CHEMISTRY 11
SOLUTION WORKSHEET #6
Precipitation Problems
In the following questions, the two solutions are mixed together and a
precipitate is formed. The precipitate is allowed to fall out of solution. We will
assume that ALL of one of the ions involved in the reaction is completely used
up (i.e. none of it still remains in solution).
a) Write the net ionic equation for the precipitate.
b) Calculate the concentration of all remaining ions in
solution after the precipitation ends. (HINT - Use a
table !!!)
1) 10.0 mL of 0.200 M Na2SO4 and 20.0 mL 0.200 M Pb(NO3)2
2) 50.0 mL of 0.500 M AlCl3 and 20.0 mL of 0.800 M Na3PO4
3) 20.0 mL of 0.250 M NaCl and 30.0 mL of 0.200 M Pb(NO3)2
ANSWERS :
1)
Pb2+(aq) + SO42-(aq) ---> PbSO4 (s)
2)
[Na+] = 0.133 M
[Pb2+] = 0.0667 M
[NO3-] = 0.267 M
3)
Pb2+(aq) + 2 Cl-(aq) ---> PbCl2 (s)
[Na+] = 0.100 M
[Pb2+] = 0.0700 M
Al3+(aq) + PO43-(aq) ---> AlPO4 (s)
[Al3+] = 0.0692 M
[Cl-] = 0.577 M
[Na+] = 0.369 M
[NO3-] = 0.240 M
Stoichiometry of Precipitation Reactions.
1.
2.
3.
4.
5.
6.
Identify the species present.
Identify what reacts and write the net ionic equation.
Calculate the moles of reactants.
Determine the limiting reactant.
Calculate the moles of product using the limiting reactant.
Convert to the required units.
Examples:
1. Calculate the mass of PbI2 produced when 1.0 L of 0.30M Pb(NO3)2 is mixed
with 1.5 L of 0.20 M NaI.
2. What mass of Na2CrO4 is needed to precipitate all of silver ions in a 2.0 L of a
0.30 M solution of AgNO3?
3. What volume of 0.200 M of K3PO4 is required to precipitate all of the lead
ions in 0.50 L solution of 0.30 M Pb(NO3)2?
4. What mass of CaCO3 is produced when 100.0 mL of a 0.300 M CaCl2
solution is mixed with 100.0 mL of 0.500 M Na2CO3 solution.
* 5. A 25.0 mL of 1.00 M NaCl is mixed with 35.0 mL of2.20 M AgNO3. A
precipitate is formed and falls out of solution. Calculate the concentrations of all
ions remaining in solution after the precipitation stops.