posted by Rachel on .
Answer the following two questions about the equivalence point for the titration of 27.8 mL of 0.235 M hypobromous acid (pKa = 8.64) with 0.214 M KOH.
1)Predict if the solution will be acidic, basic or neutral at the equivalence point.
2)Calculate the pH of the solution at the equivalence point.
HBrO + KOH ==> KBrO + H2O
1)What do you have at the equivalence point? That is a soln of KBrO. It is the salt of a strong base and a weak acid; therefore, the solution MUST be basic.
2) The pH at the equivalence point is determined by the hydrolysis of the salt.
............BrO^- + HOH ==> HBrO + OH^-
Set up ICE chart.
You have M x L = 27.8 x 0.235 = about .0065 moles HBrO(you need to be more exact). The equivalence point will be about 0.0065/0.214 = about 30 mL KOH.
The salt (KBrO) is then M = moles/L = 0.0065/(28+30) = about 0.11M
Substitute into Keq as follows:
Kb = (Kw/Ka) = (x)(x)/(0.11)
Solve for x, convert to pOH, then convert to pH.