Question

The half equivalence point of a titration occurs halfway to the end point, where half of the analyte has reacted to form its conjugate, and the other half still remains unreacted. If 0.280 moless of a monoprotic weak acid (Ka= 6.1 x 10-5 is titrated with NaOH what is the pH of the solution at the half-equivalence point?

Answer 1

The pH at the half-equivalence point of the titration of a monoprotic weak acid with NaOH is equal to the pKa of the weak acid. Since the Ka of the acid is 6.1 x 10^-5, the pH at this point is approximately 4.21.

Step-by-step explanation:

At the half-equivalence point in the titration of a monoprotic weak acid with NaOH, half of the analyte, weak acid, has reacted with the base to form its conjugate base, and the remaining half is unreacted. According to the provided information that states the pH equals the pKa at the half-equivalence point of the titration of a weak acid, we can use the given acid dissociation constant (Ka) to calculate the pH.

The Ka for the weak acid is 6.1 x 10-5, and to find the pKa, we take the negative logarithm (base 10) of the Ka: pKa = -log(Ka) = -log(6.1 x 10-5), which results in a pKa (and therefore the pH at the half-equivalence point) of approximately 4.21.

Therefore, the pH of the solution at the half-equivalence point, when titrating 0.280 moles of this weak acid with NaOH, is 4.21.