First question: Find the empirical formula for 15.8% Al, 28.1% S, 56.1% O. I know how to do it, but I keep getting the wrong answer. The answer is Al2S9O12.

Hi Malvi
calculate no of moles for each element and convert it to simplest ratio.I am sure till this point you must be correct .
Al =1
S = 1.5
O = 6
Now here S is 1.5 which is can neither be approximated as 1 nor as 2 so what we will do -multiply all numbers by 2 to get whole number.
Al =1 X2 = 2
S = 1.5 X2= 3
O = 6 X2= 12
In the quiz answer should be Al2S3O12
I hope you agree with the above formula .
I have edited the formula in the quiz also.
For the second wrong question which you attempted in AP quiz in  chemtopper courses
Convert mass of P4----moles of P4------moles of H3PO4 ------mass of H3PO4
whatever mass will come that is the theoretical yield
take ratio of actual with theoretical and multiply it by 100%
I am getting theoretical yield somewhere near 65 g
Just try once more .

What is the name for Fe2(CO3)3
I got it wrong on the quiz

And also, what is potassium trinitride? How is that K3N? Wouldn't it be KN3?

2nd one

3rd one

What is the name for Fe2(CO3)3
I got it wrong on the quiz

And also, what is potassium trinitride? How is that K3N? Wouldn't it be KN3?

Fe2(CO3)3----Iron(III)carbonate

Actually it should be Potassiumnitride
K3N

Quote from: malvi on October 15, 2009, 10:13:57 PM
3rd one

This is also based on Molarity
Molarity = no of moles / Volume in L