Solution Concentration
(Molar Conversions Extended)
The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution.
Concentration may be described quantitatively using the words concentrated and dilute. Concentrated solution contains a large amount of solute. Conversely, a dilute solution contains a small amount of solute.
Molarity
One of the most common units of solution concentration is molarity. Molarity (M) is the number of moles of solute dissolved per liter of solution. It is also known as molar concentration. The unit M is read as molar. A liter of solution containing one mole of solute is 1M solution which is read as
1 molar solution.
Molarity (M)= moles of solute
liters of solution
Calculating Molarity a) Calculate the molarity of 100.0 ml of an aqueous solution containing 0.85 mole of dissolved potassium chloride.
Mole of solute= 0.85 mole KCl
Volume of solution= 100.0 ml
M= ____?
100 mlx 1L iter = 0.1000L 0.085 mol KCl = 0.85 M
1000 ml 0.1000L
Try this: Write solution on your notebook.
1.
A 100.5 ml intravenous (IV) solution contains 5.10 g of glucose (C
6
H
12
0
6
). What is the molarity of this solution? (Answer: 0.282 M)
2.
What is the molarity of an aqueous solution containing 40.0 g of glucose (C
6
H
12
0
6
) in a 1.5 L of solution? ( Answer: 0.148 M)
Preparing Molar Solutions Write solution on your notebook.
How do you prepare 1L of a 1.50 M aqueous solution of sucrose (C
12
H
22
0
11
) for an experiment?
(Note: 1.50 M means there are 1.50 moles of solute (sucrose) dissolved in a liter of solution).
(Answer: 513 g (C
12
H
22
0
11
/1 L solution)
Molality
The volume of solution changes with temperature as it expands or contracts. The change in volume alters the molarity of the solution. Masses, however, do not change with temperature. Because of this, it is sometimes more useful to describe solutions in terms of how many solutes are dissolved in a specific mass of solvent. Molality (m) is the ratio of the number of moles of solute dissolved in 1 kilogram of solvent. The unit m is read as molal. A solution containing one mole of solute per kilogram of solvent is one molal solution.
Molality (m)= moles of solute = moles of solute
Kilogram of solvent 1000 g of solvent
Calculating Molality
In the lab, a student adds 4.5 g of sodium chloride (NaCl) to
100.0 g of water. Calculate the molality of the solution.
Mass of water= 100.0 g
Mass of NaCl= 4.5 g m=____ ? mol/kg
4.5 g NaCl x 1mol NaCl = 0.077 mol NaCl
1000 g H2O
100.0 g H20 x 1kilogram = 0.1000kg H2O
58.44 g m= moles of solute 0.077 mol NaCl = 0.77 mol/kg
kilogram of solute 0.1000 kg H2O
Try this: Write your solution on your notebook.
1.
What is the molality of a solution containing 10.0 g of Na2SO4 dissolved in 1000.0 g of water?
(Answer: 0.0704m)
2.
What is the molality of a solution containing 30.0 g of naphthalene (C10H8) dissolved in 500.0 g of toluene? ( Answer: 0.468 m)
Seatwork: Show complete solution on a size 1.
1.
What is the molarity of a bleach solution containing 9.5 g of NaOCl per liter of bleach?
2.
Calculate the molarity if a 1.60 L of solution containing 1.55 g of dissolved potassium bromide.
3.
How many grams of calcium chloride would be dissolved in 1.0 L of a 0.10M solution calcium chloride?
4.
A liter of of 2M sodium hydroxide solution contains how many grams of sodium hydroxide?
5.
Calculate the molality of the following solution: a) 15.7 g NaCl in 100.0 g H2O b) 20.0 g CaCl2 in 700.0 g H2O