Question

Assume that 28.0mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of the monoprotic strong acid HA.

A.) How many moles of HA have been added at the equivalence point?

B.) What is the predominant form of B at the equivalence point? BA (aq), B(aq), BA-(aq), BOH-(aq), or BH+(aq)?

C.) Is the pH more than, less than, or equal to 7 at the equivalence point?

D.) Which indicator, phenolphthalein or methyl red, is likely to be the better choice for this titration?   

Answer 1

V1 = 28 ml

M1 = 10 M B

B + H2O <--> HB+ and OH-

V2 = ?

M2 = 0.10 M HA

a)

For equivalence point

M1*V1 = M2*V2

Moles of Acid = Moles of Base = M1*V1 = 28ml*.10 = 2.8 mmol of Base or 2.8*10^-13 mol of Acid

n = 2.8*10^-3 mol of Acid

b)

In equivalence point:

HA ----> H+ and A-

B + H2O ----> HB+ and OH-

The weak base will be converted to a salt, that is, B will be in ionic form

B will attract H+ ions

BH+(aq)