Question

. Calculate the pNa of a solution prepared by adding 55.0 mL of 0.90 M NaNO₃ to 45.0 mL of 0.50 M Na₂SO₄

Answer 1

Solution :-

Lets calculate the moles of Na+ in each solution

Moles = molarity * volume

Moles of Na+ in NaNO3 = 0.90 mol per L * 0.055 L = 0.0495 mol

Moles of Na+ in Na2SO4 = 0.50 mol per L * 0.045 L * 2 = 0.045 mol Na+

Total moles of Na+ = 0.0495 mol + 0.045 mol = 0.0945 mol

Total volume = 55 ml + 45 ml = 100 ml = 0.100 L

New molairity of Na+ = moles / total volume

                                        = 0.0945 mol / 0.100 L

                                       = 0.945 M

Now lets calculate the PNa

PNa = - log [ Na+]

pNa = - log [0.945]

pNa= 0.0246