Unit 7 Notes: Moles, Molar Mass, and Stoichiometry

Unit 7: Moles, Molar Mass, and Stoichiometry

Overview

  • This unit reviews the mole concept, mass measurement, and unit conversions.
  • It covers predicting and measuring the mass of reactants and products in chemical reactions.
  • Textbook connections: Chapter 12 Lesson 64, Chapter 14 Lessons 76, 77, 78, and Chapter 17 Lessons 91, 92, 93.

Topics

  1. The Mole and Molar Mass
    • Related textbook sections: Ch 12 Lesson 64, Ch 14 Lessons 76, 77, 78
  2. Mole Ratio and Chemical Equations
    • Focus on the limiting reactant.
    • Related textbook section: Ch 17 Lesson 91
  3. Stoichiometry
    • Gram-to-mole conversions.
    • Measuring amounts of reactants and products in chemical equations.
    • Related textbook sections: Ch 17 Lesson 92 and 93

Success Tips

  • Bring your textbook to class and read it.
  • Take notes in your chemistry notebook and read them.
  • Find notes on Google Classroom.
  • Bring a calculator.
  • Give your attention in class and take notes when instructed.
  • Note anything the instructor indicates might be on the test.
  • Be prepared to think and collaborate with classmates.
  • Attend tutorials for extra help.

Applications and Relevance

  • Measuring and explaining concentrations in groundwater, dosages, and nutrition.
  • Applications in toxicity, pollution cleanup, and medicine.
  • Thermodynamics: the flow and conservation of energy (related to physics).

Key Terms

  1. Mole
  2. Molar Mass
  3. Mole Ratio
    • The coefficients in a balanced chemical equation indicate the mole ratios of reactants and products.
    • Example: CuSO4(aq)+2NaOH(aq)→Cu(OH)2(s)+Na2SO4(aq)CuSO4 (aq) + 2NaOH(aq) \rightarrow Cu(OH)2(s) + Na2SO4 (aq)
    • In the example above, the ratio of CuSO4 to NaOH is 1:2.
  4. Limiting Reactant
    • The reactant that is present in less than the required amount based on the stoichiometry of the reaction.
    • The reaction cannot proceed if there is less than the required number of moles of the limiting reactant.
  5. Stoichiometry
    • The measurement of reactants and products in a chemical reaction.
    • Determining how many grams or moles of reactants are required or how many grams or moles of products are produced.

Cyanide and Toxicity

  • Hydrogen cyanide (HCN) and sodium cyanide (NaCN) are poisons.
  • They interfere with hemoglobin in the blood.
  • HCN: H+H^+ bonds to the CN−CN^- ion.
  • NaCN: Na+Na^+ bonds to the CN−CN^- ion.
  • Hemoglobin (Hb) is a complex protein containing iron, which binds with oxygen (Hb:O2Hb:O_2).
  • Reaction with Cyanide: Hb:O<em>2(aq)+CN−→Hb:CN(aq)+O</em>2(g)Hb:O<em>2 (aq) + CN^- \rightarrow Hb:CN (aq) + O</em>2 (g)
  • Cyanide compounds disrupt the ability of blood cells to carry oxygen.

Mole and Avogadro's Number

  • Chemists use the mole to describe the number of particles in a sample.
  • 1 mole = 6.02 x 10^23 atoms or molecules.
  • Avogadro's Law: Equal volumes of gases contain the same number of particles at the same temperature and pressure.
  • STP (Standard Temperature and Pressure): 1 atm and 273 K.
  • At STP, any gas occupies 22.4 L and contains 6.02 x 10^23 particles.

Molar Mass

  • Small amounts of a substance can contain a large number of atoms.
  • The mole is a counting unit: 1 mole = Avogadro's number = 6.02 x 10^23
  • The mass of 1 mole of a substance is its molar mass.

Molar Mass Practice Problems

  • Calculate the molar masses of the following:
    1. NH3NH_3 (Ammonia)
    2. CO32−CO_3^{2-} (Carbonate ion)
    3. C<em>6H</em>12O6C<em>6H</em>{12}O_6 (Glucose sugar)