It takes 12.5mL of a 0.30M HCl solution to neutralize 285mL of NaOH solution.
What is the concentration of the NaOH solution?

Molarity NaOH = 0.0263M

Explanation:

Molarity Acid x Volume Acid = Molarity Base x Volume Base

12.5ml x 0.60M = 285ml x M(base)

M(base) = 12.5ml x 0.60M / 285ml = 0.0263M

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%