Na3AsO4 is a salt of a weak base that can accept more than one proton. If 18.4 g of Na3AsO4 is dissolved in water to make 250mL of solutions how many moles of sodium cations are in the solution? Answer in units of mol.

0.266 moles of Na⁺

Explanation:

First step we dissociate the salt:

Na₃AsO₄  →  3Na⁺  +  AsO₄⁻³

From 1 mol of sodium arsenate, we must have 3 moles of sodium cation and 1 mol of arsenate.

We determine the moles of salt:

18.4 g . 1 mol/ 207.89 g = 0.0885 moles of salt.

We apply the followring rule of three:

1 mol of salt has 3 moles of Na⁺

0.0885 moles of salt may have (0.0885 . 3) / 1 = 0.266 moles of Na⁺

1 is the answer to this problem