1. Unit 9 Solution Chemistry, a Introduction
Dissolution Of Ionic Crystals In Water
Dissolution Of Molecular Substances In Water
Electrical Conductivity
Electrolytes
van’t Hoff Factor
Units of Concentration
Diluting and Concentrating Solutions
Solution Chemistry, b
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2. solutions Matter Pure substances Mixtures Compounds Elements
Homogeneous
Heterogeneous
solutions

3. We will focus our attention primarily on solid-liquid solutions
We will focus our attention primarily on solid-liquid solutions. In this case the solid is the solute, or substance being dissolved by the liquid, or solvent. The liquid is generally water. An example would be dissolving salt in water.
The composition of a solution can vary and its components can be physically separated, but each part is identical to every other part of the mixture (a salt solution tastes salty throughout). Allowing a salt solution to evaporate will leave the dry salt residue.

4. A solution with a relatively high amount of solute is said to be more than one that is more One holding the maximum quantity of solute is said to be
concentrated
dilute
saturated

5. Dissolution Of Ionic Crystals In Water
1. First the water molecules draw near the Na+ and Cl- ions in the crystal lattice.
Then the negative part of the H2O dipole pulls on the sodium ion.
In a similar fashion the attraction of the positive end of the water dipole pulls on the chloride ion.
The ions actually separate from the crystal lattice.
Chemist6ry. Zumdahl. Copyright©2000 by Houghton Mifflin

6. 2. Then, the water molecules surround the freed ions
2. Then, the water molecules surround the freed ions. The appropriate water dipole-ion attraction occurs (as diagrammed).
Chemistry. Zumdahl. Copyright©2000 by Houghton Mifflin
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7. Dissolution Of Molecular Substances In Water
Sugars are molecular substances that, like ionic compounds, dissociate from their crystal lattice. However, there is a big difference. Sugar does not dissociate into ions. The individual sugar molecule remains intact. Water surrounds each sugar molecule after it is separated from the crystal.
C6H12O6(s)  C6H12O6(aq)
H2O
C12H22O11
C12H22O11

8. Electrical Conductivity
The passage of electricity occurs when a voltage is applied to an electrical conductor such as metal. The electrical current results from the movement of electrons through the conductor.
Gold bar

9. In addition, electrical current will result when a voltage is applied through certain solutions. The NaCl solution will conduct a current because it contains ions. The ions in the solution environment are mobile and respond to a voltage. The sugar solution will not conduct a current because there are no free ions — only neutral molecules (water and sucrose).

10. For this reason NaCl is called an electrolyte, a substance that conducts electricity when dissolved in water.
Sugar is a nonelectrolyte because it does not conduct a current when dissolved in water.
Pure water is a very low conductor due to some ionization.

11. Electrons through metal conductor No Not soluble
Substance
Conductivity?
Reason
Electrolyte?
Reason
Ag(s)
Yes
Electrons through metal conductor No
Not soluble
Ag(l)
Yes
Electrons through metal conductor No
Not soluble
NaCl(aq)
Yes
Mobile Ions in solution
Yes
Dissociates into ions when dissolved
NaCl(l)
Yes
Mobile Ions in liquid
Yes
Dissociates into ions when dissolved
NaCl(s) No
Ions immobile in crystal lattice
Yes
Dissociates into ions when dissolved
AgCl(aq)
Slight
Very few free ions in solution
Slight
Dissociates into ions only slightly when dissolved
C6H12O6(s) No
No ions or free electrons in solution No
No ions formed when dissolved
C6H12O6(aq) No
No ions or free electrons in solution No
No ions formed when dissolved
C6H12O6(l) No
No ions or free electrons in solution No
No ions formed when dissolved

12. Q Specify the van’t Hoff Factor for each of the following:
The degree that substances dissociate when dissolved in water is called the van’t Hoff Factor, i. For sodium chloride it is 2 because one mole of sodium ion, Na+, and one mole of chloride ion, Cl-, forms for every mole of NaCl dissolved.
Q Specify the van’t Hoff Factor for each of the following:
calcium bromide
cesium oxide
ethanol
CaBr2  Ca2+(aq) + 2Br-(aq) = 3
Cs2O  2Cs+(aq) + O2-(aq) = 3
C2H5OH(l)  C2H5OH(aq) = 1

13. Units of Concentration
When interested in experiments with a salt such as CuSO4 we weigh out the portion we need, usually in grams..

14. Units of Concentration
Many chemical reactions, however, are carried out by mixing chemicals that are already dissolved in water. In that case, the CuSO4 is not weighed as crystals since it is immersed in water. To solve problems when chemicals react in an aqueous environment we use the idea of concentration instead of mass.

15. Units of Concentration
Chemists measure the concentration of solutions several ways. In chemistry we will frequently use the unit called molarity, which is the ratio of moles of solute per liter of solution:
molarity, M =
In dilute solutions, the concentration of solute is relatively low compared to a concentrated solution.

16. Units of Concentration
The diagrams and descriptions following show how to prepare one liter of a 1 molar (1.000 M), solution of NaCl. This is the recipe:
1. Weigh out mole of NaCl, or g.
2. Carefully pour it into a specially marked liter volumetric flask.
3. Add about 200 mL distilled water.
4. Shake until dissolved.
5. Add distilled water to the liter mark. Note: this step is done after the initial mixing. Adding a solute to water changes the volume in different ways.
6. Mix thoroughly.

17. Units of Concentration
Q Suppose you needed to prepare 500 mL of a M NaCl solution. How would you carry out this procedure? What would you need?
1. Weigh out mole of NaCl, or g.
2. Carefully pour it into a specially marked liter volumetric flask.
3. Add about 200 mL distilled water.
4. Shake until dissolved.
5. Add distilled water to the 0.50-liter mark.
6. Mix thoroughly.

18. Units of Concentration
Solving problems involving molarity will at times require simple “plug-in-the-formula” procedures, at other times lengthier dimensional analysis sentences.
Q What is the molarity of a 500-mL solution containing 1.75 mole of sodium hydroxide?
Molarity = moles solute/liter of solution
= 1.75 mol/0.500 L
= 3.50 mol/L
Q How many moles of sodium hydroxide are needed to make 750. mL of a M solution?
= mol NaOH
0.300

19. Units of Concentration
Q What is the molarity of a 250.-mL solution containing 56.0 g of sodium hydroxide?
Q What volume solution will be prepared if 42.0 g of sodium hydroxide are used to make a 0.42 M solution?
= mol/L NaOH
5.60
= L NaOH
2.50

20. More Practice
Calculate the molarity of a solution that contains 5.78 grams of calcium chloride dissolved to get a mL solution. (ans M)
How many grams of solute are in mL of a M hydrochloric acid solution? (ans g)
3. How many liters of solution can be prepared if 35.8 grams of sodium chloride are used to make a M solution? (ans L)

21. Diluting and Concentrating Solutions

22. Preparing a special solution
Diluting and Concentrating Solutions
Preparing a special solution
Step 1
suegregg.com

23. Diluting and Concentrating Solutions
Step 2

24. Diluting and Concentrating Solutions
Step Serves eight

25. Diluting and Concentrating Solutions
Dilution is a process where water is added to an existing solution. The solute’s concentration thereby decreases. The problems associated with this topic use the molarity formula. Keep in mind, though, that the total number of moles of solute is the same after the water is added.

26. Diluting and Concentrating Solutions
Dilution diminishes the concentration because the particles are separated.
Add water
Add 50 mL
CuSO4

27. Dilution reduces the concentration of the solute proportionally.
Diluting and Concentrating Solutions
Dilution reduces the concentration of the solute proportionally.
0.40 L water

28. Diluting solutions follows a numerical format
Diluting and Concentrating Solutions
Diluting solutions follows a numerical format
moles 1 = moles 2
moles 1 = M1L1
moles 2 = M2L2
Then
M1L1 = M2L2

29. Q. Water is added to a beaker containing 200. mL of 0. 750 M HCl
Q Water is added to a beaker containing 200. mL of M HCl. The new concentration is M.
a) What is the volume of the solution after dilution?
0.500 M HCl
 L2
0.750 M HCl
200. mL
MlL1 = M2L2
0.750 x = x L2
0.300 L = L2

30. b) How much water had to be added to the original solution to dilute it to 0.500 M?
0.500 M HCl
 L2
0.750 M HCl
200. mL
L2 – L1
0.300 L – L = L

31. How chemists dilute solution
2. Dilute with water
1. Add your concentrated solution to the volumetric flask
3. Invert several times

32. In some cases, more of a solute is added to a solution to
make it more concentrated.
Q A person adds 0.50 mole of sugar crystals to a 1.00-liter solution containing already 1.00 mole of sugar. The new sugar completely dissolves and makes the solution volume increase to 1.05 liter. What is the concentration of the new solution?
1.00-liter
1.05-liter
1.00 mole
sugar
add 0.50 mole of sugar
moles1 + moles added
New molarity =
Total volume
1.00 mol mol
1.05 L
1.43 mol/L

33. Medicinal
Recommended Daily Intake: 50cc/kg Body weight (divided between 3-5 feedings per day/) Example: 2 lb. (0.9 kg) guinea pig would be fed a total 45 cc per day when mixed at a 1:1 ratio, adjust feeding amounts accordingly if more water is added, to account for dilution effect
Casey

34. Chemists use fancy equipment to do dilutions

35. The process of dilution can be harmful, such as the dilution of harsh reagents in our ground water.

36. Microbiologists go to great lengths to make serial dilutions to study enzyme activity and other metabolic phenomena

37. More Practice
mL of a M glucose (C6H12O6) solution is diluted with water to a concentration of M.
a) What is the volume of the new solution? (ans. 375 mL)
b) How much water had to be added to the original solution?
(ans. 125 mL)
2. Water was added to 1,250 mL of a M potassium sulfate solution. The final volume was 1,860 mL. Determine the final concentration of the solution. (ans M)

38. Other Concentration Units

39. Other Concentration Units
Besides molarity we will present two other units of solution
concentration. One is called weight fraction or percentage with the
symbol w/w:
Q A sample of g of potassium chloride is dissolved in g of water.
a) What is the fraction (w/w) of KCl in this solution?
b) What are the units for this number?
Mass of solution
Mass of solute
0.892 g g
0.892 g g
0.892 g = = =
Generally unitless but in this case it is
g KCl/g solution

40. Substance Density (g/mL) Density is a measure of the compactness of
Other Concentration Units
Density is a measure of the compactness of
substances. A relative measure of density is given in
this table:
Substance
Density (g/mL)
Air
0.001
Balsa wood
0.16
Water
1.00
Table salt
2.16
Iron
7.9
Gold
19.32

41. Q. A solution is prepared by dissolving 3
Q A solution is prepared by dissolving 3.76 g of calcium nitrate in g of water. The total volume of the solution is 39.4 mL.
a) Calculate the density of the solution.
b) Calculate the molarity of the solution.
Volume of solution
Mass of solution
g Ca(NO3)2 =
= 1.05 g/mL
39.4 mL
= mol/L Ca(NO3)2
0.582

42. More Practice
1. Calculate the fraction by mass (w/w) of 3.76 grams of KNO3 in 95.0 grams of water. (ans )
2. If a chemist dissolves 6.88 g of glucose, C6H12O6, in g of water the total volume is mL. Calculate the density of this solution. (ans g/mL)