ch. 12.3 concentration of a solution the concentration of a solution is a measure of the amount of...
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Ch. 12.3 Concentration of a Solution
• The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution.
• Chemists commonly use several different ways to quantitatively express the concentration of a solution. These include:
Percent Composition by mass Parts per million / Part per billion Molarity (M) Molality (m)
Percent Composition by Mass• Sometimes the amount of solute present in
the solution is expressed as a percent by mass.
grams of solute
• % Composition = ------------------------- x 100
grams of solution
Remember: solution is the solute and solvent together
Percent Composition Sample Problems
1. What is the percent composition of a solution that contains 115 g NaCl dissolved in 500 g of H2O?
2. How many grams of KMnO4 are needed to make 500 g of a 12.0% KMnO4 solution?
Parts per Million (ppm) andParts per Billion (ppb)
ppm =mass of solute in solution
total mass of solution 106
Parts per Million (ppm)
Parts per Billion (ppb)
ppb =mass of solute in solution
total mass of solution 109
What Do You Think?
• A 900.0 g sample of sea water is found to contain 0.0067 g Zn. Express this concentration in ppm.
Molarity (M)• Molarity (M) is the number of moles of solute
per liter of solution.
moles of solute (mol)
• Molarity (M) = --------------------------------
liters of solution (L)
Video
Molarity Sample Problems
1. What is the molarity of a 0.500 L sample of solution that contains 60.0 g of sodium hydroxide (NaOH)?
2. How many grams of sodium chloride (NaCl) are required to prepare 250.0 mL of a 3.00 M solution?
Molality (m)• Molality is the concentration of a solution expressed
in moles of solute per kilogram of solvent.
moles of solute (mol)
• Molality (m) = -----------------------------------
kilogram of solvent (kg)
Molality Sample Problem
1. A solution was prepared by dissolving 17.1 g of glucose, C6H12O6, in 275 g of water. What is the molality (m) of this solution?
Dilutions
• When preparing dilutions, you use the following equation.
–M1V1=M2V2
• As volume goes up, molarity goes down. You have diluted the solution. As volume goes down, the amount of solute in solution increases in concentration.
• Think of diluting your kool aid.
Dilutions practice
1. If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it?
2. If I dilute 250 mL of 0.10 M lithium acetate solution to a volume of 750 mL, what will the concentration of this solution be?
Wrapping It Up• Reflect on what you have learned concerning the today’s
topic.
• Respond to the following…– What is the most important thing you learned today?– What is one question you would still like answered?– What is a way what you have learned today connects with
what you knew before?