Lesson 2: Moles = Mass/Molar Mass (m=nM)

Overview:

In this lesson we will work towards applying how chemists are able to identify the identity of an unknown substance with the use of mass spectrometry. To do this we will learn about percentage composition and the law of definite proportions. With this knowledge you will refer to the periodic table to connect the relationships between Avogadro’s number, the mole concept, and the molar mass of any given substance.

Learning Goals:

  • I will be able to use the following vocabulary related to quantities in chemical reactions: molar mass, percentage composition, and the law of definite proportions. (D2.1)
  • I will be able to conduct an inquiry to calculate the percentage composition of a compound, specifically for a hydrate. (D2.2)
  • I will be able to find the molar mass of compounds by using the periodic table. (D2.3)
  • I will be able to solve problems related to quantities in chemical reactions by applying the formula, m=nM. (D2.3)
  • I will be able to describe the relationship between Avogadro’s number, the mole concept, and the molar mass of any given substance. (D3.2)

Success Criteria:

  1. Relate the molar mass to the average atomic mass of an element.
  2. Calculate the molar mass of a compound from the chemical formula of the compound.
  3. Calculate the amount in moles, the molar mass, or the mass of a pure substance when given the other two quantities.
  4. Calculate the number of entities in a sample.
  5. Calculate the number of atoms or ions in a sample of a compound.
  6. Identify the percentage composition of a compound as the proportion of each element in the compound, by mass.
  7. Calculate the percentage composition of a compound from experimental data.
  8. Calculate the percentage composition of a compound from the chemical formula of the compound.
  9. Explain the law of definite proportions in terms of the uniform percentage composition of any size sample of a compound.

Time Allocation:  2 hours

Learning Activities:

Read Nelson 6.4 - Molar Mass
Read Nelson 6.5 - Mass and Number of Entities
Read Nelson 6.6 - The Composition of Unknown Compounds
In the playlist below, video:

Task:

Solve questions 1, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 from Nelson 6.4 on page 277.
Solve questions 1, 2, 3, 4 and 5 from Nelson 6.5 on page 283.
Solve questions 1, 2, 4, 6 and 8 from Nelson 6.6 on page 288.

Reflect:

Additional Resources: