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Opener – do on a sheet of paper (or GOOS Paper!) and we will be correcting in 5 minutes

Opener – do on a sheet of paper (or GOOS Paper!) and we will be correcting in 5 minutes. Calculate the percent composition of phosphoric acid, H 3 PO 4 (used to give carbonated beverages a tart taste). Empirical Formulas. Methanal , CH 2 O Ethanoic acid, C 2 H 4 O 2 Same % composition!

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Opener – do on a sheet of paper (or GOOS Paper!) and we will be correcting in 5 minutes

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  1. Opener – do on a sheet of paper (or GOOS Paper!) and we will be correcting in 5 minutes • Calculate the percent composition of phosphoric acid, H3PO4 (used to give carbonated beverages a tart taste)

  2. Empirical Formulas

  3. Methanal, CH2O • Ethanoic acid, C2H4O2 • Same % composition! • 40.0% C, 6.7% H, 53.3% O

  4. Very different properties • Methanal – formaldehyde and preservation of specimens

  5. Ethanoic acid - vinegar

  6. Therefore, the best way to identify an unknown is to identify its chemical formula. • Let’s use the previous percent composition as our next example

  7. 40.0% C, 6.7% H, 53.3% O • We want to work with a convenient sample size, so we will use 100 g • We can do this because the percentages will be the same, no matter what our sample size is.

  8. So now we are looking at • 40.0 g of carbon, • 6.7 g hydrogen, • 53.3 g oxygen

  9. Next we determine the amount

  10. Next we determine the amount

  11. What do we notice? • The ratio of carbon : oxygen is just about 1:1 • The amount of hydrogen is almost double this • C:H:O = 1:2:1 CH2O

  12. One way to determine ratios • Divide each amount by the smallest amount. • In this way the smallest amount becomes “1” and other amounts have higher values, relative to 1.

  13. Empirical formula: Simplest whole number ratio of atoms or ions in a compound.

  14. Molecular formula: Exact number of each type of atom in a compound.

  15. Determining empirical formulas

  16. example • Determine the empirical formula of a compound with 35.4% Na, and the remainder is N.

  17. What about more complex compounds?

  18. 69.9% iron, 30.1% oxygen

  19. Ratios from fractions

  20. Last One! 3 elements: 52.2% C, 6.15% H, 41.7% O

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