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Chapter 8 – Chemical Composition

Chapter 8 – Chemical Composition. Counting by Weighing Nails Atoms Moles Molar Mass Percent Composition of Compounds Empirical Formulas Molecular Formulas. Example 1. Helium atoms weigh 4.003 amu each on average. How many helium atoms are present in 1.0 x 10 25 amu?

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Chapter 8 – Chemical Composition

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  1. Chapter 8 – Chemical Composition • Counting by Weighing • Nails • Atoms • Moles • Molar Mass • Percent Composition of Compounds • Empirical Formulas • Molecular Formulas

  2. Example 1 Helium atoms weigh 4.003 amu each on average. • How many helium atoms are present in 1.0 x 1025 amu? • How much would 10 billion helium atoms weigh? (Assume 2 sig figs)

  3. Example 2 Sodium atoms weigh 22.99 amu on average. • How much would 6.022×1023 sodium atoms weigh in amu? • Convert your answer from amu to g. (1 g = 6.022×1023 amu)

  4. Example 3 How many moles of magnesium are in 10.0 g of magnesium?

  5. Example 4 How much do 5.00 moles of aluminum metal weigh?

  6. Example 5 How many atoms are present in 2.0 g of carbon?

  7. Example 6 Calculate the molar mass of each of the following compounds or elements: • nitrogen gas • carbon tetrachloride • ammonium phosphate

  8. Example 7 How many moles of hydrogen atoms are in: • 10.0 moles of H2? • 3.6 moles of HCl? • 4.0 moles of HC2H3O2?

  9. Example 8 How many moles of sodium acetate are present in 100.0 g?

  10. Example 9 How much would 2.5 moles of dinitrogen pentoxide weigh in grams?

  11. Example 10 Find the percent composition of calcium bromide.

  12. Example 11 Find the percent composition of H2SO4.

  13. Example 12 Write the empirical formula for each of the following compounds. • S2Cl2 • C6H12O6 • HNO3 • C8H14

  14. Example 13 When a 2.500-g sample of an unknown oxide of mercury is decomposed into its elements, 2.405 g of mercury are produced. What is the empirical formula of this compound?

  15. Example 14 The percent composition of benzamide is given below. Find its empirical formula. 69.40%C 5.82%H 11.57%N 13.21%O

  16. Example 15 The empirical formula of an organic compound is CH and its molar mass is 78.1 g/mole. What is the molecular formula of this substance?

  17. Example 16 The percent composition of caffeine is given below and its molar mass is known to be 194.19 g/mole. Find both the empirical formula and the molecular formula of caffeine. 49.48%C 5.19%H 28.85%N 16.48%O

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