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# Molecular formula

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### Molecular formula

1. 1. Empirical and Molecular Formula and Percentage Composition Stoichiometry Math of Chemistry
2. 2. Percents % = part whole x 100
3. 3. Percentage Composition <ul><li>Percent Composition is finding the percent by mass of each element in a compound using the periodic table. </li></ul>
4. 4. Percentage Composition <ul><li>An 8.20 gram piece of magnesium combines with 5.40 grams of oxygen to form a compound. </li></ul><ul><li>What is the percent composition of this compound? </li></ul>
5. 5. Percentage Composition <ul><li>How many grams of Ca are in 64.3 grams CaCl 2 ? </li></ul>
6. 6. You Try <ul><li>How many grams of Oxygen are in 19.2 grams Na 3 PO 4 ? </li></ul>Oxygen
7. 7. Finding a ratio <ul><li>If a school has 30 boys and 60 girls, what is the ratio of boys to girls? </li></ul>
8. 8. Finding a whole number ratio in its lowest terms <ul><li>If a school has 27 boys and 18 girls, what is the ratio of boys to girls? </li></ul>
9. 9. Finding a whole number ratio in its lowest terms <ul><li>If a school has 75 boys and 60 girls, what is the ratio of boys to girls? </li></ul>
10. 10. Finding a whole number ratio in its lowest terms <ul><li>A certain compound contains 4.14 moles of Mg and 2.76 moles of P. </li></ul><ul><li>Find the mole ratio between Mg and P. </li></ul><ul><li>Write the formula. </li></ul>
11. 11. Empirical Formula <ul><li>An Empirical formula gives the lowest whole number MOLE ratio between the atoms in a compound. </li></ul>
12. 12. The Math <ul><li>A compound contains 0.900 grams of calcium and 1.60 grams of chlorine. </li></ul><ul><li>Find its empirical formula. </li></ul>
13. 13. The Math <ul><li>A compound is analyzed and found to consist of 36.0 % aluminum and 64.2 % sulfur. </li></ul><ul><li>Find its empirical formula. </li></ul>
14. 14. You Try <ul><li>What is the empirical formula of a compound that is 66.0 % Ca and 34.0 % P? </li></ul>
15. 15. Molecular Formula <ul><li>A Molecular formula gives the actual ratio between the atoms in a compound. </li></ul><ul><li>For Ionic compounds, the empirical and molecular formulas are the same. </li></ul>
16. 16. Molecular Formula <ul><li>For molecular compounds, the molecular formula is a multiple of the empirical. </li></ul><ul><li>Example: </li></ul><ul><li>C 6 H 6 is benzene. What is benzeneâ€™s empirical formula? </li></ul>
17. 17. The Math <ul><li>A compound contains 31.10 grams of carbon and 7.872 grams of hydrogen. </li></ul><ul><li>Find its empirical formula. </li></ul>
18. 18. Molecular formula <ul><li>Vitamin C is ascorbic acid. It has a percentage composition of 40.9 % carbon, 4.58 % hydrogen, and 54.5 % oxygen with a molecular mass of 176.1 u. </li></ul><ul><li>Find its empirical and molecular formulae. </li></ul>
19. 19. Review Molecular formula <ul><li>Aspirin, acetylsalicylic acid, contains 60.0 % carbon, 4.48 % hydrogen, and 35.5 % oxygen with a molecular mass of 180 u. </li></ul><ul><li>Find its empirical and molecular formulae. </li></ul>
20. 20. Hydrates <ul><li>Hydrates are compounds with water molecules trapped in their crystal structure. </li></ul><ul><li>The water is weakly bonded and can be removed by heating the substance. </li></ul>
21. 21. Quiz Review <ul><li>A particular hydrate of MgSO 4 contains 51.14 % water. </li></ul><ul><li>Find the formula for the hydrate. </li></ul>
22. 22. Quiz Review <ul><li>Find the percentage of water in the hydrate, Na 2 CO 3 * 10 H 2 O. </li></ul>
23. 23. Quiz Review <ul><li>Find the percentage of oxygen in P 2 O 5 . </li></ul><ul><li>How many grams of oxygen are in 25.5 grams of P 2 O 5 ? </li></ul>