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Empirical Formulas

Empirical Formulas. Percent Composition. Used to describe the composition by mass of various substances. Give individual percentage by mass of each element in a compound. Percentage is always. Practice.

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Empirical Formulas

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  1. Empirical Formulas

  2. Percent Composition • Used to describe the composition by mass of various substances. • Give individual percentage by mass of each element in a compound. • Percentage is always

  3. Practice • Calculate the percent composition of R-22, chlorodifluoromethane, CHF2Cl, the refrigerant used in home air conditioners.

  4. Empirical and Molecular Formulas • Consider the following compounds • Ethylene, C2H4 • Propylene, C3H6 • Cyclobutane, C4H8 • Cyclohexane, C6H12 • All have different molecular formulas • Molecular formula – a formula telling exactly how many atoms of each type are present in a molecule

  5. Empirical and Molecular Formulas Consider the following compounds Ethylene, C2H4 Propylene, C3H6 Cyclobutane, C4H8 Cyclohexane, C6H12 All have the same empirical formula, CH2 Empirical formula – a formula describing the lowest whole number ratio of atoms in a compound

  6. Empirical Formulas • We typically have the ability to calculate the empirical formula of a compound relatively easily • To Determine the Empirical Formula • Convert the amounts of each element to moles. • Divide by the smallest number of moles to get the simplest ratio. • Adjust the ratio to get the lowest whole number ratio.

  7. A Simple Rhyme for a Simple Formula by Joel S. Thompson Percent to mass Mass to mole Divide by small Multiply ‘til whole

  8. Practice A 100.0g sample of a compound is found to contain 32.38g sodium, 22.65g sulfur and 44.99g oxygen. What is the empirical formula of the compound?

  9. Practice A compound contains 26.56% potassium, 35.41% chromium and the remainder is oxygen. What is the empirical formula?

  10. Adjusting the Ratio • What do you do if you get a ratio with something that ends in • 0.50? • Multiply by 2 • 0.33 or 0.66? • Multiply by 3 • 0.25 or 0.75? • Multiply by 4 • 0.20, 0.40, 0.60, or 0.80? • Multiply by 5

  11. Practice • Isoamyl acetate is the component of bananas that give them their smell. It is 64.58%C, 10.84%H, 24.58% O. What is the empirical formula?

  12. Empirical to Molecular Formula What is the molecular formula of a compound with an empirical formula of CH2 and a molar mass of 84.156 g/mol? • Use the ratio of the molar mass of the empirical formula to the molar mass of the compound.

  13. Empirical to Molecular Formula What is the molecular formula for a sample of compound that consists of 0.44g hydrogen and 6.92g oxygen? The molar mass of the compound is 34.00g/mol.

  14. Practice Theobromine, a stimulant in chocolate that is very similar to caffeine, has a molecular weight of 180.18g/mol, and is 46.66% C, 4.48% H, 31.10% N, and 17.76% O. What is the empirical and molecular formula of this compound?

  15. Extra Practice Lycopene, the stuff in tomatoes that contributes to their red color and supports prostate health in men, has a molar mass of 536.90g/mol. It is 89.49%C and 10.51%H by mass. What are the empirical and molecular formulas of this compound? Quintin

  16. Hydrates A hydrate is a compound that has water loosely bound to it. The formula of the compound is written as: formula· x H2O where x is the number of moles of water per mole of compound For example, cobalt(II)chloride hexahydrate is: CoCl2·6H2O

  17. Hydrates Heating a hydrate causes the water to evaporate, leaving only the anhydrous salt (the part of the hydrate that is not water). For example, if you heat CoCl2·6H2O, the water will evaporate, leaving only CoCl2, which is the anhydrous salt.

  18. Practice 100.0g of a hydrate of copper(II) sulfate is heated until the water is lost and 63.93g of the anhydrous salt remain. What is the formula of the hydrate?

  19. Practice • Ascorbic Acid, Vitamin C, is 40.92%C, 4.58%H, and 54.50%O. It has a molar mass of 176.14g/mol What are the empirical and molecular formulas?

  20. Practice • Isoamyl acetate is the component of bananas that give them their smell. It is 64.58%C, 10.84%H, 24.58% O. What is the empirical formula? • Theobromine, a stimulant in chocolate that is very similar to caffeine, has a molecular weight of 180.18g/mol, and is 46.66% C, 4.48% H, 31.10% N, and 17.76% O. What is the empirical and molecular formula of this compound? • Lycopene, the stuff in tomatoes that contributes to their red color and supports prostate health in men, has a molar mass of 536.90g/mol. It is 89.49%C and 10.51%H by mass. What are the empirical and molecular formulas of this compound? • Ascorbic Acid, Vitamin C, is 40.92%C, 4.58%H, and 54.50%O. It has a molar mass of 176.14g/mol What are the empirical and molecular formulas?

  21. Test Review Practice • 20.0g of a hydrate of iron(III) nitrate is heated until all the waters of hydration are lost. 11.97g of anhydrous salt remains after heating. What is the formula of the compound? • Glycerin is a thick liquid that is used in a wide variety of situations. It is 39.12% C, 8.756% H, and 52.12% O and has a molar mass of about 92g/mol. What is the molecular formula of glycerin? • Galactaric acid is a sugar acid derived from galactose. It is 34.29% C, 4.797%H, and 60.91% O and has a molecular weight around 210amu. What is the molecular formula of galactaric acid?

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