A 50.0 mL sample of 1.54*10-2 M NaSO4 is added to 50.0 mL of 1.28*10-2 Ca (NO3) 2. What percentage of the Ca2 + remains unprecipitated?,

The reaction would be as shown below;

Na2SO4 + Ca (NO3) 2 = CaSO4 + 2 NaNO3

The moles of NaSO4 will be;

= 0.05 * 0.0154 = 0.00077 moles

While the number of moles of Ca (NO3) 2

= 0.05 * 0.0128 = 0.00064 moles

The mole ratio of sodium sulfate and calcium nitrate is 1:1

Ca (NO3) 2 is the limiting reactant, so ignoring the Ksp of CaSO4, zero percent of the Ca^2 + ions remain unprecipitated.