Gravimetric Analysis Gravimetric Analysis is a common way to use precipitation reactions identity of an unknown sample. In the process, a soluble sample of an unknown compound is mixed with an excess amount of a known solution that will cause one of the ions from the unknown sample to fully precipitate out. Example: Identify an unknown alkali hydroxide (alkali = Group IA) compound. The unknown sample has a mass of 5.30 grams. Then, 4.80 grams of precipitate is collected after mixing with Cu(NO3)2 solution. 1st: Use a known solution with an ion that will combine with the known ion from the unknown compound solution, so it will fully precipitate out.

Cu(NO3)2 + XOH Cu(OH)2(s) +XNO3(aq)

2nd: Get the mass of the solid precipitate by filtering it and dried it. 3rd: Convert the mass of precipitate to moles of the precipitate 4th: Determine the moles of the known ion from unknown compound using Mole A = Mole B ratio.

5th: Convert moles of the ion (from the precipitate) to mass using its molar mass. 6th: Determine the mass percent composition of known ion in the given amount of the unknown compound sample. 7th: Determine Mass Percent of other possible compounds using their chemical formulas and molar masses.