SolutionsSolutions(Stuff dissolved in (Stuff dissolved in liquids, that is, not liquids, that is, not

"answers"!)"answers"!)

SolutionsSolutions(Stuff dissolved in (Stuff dissolved in liquids, that is, not liquids, that is, not

"answers"!)"answers"!)AKA “The Molarity Unit”AKA “The Molarity Unit”

Kelley KuhnKelley KuhnCCACCA

So, what happens when ionic compounds are

placed in water?Some ionic compounds are INSOLUBLE and

do not dissolve at all in water. Some ionic compounds are PARTLY

SOLUBLE and only dissolve to a small degree in water. (Like calcium carbonate, the major ingredient in limestone, which dissolves a little and forms sink holes underground over time.)

Some ionic compounds are SOLUBLE and dissolve completely into their component ions to form electrolytic solutions that conduct electricity. (Think salt and water.)

So, what happens when covalent compounds are

placed in water?Some covalent compounds are

NONPOLAR and will not dissolve in water. They either remain as solids or if they are liquids form a separate layer from the water. (Think oil and water.)

Some covalent compounds are POLAR and dissolve in water. When they dissolve, they remain as intact molecules and the solutions are NOT electrolytic. (Think alcohol and sugar.)

COLLIGATIVE PROPERTIES

• When solutes dissolve in solutions, they change certain properties of those solutions. These properties are called COLLIGATIVE PROPERTIES, and they include boiling point, melting point, and osmotic pressure.

Colligative properties example:

For example, when salt is added to water, its freezing point is depressed (lowered). This is why the roads are salted when ice is present. As the salt dissolves in the ice, it melts at a lower temperature.

Solute, solvent, solution…get them straight!

When a compound dissolves in a solution, it is referred to as a solute and the liquid (usually water) is called the solvent.

The concentration of the solute in the solvent can be described in many ways in the science field:

• -ppm, ppb, ppt (environmental)• -mass percent (g solute/100 g

solution)• -molality (moles solute/kg solvent)• And our favorite...• -molarity (moles solute/liter solution)

MolarityMolarity is the number of moles of solute

dissolved per liter of water. Its unit is mol/L and it is abbreviated as M. So, when you see M remember that it stands for molarity NOT moles. Molarity will be used almost exclusively in this class.

To determine the molarity, follow these steps:1. Determine the number of moles of solute.2. Determine the liters of solution.3. Divide the moles of solute by the liters of solution.

Your first molarity problem….

(I know you will make me so proud!)

• What is the molarity of 100. grams of NaCl dissolved in 1250 mL of water? (Leave room for example.)

Variations on Molarity…

M = mol mol = (M)(L) L = mol L MTips:

*If solving for M, convert grams to moles and milliliters to L. Then plug them into the formula.*If solving for grams, solve for moles first and then convert the grams to moles.

Definitions for this unit

Define these terms in your notes. This is one of the homework assignments for this unit. Leave some room between each definition for any added information that I provide in class.

SATURATED SOLUTESUPERSATURED SOLVENTUNSATURATED INSOLUBLEMISCIBLE ELECTROLYTICIMMISCIBLE NONELECTROLYTIC