How do the values of measured pH for acetic acid before and after the addition o

Question

How do the values of measured pH for acetic acid before and after the addition of NaOH compare? How do you explain the changes you observe (in chemical terms)? Can you rationalize the equivalence point pH of the acetic acid-NaOH system being higher than 7.0? What species are present in solution before, at and after the equivalence point? . Why are the accepted and measured values for Ka not the same? What are the major sources of error in this experiment? Which solution had the best ability to resist changes in pH upon addition of small quantities of acid or base? Why? 108

Explanation / Answer

Ans 1 :

The pH scale ranges from 0 to 14. The 0-1 range stands for the acidic pH and 7-14 stands for an alkaline pH. The pH 7 is neutral (neither acidic nor basic).

Acetic acid is acidic in nature (pH less than 7) and NaOH is basic in nature (pH more than 7).

When NaOh is added to the acid , the reaction goes as :

CH3COOH + NaOH = CH3COONa + H2O

The reaction is called as neutralisation reaction , since the product formed is a salt.

So before the addition of NaOH , the pH is less than 7 (acidic) , but after the addition of NaOH the pH becomes more than 7, as there is formation of basic salt. (acetic acid is a weak acid and NaOH is strong base).

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