Molarity and solubility

1)  If ZnCO3 (solid) is insoluble in water, but dissolves in excess 6.0 molar HCl (aqueous), how would pull out the proper equation that would support it?

2)  How would you go about finding how many mL of 2.00 molar NaOH (Aqueous)  solution are required to neutralize 1.858 g of KHC8H4O4 (it's formula weight being 204.22)?  Any other example would do.

NaOH(aq) + KHC8H4O4 --> NaKC8H4O4(aq) + H2O(l)

3)  Potassium nitrate, KNO3, has a formula weight of 101.10.  How would I find the molar concentration of a solution prepared by dissolving 7.58 grams of potassium nitrate in enough water to prepare 250 mL of the solution?