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.
Set up your conversion using a T-bar.
The atomic mass of argon is 40.
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.