1. Assume that your vinegar contained a small amount of citric acid (a triprotic

Question

                    1. Assume that your vinegar contained a small amount of citric acid (a triprotic acid). Using the same experimental data, would you expect the molarity of this                     sample to be the same as or different than a sample which contained only pure acetic acid?                 

                    2. We added about 10mL of distilled water to the vinegar, but we did not use this volume in the calculations of molarity. Why do you think we can ignore this                     volume in the calculations?                 

                    3. How many grams of acetic acid are in a 250 mL bottle of vinegar?                 

                    4. the pka of H2po4 is 7.21. What is the pH of a solution in which the [Hpo4^2-]/[H2PO4-] ratio is (a) 10 and b (0.1)?                 

Explanation / Answer

1) molarity will be less.

2)

you can ignore the volume as long as you add distilled water as it does not contain any minerals that reacts with vinegar .

3) specific gravity of acetic acid = 1.09

given volume of vinegar = 250 ml

vinegar is 5% acetic acid .

volume of actic acid = 0.05 x 250= 12.5 ml

mass of acetic acid = 12.5 x 1.09 = 13.625 g

mass of acetic acid is 13.625 grams

4) pH = pKa + log [Hpo4^2-]/[H2PO4-]

Given [Hpo4^2-]/[H2PO4-] = 10

a) pH = 7.21 + log 10

pH = 7.21 + 1

pH = 8.21

b) pH = 7.21 + log [Hpo4^2-]/[H2PO4-]

pH = 7.21 + log 0.1

pH = 6.21

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