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Empirical and Molecular Formulas

Empirical and Molecular Formulas. Do Now: Quiz. Molecular Formula – tells the type and number of atoms in a compound Empirical Formula – the lowest whole number ratio of the atoms of the elements in a compound. Molecular Formulas: C 6 H 6 C 2 H 2 C 6 H 12 O 6 H 2 O H 2 O 2 NaOH.

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Empirical and Molecular Formulas

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  1. Empirical and Molecular Formulas Do Now: Quiz

  2. Molecular Formula – tells the type and number of atoms in a compound • Empirical Formula – the lowest whole number ratio of the atoms of the elements in a compound

  3. Molecular Formulas: • C6H6 • C2H2 • C6H12O6 • H2O • H2O2 • NaOH Empirical Formulas: • CH • CH • CH2O • H2O • HO • NaOH

  4. Remember: • Reduce molecular formulas to empirical formulas • Some molecular formulas are the same as the empirical formula • Different molecular compounds (formulas) can have the same empirical formula

  5. Determine the EF of a compound: • List known info of the element • If given a %, change the % to grams • Convert grams to moles (use mass from PT) • Determine the smallest number of moles • Divide all moles by smallest number • Are they all whole numbers? • No… multiply each number by the smallest possible whole number that will give a whole number answer • The ratios are used as subscripts for the formula

  6. Practice: • An oxide of aluminum is formed by the reaction of 4.151g of aluminum with 3.692g of oxygen. Calculate the empirical formula of this compound. • Al2O3 • A sample of lead arsenate contains 1.3813g of lead, 0.00672g of hydrogen, 0.4995g of arsenic, and 0.4267g of oxygen. Calculate the empirical formulaof lead arsenate • PbHAsO4

  7. Percent and EF: • Cisplatin has the composition (mass percent) 65.02% platinum, 9.34% nitrogen, 2.02% hydrogen, and 23.63% chlorine. Calculate the empirical formula. • PtN2H6Cl2

  8. Determining Molecular Formulas • Can be determined by using the empirical formula of a compound. • Must know 2 things: • Empirical formula • Molar mass of the compound

  9. Steps to find the MF: • Determine the EF mass • Divide: molar mass/empirical mass • Multiply the EF subscripts by the whole number.

  10. Practice: • A white powder is analyzed and found to have an empirical formula of P2O5. The compound has a molar mass of 283.88g. What is the compound’s molecular formula? • P4O10 • A compound with an empirical formula of C2OH4 and a molar mass of 88 grams per mole. • C4O2H8

  11. A combined problem: A compound used as an additive for gasoline to help prevent engine knock shows the following percentage composition: 71.65% Cl 24.27% C 4.07% H The molar mass is known to be 98.96g/mol. Determine the empirical formulas AND the molecular formula of this compound. CH2O and C6H12O6

  12. An unknown compound was found to have a percent composition as follows: 47.0% potassium 14.5% carbon 38.5% oxygen What is the empirical formula? If the molar mass of the compound is 166.22g/mol, what is the molecular formula?

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