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Chapter 11

Chapter 11. Mole. SI base unit for measuring the amount of substance The number of representative particles in exactly 12 grams of pure carbon-12 1 mole = 6.02 x 10 23 representative particles. Avogadro’s Number. 6.02 x 10 23 is called Avogadro’s number

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Chapter 11

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  1. Chapter 11

  2. Mole • SI base unit for measuring the amount of substance • The number of representative particles in exactly 12 grams of pure carbon-12 • 1 mole = 6.02 x 1023 representative particles

  3. Avogadro’s Number • 6.02 x 1023 is called Avogadro’s number • It is the number of representative particles equal to 1 mole • A representative particle is any kind of particle and depends on the substance • Water = molecule • Copper = atom • NaCl (salt) = formula unit

  4. Molar/Formula Mass • Molar/Formula mass is the mass in grams of 1 mole of any pure substance. • units are g/mol • Molar mass is equal to the atomic mass on the periodic table • Gram atomic mass: (found on periodic table) • Ex: C = 12.011 amu • This means 1 mole of Carbon = 12.011 g

  5. Let’s practice: Find the # of grams 1 mole of the following is equal to • Al • H • O • P

  6. Formula Mass/Molar Mass • Formula or Molar mass is the mass of 1 mole of a pure substance H2O – covalent compound (metal/nonmental) H = 2 x 1 g = 2 g O = 1 x 16 g = 16 g total = moles x avg. atomic mass= 18 g

  7. Let’s practice: Find the # of grams 1 mole of the following is equal to • H2O2 • NaCl • Ca(NO3)2 • (NH4)3PO4 • N2O4

  8. Percent Composition • You can calculate the percentage of a certain element in a compound • Use the % Formula: (Part/Whole) x 100 = • 1st- we need the formula mass or the whole • 2nd – we need the part found in the compound • 3rd – divide and multiple by 100

  9. Example: What is the % of Hydrogen in H2O? 1st: Gram atomic Mass • H2O – covalent compound (metal/nonmental) H = 2 x 1 = 2 O = 1 x 16 = 16 total = moles x avg. atomic mass= 18 g 2nd: Hydrogen has a mass of 2g 3rd: %H = (2g/18g) x 100 = 11.11%

  10. What is the percent of oxygen in in H2O? • The percent of each element in a compound should add and equal 100.

  11. Lets practice: Find the percent composition of each of the elements in the following compounds. • Fe2O3 • Cu2S

  12. Molar Mass can be used as a Conversion Factor • What is the mass in grams of 2.5 mol of NaCl? • Steps • 1st : get the formula/molar mass of the compound • 2nd: convert Na = 1 x 23 = 23 Cl = 1 x 35.5 = 35.5 = 58.5g ?g = 2.5 mol NaCl 58.5 g NaCl = 146 g NaCl 1 mol NaCl

  13. Avogadro’s number as a conversion factor • 1 mole = 6.02 x 1023 representative particles • Representative particles can be atoms, molecules, particles, formula units, pieces, etc • How many molecules are in 3.5 moles of CO2? ?molecules = 3.5 mol CO2 6.02 x 1023 molecules = 1 mol NaCl 2.1 x 1024 molecules CO2

  14. Volume Conversions • At STP 1 mol = 22.4 liters of a gas • What volume will 54.6 grams of CO2 occupy at STP? ?liters = 54.6 g CO2 1 mol CO2 22.4 liters CO2 = 44 g CO2 1 mole CO2 27.8 liters of CO2

  15. Let’s practice: • How many grams are in 0.817 moles of C2H2O6? • How many moles are in 60 grams of CaC03? • How many formula units of CaCl2 are in 45 grams?

  16. Empirical Formulas • The simplest whole number formula/ratio of a compound. This means the equation cannot be reduced anymore. • Smallest whole number ratio • Example: An unknown sample contains 25% H and 75% C. What is the empirical formula

  17. Steps: 1st Convert % to grams (Assume you have 100 grams total) 2nd Convert grams to moles by using the atomic mass 25 % = 25 grams H 75 % = 75 grams C 25 % = 25 g H x (1mol H/1g H) = 25 mol H 75 % = 75 g C x (1mol C/12 g C) = 6.25 mol O

  18. H = 25 mol/ 6.25 mol = 4 • C = 6.25 mol / 6.25 mol • = 1 CH4 3rd Divide by the smallest # of moles to get the ratio 4th Put numbers as subscripts of elements in formula 5th if a whole number is not found after dividing, multiply by a factor to make it a whole # (must multiply all numbers by the same factor)

  19. Molecular Formula • Indicates the actual amount of atoms present • Must have molecular weight to determine molecular formula

  20. Steps: • Determine the empirical formula • Determine the empirical weight (molar mass of the empirical formula) • Divide the molecular weight given by the empirical weight you calculated • If one, then the empirical formula is the same as the molecular formula

  21. If the answers from step 3 is a whole number, then take the answer and multiply all coefficients in the equation by the number. • If it is not a whole number you must multiple by a factor to make it a whole number then multiply each of the subscripts by it. This will give the molecular formula.

  22. Molecular Formula Example • What is the molecular formula of a compound with a molecular mass of 64 g/mol and an empirical formula of CH4? • CH4 empirical mass = (12) + (4 x 1) = 16g/mol • Molecular mass = 64 g/mol • 64 / 16 = 4 • Multiply subscripts by 4 • New formula is C4H16

  23. Hydrates • A compound that contains a certain amount of water molecules • Example: CuSO4. 5H2O • Copper sulfate pentahydrate • Hydrates can be dehydrated by heating • The dehydrated form can be used to absorb moisture from the air – like those packets you find in your shoe boxes – deliquescent

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