Question

1,When aqueous sodium hydroxide is added to a solution containing lead(II) nitrate, a soHowever, when additional aqueous hydroxide is added the precipitate redissolves forming a soluble [Pb(OH)4]2–(aq) complex ion.lid precipitate forms.
2,The Ksp of strontium carbonate, SrCO3, is 5.60 × 10-10. Calculate the solubility of this compound in g/L.
3,Calculate the pH at the equivalence point for the titration of 0.240 M methylamine (CH3NH2) with 0.240 M HCl. The Kb of methylamine is 5.0× 10–4.

Answer 1

The first question makes no sense due to typos (and I think parts have been omitted).
The second one is
...........SrCO3 ==> Sr^2+ + CO3^2-
I..........solid.....0........0
C..........solid.....x........x
E..........solid.....x........x

Substitute the E line into Ksp expression and solve for x = solubility SrCO3.

#3. The pH will be determined by the hydrolysis of the salt which will be methylamine hydrochloride. And the concn of the salt will be 0.240/2 = 0.120M.
....CH3NH3H^+ + H2O ==> CH3NH2 + H3O^+
I.....0.120..............0........0
C......-x................x........x
E...0.120-x..............x.........x

Ka for CH3NH2*HCl = (Kw/Kb for CH3NH2) = (x)(x)/(0.120-x)
Solve for x = (H3O^+) and convert to pH.