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The Mole and Mass Percentages

CHM 101

The Mole andMass PercentagesCHM 101
https://www.youtube.com/watch?v=TEl4jeETVmg
https://youtu.be/HdEHla5NrGc
https://youtu.be/tuzRNCRj0CM
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Eggs are counted in dozens

Paper is counted in reams (one ream or pack of paper = 500 sheets). Mardi Gras beads are still sold by the gross (144 or 12 doz) and so on. The mole is the chemist's counting unit. You do not even have to think about how many eggs is in 2 dozen...hopefully, you will become that comfortable with the mole as a counting unit.
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The Mole chart

A picture is always helpful but DO NOT forget that the numbers we are working with have units and dimensional analysis is still the way to go when doing conversions. The conversion between particles and moles is 6.02 x 10^23 (Avogadro's number or N) particles/mole. As the chart chows, you will multiply in one direction and divide in the other direction. When you divide, the conversion factor is 1 mole/6.02 x 10^23 particles.
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We can use the same idea when we "take apart" a molecule

We already know that N is Avogadro's number and this is what we use to go back and forth between particles (atoms, molecules, formula units, ions) but what is "n" in this picture? The lower half of this diagram represents moles of water (mole A) and moles of oxygen atoms (n is subscript for O in H2O) (mole B). The same thing can be done for hydrogen; what would "n" be for hydrogen?
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Molar Mass-the conversion between moles and mass

We have balances in the lab that measure mass but not moles or atoms. Mass is the "everyday" unit and the one we can actually measure. If you are trying to go from moles to mass for most elements, the molar mass is represented by the atomic mass on the PT. For compounds, you must add up the atomic masses to get the molar mass.
https://www.youtube.com/watch?v=HMAOrGpkTsQ

The slideshare linked below on "How Big is the Mole?" is very helpful

There are numerous analogies to help you conceptualize the size of a mole (such as how much guacamole can you make from a mole of avocados) as well as worked out examples.
https://www.youtube.com/watch?v=AsqEkF7hcII
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Average Atomic Mass

We studied isotopes at the very beginning of this course. Now that we are getting into the math of chemistry, we can finally understand where those atomic masses that are on the PT come from and how they are related to the mass numbers we used before.
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Mass percentages

It is a percentage-always going to "part"/"whole" x 100! In chemistry, this can be approached in two ways: from the formula as the picture represents or from actual data from the lab. We will do both in our practice and you will do an experiment determining the percentage of water in a hydrated compound.

What can you do to help your understanding?

Chemistry is a subject that must be practiced everyday if possible. Work through the lecture examples stopping the video clips and then restarting to check yourself. Take advantage of the practice in Mastering Chemistry to give you the practice you need to be successful. DO NOT PROCRASTINATE! Check announcements on Blackboard everyday. Keep a printed copy of the most recent course calendar next to your work area. Email me with questions!!