Answer to Question #55915 in General Chemistry for jocelyn

Question

gravimetric analysis relies on two basic principles of chemistry
the law of conservation of mass and the law of constant composition. Briefly explain how this is true

Answer 1

In your case for the precipitation of barium sulfate.
The law of conservation of mass says that all barium from the solution can be isolated in form of barium sulfate during the precipitation reaction. Thus, quantity of barium in precipitate will be the same as it was in starting solution.
The law of constant composition says that all barium will be transformed into barium sulfate of defined formula BaSO4. Thus, you can be sure about the molar weight of precipitate formed and use it in calculation of quantity of barium in starting solution without any doubts.
Summarization of these two laws allows you to calculate the quantity of barium in analyzed solution based on quantity of barium sulfate formed.