Strong Acid/Strong Base Titration

With strong acids titrated with a strong base, we do not need to account for the acid and base equilibrium constants.

The strong acid analyte is HBr, with initial concentration F_HBr. Strong base titrant is NaOH, with concentration F_NaOH

Using the systematic approach to solving chemical equilibrium problems

Chemistry:

Charge Balance:

Mass Balance:

Equilibrium Equation:

Substitute [OH^-]=K_w/[H₃O⁺], [Br^-]=F_HBr, and [Na⁺]=F_NaOH, into charge balance equation

Solve for [H₃O⁺]...

1) Formal concentrations are adjusted for the volume change upon titration.

Regions in the Strong Acid/Strong Base Titration

Initial (Region 1) F_NaOH=0 and

½ way to the equivalence point (Region 2) F_NaOH=½F_HBr or F_NaOH=F_HBr-F_NaOH

At the equivalence point (Region 3) F_HA=F_NaOH and...

Past the equivalence point (Region 4) all acid has been consumed. Thus one need only account for excess base.

Resulting Prediction for a Strong Acid/Strong Base Titration

The resulting titration curve is shown to the right. As usual, we plot the pX, in this case X=[H⁺] , versus volume of titrant. The plot is for 20 mL of a 0.1 F HCl analyte being titrated with 0.1 F NaOH titrant. The blue diamonds are the points calculated above. The smooth curve is a log plot of the root to the governing quadratic [H⁺] equation

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This page was created by Professor Stephen Bialkowski, Utah State University.

Last Updated Monday, August 28, 2006