Presentation on theme: "Chapter 7: Chemical Formulas and Chemical Compounds"— Presentation transcript:
1 Chapter 7: Chemical Formulas and Chemical Compounds Section 3: Using Chemical Formulas
2 OverviewWe will calculate the formula mass or molar mass of any given substance.We will work on molar conversions for molecules.We will calculate the number of molecules or formula units in a given molar amount.We will calculate the percent composition of a chemical compound.
3 Formula MassThe sum of all average atomic masses (molar masses) of all the atoms represented in the chemical formula.Recall the average atomic mass of H = 1.01g, which is the same as the molar mass of H which equals 1.01g/mol.So what is the formula mass of H2O2?2 H x 1.01 g = 2.02 g2 O x g = gTotal H + Total O = g
4 Molar MassIt is found the same way. They are numerically equal to each other.So what is the molar mass of H2O2?2 H x 1.01 g/mol = 2.02 g/mol2 O x g/mol = g/molTotal H + Total O = g/mol
5 Molar ConversionsRecall the value of g/mol can be used to convert the number of moles of a substance to moles or grams.Also remember that to find the number of molecules in a substance you will need to how many moles of the substance and take that times Avogadro’s Number.1 mol = 6.022x1023 = molar mass = 22.4 L (STP)
6 Percent Composition The percent by mass of each element in a compound. So what is the percent composition of H2O2?First find the formula mass.2 H x 1.01 g = 2.02 g2 O x g = gTotal H + Total O = gThen divide the total mass of each element by the formula mass and take it times 100.H = 5.94% O = 94.06%