3. The Mole Concept
A Mole is:6.02 x 1023 of anything.The formula mass in grams of a substance contains one mole of particles.Na = Avogadro's Number = 6.02 x 1023Spreading a "mole" of marbles over the entire surface of the earth would produce a layer about three miles thick.When will the World's computers have a mole of digital data stored in them?
Important mole conversion factors:
1 mole = 6.02 x 1023 particles = formula mass in gramsMolar mass - the mass of a single atom of an element (in amu) is numerically equal to the mass of one mole of those atoms (in grams).From the Periodie Table, the mass of one atom of chromium is 51.9961 amu.
The mass of one mole (6.02 X 1023) of chromium atoms is 51.9961 grams.Coefficients in a chemical equation are normally used to indicate a ratio of reacting molecules. They also indicate a ratio of reacting moles. The mole concept allows chemists to use chemical equations to determine the "weight" of reactants and products in chemical reactions.For example: 2Mg(s) + O2 (g) → 2MgO(s)The balanced equation above shows that the product is 2 molecules of magnesium oxide. That also means 2 moles of magnesium oxide. By calculating the molar mass of MgO, then multiplying by the coefficient 2, the mass of MgO produced can be predicted from the balanced equation.
Examples of Mole Conversion Calculations:These problems are set up correctly using dimensional analysis.
Use a calculator to find each answer.Given 12.210 grams of carbon, how many atoms do you have?Given 18 grams of water, how many molecules do you have?Given 3.5 moles of NaCl, how many grams do you have?What is the mass of 6.02 x 1023 molecules of silver nitrate?Important Tips:Setting up the dimensional analysis problem correctly, with the proper conversion factors, is as important as the answer.
Form the habit of working neatly, canceling units, and circling the answer.
Remember, units are as important as numbers in the answer.
Use significant figures to round off the final answer.
Mole Calculations If you can work the problem below, you truly understand the mole concept!What mass of calcium chloride contains the same number of calcium atoms as 100 g of calcium hydroxide?The answer is 148 grams of calcium chloride. Do not look at the solution before doing your best to work the problem for yourself.