Stoichiometry: Calculations with Chemical Formulas and Equations

The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 3.

32) The molecular formula of aspartame, the artificial sweetener marketed as NutraSweet®, is C₁₄H₁₈N₂O₅.

       (a) What is the molar mass of aspartame?

       (b) How many moles of aspartame are present in 1.00 mg of aspartame?

       (c) How many molecules of aspartame are present in 1.00 mg of aspartame?

       (d) How many hydrogen atoms are present in 1.00 mg of aspartame?       

48) (a) The characteristic odor of pineapple is due to ethyl butyrate, a compound containing carbon, hydrogen, and oxygen. Combustion of 2.78 mg of ethyl butyrate produces 6.32 mg of CO₂, and 2.58 mg of H₂O. What is the empirical formula of the compund?

      (b) Nicotine, a component of tobacco, is composed of C, H, and N. A 5.250-mg sample of nicotine was combusted producing 14.242 mg of CO₂ and 4.083 mg of H₂O. What is the empirical formula for nicotine? If the substance has a molar mass of 160 ± 5 g/mol, what is its molecular formula?

50) Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as MgSO₄•xH₂O, where x indicates the number of moles of water per mole of MgSO₄. When 5.061 g of this hydrate is heated to 250°C, all the water of hydration is lost, leaving 2.472 g of MgSO₄. What is the value of x?

     
60) The complete combustion of octane, C₈H₁₈, a component of gasoline, proceeds as follows: 

      2C₈H₁₈(l) + 25O₂(g)   16CO₂(g) + 18H₂O(g)     

      (a) How many moles of O₂ are needed to burn 0.750 mol of C₈H₁₈?

      (b) How many grams of O₂ are needed to burn 5.00 g of C₈H₁₈?

      (c) Octane has a density of 0.692 g/mL at 20°C. How many grams of O₂ are required to burn 1.00 gal of C₈H₁₈?

70) Aluminum hydroxide reacts with sulfuric acid as follows:

      2Al(OH)₃(s) + 3H₂SO₄(aq) Al₂(SO₄)₃(aq) + 6H₂O(l)

     Which reagent is the limiting reactant when 0.450 mol Al(OH)₃ and 0.550 mol H₂SO₄ are allowed to react? How many moles of Al₂(SO₄)₃ can form under these conditions? How many moles of the excess reactant remian after the completion of the reaction?

99) (a) You are given a cube of silver metal that measures 1.000 cm on each edge. The density of silver is 10.49 g/cm³. How many atoms are in this cube?

      (b) Because atoms are spherical, they cannot occupy all of the space of the cube. The silver atoms pack in the solid in such a way that 74% of the volume of the solid is actually filled with silver atoms. Calculate the volume of a single silver atom.

      (c) Using the volume of a silver atom, and the formula for the volume of a sphere, calculate the radius in angstroms of a silver atom.