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7.3 Using Chemical Formulas. Review Mole: SI unit for the amount of a substance (contains avogadro’s number of particles) Avogadro’s Number: 6.022 x 10 23 particles/molecules/formulas units per 1 mol Formula Unit: smallest ratio of cations to anions. 2) Formula Mass.
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7.3 Using Chemical Formulas • Review • Mole: SI unit for the amount of a substance (contains avogadro’s number of particles) • Avogadro’s Number: 6.022 x 1023 particles/molecules/formulas units per 1 mol • Formula Unit: smallest ratio of cations to anions
2) Formula Mass • Sum of the average atomic masses of all atoms represented in a formula (Units: amu) • Ex: What is the formula mass of Ca(NO3)2?
3) Molar Mass • mass of one mole of any substance (contains avogadro’s number of particles) Units: g/mol • Ex: calculate the molar mass of Al2S3
4) Problem Solving Using Molar Mass • A) Mol to mass • Ex: What is the mass (grams) of 3.0 mol of NaOH? • 1. determine molar mass of NaOH • 2. # of moles of NaOH x molar mass
B) mass to mol • How many moles are in 135 g of NaOH? • 1. determine molar mass of NaOH • 2. grams of NaOH / molar mass
C) Moles to molecules / molecules to moles • How many molecules of H20 are present in 1.5 mol? • 1. mol NaOH x Avogadro’s #
6. Determining % Composition • A) from chemical formula • Ex – Find the % composition of copper (II) sulfate? • Formula -> molar mass -> mass of each element as % • (disregard letter 6.B)
6) Determing % Composition • B) from mass data