Question

What is the molar concentration of Na⁺ ions in 0.0300 M solutions of the following sodium salts in water?

a) NaBr

b) Na₂SO₄

c) Na₃PO₄

Answer 1

Solution:

a) NaCl is a uni-univalent electrolyte. The dissociation of NaCl in water is given as,

NaCl(aq) = Na+ (aq) + Cl-(aq)

0.0300 M --- 0.0300 M ----0.0300 M

Thus, [Na+] = 0.0300 M

b) Na2SO4 is a uni-bivalent electrolyte, it dissociated in water as,

Na2SO4 (aq) = 2Na+ (aq) + SO4^2- (aq)

0.0300 M --------2 x 0.0300 M -----0.0300 M

Thus,

[Na+] = 2 x 0.0300 M = 0.0600 M

c) Na3PO4 is a uni-trivalent electrolyte, it dissociated as,

Na3PO4 (aq) = 3Na+ (aq) + PO4^3- (aq)

0.0300 M ---------3 x 0.0300 M ----0.0300 M

Thus, [Na+ ] = 3 x 0.0300 M = 0.0900 M