Molarity

1
WRONG
7.85 kg KCl are dissolved in 2.38 L of solution.
Find molality.
24.8 g table sugar (i.e., sucrose, C12H22O11) are
mixed into 450 g water. Find molality.
2
What mass of CaF2 must be added to 1,000 L of
water so that fluoride atoms are present at a
conc. of 1.5 ppm?
1 g
1000 mL
1 mol
6.02 x1023 mcule
X mcule H2O 1000 L
3.34 x 1028 mcules H2O
18 g
1 L
1 mL
1 mol
1 molecule CaF2
X 5.01 x 1022 atoms F
times

2.505 x 1022 molecules CaF2
2 atoms F
1 mol CaF2
78.1 g CaF2
X g CaF2 2.505 x 1022 molecules

3.25 g CaF2
6.02 x 1023 molecules
1 mol CaF2
3
How many moles solute are required to make 1.35 L
of 2.50 M solution?

mol M L
3.38 mol
2.50 M (1.35 L)
A. What mass sodium hydroxide is this?
40.0 g NaOH
X g NaOH 3.38 mol NaOH

135 g NaOH
1 mol NaOH
B. What mass magnesium phosphate is this?
262.9 g Mg3(PO4)2
X g Mg3(PO4)2 3.38 mol Mg3(PO4)2

889 g Mg3(PO4)2
1 mol Mg3(PO4)2
4
Find molarity if 58.6 g barium hydroxide are in
5.65 L solution.
Step 1). How many moles barium hydroxide is this?
1 mol Ba(OH)2
X mol Ba(OH)2 58.6 g Ba(OH)2

0.342 mol Ba(OH)2
171.3 g Ba(OH)2
Step 2). What is the molarity of a 5.65 L
solution containing 0.342 mol solute?
0.342 mol
M
0.061 M Ba(OH)2

5.65 L
5
You have 10.8 g potassium nitrate. How many mL
of solution will make this a 0.14 M solution?
convert to mL
6
Concentration

• SAWS Water Quality Report - June 2000

7
Molality
8
Molality

• Find the molality of a solution containing 75 g
  of MgCl2 in 250 mL of water.

75 g MgCl2
1 mol MgCl2 95.21 g MgCl2
0.25 kg water
3.2m MgCl2
9
Molality

• How many grams of NaCl are reqd to make a 1.54m
  solution using 0.500 kg of water?

0.500 kg water
1.54 mol NaCl 1 kg water
58.44 g NaCl 1 mol NaCl
45.0 g NaCl
10
Molarity of Solutions
Molarity of Solutions
Molarity of Solutions
Keys
http//www.unit5.org/chemistry/Solutions.html