21.2 Water and solutionsA solution is a mixture of two or more substances that is homogeneous at the molecular level.Homogeneous means the particles are evenly distributed.

Heterogeneous and Homogeneous Mixtures

Heterogeneous Mixture – parts of the mixture are noticeably different from one another– “Hetero” means different (Salsa – pepper,

onions, tomatoes)Homogeneous Mixture – the substances are so evenly distributed that it is difficult to distinguish on substance in the mixture from another– “Homo” means same (Steel – iron, nickel,

etc)

21.2 Water as a mixture

Muddy water is heterogeneous because it contains larger particles of soil or plant debris.

21.2 Colloids

Colloids are mixtures, and look like solutions, but their particles are too small to settle to the bottom of their container over time.Examples of colloids are mayonnaise, egg whites, and gelatin.

21.2 Tyndall effect

Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam.This distinguishes a colloid from a solution.

21.2 Suspensions

In a mixture called a suspension the particles can range widely in size. Muddy water, will settle when it is left still for a period of time.

21.2 Types of mixtures

How can you tell the difference between a solution, a colloid and a suspension?

First, try filtering it, then look for the Tyndall effect.

Solutions, Suspensions, and Colloids

Mixtures are classified based on the size of its largest particles– Solution – When substances dissolve and

form a homogeneous mixture– Suspension – Heterogeneous mixture that

separates in layers over time– Colliod – particles intermediate in size and

small are in solution and large are in suspension – combination of both solution and suspension

21.2 Water and solutions

A solution contains at least two components: a solvent, and a solute.The solvent is the part of a mixture that is present in the greatest amount.

Which of these is the solvent?

When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

21.2 Solubility

The term solubility means the amount of solute (if any) that can be dissolved in a volume of solvent.

Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

Chalk and talc do not have solubility values.These substances are insoluble in water because they do not dissolve in water.

A solution is saturated if it contains as much solute as the solvent can dissolve.Any solute added in excess of the substance’s solubility will not dissolve.

What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

A solution is saturated if it contains as much solute as the solvent can hold.An examples of a saturated solution is air. Air can be saturated with water. (We call it humidity!)

21.2 Solubility

For something to dissolve in water, the water molecules need to break the bonds between the solute molecules. Water dissolves each substance differently because the chemical bond strengths between atoms found in different solutes are not the same.

21.2 Equilibrium

When a solute like sugar is mixed with a solvent like water, two processes are actually going on continuously.– Molecules of solute dissolve and go into

solution.– Molecules of solute come out of solution

and become “un-dissolved.”When the rate of dissolving equals the rate of coming out of solution, we say equilibrium has been reached.

When a solution is unsaturated its concentration is lower than the maximum solubility.A supersaturated solution means there is more dissolved solute than the maximum solubility.

21.2 Solutions of gases and liquids

Some solutions have a gas as the solute.In carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

When temperature increases, the solubility of gases in liquid decreases.

The variety and no. or organisms is controlled somewhat by the relationship between dissolved oxygen and temperature.

The concentration of dissolved oxygen in water is important for fish and aquatic life.

Oil and vinegar salad dressing separates because oil is not soluble in vinegar (mostly water). Liquids that are not soluble in water may be soluble in other solvents.