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. To see the solution to a problem or to return from the solution, click on the number of the problem.


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 remain 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.

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