Chemical Concept Demonstrated: Molarity of aqueous solutions
After the two solutions are mixed, a precipitate forms within the beaker.
Explanations (including important chemical equations):
Pb(NO3)2 + 2 KI --> PbI2 + 2 KNO3
Pb(NO3)2 + K2Cr2O7 --> PbCr2O7 + 2 KNO3
Weighing the two solutions is not a useful approach to finding the amount of product formed. When working with solutions, it is necessary to know the molarity of the solution rather than its weight. Molarity, by definition, is the measure of the number of moles of solute in each liter of solution. By knowing the volumes of the solutions used, it is then possible to calculate the moles of reactants in the solution. The moles of reactants can then be used to predict the amount of product formed.