1. Properties of Solutions
Objectives:
Identify the factors that determine the rate at which a solute dissolves.
Identify the factors that affect solubility

2. Definitions Solution - homogeneous mixture
Solute - substance being dissolved
Solvent – does the dissolving (present in greater amount)

3. Solutions What the solute and the solvent are determines
whether a substance will dissolve and how much will dissolve.
Stirring
In order to dissolve the solvent molecules must touch the solute.
Solvent molecules hold on to and surround the solute
Stirring moves fresh solvent next to the solute.
Dissolves faster
Particle Size
The solvent touches the surface of the solute.
Smaller pieces increase the amount of surface of the solute.
Solvent and solute touch each other more often
Smaller particles dissolve faster
Temperature
Higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often.
More pieces are broken off
Speeds up dissolving.
Usually increases the amount of solid that will dissolve.

4. Solution Definitions solution:
a homogeneous mixture in which the solute is dissolved in the solvent
-e.g., Salt water
alloy:
a solid solution of metals
-- e.g., bronze = Cu + Sn; brass = Cu + Zn
refers to two gases or two liquids that form
a solution; more specific than “soluble”
miscible:
Solutions
– A homogeneous mixture in which substances present in lesser amounts, called solutes, are dispersed uniformly throughout the substance in the greater amount, the solvent
– Aqueous solution — a solution in which the solvent is water
– Nonaqueous solution — any substance other than water is the solvent
– Water is essential for life and makes up about 70% of the mass of the human body.
– Many of the chemical reactions that are essential for life depend on the interaction of water molecules with dissolved compounds.
-- e.g., food coloring and water

5. Solutions Solute Solvent Solution Gaseous Solutions Liquid Solutions
air (nitrogen, oxygen, argon gases)
humid air (water vapor in air)
Liquid Solutions
solid
carbonated drinks (CO2 in water)
vinegar (CH3COOH in water)
salt water (NaCl in water)
Solid Solutions
dental amalgam (Hg in Ag)
sterling silver (Cu in Ag)
Solutions are not limited to gases and liquids; solid solutions also exist.
• Amalgams, which are usually solids, are solutions of metals in liquid mercury.
• Network solids are insoluble in all solvents with which they do not react chemically; covalent bonds that hold the network together are too strong to be broken and are much stronger than any combination of intermolecular interactions that might occur in solution.
• Most metals are insoluble in all solvents but do react with solutions such as aqueous acid or base to produce a solution; in these cases the metal undergoes a chemical transformation that cannot be reversed by removing the solvent.
Charles H.Corwin, Introductory Chemistry 2005, page 369

6. Factors Affecting the Rate of Solution
As To , rate
1. temperature
As size , rate
2. particle size
More mixing, rate
3. mixing
Formation of a solution from a solute and a solvent is a physical process, not a chemical one.
Both solute and solvent can be recovered in chemically unchanged form using appropriate separation methods.
Dissolution of a solute in a solvent to form a solution does not involve a chemical transformation.
Substances that form a single homogeneous phase in all proportions are said to be completely miscible in one another.
If two substances are essentially insoluble in each other, they are immiscible.
4. Amount of solute already dissolved
↓ conc ↑ rate

7. Non-Solution Definitions
insoluble:
“will NOT dissolve in”
e.g., sand and water
immiscible:
refers to two gases or two liquids that will NOT form a solution
e.g., water and oil
suspension:
appears uniform while being stirred, but settles over time
e.g., flour and water

8. Classes of Solutions aqueous solution: solvent = water
water = “the universal solvent”
amalgam:
solvent = Hg
e.g., dental amalgam
tincture:
solvent = alcohol (alcohol won’t dissolve salt but will
dissolve iodine which won’t dissolve in water)
e.g., tincture of iodine (for cuts)
organic solution:
solvent contains carbon
e.g., gasoline, benzene, toluene, hexane

9. Solubility Experiment 1: Add 1 drop of red food coloring A B A B
Before
Water
HOT
AFTER
COLD
A B
Miscible – “mixable”
two gases or two liquids
that mix evenly
Water
COLD
Water
HOT
You should observe that temperature effects the rate of solution. As the temperature of the liquid solvent increases, the molecules move faster, and the food coloring dissolves more quickly.
A B

10. Solubility Experiment 2: Add oil to water and shake T0 sec T30 sec
AFTER
Before
Immiscible – “does not mix”
two liquids or two gases
that DO NOT MIX
Oil
You should observe that for solutions to mix they must be chemically similar. Polar and polar molecules will mix, non-polar and non-polar molecules will mix, but polar and non-polar molecules will not mix. The reasons for this will be explained later.
Remember, ‘like dissolves like’. polar dissolves polar
non-polar dissolves non-polar
Water
Water
T0 sec
T30 sec

11. Muddy Water: Dissolved Solids
Experiment 3:
Add soil to water, shake well, and allow to settle
AFTER
Before
Muddy
Water
Water
T1 min T5 min

12. Centrifugation
Spin sample very rapidly: denser materials go to bottom (outside)
Separate blood into serum and plasma
Serum (clear)
Plasma (contains red blood cells ‘RBCs’)
Check for anemia (lack of iron)
AFTER
Before
RBC’s
Serum
Blood
When you donate blood, the phlebotomist will check for anemia before drawing your blood. A small amount of blood will be taken from your fingertip into a thin glass tube. The blood may be placed in a centrifuge as described above to check for sufficient amounts of red blood cells. An alternate method is to drop the blood in a solution of copper sulfate. If the blood contains enough RBC’s the blood drop will sink to the bottom of the container, if it is not dense enough (lacks adequate number of RBC’s), the blood will float and you will not be allowed to donate blood. A
B C

13. Blood plasma (a solution) White blood cells Red blood cells Blood
(a suspension)
Centrifuge
Blood plasma
(a solution)
White blood cells
Red blood cells
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

14. Solubility
Solubility= maximum quantity of a solute that can be dissolved in a certain quantity of solvent at a specified temperature.
Ex. 36 g of salt will dissolve in 100 g of water at 20oC.

15. SUPERSATURATED SOLUTION
Solubility
UNSATURATED SOLUTION
Contains less solute than can be dissolved at a given temperature
SUPERSATURATED SOLUTION
Has dissolved in it more solute than it can normally hold at a given temperature.
SATURATED SOLUTION
Has dissolved in it all the solute that it can normally hold at a given temp.
Maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility.
– Solubility is expressed as the mass of solute per volume (g/L) or mass of solute per mass of solvent (g/g) or as the moles of solute per volume (mol/L).
– Solubility of a substance depends on energetic factors and on the temperature and, for gases, the pressure.
• A solution that contains the maximum possible amount of solute is saturated.
• If a solution contains less than the maximum amount of solute, it is unsaturated.
When a solution is saturated and excess solute is present, the rate of dissolution is equal to the rate of crystallization.
• Solubility increases with increasing temperature — a saturated solution that was prepared at a higher temperature contains more dissolved solute than it would contain at a lower temperature, when the solution is cooled, it can become supersaturated.
increasing concentration

16. 3 factors that effect solubility
1. Nature of the solute and solvent
2. Temperature
3. Pressure

17. 1. Nature of solute and solvent
“Rule”: LIKE DISSOLVES LIKE
polar solvents dissolve polar solutes. (ex. Salt in water)
Non-polar solvents dissolve non-polar solutes. (Styrofoam in acetone)
Water is polar (because it’s bent).
It will therefore tend to dissolve other polar molecules or ions.
For example, most salts, alcohols and sugars dissolve in water.
Alcohols and sugars all contain the O-H part of a molecule which makes them polar: O X
. . H

18. 2. Temperature
Increase in temp = increase in solubility of a solid substance
Increase in temp = decrease in solubility of gaseous substance (pop when warmed loses its fizz faster)

19. Solubility vs. Temperature
200
180
160
140
120
100 80 60 40 20 KI
KNO3
Solubility (g solute / 100 g H2O)
NaNO3
The general rule of thumb is that solubility of solids increases with increases in temperature.
Maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility.
– Solubility is expressed as the mass of solute per volume (g/L) or mass of solute per mass of solvent (g/g) or as the moles of solute per volume (mol/L).
– Solubility of a substance depends on energetic factors and on the temperature and, for gases, the pressure.
• A solution that contains the maximum possible amount of solute is saturated.
• If a solution contains less than the maximum amount of solute, it is unsaturated.
When a solution is saturated and excess solute is present, the rate of dissolution is equal to the rate of crystallization.
• Solubility increases with increasing temperature — a saturated solution that was prepared at a higher temperature contains more dissolved solute than it would contain at a lower temperature, when the solution is cooled, it can become supersaturated.
Solubility of a substance generally increases with increasing temperature
No relationship between the structure of a substance and the temperature dependence of its solubility
Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds
This variation of solubility with temperature is used to separate the components of a mixture by fractional crystallization, the separation of compounds based on their solubilities in a given solvent
Fractional crystallization is a common technique for purifying compounds; the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution
Solubility of gases in liquids decreases with increasing temperature
Attractive intermolecular interactions in the gas phase are essentially zero for most substances
When a gas dissolves, its molecules interact with solvent molecules and heat is released when these new attractive interactions form, therefore, dissolving most gases in liquids is an exothermic process (Hsoln < 0)
Adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas
Na3PO4
NaCl 20 40 60 80
100
Temperature (oC)
Timberlake, Chemistry 7th Edition, page 297

20. Gas Solubility Higher Temperature …Gas is LESS Soluble CH4 O2
2.0 O2
Higher Temperature
…Gas is LESS Soluble CO
Solubility (mM)
1.0
The general rule of thumb is that the solubility of gases decreases when temperature increases.
Solubility of a substance generally increases with increasing temperature
No relationship between the structure of a substance and the temperature dependence of its solubility
Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds
This variation of solubility with temperature is used to separate the components of a mixture by fractional crystallization, the separation of compounds based on their solubilities in a given solvent
Fractional crystallization is a common technique for purifying compounds; the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution
Solubility of gases in liquids decreases with increasing temperature
Attractive intermolecular interactions in the gas phase are essentially zero for most substances
When a gas dissolves, its molecules interact with solvent molecules and heat is released when these new attractive interactions form, therefore, dissolving most gases in liquids is an exothermic process (Hsoln < 0)
Adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas He 10 20 30 40 50
Temperature (oC)

21. Solids dissolved in liquids Gases dissolved in liquidsTo
Sol. To
Sol.
As To , solubility
As To , solubility

22. 3. Pressure Gases are more soluble at... high pressures (Henry’s Law).
External pressure has very little effect on the solubility of liquids and solids, but the solubility of gases increases as the partial pressure of the gas above a solution increases.
The concentration of molecules in the gas phase increases with increasing pressure, and the concentration of dissolved gas molecules in the solution at equilibrium is also higher at higher pressures.
Relationship between pressure and the solubility of a gas is described quantitatively by Henry’s Law: C = kP, where C is the concentration of dissolved gas at equilibrium; P is the partial pressure of the gas; and k is the Henry’s law constant, which must be determined experimentally for each combination of gas, solvent, and temperature and has units of mol/(L•atm) = M/atm.
Concentration of a dissolved gas in water at a given pressure depends strongly on its physical properties.
For a series of related substances, London dispersion forces increase as molecular mass increases with the Henry’s law constants increasing smoothly.
Gases that react chemically with water do not obey Henry’s law; all of these gases are much more soluble than predicted by Henry’s law

23. Henry’s Law Pressure does not effect solids and liquids (only gases)
Henrys Law: As the pressure of the gas above a liquid increases, the solubility of the gas increases.

24. Carbonated beverages
Bottled under high pressure to force the carbon dioxide gas into the liquid

25. Equation: S1 = S2 P1 P2 Units for Solubility: g/L, g/mL, g/g
Units for Pressure:
kPa or atm

26. Henry’s Law Example:
If the solubility of a gas in water is 0.77g/L at 3.5 atm of pressure, what is its solubility (ing/L) at 1.0 atm of pressure? (Temp is held constant)
Henry’s Law: S1 = S2
P1 P2
(0.77 g/L • 1.0 atm)= S (3.5 atm.)
0.77 g/L = S2
3.5 atm atm.
S2= 0.22g/L