i. Which of the following solutions has the lowest pH (more acidic). Explain you answers.
a. a 0.1 M solution of an acid with Ka=2×10-3 or one with Ka=8×10-6
b. a 0.1 M solutions of a base with pKb=4.5 or one with pKb=6.5
To determine the solution with the lowest pH (more acidic), we need to compare the acid dissociation constants (Ka) for the solutions in option (a) and the base dissociation constants (pKb) for the solutions in option (b).
Option (a) compares two acid solutions, denoted as acid A and acid B. The Ka values for the two acids are given: Ka(A) = 2×10-3 and Ka(B) = 8×10-6.
To analyze this, we need to recall that the higher the Ka value, the stronger the acid. In this case, acid A has a higher Ka (2×10-3) compared to acid B (8×10-6). Therefore, acid A is the stronger acid, and since stronger acids have a lower pH, the 0.1 M solution of acid A will have a lower pH and be more acidic.
Option (b) compares two base solutions, denoted as base C and base D. The pKb values for the two bases are given: pKb(C) = 4.5 and pKb(D) = 6.5.
To analyze this, we need to remember that pKb is the negative logarithm of the Kb values. The lower the pKb value, the stronger the base. In this case, base C has a lower pKb (4.5) compared to base D (6.5). Therefore, base C is the stronger base, and since stronger bases have a higher pH, the 0.1 M solution of base C will have a higher pH and be less acidic.
In conclusion:
a. The 0.1 M solution of the acid with Ka = 2×10-3 has the lowest pH (more acidic).
b. The 0.1 M solution of the base with pKb = 4.5 has the lowest pH (more acidic).