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Unit 4 Review

Unit 4 Review. Terms to Remember. Precision: the narrowness of a range of numbers Accuracy: How close a measurement is to its actual value Molar Mass: the mass of a mole of any element or compound

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Unit 4 Review

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  1. Unit 4 Review

  2. Terms to Remember • Precision: the narrowness of a range of numbers • Accuracy: How close a measurement is to its actual value • Molar Mass: the mass of a mole of any element or compound • Atomic Mass: the number of grams of an element that is numerically equal to the atomic mass of the element in amu

  3. More Terms to Remember • Empirical Formula: smallest whole number ratio of the formula of a compound • Molecular Formula: a multiple of the empirical formula that is not necessarily in the lowest whole number ratio • Avogadro’s number: 6.02 x 1023 = 1 mole = 1 relative mass

  4. Practice Problems • What is the percent composition of C in C6H12O6? • If 5.24g of Ca combine with 9.46g of F to form a compound, what is the percent composition of both Ca and F? • Find the empirical formula for a compound which contains 32.8% chromium and 67.2% chlorine. • Determine which of the following is/are empirical formulas • C6H12O2 • CO2 • C4H6

  5. Solutions to Practice Problems • C = 12 x 6 = 72 O = 16 x 6 = 96 H = 1 x 12 = 12 C6H12O6=72 + 12 + 96 = 180 % mass C = 72/180 x 100 = 40% • Total mass of compound = 5.24 + 9.46 = 14.7 g % mass Ca = 5.24/14.7 x 100 = 35.6% % mass F = 9.46/14.7 x 100 = 64.3% 11. 32.8 g Cr x 1 mole = 0.631 moles 0.631/0.631= 1 CrCl3 52 g Cr 67.2 g Cl x 1 mole = 1.92 moles 1.92/0.631 = 3.04 35 g Cl 12. Determine which of the following are empirical formulas. • C6H12O2 • CO2 • C4H6

  6. Practice Problems • Draw a picture of a dart board in such a way that the darts represent a precise but not accurate thrower. • Avogadro’s number is equal to….. • How many Chloride ions are in 5 molecules of NaCl • How many sulfate ions are in 7 moles of Na2SO4? • What is the molar mass of Cu(CH3COO)2?

  7. Solutions to Practice Problems 1. • 6.02 x 1023 • 5 • 7 moles x (6.02 x 1023 atoms) = 4.21 x 1024 sulfate ions 1 mole • Cu = 64 H = 1 x 6 = 6 C = 12 x 4 = 48 O = 16 x 4 = 64 Cu(CH3COO)2 = 64 + 48 + 6 + 64 = 182 g

  8. Practice Problems 6. How many moles of Silicon atoms are in 5.03 x 1027 atoms of Silicon? • How many atoms are in 6.5g of Hg (mercury)? • How many molecules are in 5.62 moles of BaCl2?

  9. Solutions to Practice Problems 6. (5.03 x 1027) x 1 mole = 8360 atoms (6.02 x 1023) • 6.5g x (6.02 x 1023) =1.96 x 1023 atoms 201 g 8. 5.62 moles x (6.02 x 1023) =3.38 x 1024 molecules 1 mole

  10. Practice Problems • How many sig figs are in the following: • 0.0238 • 100. • 102.003400 • 500 • What is the sum of 54 and 62.5 in the correct number of sig figs? • What is the product of 34.23 and 10 in the correct number of sig figs?

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