Lecture notes: CHEM103 – November 18, 2008
1. Conversions between mass & moles
a. Molar mass calculations
2. Conversions using solution concentrations
a. “moles per liter” or M (molar, molarity)
b. dilution of solutions
3. Percent composition of solids, liquids, solutions
4. Finally – STOICHIOMETRY
Conversions between mass & moles
conversion of atoms to moles; moles to mass; mass to atoms
Mass of 2.0 moles of Al?
Remember: NA = 6.022x1023 mol-1
and… 1 amu = 1.6606x10-24 g
Al: 26.98154 amu = ? (g)
1 mole of Al atoms = ? (g)
…so amu = g/mole!
K2O: molar mass (g/mol)?
How many moles of potassium oxide in 42 grams?
aluminum oxide: molar mass (g/mol)?
How much mass is in 0.4260 moles of Al2O3?
How many calcium atoms in 25.00 g?
Conversions using solution concentrations
(molar, OR molarity, OR “M” BUT REALLY, moles/liter)
conversions between volume, mass, molarity and moles
NOTE: molar concentration indicated by use of [x] square brackets.
additional NOTE: when doing calculations, ALWAYS convert M to moles/liter;
and do not abbreviate moles as “m” – it will confuse you when you least expect it…
1 mL of 16 M HCl: how many moles of HCl are in the solution?
1 mole of HCl: how much volume of 16 M solution is needed?
What mass of acid is required to make 25.0 mL of 1.0 M oxalic acid?
(oxalic acid molar mass = 90.03 g/mole)
A mass of 0.15 g NaCl is dissolved in 100 mL of water: what is the molarity of the product(s)?
If you have 100 mL of 0.15 M CaCl2 : how many moles of chloride (Cl-) are in the solution?