1. 12-3: Concentration of Solutions
Chapter 12 - Solutions
12-3: Concentration of Solutions

2. The concentration of a solution is a measure of the amount of solute in a given amount of solvent of solution.
Sometimes solutions are called “dilute” or “concentrated”, but these are not definite terms.
Dilute means that there is a relatively small amount of solute in a solvent
Concentrated means that there is a relatively large amount of solute.
Neither of these terms has anything to do with saturation

3. Measures of Concentration
Molarity – the number of moles of solute in one liter of solution
Symbol is M
Molality – the number of moles of solute in one kg of solvent
Symbol is m

4. Molarity
A 3.0 M solution of HCl has 3.0 moles of HCl in a liter of solution.
This is NOT the same as 3.0 moles added to 1 liter of water.
The total amount of the solution AFTER adding the 3.0 moles of HCl is 1 liter.

5. Molarity To make a solution of a particular molarity:
Calculate the amount of solute needed in grams
Add the solute to an amount of solvent that is LESS than the total amount of solution desired.
Dissolve
Add enough solvent to bring the total amount of solution to the desired volume.

6. Molarity
You want to make a 3.50 M solution of NaCl and you need a total of 500. mL of the solution. How many grams of NaCl do you need?

7. Molarity
You have 1.20 L of solution and you know that it contains 43.5 g of NaCl. What is the molarity of the solution?

8. Molarity
You have 1.2 L of a 0.75 M HCl solution. How many moles of HCl does the solution contain?

9. Molarity
To produce 40.0 g of silver chromate, you will need at least 24.3 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5 L of a 6.0M K2CrO4 solution. What volume of the solution is needed to give you the 24.3 g of K2CrO4 needed for the reaction?

10. Molarity
What is the molarity of a solution that is composed of 5.85 g of potassium iodide dissolved in enough water to make L of solution?

11. Molarity
How many moles of H2SO4 are present in L of a M H2SO4 solution?

12. Molarity
What volume of 3.00 M NaCl is needed for a reaction that requires g of NaCl?

13. Molality
A m solution of sodium hydroxide is a mixture of moles of NaOH mixed with 1 kg of water.
Note that molality does not tell us anything about the total amount of the solution

14. Molality To make a solution of a particular molality:
Measure out the necessary mass of the solute
Add to exactly 1 kg of solvent
For water, 1 kg equals 1000 mL

15. Molality
A solution was prepared by dissolving 26.4 g of sucrose in 250. g of water. What is the molal concentration of the solution? Sucrose is C12H22O11, and its molar mass is g/mol

16. Molality
What is the molality of a solution composed of 255 g of acetone, (CH3)2CO, dissolved in 200. g of water?

17. Molality
What quantity, in grams, of methanol (CH3OH), is required to prepare a m solution in 400. g of water?

18. Molality
How many grams of AgNO3 are needed to prepare a m solution in 250. g of water?

19. Molality
What is the molality of a solution containing 18.2 g HCl and 250. g of water?