Why is magnesium ascorbate, which is a conjugate base of a weak acid, acidic? Why are magnesium ascorbate and potassium acetate, which are salts of strong bases with weak acids, acidic?
I discovered with litmus paper that magnesium ascorbate is acidic and found out from https://foodb.ca/compounds/FDB015417 that potassium acetate should also be acidic.
How can this be? Shouldn’t conjugate bases of weak acids, ascorbate and acetate in this case, be basic and the strong dissociated spectator ions, $\ce{K+}$ and $\ce{Mg^2+}$, neutral?
$\mathrm{p}K_\mathrm{a}$ relation in the answer of Kav

Wikipedia says pKa's are 4.10 (first), 11.6 (second)

gives the hint a monobasic salt with alkali metals should be very mildly alkalic, as pKa2 is farther from pH 7.
$pH \approx \frac{\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2}}{2} = \frac{4.10+11.6}{2}=7.85$
OTOH, it will probably form a complex with Mg, affecting acidity of the 2nd hydrogen. Like
$$\ce{2 H2A(aq) + Mg^2+(aq) -&gt; [MgA2]^2-(aq) + 4 H+(aq)}$$
respectively
$$\ce{Mg(HA)2(s) -&gt;[H2O] [MgA2]^2-(aq) + 2 H+(aq)}$$
See also citrate or EDTA complexes for this effect. AFAIK, before suitable metalochrome indicators came, metal content with excess of Na2H2-EDTA had been sometimes determined by back titration using NaOH.