6.6 End-of-Chapter Material

Chapter Summary

To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the following summary and ask yourself how they relate to the topics in the chapter.

Chemical reactions relate quantities of reactants and products. Chemists use the mole unit to represent 6.022 × 1023 things, whether the things are atoms of elements or molecules of compounds. This number, called Avogadro’s number, is important because this number of atoms or molecules has the same mass in grams as one atom or molecule has in atomic mass units. Molar masses of substances can be determined by summing the appropriate masses from the periodic table; the final molar mass will have units of grams.

Because one mole of a substance will have a certain mass, we can use that relationship to construct conversion factors that will convert a mole amount into a mass amount, or vice versa. Such mole-mass conversions typically take one algebraic step.

Chemical reactions list reactants and products in molar amounts, not just molecular amounts. We can use the coefficients of a balanced chemical equation to relate moles of one substance in the reaction to moles of other substances (stoichiometry). In a mole-mass calculation, we relate the number of moles of one substance to the mass of another substance. In a mass-mass calculation, we relate the mass of one substance to the mass of another substance.

Additional Exercises

  1. If the average male has a body mass of 70 kg, of which 60% is water, how many moles of water are in an average male?

  2. If the average female is 60.0 kg and contains 0.00174% iron, how many moles of iron are in an average female?

  3. How many moles of each element are present in 2.67 mol of each compound?

    1. HCl
    2. H2SO4
    3. Al(NO3)3
    4. Ga2(SO4)3

  4. How many moles of each element are present in 0.00445 mol of each compound?

    1. HCl
    2. H2SO4
    3. Al2(CO3)3
    4. Ga2(SO4)3

  5. What is the mass of one hydrogen atom in grams? What is the mass of one oxygen atom in grams? Do these masses have a 1:16 ratio, as expected?

  6. What is the mass of one sodium atom in grams?

  7. If 6.63 × 10−6 mol of a compound has a mass of 2.151 mg, what is the molar mass of the compound?

  8. Hemoglobin (molar mass is approximately 64,000 g/mol) is the major component of red blood cells that transports oxygen and carbon dioxide in the body. How many moles are in 0.034 g of hemoglobin?

Answers

  1. 2,330 mol

    1. 2.67 mol of H and 2.67 mol of Cl
    2. 5.34 mol of H, 2.67 mol of S, and 10.68 mol of O
    3. 2.67 mol of Al, 8.01 mol of N, and 24.03 mol of O
    4. 5.34 mol of Ga, 8.01 mol of S, and 32.04 mol of O

  5. H = 1.66 × 10−24 g and O = 2.66 × 10−23 g; yes, they are in a 1:16 ratio.

  7. 324 g/mol