The method and the results are on the net ionic equation lab. Do the analysis yourself first, then check the answers below.
Quick answer: A net ionic equation shows only the species that change, leaving out spectator ions. These answers go with the AP Chemistry lab on net ionic equation: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Here are the net ionic equation lab answers for AP Chemistry: graph, calculations, uncertainties and conclusion. First do the lab yourself, then compare, and go back to the lesson if needed.
Model answers use the sample data. Your masses will differ a little, but the shape of the graph and the position of the break at about 33 mL should agree. Show conversions from volume to moles and give masses to two or three significant figures.
10.0 mL: 0.00300 mol CO₃²⁻ < 0.0100 mol Ca²⁺, so Na₂CO₃ is limiting. 40.0 mL: 0.0120 mol CO₃²⁻ > 0.0100 mol Ca²⁺, so CaCl₂ is limiting.
Question 4 Theoretical mass
20.0 mL: n = 0.00600 mol, m = 0.601 g. 50.0 mL: Ca²⁺ limiting, n = 0.0100 mol, m = 1.00 g.
Question 5 Percent yield
20.0 mL: 0.58 / 0.601 × 100 = 96.6 percent. All five are 96 to 97 percent, so the loss is consistent, probably precipitate left on the beaker or paper.
Question 6 Graph
Mass rises in a straight line from the origin and then levels at 0.97 g. The lines meet where n(CO₃²⁻) = 0.0100 mol: V = 0.0100 / 0.300 = 33.3 mL.
Question 7 Explain the plateau
All the Ca²⁺ has precipitated; extra CO₃²⁻ stays dissolved, so the mass is fixed by the amount of Ca²⁺.
Question 8 Improve the method
Precipitate lost during transfer: rinse the beaker into the funnel. Moisture left in the precipitate: dry to constant mass. Both would otherwise change the measured mass.
