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Chemical Formula Analysis

Chemical Formula Analysis. Types of Chemical Formulas. Empirical formula – the simplest whole number ratio of elements in a compound . Ex) C 2 H 6 , empirical formula is __________________. Molecular – indicates the actual number of atoms of each element in one molecule of a compound.

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Chemical Formula Analysis

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  1. Chemical Formula Analysis

  2. Types of Chemical Formulas Empirical formula – the simplest whole number ratio of elements in a compound Ex) C2H6, empirical formula is __________________ • Molecular – indicates the actual number of atoms of each element in one molecule of a compound Ex) C6H12O6

  3. Types of Chemical Formulas(continued) Structural – represents the arrangement of atoms in a molecule

  4. % Composition of elements in a compound Def: the percent by mass of each element that makes up a compound Procedure: • 1. Calculate the molar mass of compound • 2. find the % by mass, by dividing the total mass of the element by the molar mass of the compound

  5. % Composition of elements in a compound % mass = molar mass of element x # of atoms presentx100 molar mass of cmpd Ex) Determine the percent composition of H2O.

  6. Hydrates Definition: compounds that contain water molecules trapped in their crystal lattice structure Ex) MgSO4 7 H2O (Epsom salts) - dot represents the physical separation of water molecules from the ionic compound in which they are trapped

  7. Hydrates (continued) • We can calculate the % by mass of water in a hydrate by: 1. Calculating the total formula mass of compound. 2. divide the mass of the water in the hydrate by the mass of the compound

  8. Determining Empirical Formula from Percent Composition • Problem: Determine the Empirical formula for a compound that has is 70.9% potassium and 29.1% sulfur by mass. Procedure: Step 1: Assume the percent to be the # of grams per 100 g of the compound. Therefore, we assume 70.9 g K and 29.1 g S

  9. Determining the Empirical formula (cont’d) Step 2: Find the # of moles of each element. Divide by molar mass. K = (70.9 g) S = (29.1g) (39.1 g/mol) (32.0 g/mol) K = 1.82 mol S = 0.91 mol

  10. Still going! Step 3: Divide the moles of each element by the smallest of the values K = 1.82 moles S = 0.91 moles 0.91 0.91 K = 2 S = 1

  11. The end is near! You’ve found the simplest whole # ratio of the elements that make up the empirical formula, now use them as subscripts! K2S YaY!!!!

  12. Determining Molecular formula from Percent composition Do the same procedure for finding the empirical formula, there is just one more step. Problem: A certain compound was found to consist of 80.0% carbon and 20.0% hydrogen, with a molecular formula mass of 30.0 g. Determine the molecular formula for the compound.

  13. How do we attack this thing? Step 1: Determine the empirical formula for the compound (like we just did, refer to your notes) CH 3

  14. Here’s the twist! Step 2: Determine the empirical formula mass mass = 15 g

  15. Almost there! Step 3: Divide the molecular formula mass (from question) by the empirical formula mass, to find the multiple of the empirical formula 30.0 g = 2 15.0 g

  16. Finish it up! Step 4: multiply the subscripts of the empirical formula by the result of your last step (CH3)2 C2H6

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