%Composition

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%Composition

  1. 1. % composition
  2. 2. Moles & Formulas <ul><li>A chemical formula really tells us how many moles of each element make one mol of the compound. </li></ul><ul><li>Examples: </li></ul><ul><ul><li>H 2 O means 1 mol of water is made of 2 moles of H and 1 mol O. </li></ul></ul><ul><ul><li>Na 2 SO 4 = 2 mol Na, 1 mol S, 4 mol O </li></ul></ul><ul><li>Now that we have studied the mole we can use this information to find % composition. </li></ul>
  3. 3. % Composition <ul><li>A ratio </li></ul><ul><li>Helps to identify a substance. </li></ul><ul><li>Compares masses of elements in a compound. </li></ul>
  4. 4. How to Calculate % Composition <ul><li>Write the formula (if it isn’t given). </li></ul><ul><li>Find the molar mass of the compound. </li></ul><ul><li>Divide the molar mass of each element by the molar mass of the compound. </li></ul><ul><li>Multiply by 100. (this gives a %) </li></ul><ul><li>Check your work! If you did it right all the percents will add up to 100. </li></ul>
  5. 5. <ul><li>Example: Find the % composition of Potassium Chlorate. </li></ul><ul><li>KClO 3 </li></ul><ul><li>K = 1 x 39.10 = 39.10 </li></ul><ul><li>Cl = 1 x 35.45 = 35.45 </li></ul><ul><li>O = 3 x 16.00 = 48.00 </li></ul><ul><li> 122.55g/mol </li></ul><ul><li>(39.10/122.55) x 100 = 31.91% K </li></ul><ul><li>(35.45/122.55) x 100 = 28.93% Cl </li></ul><ul><li>(48.00/122.55) x 100 = 39.17% O </li></ul><ul><li>31.91 + 28.93 + 39.17 = 100.01… remember we rounded </li></ul>
  6. 6. <ul><li>Example: Find the % composition of Ammonium Phosphate. </li></ul><ul><li>(NH 4 ) 3 PO 4 </li></ul><ul><li>N = 3 x 14.01 = 42.03 </li></ul><ul><li>H = 12 x 1.01 = 12.12 </li></ul><ul><li>P = 1 x 30.97 = 30.97 </li></ul><ul><li>O = 4 x 16.00 = 64.00 </li></ul><ul><li> 149.12g/mol </li></ul><ul><li>(42.03 /149.12) x 100 = 28.19% N </li></ul><ul><li>(12.12 /149.12) x 100 = 8.13% H </li></ul><ul><li>(30.97 /149.12) x 100 = 20.77% P </li></ul><ul><li>(64.00/149.12) x 100 = 42.92% O </li></ul><ul><li>28.19 + 8.13 + 20.77 + 42.92 = 100.01… remember we rounded </li></ul>
  7. 7. Homework <ul><li>Page 248 </li></ul><ul><ul><li>“ practice” at the top of the page do #s 1,2,3,4abcd,5a </li></ul></ul><ul><li>Page 248 Section Review #6abcd </li></ul>

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