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Acid-Base Titrations

Acid-Base Titrations. progressive addition of one reactant to another in measured volumes until an endpoint is reached. equivalence point (mL) is when the mole ratio is exactly satisfied, volume used for stoichiometry is shown by an indicator which changes color at the endpoint (pH).

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Acid-Base Titrations

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  1. Acid-Base Titrations • progressive addition of one reactant to another in measured volumes until an endpoint is reached. • equivalence point (mL) is when the mole ratio is exactly satisfied, volume used for stoichiometry • is shown by an indicator which changes color at the endpoint (pH)

  2. Buffering: area where the pH is constant/little change even thought the titrant is being added.

  3. pH Titration Curves Titration of Sample with Titrant

  4. A. Strong Base with a Strong Acid Titration of NaOHwith HCl -sudden pH change, steep curve -endpoint is at pH = 7 -H30+(aq) +OH-(aq)  H20(l)

  5. B. Weak acid with a Strong Base • Titration of HCNwith NaOH • -less steep curve • -endpoint is pH>7, • -Ex) HCN(aq) + OH-(aq)  CN-(aq) + H20(l), CN- is a weak base so pH>7 • then CN-(aq) +H20(l )HCN(aq) + OH-(aq) , OH- increases pH

  6. C) Weak Base with a Strong Acid Titration of NH3with HCl -less steep curve -endpoint is pH<7 -Ex) NH3(aq) + H30+(aq)  NH4+(aq) + H20(l), NH4+ is a weak acid so pH<7 then NH4+(aq) + H20(l )NH3(aq) + H30+(aq) , H30+ decreases pH

  7. D. Weak Base with Weak Acid Titration of F- with HCN -difficult to see endpoint without curve -pH stays near 7, either acidic or basic depending on Ka/Kb - F-(aq) +HCN (aq) HF(aq) + CN-(aq)

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