I have my first chem 1 exam on friday and I have been going through all my professors practice exams, so this is not homework. I also have all the answers, so these are just questions that I seem to keep either getting wrong, or I am simply confused as to what is being asked, rather than not knowing how to do the problem. I havent taken chemistry in over 10 years, I am an adult back in chemistry, so please be gentle. I am definitely embarrassed about some of my questions. I hope my title was specific enough, as there are a few different topics, but they are all rather geared toward the same topic.
1. a 2.000g sample of an oxide of bromine is converted to 2.936g of silver bromide. What is the empirical formula of the oxide?
*i know the answer is BrO
3. i also know that 2g BrO
3 x 1 mol BrO
3/ 127.9 g BrO
3 = 2.936 g AgBr
however, this is after the fact. How would I set this up? Im sure its a question of algebra, but I cannot figure it out. I know i could figure most of these out by trial and error, but id like to know the way.
2. Aluminum and bromine react vigorously as represented by the following equation:
2 Al(s) + 3 Br
2(l)
2 AlBr
3(s)
What mass of product, in grams, can be made by reacting 5.0 g of aluminum and 22 g of bromine?
*i thought this was a stoichiometry prob of limiting reagents. am i totally wrong? this is how i am doing it:
5g Al x 1 mol Al/26.98g x 2 mol AlBr
3/2 mol Al = .741 mol AlBr
322g Br
2 x 1 mol Br
2/159.8 g x 2 mol AlBr
3/3 mol Br
2 = .826 mol AlBr
3so the limiting reagent is Al
.741 mol AlBr
3 x 266.68 g AlBr
3/ 1 mol AlBr
3 = 197.61 g AlBr
3totally wrong. the answer is 24 g. am i totally wrong setting it up? is there an egregious math error?
3. this might be better suited for a math forum, but im here and its about molar mass, so.. (and yes, im in precalc, and i cant figure this out.)
A sample of compound M
3O
4 weighing 30.0 grams contains 20.0 grams of M. What is
the molar mass of M?
* i have no idea how to set this up.
ill stop there. Id appreciate any kicks in the right direction. thank you. (ps, i cannot preview my question, so i apologise for any formatting errors.)