Chapter 8 – Chemical CompositionExample 1Example 2Example 3Example 4Example 5Example 6Example 7Example 8Example 9Example 10Example 11Example 12Example 13Example 14Example 15Example 16Chapter 8 – Chemical Composition1. Counting by Weighinga. Nailsb. Atoms2. Moles3. Molar Mass4. Percent Composition of Compounds5. Empirical Formulas6. Molecular FormulasExample 1Helium atoms weigh 4.003 amu each on average. a. How many helium atoms are present in 1.0 x 1025 amu? b. How much would 10 billion helium atoms weigh? (Assume 2 sig figs)Example 2Sodium atoms weigh 22.99 amu on average. 1. How much would 6.022×1023 sodium atoms weigh in amu? 2. Convert your answer from amu to g. (1 g = 6.022×1023 amu)Example 3How many moles of magnesium are in 10.0 g of magnesium?Example 4How much do 5.00 moles of aluminum metal weigh?Example 5How many atoms are present in 2.0 g ofcarbon?Example 6Calculate the molar mass of each of the following compounds or elements:a. nitrogen gasb. carbon tetrachloridec. ammonium phosphateExample 7How many moles of hydrogen atoms are in:a. 10.0 moles of H2?b. 3.6 moles of HCl?c. 4.0 moles of HC2H3O2?Example 8How many moles of sodium acetate are present in 100.0 g?Example 9How much would 2.5 moles of dinitrogen pentoxide weigh in grams?Example 10Find the percent composition of calcium bromide.Example 11Find the percent composition of H2SO4.Example 12Write the empirical formula for each ofthe following compounds.a. S2Cl2b. C6H12O6c. HNO3d. C8H14Example 13When 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 ofthis compound?Example 14The percent composition of benzamide is given below. Find its empirical formula.69.40%C 5.82%H11.57%N13.21%OExample 15The 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?Example 16The 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
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