pH Titrations

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pH Titrations
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Equivalence point vs. End point

• End Point
• The point at which an acid-base indicator changes
  colour

• Equivalence Point
• The point at which stoichiometric amounts of acid
  and base have been mixed

In an ideal world, these two points are the same.
In reality the indicator changes over a pH range.
It needs to be chosen soo that the equivalence
point falls within that range.
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For example, if you were titrating sodium
hydroxide solution with hydrochloric acid, both
with a concentration of 1 mol/L, 25 mL of sodium
hydroxide solution would need exactly the same
volume of the acid - because they react 1 1
according to the equation.
NaOH(aq) HCl(aq) NaCl(aq) H2O(l)
In this particular instance, this would also be
the neutral point of the titration, because
sodium chloride solution has a pH of 7.But that
isn't necessarily true of all the salts you might
get formed.
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Strong acid vs strong base
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Strong base vs strong acid
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Strong acid vs weak base
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Strong base vs weak acid
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More complicated titration curves
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In the first part, complete at A in the diagram,
the sodium carbonate is reacting with the acid to
produce sodium hydrogencarbonate
In the second part, the sodium hydrogencarbonate
produced goes on to react with more acid - giving
off lots of CO2.
That reaction is finished at B on the graph.
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Strong Base vs. Diprotic Acid
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