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The Mole

The Mole. Remembering Terms. Atomic number- # of _________ Mass Number- # of particles in the ________ (_______ + ________) __________- average mass (in atomic mass units, amu) of all naturally occurring isotopes according to their abundance. Given: one atom 56 Fe

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The Mole

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  1. The Mole

  2. Remembering Terms • Atomic number- # of _________ • Mass Number- # of particles in the ________ (_______ + ________) • __________- average mass (in atomic mass units, amu) of all naturally occurring isotopes according to their abundance

  3. Given: one atom 56Fe • What is the atomic #? • __________ • What is the mass #? • ___________ • What is the atomic mass? • ____________ • Given: a sample of iron • What is the atomic #? • _____________ • What is the mass #? • _____________ • What is the atomic mass? • ______________

  4. Calculating Atomic Mass • Finding atomic mass of an element • Look it up on the periodic table • What is the atomic mass of Na? C? Ag? • Na ________ • C ________ • Ag ________ • Finding atomic mass of a compound • Calculate it using each element’s atomic mass from the periodic table • Remember to take into account how many atoms of each type are in the compound • What is the atomic mass of NaCl? H2O? Na3PO4? • NaCl ________ • H2O ________ • Na3PO4 ________

  5. The Mole • A name for a certain number of things • Just like • A dozen is the name for ___ things • A baker’s dozen is the name for ___ things • A gross is the name for ____ things (a dozen dozens) • A mole(mol) is the name for ________things, also known as Avogadro’s number • Atoms, molecules, formula units

  6. Using Avogadro’s Number • Calculating number of moles of each element in a compound • How many moles of Na are in 1 mol of NaCl? • _____________________________ • How many moles of Cl are in 3 moles of MgCl2? • _____________________________ • Calculating number of things • How many molecules are in 4 moles of CO2? • How many atoms are in 2.5 moles of CO2?

  7. The Mole (cont) • Definition of the Mole • A mole equals the number of atoms in 12 g of carbon-12 • Because of this definition, • Atomic mass in amu’s equals the mass in grams (molecular mass or molar mass) • What is the molecular mass of Na? C? Ag? • Na – ____________ • C – _____________ • Ag – ____________ • What is the molecular mass of NaCl? H2O? Na3PO4? • NaCl – ____________ • H2O – _____________ • Na3PO4 – ___________

  8. Molar Calculations Using Mass • Calculating # of moles from mass or mass from number of moles • How many moles of NaNO3 are in 308.25g? How many moles of O are in the sample? • How many kilograms are in 28.34 moles of NaCl?

  9. Molar Calculations Using Mass (cont) • Calculating # of things from mass or mass from number of things • How many molecules of water are in 20g? • How many atoms are in 0.37g of N2?

  10. % Composition of Compounds • Gives the % of each element in a compound by mass • (Molecular mass of element in compound/ Molecular mass of compound) x 100 • What is the % composition of each element in Na2SO3? • Na _______________________ • S ______________________ • O ________________________

  11. Empirical Formulas • Simplest, reduced formula for a compound • In (almost all) ionic compounds, the empirical formula matches the molecular formula • For example: Magnesium chloride • Molecular formula- ______ • Empirical formula- _______ • In covalent compound, they often don’t match • For example: Glucose • Molecular formula- ______ • Empirical formula- _______

  12. Calculating Empirical Formulas • Known: • % of compound that each element represents (% composition) or • how many grams of each element are in the compound • Steps • Change each element’s amount in g to amount in mol • If given % comp, the number of grams is the %.

  13. Calculating Empirical Formulas • Steps (cont) • Find the smallest amount of moles among the elements and divide each number of moles by this number • Determine the empirical formula • If the divided numbers are whole integers (or very close), then these are the subscripts for each of the corresponding elements. • If some of the divided numbers are not whole integers, multiply all of them by a # that will make all of them whole integers

  14. Calculating Empirical Formulas • What is the empirical formula of a compound that is 76.57% C, 6.43% H, and 17% O by mass? Step 1 Step 2 Step 3

  15. Calculating Empirical Formulas • What is the empirical formula for a compound that contains C, H, and O if a 20g sample has 9.054g C and 1.900g H? Step 1 Step 2 Step 3

  16. Calculating Empirical Formula • What is the formula for a hydrate if the compound contains 79.07% CaSO4 and 20.93% H20? Step 1 Step 2 Step 3

  17. Calculating Molecular Formulas • Known: • Empirical formula (and therefore empirical formula mass) • Molecular mass • Steps • Calculate empirical formula mass (same as calculating a molecular mass but use empirical formula) • Divide molecular mass by empirical formula mass to get a whole integer • Multiple all elements in the empirical formula by the whole integer to get the molecular formula.

  18. Calculating Molecular Formulas • If the empirical formula of hydroquinone is C3H3O and the molecular mass is 110 g/mol, what is the molecular formula? Step 1 Step 2 Step 3

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