1. Ch. 13 & 14 - Solutions
II. Concentration

2. What is different between the glasses of Kool-aid?

3. Solution concentration can be described generally
Dilute - reduced in strength, weak, watered down.
Concentrated – stronger, pure. Has less water.

4. What is the problem with just using dilute and concentrated as descriptions of the solution concentration?

5. Is solution B dilute or concentrated?
Solution A Solution B Solution C
Is solution B dilute or concentrated?
The terms dilute and concentrated are relative.
Scientists need a more precise way of referring to the concentration of a solution.

6. Solution concentration can be described specifically
Do you remember the “mole” from Stoichiometry?
What is a mole?
How might you use it to describe the concentration of a solution?

7. A. Concentration The amount of solute in a solution.
Describing Concentration
% by mass - medicated creams
% by volume - rubbing alcohol
ppm, ppb - water contaminants
molarity - used by chemists
molality - used by chemists

8. The ratio of the moles of solute to the volume of solution in liters.
Molarity
The ratio of the moles of solute to the volume of solution in liters.
Moles of solute
Molarity (M) =
Volume in Liters of Solution

9. How to read Molarity 6.0 M NaCl Read: “6 molar solution of NaCl”
Can be abbreviated 6M solution
You must be careful to label the molarity with a capital M so that it is not confused with m for molality.

10. How to make a 6M NaCl solution using molarity
(a) Add 6 moles NaCl to the volumetric flask. How would you measure that?
6 molesNaCl g NaCl
1 mole NaCl
= 351 g NaCl

11. How to make a 6M NaCl solution using molarity
(b) Add distilled or deionized H2O to dissolve and mix the NaCl
(c) Fill the flask with dH2O until you reach the 1000mL line.

12. Types of Calculations with Molarity:
1. Finding concentration of a solution. 2. Finding the mass of solute needed. 3. Finding the volume of solution made.

13. Finding Concentration
Antifreeze is a solution of ethylene glycol, C2H6O2 in water. If 4.50 L of antifreeze contains 27.5 g of ethylene glycol, what is the concentration of the solution?
27.5 g C2H6O2
1 mol C2H6O2
62.08 g C2H6O2
4.5 L
= mol/L or
M C2H6O2

14. Finding Mass
What mass of sodium carbonate, Na2CO3, is present in 50 ml of a 0.750M solution?
Conversion Factor
50 ml
1 L
0.750 mol
g Na2CO3
1000 mL
1 L
1 mol Na2CO3
= 3.97 g Na2CO3

15. Finding Volume
Conversion Factor
What volume of 1.50 mol/L HCl solution contains 10.0 g of hydrogen chloride?
10.0 g HCl
1 mol HCl
1 L
36.46 g HCl
1.50 mol
= L or 183 mL

16. Practice Problems

17. Practice Problems
1. A L aqueous solution contains 90.0 g of ethanol, C2H5OH. Calculate the molar concentration of the solution in mol/L.

18. Practice Problem
2. What mass of NaCl are dissolved in 152 mL of a solution if the concentration of the solution is M?

19. Practice Problem
3. What mass of dextrose, C6H12O6 is dissolved in 325 mL of M solution?

20. Practice Problem
4. A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a M solution. What is the volume of the solution?

21. Practice Problem
5. A solution of sodium carbonate, Na2CO3, contains 53.0 g of solute in 215 mL of solution. What is its molarity?

22. Practice Problem
6. What is the molarity of a solution of HNO3 that contains 12.6 g of solute in 5.00 L of solution?

23. B. Molality
mass of solvent only
1 kg water = 1 L water

24. B. 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

25. B. Molality
How many grams of NaCl are req’d to make a 1.54m solution using 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

26. Practice Problem What is the molality of a solution made
from 2.4 moles of NaCl and 0.80 kg of
water?

27. Practice Problem What is the molality of a solution made
from 63 g of HNO3 in 0.50 kg of water?

28. How much water is needed to make a 0.50 m solution from 3.2 g of NaCl?
Practice Problem
How much water is needed to make a 0.50 m solution from 3.2 g of NaCl?

29. Practice Problems
What mass of CH3OH is needed to add to 1.20 kg of water to make a 3.00 m solution?

30. C. Dilution
Preparation of a desired solution by adding water to a concentrate.
Moles of solute remain the same.

31. C. Dilution
What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?
GIVEN:
M1 = 15.8M
V1 = ?
M2 = 6.0M
V2 = 250 mL
WORK:
M1 V1 = M2 V2
(15.8M) V1 = (6.0M)(250mL)
V1 = 95 mL of 15.8M HNO3

32. Dilution Practice Water is added to 200. mL of a 2.0 M
solution of CaCl2 to increase the volume of
the solution to 400. mL. What is the new
concentration?

33. Dilution Practice To what volume must 1.0 L of a 6.0 M
solution of HCl be diluted in order to
prepare a 0.2 M solution?

34. D. Preparing Solutions 1.54m NaCl in 0.500 kg of water
500 mL of 1.54M NaCl
mass 45.0 g of NaCl
add water until total volume is 500 mL
mass 45.0 g of NaCl
add kg of water
500 mL water
45.0 g NaCl
500 mL
mark
volumetric
flask

35. D. Preparing Solutions 250 mL of 6.0M HNO3 by dilution
measure 95 mL of 15.8M HNO3
95 mL of 15.8M HNO3
combine with water until total volume is 250 mL
250 mL mark
Safety: “Do as you oughtta, add the acid to the watta!”
water for safety

36. Solution Preparation Lab
Turn in one paper per team.
Complete the following steps:
A) Show the necessary calculations.
B) Write out directions for preparing the solution.
C) Prepare the solution.
For each of the following solutions:
1) mL of 0.50M NaCl
2) 0.25m NaCl in mL of water
3) mL of 3.0M HCl from 12.1M concentrate.