reference Appendix on guidelines for laboratory writing) (20 pts additional) 4. In part II of the lab, you are given three buffer solutions. One solution is a very good buffer, 5.

Explanation / Answer

(1)

Assume that we take 1 L of this solution, so mass of this solution = Density*Volume = 1*1000 = 1000 g

Assuming the molar conc of this solution as 'C' molar, we have:

Moles of acetic acid = C*1 = C

Mass of acetic acid in 1 L solution = Moles*MW = C*60

So,

Mass% of acetic acid in solution = (Mass of acid/Volume of solution)*100 = (C*60/1000)*100 = C*6 %

Put the value of C in above formula to calculate the mass %.

Hope this helps !

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