1. Chapter 12
Solutions

2. Types of Mixtures 1. Solutions
AKA Homogeneous Mixtures/can only be separated by evaporation
Atoms, molecules, or ions are thoroughly mixed, resulting in a mixture that has the same composition and properties throughout
Made by having one substance dissolved into another
Soluble: capable of being dissolved
Insoluble: unable of being dissolved

3. Components of solutions
Solvent: the dissolving medium
Water is the universal solvent (aqueous solutions or hydrated solutions)
Alcohol is also used frequently as solvent (tinctures)
Solvent is greatest quantity
Solute: the substance that is dissolved
Usually designated as the component that is of lesser quantity
Once dissolved, the solute particles can no longer be seen (usually less than 1 nm in diameter)
As long as conditions do not change, solutes will remain in solvent indefinitely

4. Types of solutions Gas-gas: air
Gas-liquid: carbon dioxide and water (pop)
Liquid-liquid: fruit juice
Liquid-solid: dental amalgam
Solid-liquid: sugar water
Solid-solid: alloys

5. Suspensions
Occur when particles are too large to remain in the solvent unless constantly agitated
Particles are usually over 1000nm in diameter
Would be identified as heterogeneous mixture
Can be separated by a filter

6. 3. Colloid Particles are intermediate of solutes and suspensions
Particles are between nm
Particles become dispersed in a dispersing medium (think fog)
See table 2 page 404 for ex.
Can not be filtered, but will scatter light (tyndall effect)
Also see brownian motion (dust particles in air)

7. Electrolytes versus nonelectrolytes
An electrolyte is a substance that will conduct an electric current when in an aq. Soln.
Ionic compounds and polar covalent molecules in water generally are electrolytes
A nonelectrolyte is a substance that will not conduct an electric current when in an aq. Soln.
Nonpolar covalent molecules generally are nonelectrolytes

8. Factors affecting the rate of dissolution
Increase the surface area of the solute
Crushing/grinding will increase the amount of surface area a solvent affects
Agitate the solution
Think KMT, faster moving particles have more collisions, more collisions increase the amount of solvent affecting the solute
Heating the solvent
KMT

9. Solubility
Soln equilibrium: the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates
When in equilibrium in a closed system, the solution is saturated (holds the max. amount of solute at given conditions)
When a soln has less than max, it is said to be unsaturated
When holds more solute than a saturated soln has under the same conditions, called supersaturated
Requires heating and allowing soln to cool to saturated point
As long as undisturbed, solute will remain dissolved. Disruptions will cause excess to precipitate (rock candy)

10. Solubility is related to polarity.
Solubility of a substance is the amount of the substance required to form a saturated soln with a specific amount of solvent at a specified temperature (if gas, pressure must also be stated)
The rate of dissolution is not related to the solubility (at that temperature) Max amount of solute that dissolves to reach equilibrium is always the same under same conditions
Solubility is related to polarity.
“like dissolves like” (polar dissolves polar, nonpolar dissolves nonpolar, nonpolar doesn’t dissolve polar)

11. Liquid solvents and solutes
If the liquids are not soluble in each other, use term immiscible instead of insoluble
If the liquids are soluble in each other, use term miscible instead of soluble

12. Effects of Pressure on Solubility
Changes in pressure have little effect on the solubilities of liquids or solids
Pressure increases the ability of gas to dissolve in liquid (increase P, increase solubility)

13. Henry’s Law
chemical law stating that the amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas over the liquid, provided no chemical reaction takes place between the liquid and the gas.
It is named after William Henry (1774–1836), the English chemist who first reported the relationship

14. An everyday example of Henry's law is given by carbonated soft drinks such as colas (and also by beers and sparkling wines).
Before the bottle or can is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure.
The drink itself contains dissolved carbon dioxide. When the bottle or can is opened, some of this gas escapes, giving the characteristic hiss
Because the pressure above the liquid is now lower, some of the dissolved carbon dioxide comes out of solution as bubbles----this is called effervescence (think Mentos and diet pop)
If a glass of the drink is left in the open, the concentration of carbon dioxide in solution will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat"

15. Henry's law can be put into mathematical terms (at constant temperature) as
where p is the partial pressure of the solute, c is the concentration of the solute and kH is a constant with the dimensions of pressure divided by concentration.
The constant, known as the Henry's law constant, depends on the solute, the solvent and the temperature.

16. Pressure-Solubility Law (Henry's Law) The concentration of a gas in a liquid at any given temperature is directly proportional to the partial pressure of the gas on the solution.  
Cg = kgPg
where Cg = the concentration of the gas, kg is the proportionally constant for that gas and Pg is the partial pressure of the gas above the solution.  Constant temperature is assumed.  This equation  is true only at relatively low concentrations and pressure and for gases that do not do react with the solvent.
A more useful expression of Henry's Law is  
C1=   C2 P1        P2

17. At 20oC the solubility of N2 in water is 0
At 20oC the solubility of N2 in water is g/L when the partial pressure of nitrogen is 580 torr.  What will be the solubility of N2 in water at 20oC when its partial pressure is 800 torr?
C1 = g/L          C2 = ?  P1 = 580 torr               P2 = 800 torr
C2 = C1  X  P2                           P1                  =  g/L X 800 torr                                 580 torr                  =  g/L
The solubility under the higher pressure is g/L

18. Enthalpy of solution
The enthalpy of solution (or enthalpy of dissolution) is the enthalpy change associated with the dissolution of a substance in a solvent at constant pressure.
We will expand on this later

19. Solution Composition
Perhaps the most important property of a solution is its concentration
In order to quantify the concentrations of solutions, chemists have devised many different units of concentration each of which is useful for different purposes.

20. Weight percent = wt of solute wt of solution x 100%
What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in g of water?
Determine total weight of solution:4.6 g g glucose-water solution
Calculate percent:
Weight % glucose =  4.6 g glucose  x 100 = 3.1%glucose g solution

21. How would you prepare 400. g of a 2.50% solution of sodium chloride?
Analysis: We need to find out how much salt is needed and how much water is needed.
Determine weight of salt:
400. g x 2.50% salt = 10.0 g salt
400. g solution x    2.50 g salt  g solution = 10.0 g salt
Determine weight of water:
400. g total
- 10. g salt
390. g water
Answer: Dissolve 10.0 g salt in 390. g water.

22. Molarity
The term concentration is used to indicate the amount of solute dissolved in a given quantity of solvent or solution.
The most widely used way of quantifying concentration in chemistry is molarity.
The molarity (symbol M) of a solution is defined as the number of moles of solute in a liter volume of solution:

23. Molarity abbreviated M.
For example, calculate the volume of a 1.5 M solution of HCl necessary to completely react with 0.32 moles of NaOH:

24. What is the molarity of a solution made by dissolving 20 grams of NaCl in 100 mls of water?
M solution

25. Calculate the number of moles of CaCl2 in 0. 78 liters of a 3
Calculate the number of moles of CaCl2 in 0.78 liters of a 3.5 M solution:

26. How many liters of a 2.0 M solution of HNO3 do we need to have 5 moles of HNO3?

27. Dilution alters the molarity (i. e
Dilution alters the molarity (i.e. concentration) of the solution but not the total number of moles of molecules in the solution (in other words, dilution does not create or destroy molecules).
One of the standard equations for determining the effects of dilution upon a sample is to set up an equation comparing (concentration)*(volume) before and after dilution
Since (concentration)*(volume) gives us the total number of moles in the sample, and since this does not change, this value before and after dilution are equal:

28. X liters = 0.075 liters (or 75 mls)
(concentration)*(volume) = (concentration)*(volume)
(moles/liter)*(liter) = (moles/liter)*(liter)
moles = moles
How much of a 5 M stock solution of NaCl will you need to make up 250 mls of a 1.5 M solution?
X liters = liters (or 75 mls)

29. What is the concentration of water?
Molecular weight of H2O = 18.0g/mole
Density of H2O = 1g/ml or 1000g/L
Pure water is 55.6M H2O

30. Molality An alternative unit of concentration to molarity is molality.
The molality of a solute is the number of moles of that solute divided by the weight of the solvent in kilograms.
For water solutions, 1 kg of water has a volume close to that of 1 liter, so molality and molarity are similar in dilute aqueous solutions.

31. molality (M) = moles solute/kg of solution
To convert a volume and a molality of a solution to moles of solute, simply solve the above equation for moles of solute:
moles solute = molality * kg of solution

32. If you have 10. 0 grams of Br2 and dissolve it in 1
If you have 10.0 grams of Br2 and dissolve it in 1.00 L of cyclohexane, what is the molality of the solution? The density of cyclohexane is kg/l at room temperature.
10 g / (159.8 g/mole) = moles BR2
1.00 L * kg/l = kg (convert the volume of solvent to the weight of solvent using the density)
0.063 moles Br2/ kg cyclohexane = molal

33. Normality
When you need to compare solutions on the basis of concentration of specific ions or the amount of charge that the ions have, a different measure of concentration can be very useful. It is called normality
Normality, the number of molar equivalents of solute per liter of solution, has the units equivalents / L which are abbreviated N.

34. The normality of a solution is simply a multiple of the molarity of the solution. Generally, the normality of a solution is just one, two or three times the molarity. In rare cases it can be four, five, six or even seven times as much.