Transcript Chapter 13 Section 2

Section 2 - Concentration and Molarity
Concentration
In a solution, the solute is distributed evenly throughout the solvent. This
means that any part of a solution has the same ratio of solute to solvent as
any other part of the solution. This ratio is the concentration of the solution.
Calculating Concentration
Parts Per Million
Concentrations can be expressed in many forms. One unit of concentration
used in pollution measurements that involve very low concentrations is
parts per million, or ppm. Parts per million is the number of grams of solute
in 1 million grams of solution. For example, the concentration of lead in
drinking water may be given in parts per million.
Formula for Parts Per Million from reference table.
Used for concentration that are very small.
Molarity
It is often convenient for chemists to discuss concentrations in terms of the
number of solute particles in solution rather than the mass of particles in
solution. Since the mole is the unit chemists use to measure the number
of particles, they often specify concentrations using molarity. Molarity
describes how many moles of solute are in each liter of solution.
The symbol M is read as “molar” or as “moles per liter.” Any amount of
this solution has the same ratio of solute to solution.
Calculating with Molarity
In working with solutions in chemistry, you will find that numerical
Calculations often involve molarity. The key to all such calculations is the
definition of molarity, which is stated as an equation below from the reference
table.
Dilution: The process of adding more solvent to a solution.
Dilution Formula:
M1 = Initial Molarity of solution
V1 = Initial Volume of solution
M2 = Final Molarity of solution
V2 = Final Volume of solution
M1V1 = M2V2
Questions:
When 0.50 liter of a 12 M solution is diluted to 1.0 liters, the molarity of the
new solution is
1. 6.0 M
2. 2.4 M
3. 12 M
4. 24 M
The molarity (M) of a solution is equal to the
1. number of grams of solute/liter of solvent
2. number of grams of solute/liter of solution
3. number of moles of solute/liter of solvent
4. number of moles of solute/liter of solution
What is the total number of grams of NaOH (formula mass = 40.) needed
to make 1.0 liter of a 0.20 M solution?
1. 20. g
2. 2.0 g
3. 80. g
4. 8.0 g
What is the molarity of a solution that contains 30. grams of NaOH in
500. milliliters of solution?
1. 0.75 M
2. 1.3 M
3. 1.5 M
4. 2.6 M
When 20. milliliters of 1.0 M HCL is diluted to a total volume of 60. milliliters,
the concentration of the resulting solution is
1. 1.0 M
2. 0.50 M
3. 0.33 M
4. 0.25 M
How many liters of a 0.5 M sodium hydroxide solution would contain 2 moles
of solute?
1. 1L
2. 2L
3. 3L
4. 4L
What is the concentration of 10. moles of copper (II) nitrate in 5.0 liters
of solution?
1. 0.50 M
2. 2.0 M
3. 5.0 M
4. 10. M
Which solution is the most concentrated?
1. 1 mole of solute dissolved in 1 liter of solution
2. 2 moles of solute dissolved in 3 liters of solution
3. 6 moles of solute dissolved in 4 liters of solution
4. 4 moles of solute dissolved in 8 liters of solution
What is the total number of moles of H2SO4 needed to prepare 5.0 liters
of a 2.0 M solution of H2SO4?
1. 2.5
2. 5.0
3. 10.
4. 20.
How many moles of solute are contained in 200 milliliters of a 1 M solution?
1. 1
2. 0.2
3. 0.8
4. 200
What is the molarity of a solution that contains 0.50 mole of NaOH
in 0.50 liter of solution?
1. 1.0 M
2. 2.0 M
3. 0.25 M
4. 0.50 M
What is the molarity of a solution of NaOH if 2 liters of the solution
contains 4 moles of NaOH?
1. 0.5 M
2. 2 M
3. 8 M
4. 80 M
A town located downstream from a chemical plant was concerned about
fluoride ions from the plant leaking into its drinking water. According to the
Environmental Protection Agency, the fluoride ion concentration in drinking
water cannot exceed 4 ppm. The town hired a chemist to analyze its water.
The chemist determined that a 175-gram sample of the town's water
contains 0.000 250 gram of fluoride ions. How many parts per million of
fluoride ions are present in the analyzed sample?
1.43 ppm
What is the concentration of a solution, in parts per million, if 0.02 gram
of Na3PO4 is dissolved in 1000 grams of water?
1. 20 ppm
2. 2 ppm
3. 0.2 ppm
4. 0.02 ppm
If 0.025 gram of Pb(NO3)2 is dissolved in 100. grams of H2O, what is the
concentration of the resulting solution, in parts per million?
1. 0.000025 ppm
2. 2.5 ppm
3. 250 ppm
4. 4000 ppm
An aqueous solution has 0.0070 gram of oxygen dissolved in 1000. grams of
water. Calculate the dissolved oxygen concentration of this solution in
parts per million.
7.0 ppm
An aqueous solution contains 300. parts per million of KOH. Determine
the number of grams of KOH present in 1000. grams of this solution.
0.300 grams