Matter (Review and New)

• Recall that all matter can be classified as a mixture or a substance. Up to now we have concentrated on how to classify matter as substances (elements and compounds).

• Now, we are going to concentrated on how to classify mixtures.

Mixtures

Heterogeneous Mixtures• There are two types of heterogeneous

mixtures: suspensions and colloids

Suspensions• Particles are evenly dispersed

• Particles in suspensions may be filtered out

ex: you can separate sand and water

• Particles may settle out (separate) and are large in size

1) Immiscible liquids do not mix

ex: oil and water

a) immiscible liquids can be separated by pouring the less dense liquid off the top

(called decanting)

Colloids• Particles are smaller than the particles in

suspensions but are larger than the particles in a solution

• Particles cannot be filtered

• Particles do not settle out

• Tyndall effect scattering of light by a colloid

Particle SizeSuspensions > Colloids > Solutions

• Examples of colloids: gelatin desserts, whipped cream, smoke, and fog

• Emulsion is a colloid in which liquids that normally do not mix are spread throughout each other– Examples:

1) Mayonaise egg yolk holds oil and vinegar together

2) Bile allows your body to breakdown fat

a) emulsifier substance that holds the immiscible liquid together

Homogeneous Solutions (Solutions)

• Homogeneous mixtures are uniform throughout; all samples are the same

• All homogeneous mixtures are solutions

• A solution is a homogeneous mixture of two or more substances uniformly dispersed throughout a single phase

• Solutions are made of solutes and solvents

1) solute – what is dissolved

2) solvent – what does the dissolving; present in the greatest amount

Miscible Liquids mix to form solutions

• Miscible is defined as 2 or more liquids that form a single layer when mixed

Ex: rubbing alcohol (water and isopropanol)

• Miscible liquids can be separated by distillation (boiling off one liquid)

a) Distillation only works with liquids that have different boiling points

Other States of Matter (beside liquids) can form solutions

1) Many common solutions are solids dissolved in liquids (salt water)

2) Solutions can be made by dissolving a liquid in another liquid (vinegar is made of acetic acid dissolved in water)

3) Gases dissolved in gases are solutions (air)

4) Gases can be dissolved in liquids (CO2 dissolved in water gives soda the fizz)

5) Gases can be dissolved in solids to make solutions (moth balls)

6) Solids dissolved in solids make a solution (brass is made of copper and zinc)

a) An alloy defined as a solid or a liquid mixture of two or more metals.

Solutions• A solution is a mixture that has the same

composition, color, density, and taste throughout.

• The atoms in a solution are evenly spread out.

• Solutions are homogeneous

Phases of Solutions• Solutions can exist in the solid, liquid, and

gas phases

• All mixtures of gases are solutions, including air

• Solutions in the solid phase are called alloys.

Examples of alloys are:

Brass, coins

Solutes and Solvents• Solute is the substance that is being

dissolved.

• Solvent is what does the dissolving (typically water)

• Example: Salt water

Salt is the solute

Water is the solvent

Water: A polar molecule• Polar slightly positive and slightly negative

ends

• Because water is a polar molecule, it is known as the Universal Solvent

• Oxygen end has a slightly (-) charge, Hydrogen has a slightly (+) charge.

O-

H+ H+

Dissolving a Solid in a Liquid• Dissolving salt in water.• NaCl is held together by an ionic bond. However, the

Cl end is more negative than the Na end.

• Step One

The moving water molecules collide with the salt molecules as the water’s negative ends are attracted to the positive ends of the salt molecules.

Na+ Cl-

O-H+

H+Na+ Cl-O-H+

H+

• Step Two:

The water molecules surround and pull the salt molecule apart creating Na+ and Cl- into solution.

The attractive forces between the water and salt molecules are stronger than the forces holding the NaCl molecule together.

Na+ Cl-

H+

H+

O-O-

H+

H+

• Step Three

The water molecules and salt molecules spread out to form a homogeneous solution.

The process continues until all the salt molecules have dissolved.

Non polar Molecules• Non polar materials have no positive or

negative ends.

• Are not attracted to water, so they do not dissolve easily in water

• Examples: oil, soap

Rate of Dissolving1) Stirring will increase the dissolving rate. By

stirring a solution, more fresh solvent comes into contact with the solute.

2) Crushing the solvent will increase the dissolving rate. Crushing creates more surface area for the solvent to interact with.

3) Increasing the temperature will also increase the dissolving rate. Increasing the temperature speeds up the movement of the solute molecules creating more solute/solvent collisions

How much can dissolve?• Solubility is the maximum amount of solute that can

be dissolved in a given amount of solvent at a given temperature.

Each beaker contains the same amount of water and water of the same temperature. Only 1g of “A” dissolves in 100 mL of water, but more than 3g of “B” dissolves in the same amount of water at the same temperature. Substance B is more soluble.

Solubility Curves• Compare the solubility of different

substances at different conditions

Notice that for most solutes, as temperature increases more solute is able to dissolve.

• How much potassium nitrate will dissolve at 80°C in 100 g of water?

• How much potassium nitrate will dissolve at 80°C in 100 g of water?

160 g

• At what temperature will 100 g of potassium bromide dissolve in 100 g of water?

• At what temperature will 100 g of potassium bromide dissolve in 100 g of water?

95°C

Concentration• Concentrated solution large amount of

solute in the solvent

• Dilute solution small amount of solute in the solvent

“watered down”

Types of Solutions1) Saturated Solutions contains all the

solute it can hold at a given temperature.

2) Unsaturated Solutions can dissolve more solute at a given temperature.

3) Supersaturated Solution contains more solute than a saturated solution at the same temperature

a) unstable if you disturb them, crystals will form

The Solubility of Gases• Depend on the temperature and pressure

• Increase temperature then solubility of gas decreases because the gas molecules move around faster and escape the liquid.

• Increase pressure then solubility of gas increases because the pressure holds the gas molecules in the liquid.

Gas solubility and fish• Amount of oxygen

gas in water decreases as temperature increases.

• Fish will go to the bottom of ponds or lakes during warm weather because that is where the oxygen is located.