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What is a mole?

BL

In this assignment you will calculate the mass of 5 moles and 5 micro-moles of your element super hero. In just this one sentence there are two terms you may not be familiar with.

This reminds kids that grams and kilograms are not a unit of weight in chemistry.
The difference between mass and weight may be tricky. Newtons (N) are a unit of force or weight. Newtons of force come across as weight for our mole in the gravitational attraction of a celestial object it happens to be standing on. One newton is the force needed to accelerate a one kilogram object at the velocity of 1 m per second. Mass is a property that goes with the object no matter where it goes.

What is mass?

Mass is an intrinsic property of a physical body that determines its resistance to acceleration and its strength of gravitational attraction to other bodies. Some common units of mass are grams, kilograms, daltons, and moles.

What is a mole?

Since 2018 a mole has been defined as the number of atoms in 12 grams of carbon 12. When I was in high school, a mole was defined based on the number of atoms in 1 gram of hydrogen….not deuterium or tritium! So 12 grams of carbon 12 contains 6.02214076×1023 carbon particles.

Class Discussion:

  • Why not use carbon 14 or H2 deuterium?
  • Could you have one mole of electrons or one mole of elephants?

Head counts are important when looking at how chemicals interact with one another. Metallic copper may be oxidized with oxygen gas, O2., to form cuprous oxide. or cupric oxide.

Metallic copper may react with oxygen to form cuprous and cupric oxides. Writing mass amounts in terms of moles allows us to keep a head count of proportions of copper and O2.
Different proportions of metallic copper and oxygen will give different copper oxides.

4Cu + O2 → 2 CuO (cuprous) or 2 Cu + O2 → 2 CuO (cupric)

Measuring amounts in grams is fine for baking. When you want the right product, counting heads in moles becomes necessary.

What does 6.02214076×1023 mean?

Some of you may have forgotten scientific notation. Scientific notation is a ways of expressing very large or very small numbers as a number between 1 and 10 multiplied by an exponent of 10. These are some examples to jog your memory

This image reminds the student what scientific notation is all about.
Writing out very small or very large numbers can be exhausting. Writing these numbers as a number between 1 and 10 multiplied by an exponent of 10 makes life easier.

Now for the assignment

Do this for your element following our mole friend’s example. Our mole friend’s hero element is antimony. Antimony has an atomic mass of 121.76 Daltons, that is the same thing as grams per mole.

Recall that the same values in the numerator and denominators of fractions cancel each other out. Red squares are drawn around units that do not get cancelled out. These units are part of our mole friend’s answer.

Our mole friend thought that 0.000609 g Sb was kind of an awkward expression. It decided to multiply this value by 1000 to get the same mass in milligrams. It could have added this conversion to the big fraction that scientists refer to as dimensional analysis.

Published by BL

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