How to predict products and precipitates?

Question

did i do it right? i am unsure about first and last couple.

balanced equation..............precipitate

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Ca(OH)2 2HF -> CaF2 2H2O...................none?

Pb(NO3)2 K2CrO4 -> PbCrO4 2KNO3......PbCrO4

NaC2H3O2 H2SO4 -> NaSO4 C2H3O2....C2H3O2

3Cu(OH)2 2H3PO4 -> Cu3(PO4)2 6H2O...Cu3(PO4)2

2AgNO3 Na2CO3 -> Ag2CO3 2NaNO3.....Ag2CO3

Zn H2CO3 -> ZnCO3 H2 ...........................none?

Pb(OH)2 Hg2S -> PbS 2Hg(OH) ................none?

Answer 1

Ca(OH)2 2HF -> CaF2 2H2O...................none?

Pb(NO3)2 K2CrO4 -> PbCrO4 2KNO3......PbCrO4

NaC2H3O2 H2SO4 -> NaSO4 C2H3O2....C2H3O2

3Cu(OH)2 2H3PO4 -> Cu3(PO4)2 6H2O...Cu3(PO4)2

2AgNO3 Na2CO3 -> Ag2CO3 2NaNO3.....Ag2CO3

Zn H2CO3 -> ZnCO3 H2 ...........................none?

Pb(OH)2 Hg2S -> PbS 2Hg(OH) ................none?

Ca(OH)2 + 2HF -> CaF2(s)  + 2H2O(l)

CaF2 is insoluble in water.  H2O is undissocieated.  The formation of either one would have this a "reaction".

Pb(NO3)2 + K2CrO4 -> PbCrO4(s) +  2KNO3(aq) ......PbCrO4

lead (II) chromate is insoluble in water

NaC2H3O2 + H2SO4 -> NaSO4(aq) + HC2H3O2(aq)....C2H3O2 ???

Acetic acid, HC2H3O2, is a weak acid, and is undissociated

3Cu(OH)2 + 2H3PO4 -> Cu3(PO4)2(s) + 6H2O(l)...Cu3(PO4)2

Yes, copper (II) phosphate is insoluble

2AgNO3 + Na2CO3 -> Ag2CO3(s) + 2NaNO3(aq).....Ag2CO3

silver carbonate is insoluble

Zn H2CO3 -> ZnCO3 H2 ...........................none?

Zn + H2CO3(aq) --> ZnCO3(s) + H2

There is actually no such compound as H2CO3.  It should be:

Zn + CO2 + H2O --> ZnCO3(s) + H2(g)

Zinc carbonate is insoluble in water, plus hydrogen gas is given off

Pb(OH)2(s) +  Hg2S(s) -> PbS(s) +  2Hg2(OH)2(s) ................none?

this is the mercury (I) ion and mercury (I) only exists as Hg2^2+, so it would make Hg2(OH)2 if it reacted, ... but,

Neither of the reactants are particulararly soluble in water, and mercury (I) sulfide may be more insoluble than lead (II) sulfide so it is unlikely that they would swap anions.

======== Follow up =========

With regard to Dr A's answer, acetic acid is soluble (make that miscible) with water, but it does not ionize to any great extent.  Therefore the formation of undissociated acetic acid molecules from hydrogen ions and acetate ions would be considered a reaction.

Also, in the last reaction, Hg2(OH)2 is insoluble and as I mentioned earlier, only a negligible amount of the reactants will dissociate to start with.