Acetic acid, abbreviated HOAC, is about 1.3% dissociated in a 0.01M solution HOA

Question

Acetic acid, abbreviated HOAC, is about 1.3% dissociated in a 0.01M solution HOAc_aq H^+ + Ac(aq) a)[H+] = a)[H+] = b)pH b)pH = c)Two indicators best used to bracket the pH of this solution c) and d) The color of methyl orange in this solution d) A chemist is given a bottle of carbonated water for pH testing. She adds methyl violet to a sample and finds the color is blue-violet. To another sample she adds Congo red and the color is blue. In what pH range has she bracketed the sample? A dilute ammonia solution used for washing window glass gives a blue color with the indicator thymolphthalein. What is the minimum pH of the solution?

Explanation / Answer

1) HOAc           -->   H+                +   AcO-

Initial             0.1 M                 0                        0

Change      -(0.013 X 0.1)        (0.013 X 0.1)      (0.013 X 0.1)

Final            0.1-0.0013            0.0013                 0.0013

a) [H+] = 0.0013

b) pH = -log[H+]

pH = -log[0.0013] = 2.88

c) The indicators which can be used for weak acid = Methyl orange and congo red

d) Colour of methyl orange in solution = Red

2) the pH range of methyl violet = 0- 2.5 ( it gives yellow green to violet)

The sample is blue violet so pH should be above 2.5

pH range of congo red = 3.0 - 5.0 ( below pH 3 blue and above 5 red)

with congo red colour is blue

So the pH range will be 2.5- 3

3) The pH range of 9.3 - 10.5

Below 9.3 colourless and above 10.5 blue

So the minimum pH is 10.5

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