6.2 Empirical and Molecular Formulas

Question 1

Percent Composition equals to what?

Answer 1

Percent by mass of a given element in a compound.

Question 2

Will the percent composition be different if the ratios of elements are different?

Answer 2

Yes, and how? K2CrO4 is 40.3% Potassium by mass but K2Cr2O7 is 26.5% Potassium by mass. The number of potassium atoms did not change but others did the whole ratio changed overall.

Question 3

How to do percent composition?

Answer 3

= subscript of element * atomic mass of element/ formula mass of compound * 100

Question 4

How to find molar mass of the whole compound?

Answer 4

(subscript of element * mass of compound) and it can go on depending on how many elements are in the compound just keep adding them.

Question 5

How to get Empirical Formula of Masses?

Answer 5

1. Convert grams to moles
2. write the subscript number of moles of each element not the whole number form
3. Divide number of moles for each element by smallest number of moles and round to get whole-number ratio.

Question 6

Empirical Formula from Percent Composition

Answer 6

First assume a 100 gram sample so you can use your percent’s as grams because we don’t need to know what the actual masses are; we just need a ratio of masses.

Question 7

Converting from Empirical Formula to Molecular Formula

Answer 7

Step 1: Calculate the empirical formula mass.

Step 2: Find ratio = Molar Mass/ Empirical Formula Mass

Step 3 Multiply Empirical Formula by ratio.