1. Solutions I
Characteristics
CHM PGCC Barbara A. Gage

2. Solutions
Homogeneous mixture : has no visible boundaries because the components are mixed as individual atoms, ions, and molecules.
Solution : A homogeneous mixture is also called a solution. Solutions in water are called aqueous solutions. Although we normally think of solutions as liquids, they can exist in all three physical states.
CHM PGCC Barbara A. Gage

3. Components… Solute – substance that is dispersed or dissolved
Solvent – substance that facilitates the dispersing or dissolving
Entropy will generally make solution formation favorable!
CHM PGCC Barbara A. Gage

4. Solubility
Maximum amount of solute that dissolves in a given amount of solvent at a set temperature
NH4Cl g/100g
CHM PGCC Barbara A. Gage

5. Factors Affecting Solubility
Nature of solute and solvent…IMFs
“Like dissolves like”
If the forces are similar the components will mix…
CHM PGCC Barbara A. Gage

6. The major types of intermolecular forces in solutions.
Figure 13.1
The major types of intermolecular forces in solutions.
CHM PGCC Barbara A. Gage

7. A solution of methanol in water
Figure 13.3
Like dissolves like: solubility of methanol in water.
water
methanol
A solution of methanol in water
CHM PGCC Barbara A. Gage

8. The dissolution of an ionic compound… Solvation
Figure 4.2
The dissolution of an ionic compound… Solvation
CHM PGCC Barbara A. Gage

9. Dissolution of a polar compound…Solvation
The slightly charged ends of polar solute molecules are attracted to the polar ends of polar solvents. The molecules are surrounded by solute particles. The solute particles stay intact.
CHM PGCC Barbara A. Gage

10. To determine solubility, decide what the IMFs of the solute and solvent are first.
Solute IMFs
Solvent IMFs
Dissolve or Mix?
Ion-ion
Dipole-dipole
yes
Dispersion no
CHM PGCC Barbara A. Gage

11. Predicting Relative Solubilities of Substances
SAMPLE PROBLEM 13.1
Predicting Relative Solubilities of Substances
PROBLEM:
Predict which solvent will dissolve more of the given solute:
(a) Sodium chloride in methanol (CH3OH) or in propanol (CH3CH2CH2OH)
(b) Ethylene glycol (HOCH2CH2OH) in hexane (CH3CH2CH2CH2CH2CH3)
or in water.
(c) Diethyl ether (CH3CH2OCH2CH3) in water or in ethanol (CH3CH2OH)
PLAN:
Consider the intermolecular forces which can exist between solute molecules and consider whether the solvent can provide such interactions and thereby substitute.
SOLUTION:
(a) Methanol - NaCl is ionic and will form ion-dipoles with the -OH groups of both methanol and propanol. However, propanol is subject to the dispersion forces to a greater extent.
(b) Water - Hexane has no dipoles to interact with the -OH groups in ethylene glycol. Water can H bond to the ethylene glycol.
(c) Ethanol - Diethyl ether can interact through a dipole and dispersion forces. Ethanol can provide both while water would like to H bond.
CHM PGCC Barbara A. Gage

12. Factors Affecting Solubility
Nature of solute and solvent…IMFs
Temperature
As temperature increases, particle motions and interactions increase.
CHM PGCC Barbara A. Gage

13. What is the general trend for solids?
Solubility Curves
What is the general trend for solids?
For gases?
Why are they different?
CHM PGCC Barbara A. Gage

14. DHsoln = DHsolute + DHsolvent + DHmix
Heats of solution and solution cycles
1. Solute particles separate from each other - endothermic
solute (aggregated) + heat solute (separated) DHsolute > 0
2. Solvent particles separate from each other - endothermic
solvent (aggregated) + heat solvent (separated) DHsolvent > 0
3. Solute and solvent particles mix - exothermic
solute (separated) + solvent (separated) solution + heat DHmix < 0
DHsoln = DHsolute + DHsolvent + DHmix
CHM PGCC Barbara A. Gage

15. Solution cycles and the enthalpy components of the heat of solution.
Figure 13.4
Solution cycles and the enthalpy components of the heat of solution.
Exothermic solution process
Endothermic solution process
CHM PGCC Barbara A. Gage

16. Endo- and Exothermic Dissolvers
Endothermic dissolvers can be used to form chemical cold packs because the solvent (water) becomes cold as it provides energy for the dissolving process.
Exothermic dissolvers provide the basis for chemical hot packs since the energy released heats the solvent.
CHM PGCC Barbara A. Gage

17. Factors Affecting Solubility
Nature of solute and solvent…IMFs
Temperature
Molar Mass
The larger the solute molecule the more solvent molecules are required to keep the solute in solution.
Solvation shell of water molecules for Na+ (left) and a larger peptide (right)
CHM PGCC Barbara A. Gage

18. Factors Affecting Solubility
Temperature
Nature of solute and solvent…IMFs
Molar Mass
The larger the molecule the more solvent molecules are required to keep the solute in solution.
Pressure (for gases only)
CHM PGCC Barbara A. Gage

19. The higher the pressure over the solution, the greater the solubility of the gas (Henry’s Law).
The “bends”…
CHM PGCC Barbara A. Gage

20. Electrolytes
If a solute conducts electricity when dissolved it is called an electrolyte.
Solutes that dissolve but do not form ions form non-conducting solutions and are called non-electrolytes.
A solute that dissociates partially and conducts electricity on a limited basis is called a weak electrolyte.
CHM PGCC Barbara A. Gage

21. The electrical conductivity of ionic solutions.
Figure 4.3
The electrical conductivity of ionic solutions.
CHM PGCC Barbara A. Gage

22. Colloids and Suspensions
When a solute is suspended in a solvent the result is a heterogeneous mixture that may appear homogeneous. Such mixtures are called colloids or colloidal suspensions. These generally do not settle in the short term.
Suspensions are heterogeneous mixtures that do settle in the short term. They require shaking before dispensing.
CHM PGCC Barbara A. Gage

23. Colloids and Suspensions
Both colloids and suspensions scatter light. A true solution will not scatter light because the dispersed solute particles are too small to affect the path of the light.
Colloid True solution
CHM PGCC Barbara A. Gage

24. Types of Colloidal Suspensions
Dispersed Material
Dispersing material
Gas
Liquid
Solid
Liquid aerosol
Cloud, fog
Solid aerosol
Smog, smoke
Foam
Shaving cream
Emulsion
Milk, plasma, mayonnaise
Sol
blood
Solid foam
Styrofoam
Gel
Gelatin, opal
Solid sol
Colored glass
CHM PGCC Barbara A. Gage