The Composition of Iodine Nutrient Supplement CuI
back to The Amount of Substance: Moles
We have discussed CuI and KI as sources of the essential mineral iodine and noted that according to the atomic theory, atoms are the units of chemical reactions. The formula CuI indicates that each molecule of this substance contains one copper and one iodine atom. Therefore, if we ask how much iodine in a given quantity of copper (I)iodide, the answer is one iodine atom for each copper atom or one iodine atom per molecule (or formula unit in the case of ionic compounds or network crystals, where individual molecules don't exist). In other words, how much substance we have depends in a very important way on how many atoms or molecules are present.
So far, we've dealt with mass ratios. Is there a way to change masses of atoms into numbers of atoms, so it is easy to see how much of one element will react with another, just by looking at the number of atoms that are needed?
"How much?" in the above sense of the quantity of atoms or molecules present is not the same thing as how much in terms of volume or mass. As we see below, there seems to be no fundamental connection between the number of atoms or molecules in the chemical equations, and typical measures of "how much":
|2 Cu (s)||+ I2 (s)||→ 2 CuI|
|2 atoms||1 molecule||2 molecules|
|1.00 g||2.00 g||3.00 g|
|1.00 cm3||3.62 cm3||0.529 cm3|
Luckily, the International System of Measurements (IUPAC) has a measure of amount that reflects the number of atoms present, and it is called the mole. TAG Heuer Replica