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Daily Science pg. 74

Daily Science pg. 74. How many atoms are in 3.6 mol of calcium? How many moles are in 1.45 x 10 24 atoms of sodium? What is the molar mass of K 2 SO 4 ? How many grams of CO are in 2.9 moles? How many moles is 236 g of NaOH ? What is the mass of 7.6 x 10 23 atoms of KF?

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Daily Science pg. 74

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  1. Daily Sciencepg. 74 • How many atoms are in 3.6 mol of calcium? • How many moles are in 1.45 x 1024 atoms of sodium? • What is the molar mass of K2SO4? • How many grams of CO are in 2.9 moles? • How many moles is 236 g of NaOH? • What is the mass of 7.6 x 1023 atoms of KF? • How many atoms are in 192 g of MgCl2?

  2. Empirical and mOlecular Formulas Pg. 73

  3. Determining moles in a compound • Formulas tell us ratios of the number of atoms in the compound • Ex. Freon is CCl2F2 • There is 1 C, 2 Cl, and 2 F • We can figure out how many moles of one element there are in a given compound. • Moles of compound x # of atoms of element 1 mole of compound

  4. Ex. • How many moles of F are in 5.50 moles of CCl2F2? • Calculate the number of moles of each element in 1.25 moles of C6H12O6.

  5. Percent composition • First, find the molar mass of the compound • Multiply the mass of one element by its subscript • Divide the mass of one element by the total mass in the compound • Multiply by 100 • Ex. H2O

  6. Ex. • Determine the percent by mass of each element in the compound CaCl2.

  7. Empirical Formulas • Empirical formula = the formula with the smallest whole number ratio of the elements • If you know the percent composition of the element, divide the amount of that element by its molar mass. • This tells you # moles of that element. • If it is written as a percent, assume there are 100 g of the compound • If the numbers aren’t whole numbers, divide by the smaller value • If the numbers still aren’t whole numbers, multiply by the smallest factor that will make them whole

  8. Ex. • Compound with 40.05% S and 59.95% O • Determine the empirical formula for methyl acetate which has the following chemical make up: 48.64% C, 8.16% H, and 43.20% O.

  9. Molecular formulas • Sometimes the empirical formula is the same for two different compounds • When that happens, you take the experimentally determined molar mass of the compound and divide it by the mass of the empirical formula • This gives you a whole number (n) that must be multiplied into the empirical formula

  10. Ex. • Succinic acid is composed of 40.68% C, 5.08% H and 54.24% oxygen and has a molar mass of 118.1 g/mol. Determine the empirical and molecular formulas for succinic acid.

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