Chemistry Unit 4: The Mole and Chemical Calculations


  • Use Avodagro’s number and what we know about the mass of atoms and different elements to do useful calculations about chemicals.

Course Essential Questions

  • How can we learn about things that are too small to see?

Unit Essential Questions

  1. How do chemists count particles?


  1. very small things can be "counted" if their individual masses are known.

Prior Knowledge

  1. Use of the terms law, theory, hypothesis, model as used in science. (Ch 2.1 or biology notes for review)
  2. Symbols and names for 44 common elements, and their location on the periodic table

Prior Skills

  1. Count the number and types of atoms in a chemical formula
  2. Use dimensional analysis to convert between units of measure

Students will know....

  1. The difference between relative atomic mass and atomic mass number.
  2. The relationship between Avogadro's Number, 1 mole, and the mass in grams of a substance.

Students will be able to....

  1. Explain what all atoms of a given element have in common.
  2. Explain how isotopes of an element are similar and how they differ.
  3. Calculate the relative atomic mass of an element, given percents and mass numbers of a set of its isotopes.
  4. Find the molar mass of an element on the periodic table, or calculate the molar mass of a compound.
  5. Create conversion factors from molar masses and use them to convert between grams and moles.
  6. Calculate percent composition of elements in a formula
  7. Given an analysis in percent composition or mass, calculate the probable empirical formula.
  8. Given the empirical formula and molar mass for a compound, calculate the likely molecular formula.
  9. Use data obtained in lab for water of hydration to write a formula for a hydrated compound.
Chapter 3.3 Counting Atoms
  • Explain how protons (atomic number) determine the identity of an atom.
  • Explain the relationship between atomic number, mass number, and numbers of protons, neutrons, and electrons in an atom.
  • Atoms with the same number of protons but different numbers of neutrons are isotopes of the same element.
  • The unified atomic mass unit (u; amu) is based on the mass of the C-12 atom (1.660540 X 10-24 g).
  • The average atomic mass of an element is calculated using a weighted average of the atomic masses of all naturally occurring isotopes of the element.
  • Avogadro's number: the number of representative particles in an element as 6.022 X 1023particles = 1 mole. Use this relationship to convert between moles and representative particles.
  • 1 mole = the average relative atomic mass in grams. Use this equality to convert between grams and moles.
  • Calculate molar mass, and use molar mass in a mass-moles conversion.
Calculations Involving Moles
  • Explain the meaning and an application for the percent composition, empirical formula, and molecular formula of a compound.
  • Given a chemical formula, calculate the percent composition of each element.
  • Given the percent by mass as determined in lab, propose a probable empirical formula.
  • Given the empirical formula and them olar mass of a compound, calculate the molecular formula.
  • Use water of hydration data to calculate a formula.



Daily Learning Activities

Day 9

9/24 & 9/25

Day 10

9/26 & 9/30

  • Monatomic Ion Quiz 2
  • Counting by Weighing
  • Assignment: Continue with reading Chapter 3 Section 3 to answer the question "How do chemists count particles?"

Day 11

10/1 &10/2

  • Rewrite conversion factors in Counting by Weighing Lab
  • application of conversion factors - particle ratios from Counting by Weighing
  • How big is a mole? Introduction to Avogadro's number

Day 12

10/3 &10/6

  • Definition of the mole
  • Handout: Notes on the Mole
  • Calculating and using molar mass
  • Conversion factors, revisited: (review on pg 84 of textbook)
    • moles - representative particles <—> moles
    • moles - grams <—> moles

Day 13

10/7 &10/8

Percent Composition and Empirical Formula

Day 14A


Day 14B


Day 15A

10/14 &10/16

Day 15B

10/14 &10/16

  • Data Collection - Avogadro's Number and the Mole
  • When finished, work on the calculations and data analysis.
  • If you finish that, move on to the Lab Safety handout and work on Part 1, 2, and 3.
Day 16A10/17 &10/20
  • Data Collection - Avogadro's Number and the Mole
  • When finished, work on the calculations and data analysis.
  • If you finish that, move on to the Lab Safety handout and work on Part 1, 2, and 3.
Day 16B10/17 &10/20
  • Safety, Part 1
  • Percent Composition Quiz
  • Avogadro's Number Peer Review
Day 1710/21 &10/22
  • Peer Review - Avogadro's Number and the Mole Lab (B day) Due NEXT CLASS
  • Empirical and Molecular Formula Quiz
  • Prep for Molympics
Day 1810/23 &10/24
  • Lab books are due TODAY.
  • Molympics!
Day 1910/27 &10/28
Day 2010/29 &11/3
Day 21 11/4 & 11/5
  • Proficiency - Unit 3, Atomic Structure, Moles, and Mole Calculations
  • Review of atomic structure through Rutherford.
  • Assignment: Read Ch 4.1 using the Reading Guide (blue paper.)

Next Generation Science Standards:

PS1.A.1 Each atom has a charged sub-structure consisting of a nucleus, which is made up of protons and neutrons, surrounded by electrons.

PS1.B.3 The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

PS1.A.2 The periodic table orders elements horizontally by the number of protons in the atom’s nucleus and places those with similar chemical properties in columns. The repeating patterns of this table reflect patterns of outer electron states.

SEP 2 Developing and using models

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This work by Luann Christensen Lee is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Copyright 1989-2017 L.C.Lee,

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