V. Properties and uses of solutions

• A. Affecting Freezing and boiling points• 1. Adding a solute will affect some of its

properties called colligative properties.

• a. colligative properties are those that depend on the concentration of the solution NOT on the identity of the solute dissolved in it

• 2. Adding solutes will usually decrease the freezing point and increase or raise the boiling

point. • a. Ex: putting salt on icy roads lowers the

freezing point of water so it has to get colder for ice to form –

• it’s an endothermic process so it absorbs heat from the surroundings & into the water (this is also used in making ice cream!)

B. Concentration

• B. Concentration – Measurement of amount of solute in a given solution

• 1. Concentration relates the amount of solute in a given mixture.

• Ex: 3M HCl acid or .5M NaOH

• 2. Molarity – The number of moles of solute in one liter of solution.

• a. Large molarity means it is concentrated (strong) or has a large amount of solute.

Ex: 3M HCl is stronger than 1M HCl• b. Calculation of Molarity ------ • molarity (M) = moles of solute (mol) Volume of solution (L)

Example

• What is the molarity of 3.5 moles of HCl in 0.5L of water?

• molarity (M) = moles of solute (mol) Volume of solution (L)

• 3.5mol = 0.5 L

7M HCl solution

• C. Dilution – Making a concentrated solution less concentrated.

• 1. Most acids are purchased concentrated so they must be diluted to have a safer concentration.

• **Remember always add acid (or bases) to water, not the other way around**

Reverse OsmosisOsmosis is the diffusion of water through a semipermeable membrane (like cell membranes or dialysis tubing)

*We use this to purifiy drinking water

*Reverse Osmosis is using energy to “force” the water to go in the opposite direction! And it requires energy!

*It occurs naturally & doesn’t require energy!

*The water moves from an area of greater concentration or greater purity to an area of lesser concentration or lesser purity

Reverse Osmosis is using energy to “force” the

water to go in the opposite direction! That means from an area of

lesser amount to an area of greater amount.

Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 267

Natural osmosis – water would diffuse in this direction.

Reverse osmosis – water if FORCED in this direction