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Percent Composition

Percent Composition. Parts of a Whole. Percent. Short for per centum …”by the hundred” Part of a whole If there are 10 people in a room and 4 of them have blue eyes, what percentage of people have blue eyes?. Composition. Chemical formula Molar mass. Percent Composition.

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Percent Composition

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  1. Percent Composition Parts of a Whole

  2. Percent • Short for per centum…”by the hundred” • Part of a whole • If there are 10 people in a room and 4 of them have blue eyes, what percentage of people have blue eyes?

  3. Composition • Chemical formula • Molar mass

  4. Percent Composition • Write the formula • Find the molar mass • Determine the percentage of the part in question

  5. Problem #1 • Determine the percent composition of water.

  6. Problem #1—Step 1 • Write its formula • H2O

  7. Problem #1—Step 2 • Determine its molar mass • H—2 x 1.01 = 2.02 • O—1 x 16.00 = 16.00 18.02 g/mol

  8. Problem #1—Step 3 • Determine the portion that each element makes up by its mass and multiply by 100…determine the percent composition • H—2 x 1.01 = 2.02 x 100 = 11.2% H 18.02 • O—1 x 16.00 = 16.00 x 100 = 88.8% O 18.02

  9. Problem #2 • Determine the percent composition of aluminum carbonate.

  10. Problem #2—Step 1 • Write its formula • Al2(CO3)3

  11. Problem #2—Step 2 • Determine its molar mass • Al—2 x 26.98 = 53.96 • C—3 x 12.01 = 36.03 • O—9 x 16.00 = 144.00 233.99 g/mol

  12. Problem #1—Step 3 • Determine the percent composition • Al—2 x 26.98 = 53.96 x 100 = 23.1% Al 233.99 • C—3 x 12.01 = 36.03 x 100 =15.4% C 233.99 • O—9 x 16.00 = 144.00 x 100 =61.5% O 233.99

  13. Problem #3 • A compound contains only copper and chloride ions. It is found to be 47.3% copper. Determine the formula of the compound.

  14. Problem #3—Step 1 • Determine the possible formulas • Copper can have charges of 1+ or 2+ • So, your choices are: CuCl and CuCl2

  15. Problem #3—Step 2 • Determine both molar masses • Cu—1 x 63.55 = 63.55 • Cl—1 x 35.45 = 35.45 99.00 g/mol • Cu—1 x 63.55 = 63.55 • Cl—2 x 35.45 = 70.90 134.45 g/mol

  16. Problem #3—Step 3 • Determine the percentage of copper in each. • Cu—1 x 63.55 = 63.55 x 100 = 64.2% Cu 99.00 • Cu—1 x 63.55 = 63.55 x 100 = 47.3% Cu 134.45 So, the answer is CuCl2

  17. Problem #4 • A compound is known to contain 41.7% magnesium. Determine if the compound is magnesium fluoride, magnesium hydroxide, or magnesium oxide.

  18. Problem #4—Step 1 • Determine the formulas • MgF2 • Mg(OH)2 • MgO

  19. Problem #4—Step 2 • Determine all three molar masses • Mg—1 x 24.31 = 24.31 • F—2 x 19.00 = 38.00 62.31 g/mol • Mg—1 x 24.31 = 24.31 • O—2 x 16.00 = 32.00 • H—2 x 1.01 = 2.02 58.33 g/mol • Mg—1 x 24.31 = 24.31 • O—1 x 16.00 = 16.00 40.31 g/mol

  20. Problem #4—Step 4 • Determine the percentage of magnesium in each. • Mg—1 x 24.31 = 24.31 x 100 =39.0% Mg 62.31 • Mg—1 x 24.31 = 24.31 x 100 = 41.7% Mg 58.33 • Mg—1 x 24.31 = 24.31 x 100 =60.3% Mg 40.31

  21. Problem #4—Answer • Mg(OH)2

  22. Practice, practice, practice

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