Question

Please help?

3. When dissolved in water, will aluminum acetate produce an acidic, basic, or neutral solution? Explain. Ka for Al(H20)63+ = 1.4 x 10-5 Ka for HC2H302 = 1.8 x 10-5

I know the solution will be acidic because Kb of acetate > Ka of Al(H2O)6^3+, but I don't understand why you would even compare the Kb with the Ka

Answer 1

yes. weak compounds acidity order compare based on Ka and Kb values.

more Ka value more acidic with in comparison in acids

more Kb value more basic with in comparison in bases

in case of comparision with acids and bases Ka and Kb values are compared

if acid Ka > base Kb ------------> acidic nature is dominent

if acid Ka < base Kb --------------> basic nature is dominent

if acid Ka = base Kb ---------------> it is neutral

pKa of acid = -log (1.4 x 10^-5) = 4.85

Kb of CH3COO- = 1.0 x 10^-14 / 1.8 x 10^-5

                           = 5.56 x 10^-10

pKb = -log Kb

         = 9.26

formula in case of weak acid + weak base

pH = 7 + 1/2 [pKa - pKb]

pH = 7 + 1/2 [4.85 - 9.26]

pH = 4.80

pH < 7 . so the salt will be acidic .