1)Explain what the ideal properties of a pH indicator are. 2)During the latter p
ID: 853876 • Letter: 1
Question
1)Explain what the ideal properties of a pH indicator are.
2)During the latter part of the lab, you titrated acetic acid with sodium hydroxide. Prior to the titration, you added two drops of a phenolphthalein solution this solution was 1% w/w (weight/weight) in ethanol. Why is adding a few drops of this solution preferable to adding a small amount of solid phenolphthalein?
3)It is likely that the pH of the NaCl solution did not read the expected pH of 7. Besides dissolved salts, what else in the solution could affect pH? Explain.
Explanation / Answer
1
A it should show change in colour with change in pH
B they are usually weak acid and base
C they should dissociate in water slightly to form ions
D the dissociation constant of indicator is KIn
E the colour change should be distinct and at a low pH range
F the pH range should lie plys minus one to the pKIn value
2 if we add solid indixator directly it will nit be soluble in water and hence will not dissociate to give uts ionic form whuch is essential for change in colour. So ut is dissolved in alcohol so that it may dissciate in the aqueous solution.
3. The pH of distilled water is 7. If we add NaCl in it, it will dissociate into ions. And will not hydolysed into acid or base as weak salts do. So ideally their dissolution should not affect the pH of distilled water. But if there is a change in pH then it is only beacause of other salrs which hydrolyse into weak base or acids. The pH may deacrease due to dissolution of carbon dioxide in the water.which make water a little acidic
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