Chapter 18 Notes I Solutions & Solubility Factors Affecting Solubility

What is a Solution? A solution is the same thing as a homogeneous mixture (a mixture with the exact same composition throughout).

Parts of a Solution Solute-the substance that is being dissolved in a solution Solvent-the substance in a solution that is being dissolved into.

Solution of Two Liquids When two liquids are able to dissolve into each other, they are called miscible. If not, they are called immiscible.

What can be dissolved? Remember the saying “like dissolves like” Polar solvents (like water) will only dissolve polar or ionic compounds. *

How does solvation occur? IMFs between polar molecule pull ions away from solid. *

Solubility Solubility is the amount of a substance that will dissolve into a quantity of solvent (at a given temperature)

Solubility Rules There are several sets of rules that can help you to decide if a substance will be soluble in water or not. More on this later!!!

Solubility, cont’d A solvent (like water, for example) can only hold so much of a solute.

If a solvent cannot hold any more of a solute (at that temperature) it is called saturated. If the solvent can hold more solute, it is called unsaturated.

Sometimes, a solution can hold more of a solute than it should theoretically hold. This type of solution is called supersaturated. How could this occur?

Factors Affecting Solubility Generally, a substance’s solubility increases as temperature is increased. (This is not true of most gases). Why? The solvent’s particles are moving faster, and so they have more energy to break bonds.

In gases, pressure affects solubility. The higher the pressure, the more gas is soluble in a solvent. What is an example of this?

Reading Solubility Charts

Concentration Concentration-the amount of solute that is dissolved into a solvent Concentrated-when a solution has a high concentration of solute Dilute-when a solution has a low concentration of solute

Concentration… Concentration can be described in terms of “weak” or “strong”, “concentrated” or “dilute”, but these are both relative terms and can be subjective.

So how do we measure concentration objectively? There are lots of ways!

Molarity Molarity is one way to measure concentration; it is the number of moles of solute per liter of solution. The unit of molarity is mol/L, which can be abbreviated with an uppercase M.

Practice Problem #1 What is the molarity of a solution that contains 0.15mol of MgCl 2 in a 1.13L solution?

Practice Problem #2 A saline solution contains 0.020mol of NaCl in exactly 100mL of water. What is the molarity of this solution?

Practice Problem #3 How many moles of solute are present in a 1.5L sample of 0.24M Na 2 SO 4 ?