Mr. Chapman Chemistry 20

Converting from grams to moles Need: Moles and Mass worksheet.

 To convert from grams to moles, we multiply the number of grams by the molar mass of the compound or element.  To convert from moles to grams, we multiply the number of moles by the molar mass of the compound or element. EVERY MOLE OF SODIUM HAS A MASS OF g g of SODIUM CONTAINS 6.022x10 23 atoms of sodium

 An empirical formula of a compound is the smallest, whole number ratio of atoms in a compound.  For example, the molecular formula for glucose is C 6 H 12 O 6. The empirical formula for glucose is CH 2 O.  We can find the empirical formula for a compound if we know the mass percentage of each element in the compound.

1. Find the empirical formula of a compound that is 48.38% carbon, 8.12% hydrogen, and 53.5% oxygen by mass. Note: As with most stoichiometry problems (which we will learn about), it is necessary to work in moles. The ratio of the moles of each element will provide the ratio of the atoms of each element.

 Get the mass of each element by assuming a certain overall mass for the sample (100 g is a good mass to assume when working with percentages).

 Convert the mass of each element to moles of each element using the atomic masses.

 Find the ratio or the moles of each element by dividing the number of moles of each by the smallest number of moles.

 Use the mole ratio to write the empirical formula.

 What is the empirical formula of a compound that is 75% carbon and 25% hydrogen?