Mystified by the "Mole"?  Stop it - this minute


  A MOLE is a word that stands for a NUMBER.

  Just as A DOZEN is a word that stands for a number.

  "Dozen" means 12.  "Mole" means 6.02x1023.  That's all.

  Why is 12 called a dozen? For convenience. Why is 6.02x1023 called a mole? For convenience.

We will now have a quiz:
1. What name is given to the number 12?
2. If you have a dozen apples, how many apples do you have?
3. What name is given to the number 6.02x1023?
4. If you have a mole of copper atoms, how many copper atoms do you have?
5. If you have a mole of eggs, how many eggs do you have?

  Who decided that the number 6.02x1023 would be worth having a name for? Well, of course, that was Amadeo Avogadro, the Count of Quaregna. So 6.02x1023 is sometimes called "Avogadro's number." We could go around saying "3 times Avogadro's number of iron atoms" or "this solution has 0.01 times Avogadro's number of sugar molecules per liter," but isn't it much easier to say "3 moles of iron" or "this solution is 0.01 molar sucrose?"

Advanced Quiz:
1. Which would be more convenient?
  (A) Go in the store and count out 36 eggs
  (B) Go in the store and count out three cartons of a dozen eggs each.

2. Which would be more convenient?
  (A) Burn 1 mole of carbon with 2 moles of sulfur and measure the energy yield
  (B) Burn 602,000,000,000,000,000,000,000 atoms of carbon with 1,204,000,000,000,000,000,000,000 atoms of sulfur and measure the energy yield.

3. A chemical reaction that combines 2 atoms of sulfur with one atom of carbon makes one molecule of carbon disulfide. In order to use up all the carbon and all the sulfur, you could combine... (list all correct answers)
  (A) the same number of sulfur atoms as of carbon atoms
  (B) twice as many atoms of sulfur as atoms of carbon
  (C) the same number of moles of sulfur as of carbon
  (D) twice as many moles of sulfur as of carbon
  (E) 1,204,000,000,000,000,000,000,000 sulfur atoms and 602,000,000,000,000,000,000,000 carbon atoms
  (F) 2 moles of sulfur and 1 mole of carbon
  (G) 2 grams of sulfur and 1 gram of carbon

4. Now suppose you want to label the eggs by how big they are. Small eggs weigh about 1.33 ounces; medium 2 ounces; large 2.33 ounces; extra large about 2.67 ounces; jumbo about 3 ounces. As you see, one extra large egg weighs twice as much as one small egg. Which of the following is(are) true (list all correct answers)
  (A) A dozen eggs is a dozen eggs -- they all weigh the same by the dozen
  (B) One dozen extra large eggs weighs twice as much as one dozen small eggs

5. A table of atomic masses catalogues atoms by their mass. The "atomic mass" is the mass of one mole of an element. The atomic mass of carbon is 12.00 grams/mole. The atomic mass of sulfur is 32.06 grams/mole. The mass of one carbon atom is 0.00000000000000000000001993 grams. The mass of one sulfur atom is 0.00000000000000000000005326 grams. In which of the following cases is all the carbon and all the sulfur used up in combining to make carbon disulfide (list all correct answers).
  (A) Combine 0.00000000000000000000001993 grams of carbon with 0.00000000000000000000005326 grams of sulfur
  (B) Combine 1 mole of carbon with 1 mole of sulfur
  (C) Combine 0.00000000000000000000001993 grams of carbon with 0.00000000000000000000010652 grams of sulfur
  (B) Combine 1 mole of carbon with 2 moles of sulfur

Did you notice that the atomic mass has units? What are the units of atomic mass?

  There is, of course, a reason why 6.02x1023 is special enough to be given a name. It is (approximately) the number of atoms of hydrogen, the element with the smallest atoms, that makes up one gram of hydrogen. Of course, the amount of mass that is called "one gram" was arbitrary, and was originally defined by the mass of an arbitrarily chosen piece of platinum-iridium alloy kept in an underground vault outside of Paris, the so-called "primary standard" of mass, designated to be one kilogram.

  Who decided that the number 12 would be important enough to be given a name ("dozen")? Good question. That can be a research project for you.

For homework:
  1. If you had a mole of eggs, and piled them in a layer that covered the earth's surface, estimate how high a pile you would have, and chose the answer below that is closest to your estimate. The radius of the earth is 6,400 km. Extra large eggs.
(A) 5 meters
(B) 50 meters
(C) 500 meters
(D) 5 km
(E) 50 km
(F) 500 km
  What a fabulous problem! It requires estimation, perhaps some measurement, lots of ingenuity.
-- the answer is (E).

For extra credit:
  2. Make a rough estimate of what the "atmospheric pressure" would be at the bottom of this pile due to the weight of the eggs? Make reasonable measurements or assumptions about the mass or density of eggs, etc. Express the result in "atmospheres of pressure." The pressure of one atmosphere is 15 pounds per square inch.
(A) 4 atmospheres
(B) 40 atmospheres
(C) 400 atmospheres
(D) 4,000 atmospheres
(E) 40,000 atmospheres
(F) 400,000 atmospheres
-- the answer is (D).

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