sketch the titration curve to show how the pH changes during the addition of NaOH to propanoic acid?

Question

Sketch the titration curve to show how the pH changes during the addition of 40cm3 of 0.10moldm-3 NaOH to 30cm3 of 0.10moldm-3 propanoic acid. The answer is: Curve starts between pH 2 and 4, flattening at pH 12-14; steep rise of 3 to 4 units in range pH 6 to 11; steep rise at 30cm3.........I don't understand how they came to this answer. Because the volumes of the two reactants are different, is there some sort of calculation involved? why is there a steep rise at 30cm3? For strong base/weak acid graphs isn't the vertical range supposed to be 7 and 10?? I'm so confused, please help....

Lavinia Carroll · Accepted Answer

http://www.kentchemistry.com/links/AcidsBases/titr... see the way way bottom of the page

Lavinia Carroll · Answer

Initial pH is between 2 and 4 because that is the pH of weak acid propanoic acid.NaOH and the acid reacts as such:NaOH + CH3CH2COOH --> CH3CH2COONa + H2OAs titration proceeds, we get a buffer system consisting of the unreacted weak acid and the salt that is formed. (Gentle rise in pH)Then there is a sharp rise in pH at 30cm3 because that is the equivalence point, as given in the question, meaning all the acid and base have reacted in stoichiometric amounts.And finally, at equivalence point, we have a basic salt which undergoes anion hydrolysis:CH3CH2COO- + H2O  CH3CH2COOH + OH-Equivalence pH should be above 7. I don't think the range is restricted to 7 and 10...(Hope this helps. The explanation I have given is according to the A-level standard, not sure whether it's applicable to you)

Lavinia Carroll · Answer

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Lavinia Carroll · Answer

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sketch the titration curve to show how the pH changes during the addition of NaOH to propanoic acid?

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