I can calculate the molar mass of a compound knowing its molecular formula.
I can convert between number of moles and mass of a compound using moles to mass, mass to moles conversion factors.
I can calculate quantities of a substance or its relative number of particles using dimensional analysis and the mole concept.
Molar mass- mass - moles- grams- Conversion factor- Dimensional Analysis- Avogadro's Number- particles- atoms.
The mole is an amount unit similar to familiar units like pair, dozen, gross, etc. It provides a specific measure of the number of atoms or molecules in a bulk sample of matter. A mole is defined as the amount of substance containing the same number of discrete entities (such as atoms, molecules, and ions) as the number of atoms in a sample of pure 12C weighing exactly 12 g.
1 mole of any element contains the same number of atoms as 1 mole of any other element. The masses of 1 mole of different elements, however, are different, since the masses of the individual atoms are drastically different. The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol). (See figure 4)
Dimensional analysis (also called factor label method or unit analysis) is used to convert from one set of units to another. This method is used for both simple (feet to inches) and complex (g/cm3 to kg/gallon) conversions and uses relationships or conversion factors between different sets of units. Below are useful examples in Chemistry.
You can use the molar mass to convert from grams to moles or from moles to grams. See example 1.
You can use the Avogadro's number to convert from moles to particles and from particles to moles. See example 2.
You can use both molar mass and Avogadro's number to convert from grams to particles or atoms and from particles/atoms to grams see videos below for more help.
Determine the number of moles of CO2 in 454 grams of CO2
First, look up the atomic masses for carbon and oxygen from the periodic table. The atomic mass of C is 12.01, and the atomic mass of O is 16.00. The formula mass of CO2 is:
12.01 + 2(16.00) = 44.01
Thus, one mole of CO2 weighs 44.01 grams. This relation provides a conversion factor to go from grams to moles. Using the factor 1 mol/44.01 g:
moles CO2 = 454 g x 1 mol/44.01 g = 10.3 moles
2. Determine the mass in grams of H2SO in 3.60 mol of H2SO
First, look up the atomic masses for hydrogen, sulfur, and oxygen from the periodic table. The atomic mass is 1.008 for H, 32.06 for S, and 16.00 for O. The formula mass of H2SO4 is:
2(1.008) + 32.06 + 4(16.00) = 98.08
Thus, one mole of H2SO4 weighs 98.08 grams. This relation provides a conversion factor to go from grams to moles. Using the factor 98.08 g / 1 mol:
grams H2SO4 = 3.60 mol x 98.08 g / 1 mol = 353 g H2SO4
3. How many moles of potassium chloride (KCl) are in 4.0 L of a 0.65 M solution?
0.65 moles/L x 4.0 L= 2.6 moles KCl