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Quantitative Composition of Compounds

Quantitative Composition of Compounds. Define the MOLE Determine molar mass of compounds Calculate percent composition of compounds Distinguish the differences between (and be able to calculate) empirical formulas and molecular formulas. Composition of Compounds.

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Quantitative Composition of Compounds

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  1. Quantitative Composition of Compounds Define the MOLE Determine molar mass of compounds Calculate percent composition of compounds Distinguish the differences between (and be able to calculate) empirical formulas and molecular formulas

  2. Composition of Compounds • Ratios of ingredients determines end result • Ratios in chemical compounds • Determine identity of the substance • Changing changes the entire compound • Example

  3. Chemical Measurements • How can we measure masses of atoms? • Counting by weighing

  4. Chemical Measurements • Atomic mass: • Mole (mol):

  5. Chemical Measurements • Avogadro’s number: • Molar mass:

  6. The Mole • Mole – unit for counting atoms

  7. The Mole • Molar Mass • Grams of element (or compound) that contain Avogadro’s number of atoms

  8. The Mole • The atomic mass expressed in grams is the molar mass of an element • One mole of any element contains Avagadro’s number of atoms

  9. The Mole • Can now convert between: • 25.0 g of iron is how many moles? mass moles molecules

  10. The Mole • How many grams of Na are in 2.55 moles? • How many atoms of Carbon are in 2.35 grams?

  11. Molar Mass of Compounds • One mole of a compound contains 6.022 x 10-23 formula units of that compound

  12. Molar Mass of Compounds • Molar mass – add molar masses of all atoms • What is the molar mass of H2O? • What is the molar mass of Ca(OH)2?

  13. Molar Mass of Compounds • How many molecules are there in a 3.46 g sample of HCl? = 5.71 x 1022 molecules

  14. Molar Mass of Compounds • If you burned 6.10 x 1024 molecules of ethane (C2H6) what mass of ethane did you burn? = 304.7 g C2H6

  15. Moles and Gases • At the same temperature and pressure, equal volumes of gases contain the same number of gas particles • STP = Standard Temperature (00 C) and Pressure (1 atmosphere)

  16. Moles and Gases • A student fills a 1.0 L flask with CO2 at STP. How many molecules of gas are in the flask?

  17. Moles and Gases • A container with a volume of 893 L contains how many moles of air at STP? • A chemical reaction produces 0.37 moles of N2 gas. What volume will that gas occupy at STP?

  18. Percentage Composition of Compounds • Mass of one element in a compound compared to the total mass of the whole compound • Two ways to determine…

  19. Percentage Composition of Compounds – from Formula • Calculate the molar mass • Divide the total mass of each element in the formula by the molar mass and multiply by 100. Total mass of element x 100 = % of element molar mass

  20. Percentage Composition of Compounds – from Formula • What is the percent composition of each element in table salt (NaCl)? Should equal 100%

  21. Percentage Composition of Compounds – from Experimental Data • Calculate the mass of the compound formed • Divide the mass of each element by the total mass of the compound and multiply by 100

  22. Percentage Composition of Compounds • A sample of 2.45 g of aluminum oxide decomposes into 1.30 g of aluminum and 1.15 g of oxygen. What is the percent composition of each element?

  23. Percentage Composition of Compounds • Find the percentage composition of a compound that contains 1.94 g of carbon, 0.480 g of hydrogen, and 2.58 g of sulfur in a 5.00 g sample of that compound.

  24. Empirical Formula • A formula that gives the SIMPLEST whole-number ratio of elements in that compound Ratio of atoms(formula) Ratio of masses (percent composition)

  25. Empirical Formula • What is the empirical formula of a compound containing 40% carbon, 53.3% oxygen, and 6.7% hydrogen? = 1 Divide by smallest number = 1 = 2

  26. Empirical Formula • Determine the empirical formula of a compound containing 5.75 g Na, 3.5 g N, and 12.0 g O

  27. Empirical Formula • Determine the empirical formula of a compound containing 2.644g of gold and 0.476 g of chlorine.

  28. Molecular Formula • Formula that gives the actual number of atoms in a given compound • Some compounds may have same empirical formula but actually be very different • Sometimes empirical formula and molecular formula are the same • Compare molar mass with empirical formula mass

  29. Molecular Formula • Ribose has a molar mass of 150 g/mol and a chemical composition of 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen. What is the molecular formula for ribose?

  30. Molecular Formula • Find the molecular formula of a compound that contains 42.56 g of palladium and 0.80 g of hydrogen. The molar mass of the compound is 216.8 g/mol. • Octane, a compound of hydrogen and carbon, has a molar mass of 114.26 g/mol. If the compound contains 18.17 g/mol hydrogen, what is its molecular formula?

  31. Homework • Questions #1, 6-10 • Paired Exercises #11-31 odd (a, b, c only); 33; 37-41 odd • Additional Exercises #43, 47, 50 & 51 • NO CLASS TUESDAY – Study help??? • Morning, afternoon, evening? • TEST THURSDAY – Chapters 11, 6 & 7

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