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The Mole Concept

The Mole Concept. Review: Avogadro’s Number. Avogadro’s Number (symbol N) is named in honor of Italian chemist Amadeo Avogadro It tells us the number of atoms in 1 mole of a substance The value of Avogadro’s number is 6.02x10 23. Review: Mole.

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The Mole Concept

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  1. The Mole Concept

  2. Review: Avogadro’s Number • Avogadro’s Number (symbol N) is named in honor of Italian chemist Amadeo Avogadro • It tells us the number of atoms in 1 mole of a substance • The value of Avogadro’s number is 6.02x1023

  3. Review: Mole • The mole (symbol mol) is a unit of measure for an amount of a chemical substance • We define it as the amount of substance that contains Avogadro’s number of particles • The individual particles can be atoms, molecules, formula units, etc.

  4. Review: Mole • 1 Mole= Avogadro’s number (N) • Avogadro’s number =6.02x1023particles • 1 Mole=6.02x1023 particles

  5. Mole Analogies • If 6.02x1023atoms of hydrogen were laid side by side, the total length would be long enough to circle the Earth 1,000,000 times • The mass of 6.02x1023 Olympic shot-put balls would equal the mass of the Earth • The volume of 6.02x1023softballs would equal the volume of the Earth • Extra Credit Question: If $6.02x1023 earns 5% interest per year, how many dollars does the account earn every nanosecond? (must show all work to receive credit)

  6. Mole Calculations: Nmoles • We can convert between the number of particles and the number of moles. • Example: • How many moles of Iodine are in 2.5x1023 molecules of I2?

  7. Mole Calculations: molesN • We can convert between the number of moles and the number of particles. • Example: • How many molecules of chlorine are in 0.250 moles of the gas?

  8. Molar Mass • Molar mass is the mass of 1 mole of a substance • For elements the molar mass is equal to its atomic mass, which we find on the periodic table • For compounds the molar mass is equal to the sum of the individual elements that make it up

  9. Molar mass examples • Find the molar mass of the following substances: • Silver metal • Magnesium nitrate • NH3 • Manganese metal • Strontium acetate • Sulfur hexaflouride

  10. Mole Calculations: gramsmol • We can convert between the mass of a substance and the number of moles. • Example • How many moles are in 87.8g of Pb?

  11. Mole Calculations: molgrams • We can convert between the mass of a substance and the number of moles. • Example • How many grams are in 3.2 moles of (NH4)3PO4 ?

  12. Mole Calculations: g  N • We can also convert between mass and the number of particles • Example: • How many molecules are present in 1.470g of O2 gas?

  13. Mole Calculations: g  N • We can also convert between the number of particles and mass • Example: • What is the mass in grams of 2.01x1022 atoms of sulfur?

  14. Percent composition • Percent composition is a list of the mass percent of each element in a compound • Before we continue we need to discuss what percentages are. • Percent expresses the amount of a single quantity compared to the entire sample

  15. Calculating % composition • Calculate the percent composition for each element in H2O

  16. Calculating % composition • Calculate the percent composition for each element in Trinitrotoluene (TNT), C7H5(NO2)3

  17. Empirical Formula • In the late 1700’s chemists were very interested in chemical reactions, especially those with oxygen. • This was because chemists could determine the formula of a compound after the reaction through the use of empirical formulas • Empirical formulas are the simplest whole number ratio of atoms in an element

  18. Empirical Formula

  19. Empirical Formula • Glycine is an amino acid found in protein. An analysis of glycine gave the following data: 32.0% carbon, 6.7 % hydrogen, 18.7% nitrogen, and 42.6% oxygen. Calculate the empirical formula for the amino acid. (Assume 100g sample)

  20. Empirical Formula • Calculate the empirical formula for caffeine. An analysis of caffeine gave the following data: 49.5% carbon, 5.15 % hydrogen, 28.9% nitrogen, and 16.5% oxygen. (Assume 100g sample)

  21. Molecular Formulas • Molecular formulas indicate the actual numbers of atoms of each element in one molecule • Benzene, styrene and acetylene, while very different substance with very different properties, all have the same empirical formula CH. • Because they are different compounds they must have different formulas and therefore different molar masses.

  22. Calculating molecular formulas • Acetylene: 26 g/mole

  23. Calculating molecular formulas • Benzene: 78 g/mole

  24. Calculating molecular formulas • Styrene: 104 g/mole

  25. Calculating molecular formulas • The empirical formula for fructose is CH2O. If the molar mass of fructose is 180g/mol, find the molecular formula of fructose.

  26. Calculating molecular formulas • Ethylene dibromide was used as a grain pesticide until it was banned in 1983. • A. Find the empirical formula if the percent composition is 12.7% C, 2.1% H and 85.1% Br. • B. If the molar mass is 180g/mol, find the molecular formula of ethylene dibromide.

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