Chapter 15.2Homogeneous Aqueous Systems

Chapter 15.3Heterogeneous Aqueous Systems

Chapter 15.2Homogeneous Aqueous Systems

Chapter 15.3Heterogeneous Aqueous Systems

Learning Objectives• Understand the “s” words and how they are

different from each other (solution, solvent, solute)

• Understand the process of solvation of ions

• “Like dissolves like” and the difference between polar and non-polar molecules when it comes to solvation.

• Electrolyte versus non-electrolyte

• Solutions vs. colloids vs. suspensions

Solution (aq) – water that contains dissolved substances

Solvent – The dissolving medium of the solution (water in this chapter)

Solute – The solid that gets dissolved

Solvent plus solute = solution

How Does a Solution FormSolvation

The ions are solvated (surrounded by solvent).

If the solvent is water, the ions are hydrated.

• Chemists use the axiom “like dissolves like”:Polar substances tend to dissolve in polar

solvents.Nonpolar substances tend to dissolve in

nonpolar solvents.

When a substance becomes solvated by water, we say it is soluble in water

Factors Affecting Solubility• Vitamin A is soluble in nonpolar compounds (like

fats).• Vitamin C is soluble in water.

Which vitamin is water-soluble and which is fat-soluble?

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.

A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.

nonelectrolyte weak electrolyte strong electrolyte

4.1

All ionic compounds are electrolytes because they break apart into ions when added to water

The next part of the textbook is about hydrates …we will skip for the upcoming TWIZ

We did do a lab where we heated a hydrate CuSO4

. 5H2O and determined how much water was released in moles.

The JELL-O mystery … what the heck is it?It is a type of homogeneous aqueous system known as a

colloid.JELL-O is a kind of strange substance which is a colloid. JELL-O is made from water with flavorings, sweetener, and gelatin mixed in. Gelatin is made from a protein called collagen which is the main protein in cartilage, the flexible material that forms your outer ear and nose. When JELL-O is added to hot water, the long collagen molecules separate from each other and mix throughout the water. But when this mixture is cooled, the collagen molecules link up with each other in a different way, forming a 3-dimensional network. Water molecules get trapped in the network and help give JELL-O its more wiggly characteristics.  (adapted from ACS website) More info about colloids

Solutions

Colloids:

Suspensions of particles larger than individual ions or molecules, but too small to be settled out by gravity.

Particles are 1 nm – 1000 nm

Example of a emulsion while doing chemistry

Tyndall Effect• Colloidal suspensions can

scatter rays of light• This phenomenon is

known as the Tyndall effect

Suspension

• A mixture in which particles are larger than in a colloid (greater than 1000 nm)

– Particles are insoluble, so they DO NOT dissolve in the liquid or gas.

– Particles can be separated using a filter.• Examples:• Salad dressing• Medicines that say“shake well before use”

Summary

Type of Aqueous System

Can you see the solute?

Particle Size

Does it scatter light?

Solution Homogeneous (Evenly dispersed) No < 1 nm No

Colloid Homogeneous (Evenly dispersed) No

Between 1 nm and 1000 nm

Yes

SuspensionHeterogeneous

(Unevenly dispersed) Yes > 1000 nmDepends on

size of particles and how they are dispersed