Question

lon concentration refers to the molar concentration of an ion in solution. It may be identical to, or greater or less than, the molar concentration of the compound containing the ion that was used to make the solution. For soluble salts, the molarity of a particular ion is equal to the molarity of that compound times the subscript for that ion. For example, 1 M of AlCl3 is 1 M in A1 and 3 M in CI . 1 M of (NH4)2SO4 is 2 M in NH4 and 1 M in SO42

Answer 1

Na₃PO₄(s)   $\to$ 3 Na⁺ (aq) + PO₄^3- (aq)

mole ratio of Na₃PO₄ and Na⁺ = 1:3

Now, moles of Na⁺ in the solution

= Molar concentration × volume (L)

= 0.500 × 275 ×10^-3

= 0.1375 .

So, moles of Na₃PO₄ = moles of Na⁺ × $\frac{1}{3}$ = 0.1375× $\frac{1}{3}$

= 0.0458.

Mass of Na₃PO₄ needed

= moles × molar mass

= 0.0458(mol) × 164 (g/mol)

= 7.52 g. ( Three significant figure)