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Determining Empirical Formula

Determining Empirical Formula. Empirical Formulas. Indicate the lowest whole number ratio of atoms of each element in a compound. The molecular formula of hydrogen peroxide is H 2 O 2 the empirical formula would be…? HO Ho, Ho, Ho…. The molecular formula of glucose is…

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Determining Empirical Formula

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  1. Determining Empirical Formula

  2. Empirical Formulas • Indicate the lowest whole number ratio of atoms of each element in a compound. • The molecular formula of hydrogen peroxide isH2O2 the empirical formulawould be…? • HO • Ho, Ho, Ho…

  3. The molecular formula of glucose is… • C6H12O6, , its empirical formula is… • CH2O … • So what’s my point? • Empirical formulas are lowest whole number ratios of atoms of each type …to determine them experimentally we need numbers of atoms!

  4. Consider the following: • Analysis of a compound at CSI North Haven Labs indicates that it contains • 32.38 g Na • 22.65 g S • 44.99 g O • How can we use this data to determine the formula?...Think… • Mass  number of atoms!

  5. Remember doing mole conversions? • Use the molar mass of element convert to moles. • A mole is a number of atoms … you now have a ratio of atoms in the compound. • Divide each mole amount by the smallest mole amount… whole # ratio??? • Use ratio to write subscripts

  6. 1.408 mol Na : 0.7063 mol S : 2.812mol O • Divide each by smallest  • 1.993 mol Na : 1 mol S : 3.981 mol O • Na2SO4

  7. Try this.. • Analysis indicates that a compound contains 78.1% Boron and 21.9% hydrogen determine the empirical formula. • Why is this one any different from the last example? • Assume you have a 100 gram sample…now how many grams of boron do you have?

  8. 7.22 mol B : 21.7 mol H • Divide through by smallest  • 1 mol B : 3.01 mol H • BH3

  9. Try this one … • Analysis of a 10.150 g sample of a compound known to contain only phosphorus and oxygen indicates a phosphorus content of 4.433 g. What is the empirical formula? • Grams of P = 4.433g Grams of O = ? • Now try it…

  10. 0.1431 mol P : 0.3573 mol O • Divide by smallest  • 1 mol P : 2.497 mol O … • Now what?...Multiply through by two to obtain whole numbers… 2 : 5 P2O5

  11. Find empirical formulas… • 36.48% Na, 25.41% S, 38.11 % O… 2. 53.70 % iron and 46.30% sulfur… • 1.04 g K, 0.70 g Cr and 0.86 g O… 4. 37.51% C, 4.20% H and 58.29 % O …

  12. Quantitative Analysis • Various methods are used to determine the mass or percent composition of each element in a given compound…more about those later…

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