Download Notes - Introduction to Moles: One and Two Step Mole Calculations

Notes - Introduction to Moles: One and Two Step Mole Calculations
6 x Formula mass - (also called gram formula mass, molecular mass, gram molecular mass, formula weight,
gram formula weight, molecular weight, gram molecular weight, molar mass, and molar weight): the mass of
one mole of a compound, atom or ion.
Find the formula mass of each of the following:
sodium chloride
arsenic trichloride
potassium sulfate
ammonium phosphate
Measuring Matter: There are three ways to measure matter: by counting representative particles (typically
molecules or formula units), by mass (in grams), or by volume (in liters for gases). The method used is usually
chosen by the ease of each method and the information needed. Once a measurement has been made, it is
possible to convert between the units for the other methods.
1 mole of a compound
=
fm (in g) compound
1 mole of an element
=
6.02 x 1023 atoms of that element
1 mole of a compound
=
6.02 x 1023 representative particles (molecules or formula
units)
The mole is the link between grams, the number of representative particles and liters.
For neutral compounds, the representative particle is either the molecule (covalent) or the formula unit (ionic).
However, to simplify matters we will just use the term molecule for both.
EXAMBLES (One Step Conversions): Remember to show all work using dimensional analysis and to keep
significant figures in mind.
1. How many moles are in 18.0 grams of sugar (C6H12O6)?
2. What is the weight of 4.50 moles of barium sulfide?
3. How many molecules are in 28.6 mole of nitrogen gas?
4. How many moles are in 3.90 x 1028 molecules of methane (CH4)?
6. How many atoms of oxygen are in 2.5 moles of oxygen gas? (Diatomic alarms should be ringing in your
head-this one is sneaky)
You are now familiar with conversions between grams, moles, and molecules. We can combine these in to twostep or even three-step problems to find more information such as the number of atoms of an individual element
in a compound.
EXAMPLES: Two-Step and Three-Step Problems
5. How many molecules are in 198.5 grams of sodium chloride?
6. How many molecules are in 937 g of calcium acetate?
7. How many grams are in 3.21 x 1024 molecules of potassium hydroxide?
8. How many atoms of aluminum are in 2.00 moles of aluminum fluoride?
9. How many atoms of chlorine are in 654.5 grams of calcium chloride?
10. How many moles of carbon are in 1.00 x 1020 molecules of propane, C3H8?
11. How many grams of magnesium are in 5.55 x 1026 molecules of magnesium sulfide?
12. How many grams of silicon are in 9.7 1028 molecules of silicon dioxide?