How many moles of compound in 15.0g of potassium dichromate?

Question

hpowell885 · Answer

For a question like this, it is important to first identify the chemical formula. 
Potassium dichromate is: K2Cr2O7
Next, grab your periodic table and identify the atomic mass of each element.  You will need to multiply the atomic mass by the number of atoms present.  
K- 2(39.098)    Cr-2(51.996)   O-7(15.999)
Next, add all of your answers together and you should get an answer around 294.181 amu, (atomic mass unit).  Your answer may vary slightly depending on the version of the periodic table you are using.  
Now, you need to set up your equation.  Remember, every unit should cancel out, except for the unit you are trying to find.  
15.0 g. K2Cr2O7 ( 1 mol K2Cr2O7/ 294.181 amu K2Cr2O7) = 0.050989017 mol K2Cr2O7
(Notice that grams and atomic mass units do cancel each other out). 
This can be rounded to 0.051 moles of K2Cr2O7.