Fifty milliliters of 0.0400 M CuSO₄(aq) is mixed with 25.0 mL of 0.120 M NaOH(aq). The reaction
CuSO₄(aq) + 2 NaOH(aq) ⟶ Cu(OH)₂(s) + Na₂SO₄(aq)
proceeds to completion. After the reaction is finished and the solid is separated, what is the concentration (in mol L⁻¹) of Na⁺ ions in the remaining solution?