Calculating solubility of zinc oxide, boric acid, and aluminum sulfate at different pH values

Hope you can help....I've always struggled calculating solubilities of compounds at different pH's. I have 3 separate but related questions:

1) 1000 g of zinc oxide is added to a 1 liter container of pH neutral water (pH 7.0); the solubility of the ZnO is given as .29 g/L at pH 7.0; how much more ZnO would dissolve if the pH dropped to 6.0?

2) 1000 g of boric acid H3BO3 is added to a 1 liter solution of pH neutral water; the solubility of the boric acid is given as 57 g/L; again, how much more boric acid would dissolve if the pH dropped to 6.0?

3) Paper-maker's alum (Al2(SO4)3-14H2O has a pH of 3.0; the solution of alum used is given as 38% alum solids; it's solubility is unknown; 1000 g of the alum is then added to 1 liter of pH neutral (7.0) water; a) how much alum dissolves? What is the resultant change to the pH of the overall solution?

I really want to understand how these solubility calcs work, so do your best to make the analysis complete but yet simple.