1. SECTION 1. TYPES OF MIXTURES
CHEMISTRY CHAPTER 12
SOLUTIONS
SECTION 1. TYPES OF MIXTURES
A solution is a homogeneous mixture of two or more substances in a single phase.
The dissolved particles are very small (atoms, molecules, ions), and do not settle out.
Does not scatter light.

2. Cannot be separated by filtration.
Solutions – properties (cont.)
Cannot be separated by filtration.
Ex. – sugar in water. When sugar dissolves, all its molecules become uniformly distributed among the water molecules. The solid sugar is no longer visible.

3. The dissolving medium in a solution (present in larger amount) is called the solvent, and the substance dissolved in a solution (present in lesser amount) is called the solute.

4. Solutions may exist as gases, liquids, or solids
Solutions may exist as gases, liquids, or solids. There are many possible solute-solvent combinations between gases, liquids, and solids.
example: Alloys are solid solutions in which the atoms of two or more metals are uniformly mixed.
Brass is made from zinc and copper.
Sterling silver is made from silver and copper.

5. Solutes, Solvents, and Solutions - 75244

7. Particle Models for Gold and Gold Alloy

8. Heterogeneous mixtures Large particles that settle out on standing.
Suspensions
Heterogeneous mixtures
Large particles that settle out on standing.
Can be separated by filtration.
May scatter light.
Ex: muddy water

9. Ex: milk, shaving cream, smoke, fog
Colloids
Heterogeneous
Particles that are intermediate in size between those in solutions and suspensions
Does not settle out – particles kept suspended by the constant movement of surrounding molecules
Scatters light
Ex: milk, shaving cream, smoke, fog

10. example: a headlight beam is visible from the side on a foggy night
Tyndall Effect
Many colloids look similar to solutions because their particles cannot be seen.
The Tyndall effect occurs when light is scattered by colloidal particles dispersed in a transparent medium.
example: a headlight beam is visible from the side on a foggy night
The Tyndall effect can be used to distinguish between a solution and a colloid.

11. Colloids

12. Properties of Solutions, Colloids, and Suspensions

13. Any soluble ionic compound, such as NaCl
Solutes: Electrolytes Versus Nonelectrolytes
A substance that dissolves in water to give a solution that conducts electric current is called an electrolyte:
Any soluble ionic compound, such as NaCl
Polar molecular compounds that dissociate to give ions (ex.: HCl forms H3O+ and Cl-).

14. A substance that dissolves in water to give neutral solute molecules is a nonelectrolyte.
The solution does not conduct electric current.
Ex. - sugar

15. Electrical Conductivity of Solutions

16. Dissolving Process

17. SECTION 2. THE SOLUTION PROCESS
Factors That Increase the Rate of Dissolution (Dissolving)
They increase the rate at which solute and solvent can interact:
Increasing surface area
Stirring or shaking
Heating. At higher temperatures, collisions between solvent molecules and solute are more frequent and of higher energy.

18. Factors Affecting the Rate of Dissolution 75250

19. Solubility
For every combination of solvent with a solid solute at a given temperature, there is a limit to the amount of solid that can be dissolved.
The point at which this limit is reached depends on the nature of the solute, the nature of the solvent, and the temperature.

20. Particle Model for Soluble and Insoluble Substances

21. Particle Model for Soluble and Insoluble Substances

22. When a solute is first added to a solvent, solute molecules leave the solid surface and move about at random in the solvent.
As more solute is added, more collisions occur between dissolved solute particles. Some of them return to the crystal.
When maximum solubility is reached, molecules are returning to the solid form at the same rate at which they are going into solution.

23. Solution Equilibrium

24. Saturated Versus Unsaturated Solutions
A solution that contains the maximum amount of dissolved solute is described as a saturated solution.
If more solute is added to a saturated solution, it falls to the bottom of the container and does not dissolve.
A solution that contains less solute than a saturated solution under the same conditions is an unsaturated solution.

25. Mass of Solute Added Versus Mass of Solute Dissolved

26. Supersaturated Solutions
When a saturated solution is cooled, the excess solute usually comes out of solution.
Sometimes the excess solute does not separate, and a supersaturated solution is produced. This contains more dissolved solute than a saturated solution contains under the same conditions.

27. The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature.
example: The solubility of sugar is 204 g per 100 g of water at 20°C.

28. Solubility of Common Compounds

29. Solubility of Common Compounds

30. Solubility of a Solid in a Liquid 72521

31. Solubility varies greatly with the type of compounds involved.
Solute-Solvent Interactions
Solubility varies greatly with the type of compounds involved.
“Like dissolves like” is a rough but useful rule for predicting whether one substance will dissolve in another.
Polar and ionic solutes are more soluble in polar solvents such as water or ethanol.

32. Nonpolar solutes are more soluble in nonpolar solvents such as benzene or toluene.
Examples:
LiCl is soluble in water but not in toluene.
Fats are soluble in chloroform but not in water.

33. Dissolving Ionic Compounds in Aqueous Solution
Aqueous solutions (in water) of ionic compounds: the dissolving process is known as hydration.
Positive ions interact with the oxygens of water (slightly negative), while negative ions interact with the positive ends.

34. Ex. – lithium chloride

35. SECTION 3. CONCENTRATION OF SOLUTIONS
The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution.
Concentration is a ratio: any amount of a given solution has the same concentration.
Concentration may be expressed in several different ways.

36. Concentration Units

37. 1. Molarity
Molarity is the number of moles of solute in one liter of solution (solvent plus solute).
The symbol for molarity is M. The concentration of a one molar NaOH solution is written 1 M NaOH.

38. Ex. – what is the concentration of a solution of HCl prepared by adding 3 moles of HCl to H2O and giving a final volume of 6 liters?
= 3 mol/6 L = 0.5 mol/L = 0.5 M

39. Preparation of a Solution Based on Molarity 75263

40. The symbol for molality is m. (ex.: 1 m NaOH)
2. Molality [note – will not be tested]
Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent.
A solution that contains 1 mol of solute dissolved in 1 kg of solvent is a “one molal” solution.
The symbol for molality is m.
(ex.: 1 m NaOH)

41. Molarity vs. Molality
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42. 3. % by mass
Ex. – 25 g sugar in 75 g solution:
How much solvent is there?

43. 3. % by mass
Ex. – 25 g sugar in 75 g solution:
How much solvent is there?
75 g – 25 g = 50 g

44. % by volume
(used for liquids)
Ex. – 25 mL of ethanol is added to enough water to make 100 mL of solution. What is the percent by volume of ethanol?

45. mass per volume
Ex. – a sugar solution contains 26 g sugar in 0.50 L of solution. What is the concentration in g/L?