Chemical Formulas and Moles

Example: 1.water (C) – every molecule of water contains 2 atoms of hydrogen & one atom of oxygen - 2 molecules of H 2 O would contain 4 atoms of hydrogen & 2 atoms of oxygen x molecules of H 2 O would contain 1.20 x atoms of hydrogen & 6.02 x atoms of oxygen A simpler way of writing this last statement would be: One mole of H 2 O molecules contains 2 moles of hydrogen atoms and one mole of oxygen atoms.

The subscripts in a chemical formula can be read as the number of atoms of each element in one molecule of the compound, OR, the number of moles of each element in one mole of the compound. CO 2 contains 1 mole of C atoms and 2 moles O atoms. C 2 H 5 OH contains 2 moles of C atoms, 6 moles of H atoms, and 1 mole of O atoms. Sample Problems: 1. How many moles of each element are in 3.0 moles of H 3 PO 4 ?

2.How many moles of oxygen are there in moles of aluminum sulfate? 3.How many moles of oxygen atoms are there in 24.8 g of carbonic acid?

4.How many atoms of hydrogen are present in moles of ammonium sulfate? 5.Determine the number of oxygen atoms found in 12.3 g of sulfuric acid.

Percent Composition of a Substance Using the chemical formula of a compound, it is possible to calculate the percent composition of each element within that compound. To do this, divide the mass of the element in one mole of the compound by the molar mass of the compound, than multiply by 100%. Calculate the percent composition of sugar C 12 H 22 O 9