1. A. K+(aq) + NO3- (aq)  KNO3(s) B. Pb+(aq) + SO4-(aq)  PbSO4(s)
QUESTION:
What is the net ionic equation for the precipitation reaction that occurs when K2SO4(aq) and Pb(NO3)2 are mixed?
A. K+(aq) + NO3- (aq)  KNO3(s)
B. Pb+(aq) + SO4-(aq)  PbSO4(s)
C. Pb2+(aq) + SO42-(aq)  PbSO4(s)
Net ionic equation for a precipitation reaction shows:
Formula of precipitate (insoluble solid) on the product side
Formulas of ions that combined to form the precipitate on the reactant side.
Coefficients of ions corresponding to their subscript in the precipitate.
What is the net ionic equation for the precipitation reaction that occurs when aqueous solutions of potassium sulfate and lead nitrate are mixed?
PAUSE
CLICK
A precipitate is a compound that is insoluble in water.
Therefore, to answer this question, we just need to look for a pair of ions that will form a compound that is insoluble in water.
We use solubility rules to predict whether a a compound is soluble or insoluble in water.
Potassium sulfate gives us potassium and sulfate ions.
CALLOUT “K+ and SO42-” pointing to K2SO4
Lead(II) nitrate gives us lead(II) and nitrate ions
CALLOUT “Pb2+ and NO3-” pointing to Pb(NO3)2
According to our solubility rules… any compound containing potassium or nitrate ions are soluble in water.
Therefore, we do not expect our precipitate to have potassium or nitrate ions.
CROSS OUT K+ and NO3- in callouts
Therefore, choice A is incorrect.
CROSS OUT KNO3(s) in choice A.
Potassium nitrate is soluble in water. It will not be a precipiate.
Choice B is obviously wrong. The charge of lead(II) ion is +2, not +1.
CROSS OUT Pb+(aq)
… and the charge of sulfate ion is –2, not –1
CROSS OUT SO4-(aq)
Choice C must be correct. Indeed, solubility rules tell us that lead(II) sulfate is insoluble in water.
The net ionic equation for a precipitation reaction simply shows
CLICK the formula of the precipitate on the product side. In this case, PbSO4.
HIGLIGHT PbSO4(s) in choice C
CLICK the formulas of the ions that combined to form the precipitate on the reactant side
HIGHLIGHT Pb2+(aq) and SO42-(aq) in choice C
… and to balance the equation… coefficients for the ions correspond to their subscript in the formula of the precipitate.
In the case given here, the subscripts of lead and sulfate are both unwritten…. That is, implied to be one.
So, no coefficients are written in front of lead and sulfate ions …
remember than coefficients that are not written are implied to be one.
PAUSE END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08