Re: Two questions about lead-acid chemistry

Ed Ferris's previous post was like this :

Rather,

Pb(HSO4)2 = PbSO4 + H2SO4

The only way this reaction goes to the right is if the sulfate precipitates
(from battery acid) and the hydrogen sulfate is soluble. Do we know this
is true? The CRC Handbook says both are slightly soluble in H2SO4.

Substitute any other cation for Pb++ and the reaction goes to the left.

Your reaction in fact never happens.
In aquatic solution of acids and salts,
the reactions occurs with ions.

In solution these salt compounds do not exist, there exist ions.
( Well, in some degree there exist non charged complexes,
but they are dissociated to high degree)
Once there is HSO4-, it does not care,
if it belongs to Pb2+ or to H+.

Reactions that runs all the time in both directions are
H2SO4 <-> H+ + HSO4-
HSO4- <-> H+ + SO4(2-)
and possibly
M(2+) + SO4(2-) <-> MSO4(prec)
M(2+) + 2 HSO4- <-> M(HSO4)2 (Prec)

To form solid salt, the multiplication of concentration of involved
ions need to cross a given value.
In acid lead accumulator precipitation of PbSO4
keeps Pb2+ concentration at so low level
( about 10^-10 mol/l or so),
that formation of precipitated Pb(HSO4)2 cannot occur.

In general all depends on solubility ratio of both salts and on pH.
Well, more precisely also on level of ion complex creation.
If one of salts is much less soluble than the other,
you cannot ( at least easily ) get the other.

Both KHSO4 and K2SO4 are comparably soluble,
so what you get depends on pH.
But you do not get from solutions.
Pb(HSO4)2, Cu(HSO4)2, Zb(HSO4)2, Fe(HSO4)2......
because MSO4. nH2O precipitates sooner.
You only get concurrent presence of ions.

The fact is, that PbSO4 similar as BaSO4
is partly soluble in concentrated H2SO4,
where is minimal concentration of SO4(2-)
to keep them precipitated.
As far as there is mainly HSO4- you can say
you have solution of Pb(HSO4)2.
But you will not get it.

--
Poutnik
The best depends on how the best is defined.
.

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