Thursday, February 28, 2008Chapter 15: Solutions

15.1

Homework: Pg. 555, #1-8

•Go over homework•Introduction of Solutions

•Section 15.1

• Name some mixtures in our life.

• What is the difference between mint chocolate chip ice cream and plain chocolate ice cream?

Chapter 15: Solutions

• Solution - a homogenous mixture. A mixture in which the components are uniformly intermingled.–Solvent - the substance present in the largest amount.–Solutes - the other substance or substances.

• Aqueous solutions - solutions with water as the solvent.

ice cream?

Solubility

• What does it mean when something dissolves? sugar, salt?

Let’s look at sodium chloride.– The strong ionic forces that hold the sodium chloride

crystal together are overcome by the strong attractions between the ions and the polar water molecules.

Dissolving of solid sodium chloride.

Ionic Compounds

• Recall that ionic compounds conduct electricity when dissolved in water

• This is because it is breaking up into the cations and anions

Polar water molecules interacting with positive and negative ions of a salt.

Solubility of Polar Substances

• Water can also dissolve nonionic substances

• Polar O-H groups are attracted to the water

• Examples: sugar, ethanol

The polar water molecule interacts strongly with the polar O—H bond in ethanol.

Structure of common table sugar.

Insoluble

• Not all substances are soluble in water

• Petroleum

• Nonpolar substances are not compatible with polar water molecules

• Oil layer (less dense)

A molecule typical of those found in petroleum.

An oil layer floating on water.

“Like dissolves like”

• Other solutions besides aqueous ones.• Water dissolves most polar solutes, because the

solute-solvent interactions formed in the solution are similar to the water-water interactions present in the pure solvent.

• From aqueous solutions we can say that “like dissolves like,” in that a given solvent usually dissolves solutes that have polarities similar to its own.

Eventually there is not enough water to surround any more of the ions.

What happens then?

Solutions

• Saturated – When a solution contains as much solute as will normally dissolve at that temperature.

• Unsaturated –

• Supersaturated – it contains more solute than a solution will normally hold at that temperature

• Supersaturated solutions are very unstable. They can be made to precipitate by adding one crystal of anything or a scratch on the container or sometimes just bumping them around too much.

Rate of Dissolution

• (dissolving process)• Surface area• Stirring• Temperature• Sugar examples• (also, with temperature- most solids are

more soluble at higher temps- opposite for gases)