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Molecular Mass(Molar Mass, Molecular Weight, Gram Formula Mass)
Definitions Molar Mass is the mass of one mole of a substance (6.02 x 1023 formula units). The unit for molar mass (note it is the mass of a mole) is grams/mole. Atomic Weight is the molar mass of an element. Formula Weight is the molar mass of an IONIC compound. Molecular Weight is the molar mass of a COVALENT compound. Molecular Mass is the mass of a given molecule (NOT MOLES of molecules). The units are atomic mass units (amu). 1amu =1.660 538 782×10–27 kg 1 amu is 1/12 the mass of a carbon-12 atom which has a mass of 12.0000. Reading Simple Chemical Formulas- Each element begins with a CAPITAL letter. The subscript belongs to the element it follows and indicates how many of that atom there are. If there is only 1 atom we do not use subscripts. H2O 2 hydrogens 1 oxygen
Reading Compounds that have (parenthesis's). When there is parenthesis's around a group of atoms we must multiply each atom by the subscript to get the total number of each element. Ca(NO3)2 1 Calcium 2 Nitrogens and 6 Oxygens --> 3 x 2
Reading Compounds that have water attached (hydrates) The • represents CuSO4 that has 5 waters attached. CuSO4• 5H2O so 1 copper 1 sulfur 4 oxygens and 10 hydrogens 5 oxygens Summed up 1 copper 1 sulfur 9 oxygens and 10 hydrogens
How do we find molar mass? The molar mass is calculated by taking the sum of the atomic weights of all the atoms which form the molecule. First determine the number of each atom in the formula. 1. Water is made up of 2 hydrogens and 1 oxygen. Find the molar mass. 2. Multiply the number of each atom by its atomic weight (found on the Periodic Table of the Elements). H2O
C6H12O6
Ca(NO3)2
CaCl2 • 2H2O
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