29 - Acid-Base Titrations Strong Acid & Base, Lecture notes of Chemistry

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ACID-BASE TITRATIONS

STRONG ACID & BASE

CHEM 251 SDSU

STRONG TITRANT, STRONG

ANALYTE

• (^) The simplest acid-base titration involves a strong

analyte (e.g. HNO 3 ) and a strong titrant (e.g. KOH).

• (^) The fact that the acid/base dissociate completely

makes the calculation simpler - we do not need to

involve the Ka values.

• (^) Assume that the reaction goes to completion at all

concentrations.

PH BEFORE VEQ

• (^) Before the Veq the analyte will be the dominant species in

solution.

• (^) Any titrant added will react immediately and not directly

contribute to the pH.

• (^) The pH of the solution is only due to the remaining analyte -

need to account for dilution and loss of moles.

SAMPLE PROBLEM

Plot the titration curve for the titration of 15.0 mL of 25.0 mM KOH with 10.0 mM HNO 3. Determine the pH after the following volumes of titrant have been added: A) 0.00 mL of titrant B) 25.00 mL of titrant C) 37.50 mL of titrant D) 42.00 mL of titrant

SAMPLE PROBLEM

Plot the titration curve for the titration of 15.0 mL of 25.0 mM KOH with 10.0 mM HNO 3. Determine the pH after the following volumes of titrant have been added: A) 0.00 mL of titrant B) 25.00 mL of titrant C) 37.50 mL of titrant D) 42.00 mL of titrant

PH AFTER VEQ

• (^) Once the titration is past the Veq the titrant dominates the pH

of the solution.

• (^) As the titrant is strong there is no back reaction - the

concentration of the excess titrant directly determines the pH.

• (^) Solution pH will approach but never equal the pH of the

titrant.

TITRATION CURVE

Solution pH

Volume Titratiant Added (mL) 0 20 40 60 80 Plot the titration curve for the titration of 15.0 mL of 25. mM KOH with 10. mM HNO 3. pH at Veq Veq