Predicting Precipitates
Q and Ksp
Purpose: To quantitatively investigate precipitation reactions.
Materials:
100mL beaker
2 10mL graduated cylinders
filter paper
funnel
electronic balance
Procedure:
1. Choose 2 salt solutions that will form an insoluble precipitate when mixed. Record the
concentration of each solution.
2. Measure 10mL of each solution using a graduated cylinder.
3. Pour the 2 solutions into a beaker and record your observations.
4. Prepare a piece of filter paper and funnel to filter the precipitate.
5. Dry the precipitate over night and find the mass of the product.
6. Calculate the % yield of your product.
Solutions used:
Reactant 1: ______________________ Concentration: _______________________
Reactant 2: _______________________ Concentration _____________________
Balanced Equation (with states):
Full ionic equation:
Net Ionic Equation:
Ksp value for predicted precipitate (see table in textbook) = __________________
Diagram of Ions:
(label all reactants and ions that are in the solutions, show the precipitate and volumes of
solutions)
+
Reactant 1:

Reactant 2:
Products:
Pre Lab Quantitative Analysis :
Table 1: Molar Calculations of Reactants
Reactant 1:
Reactant 2:
Chemical formula/name
Concentration of solution
(mol/L)
Volume of solution used
Concentration of cation
(mol/L)
Concentration of anion
(mol/L)
Number of moles of cation
(mol)
Number of moles of anion
(mol)
Qualitative Observations:
Post Lab Quantitative Analysis:
Table 2: Molar Calculations for Precipitate
Chemical formula/name of
precipitate
Number of moles of cation
Number of moles of anion
Total volume of mixture
Concentration of cation
Concentration of anion
Dissociation Equation for precipitate
Qsp expression for precipitate
Qsp value (substitute and calculate)
Compare Qsp to Ksp
Qsp Ksp
Mass of filter paper: _____________________________
Mass of filter paper with precipitate: ____________________________
Mass of Precipitate: ________________________________
𝒂𝒄𝒕𝒖𝒂𝒍
% yield = 𝒕𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍 x 100 %
Results:
1. Did your observed results coincide with your prediction (Qsp vs Ksp) about whether a precipitate
will form?
2. a) Calculate the molar solubility of your precipitate using the Ksp value form the table.
b) Compare the molar concentrations of the cations and anions in your experiment to the molar
solubility value calculated in a). What do you notice?
3. In Table 2, why did you have to divide the number of moles of each ion by 20 mL? ie. why
couldn’t you just use the ion concentrations from Table 1?
4. What type of solution (unsaturated, saturated, supersaturated) have you produced?
5. Is the product of your reaction at equilibrium? How do you know?