Concentration Units– Molarity
Concentration = measure of the amount of solute in a given amount of solvent in a solution.
Solute = substance being dissolved.
Solvent = substance doing the dissolving.
Ex: Kool-Aid in Water = solution
Solute
Solvent
Solute
Solvent
Dilute
Concentrated
Concentration
There are 4 main units to measure concentration, but our focus will be on the first listed below:
1) Molarity
2) Molality
3) Percent by volume
4) Percent by mass
Ex: A student mixes 1.0 mol of NaOH with water to make .50 L of solution. What is the concentration of this solution?
Molarity = a measure of the concentration of a solution.
Units: # of moles of solute
liter of solution
mol
L
=
=
M
1.0 mol NaOH
.50 L Solution
=
2.0 M NaOH
Ex: A student mixes 80.0 g of NaOH (40.00 g/mol) with water to make .500 L of solution. What is the concentration of this solution?
80.0 g NaOH
40.00 g NaOH
1 mol NaOH
=
2.00 mol NaOH
2.00 mol NaOH
.500 L
=
4.00 M NaOH
Ex: How many grams of calcium chloride (110.98 g/mol) are needed to prepare 500. mL of a 1.00 M solution?
500. mL
1 mL
.001 L
=
.500 L
.500 L
1 L
1.00 mol
=
.500 mol CaCl2
mol
L
.500 mol CaCl2
1 mol CaCl2
110.98 g CaCl2
55.5 g CaCl2
=
Ex: A student mixes 25.75 g of Cr3(PO4)2 (345.94 g/mol) with water to make 250.0 mL of solution. What is the concentration of this solution?
25.75 g Cr3(PO4)2
345.94 g Cr3(PO4)2
1 mol Cr3(PO4)2
=
.07443 mol Cr3(PO4)2
.07443 mol Cr3(PO4)2
.2500 L
=
.2977 M Cr3(PO4)2
Ex: How many grams of Aluminum Iodide (407.68 g/mol) are needed to prepare 175 mL of a .650 M solution?
.175 L
1 L
.650 mol
=
.114 mol AlI3
mol
L
.114 mol AlI3
1 mol AlI3
407.68 g AlI3
46.5 g AlI3
=