mole concept

Introduction to the Mole Concept

• The mole is a concept used in chemistry to represent a quantity.
  • It is analogous to a dozen, which represents 12 items.
  • A mole represents approximately $6.022 \times 10^{23}$ entities (Avogadro's number).

Abbreviating "Mole"

• In formal contexts, the term "mole" might be written as "mole" but can also be abbreviated as "mol" by dropping the "e".

Conversion Problems

• The previous discussion involved converting between atoms and moles.
• Example Problem Setup:
  • Consider problem number 80, where the number of aluminum atoms is given, and the task is to convert them to moles.
  • When setting up the conversion, observe that whatever is in the numerator of the initial measurement transitions to the denominator in the new unit and vice versa.
    • This means:
      • Moles of aluminum is written above in the conversion.
      • Atoms go below the conversion factor.
    • The conversion indicates a need to divide the number of atoms by Avogadro's number to determine the moles of aluminum.

Practice with Conversion Problems

• Students are encouraged to work with peers on practice sheets, focusing specifically on problems that are not crossed out.
• Utilize T-bars for the conversion to visualize the relationships clearly.

Utilizing the Periodic Table

• Introduction of a new measurement unit: grams, which are determined using the atomic mass from the periodic table.
  • When converting moles to grams, the atomic mass provides the necessary information.
  • Example: For sodium, the atomic mass is rounded off to approximately 23 grams per mole.

Example Conversion Using Atomic Mass

• Problem Example: In number 81, the given information is 11.8 grams of argon, with the goal to convert to moles.
  1. Set up your conversion using a T-bar.
  2. The atomic mass of argon is 40.
  3. The conversion process:
     • Arrange the conversion such that grams of argon are on the bottom, and the atomic mass is appropriately placed in the equation.
     • Perform the division: $\frac{11.8 \text{ grams}}{40 \text{ grams/mole}}$ to find moles of argon.

Additional Conversion Examples

• Problem 82B involves converting moles of barium to grams.
  • Use the atomic mass of barium which is roughly 137 grams per mole for this conversion.
• Example for 83: 3.78 grams of silver to be converted to the number of atoms.
  • Use conversion factors in two steps: grams to moles using the atomic mass, then moles to atoms using Avogadro's number.
  • Atomic mass of silver is 108.
• Result: Should yield approximately $2.11 \times 10^{22}$ atoms of silver after calculations.

Continuing Practice

• Students should try additional problems, specifically numbers 84, 88A, and 89 with guidance from the instructor.
  • Number 84 involves converting platinum atoms to grams.
    • Follow similar conversion steps: atoms to moles, then moles to grams using atomic mass of platinum (195 grams/mole).
  • For number 88, conversion of cadmium atoms needs to be performed first to moles then to grams.
    • Atomic mass for cadmium is 112 grams/mole.
  • Convert the final result to kilograms as required.

Exam Preparation

• End of Chapter 2 reviewed; upcoming exam scheduled for March 2, allowing discussion and review time before the next chapter.
  • Important note: Spring break will follow next week.

Conclusion

• Recap of the day's learning, encouraging continued practice and readiness for the upcoming exam.
• Marks the end of the current session, with plans to continue learning in the next meeting.