Assume that 30.0 mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of a monoprotic strong acid HX. (a) How many moles of HX have been added at the equivalence point? (b) What is the predominant form of B at the equivalence point? (c) What factor determines the pH at the equivalence point? (d) Which indicator, phenolphthalein or methyl red, is likely to be the better choice for this titration?

Question

Assume that 30.0 mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of a monoprotic strong acid HX.  (a) How many moles of HX have been added at the equivalence point?  (b) What is the predominant form of B at the equivalence point?  (c) What factor determines the pH at the equivalence point? (d) Which indicator, phenolphthalein or methyl red, is likely to be the better choice for this titration?

Boxer Boy · Accepted Answer

c. is actually methyl red

DrBob222 · Answer

a. moles HX added = M x L.
b. B + HX ==> BH^+ + X^-
c. The hydrolysis of the salt BH^+. Said another way, the strength of BH^+ as an acid.
d. Phenolphthalein changes color at pH about 9. Methyl red changes color about 5. Which do you think?

serjon · Answer

a. 2.7 x 10 -3 moles or 0.0027 b. BH + (aq) c. Already given. d. phenolphthalein

Diggity dogg · Answer

hi to you. is this right?

Allison · Answer

For c it is both the Ka for BH^+ and concentration of BH^+ to determine pH at the equivalence point.