[fredodgers]

Hello:

I have a question regarding the above substance.  There is a question on my lab that asks what the percent sulfate is from my results.  I calculated the theoretical percentage to be about 20.25 percent.  I was to combine the Potassium Aluminum Sulfate 12 Hydrate with the Barium Nitrate and heat the combined substance.  I started with one gram of Potassium Aluminum Sulfate 12 Hydrate.  The precipitate that formed after cooling was .92 grams.  How can I calculate the percent sulfate from this info?

[Arkcon]

OK, lets start with a balanced chemical reaction.  You can start by writing the reagents as chemical formulas.  You caught me in a good mood, so I'll do one for you: KAl(SO₄)₂.12H₂O  (You can get subscripts by using the sub button in this boards reply pane)  We like to see people start a problem, so we can help you learn.  We don't give all the answers at once here.

[fredodgers]

OK, lets start with a balanced chemical reaction.  You can start by writing the reagents as chemical formulas.  You caught me in a good mood, so I'll do one for you: KAl(SO₄)₂.12H₂O  (You can get subscripts by using the sub button in this boards reply pane)  We like to see people start a problem, so we can help you learn.  We don't give all the answers at once here.

So should I convert the 1.00 grams of Aluminum Sulfate 12 Hydrate into moles?  I'm confused about how to write the chemical equation in general.  Can you explain the concept to me more in depth using 2 other substances so I can understand what's going on?

[Arkcon]

Yes, after you know the chemical reaction, you should convert grams of reactant into moles, because moles is the "units" of a chemical reaction.  You will also have to convert grams of product into moles.  And you wil have to know what the product is.  You lab notes, or the lab textbook, or your instructor should have given you much of the starting steps here -- you should have some hints about reactants and products from those sources, and you should be able to piece together a reaction, taking (good) guesses where there's gaps in your info.  Try it and see.  You' be better off at exam time -- you'll probably be given another one of these then.  And you won't have as much time to figure it out.