Pure Substances, Mixtures, and Solutions

• Pure substance: matter that has a fixed (constant) composition and unique properties. Contains only 1 type element or compound; homogeneous  Mixture : Contains at least 2

PHYSICALLY

combined compounds; can be homogeneous or heterogeneous

Homogeneous Substances

• Means same throughout 1) element : only 1 type of atom 2) compound : 2 or more

CHEMICALLY

combined elements (not easily separated from each other) ex: water, CO 2 3) Solution : a special kind of mixture 2 phases/parts (SOLUTE dissolves & SOLVENT does the dissolving) ex: moist air (H 2 O in Air); sterling silver (Cu in Ag…called an alloy)

Heterogeneous matter

• • Means different throughout Always a MIXTURE are NOT heterogeneous) (solutions are mixtures that • 2 or more PHYSICALLY combined substances (elements/compounds) • ex: blood, air, muddy water

• Matter can also be classified according to its composition. Mixtures can be homogeneous or heterogeneous .

• Mixtures can be separated into pure substances , and pure substances can be either compounds or elements .

MATTER

No Is it uniform throughout?

Yes

Heterogeneous mixture Homogeneous

No Can it be separated by physical means?

yes No

Element Pure Substance Homogeneous Mixture (solution)

Can it be decomposed into other substance by a chemical process?

yes

Compound

3 classes of MIXTURES

Solution Colloid Suspension Examples Particle Type Particle Size Scatter Light? (

TYNDALL EFFECT)

Settle while standing?

salt water, air ions, atoms small No No Separate by filtration?

No Soot, fog, mayonnaise Muddy water, Italian dressing Small Clusters Large Clusters medium yes large yes No No yes yes

[A colloid can be separated by filtration?]

A. True B. False

Homogeneus mixtures

Homogeneous mixtures components are evenly distributed among each other. You can’t see the component parts.

Homo means the same throughout.

It has a constant composition throughout.

• Homogenous mixtures are also

called SOLUTIONS : is a mixture in which the Examples:

Salt dissolved in water, sugar dissolved in water, apple juice, tea, copper (II) sulfate solution in water, alloys....

Solutions

• Well-mixed (uniform) – single phase • homogeneous • transparent • cannot be separated by filter • do not separate on standing

States of matter in solution

gas in gas gas in liquid liquid in liquid solid in liquid gas in solid liquid in solid solid in solid

Example of solutions

air ( N 2 , O 2 gases) , Ar, CO 2 , other soda pop (CO 2 in water) gasoline (a mixture of hydrocarbon compounds) Filtrated sea water ( NaCl and other salts in water) H 2 in platinum or palladium dental amalgams (mercury in silver) alloys ( brass, (Cu/Zn), sol der (Sn/Pb), Steel (Fe/C ))

heterogeneous mixtures

Heterogeneous mixture : distributed among each other. An heterogeneous mixture has detectable. This type of mixture does NOT have uniform properties.

two or more distinct phases Heterogeneous mixtures that look like solutions can be distinguished because they scatter light ( Tyndall effect ).

the components are not evenly that are usually Examples:

Sand water, oil and water, milk, sulfur and iron, granite, blood...

[

After passing through a muddy pond, the water in a stream contains dirt particles. Which of the following describes the stream?] A. [solution] B. [suspension] C. [pure substance] D. [colloid]

non transparent, non uniform, large particles, cloudy (milky) but stable system

Suspensions

• A suspension of liquid droplets or fine solid particles in a gas is called an aerosol . In the atmosphere these consist of fine dust and soot particles, and cloud droplets.

• suspension: system does not stays stable and settle • Examples of Suspensions – Mud or muddy water, is where soil , clay , or silt suspended in water. – – – – – – Flour Paint Chalk Dust Algae particles are suspended in water, as pictured to the right. powder suspended in water. particles suspended in air. in water Milk of Magnesia

Colloids

Tyndall effect: You can see the light passes through a colloid or suspension.

(particles scatter light.) emulsion: a mixture of immiscible substances (liquid-liquid). like milk and mayonnaise

[Which of the following will show the Tyndall Effect]

A. [water] B. [sugar water] C. [oxygen gas] D. [fog]

•Suspensions like coffee are easily filtered to take out the tiny solid clumps floating in the liquid.

• In colloids and many homogeneous mixtures have clumps that are so small they pass through most filters.

[Which of the following is a colloid]

A. [milk] B. [NaCl in water] C. [sand and water] D. [raisin bread]

Separating Mixtures

What is a mixture ?

• When two or more materials or substances are mixed together but do not chemically combine .

• This means they

retain original

properties.

their • This means they can be separated by physical means.

What are the different ways of separating mixtures?

• Magnetism • Hand separation • Filtration • Sifting or sieving • Extraction and evaporation • Chromatography

Magnetism

• If one component of the mixture has magnetic properties, you could use a magnet to separate the mixture. Iron, nickel, and cobalt are all materials that are magnetic.

• Not all metals are magnetic: gold, silver, and aluminum are examples of metals that are not magnetic.

Example of magnetism

• Using a magnet to separate nails from wood chips.

Hand separation

• Separating the parts of a mixture by hand.

• Only useful when the particles are large enough to be seen clearly.

• Useful for: separating parts of a salad.

Example of hand separation:

• Using your fork to separate tomatoes, lettuce, cucumber, onions, etc. in your salad.

Filtration

• Used when separating a solid substance from a fluid (a liquid or a gas) by passing a mixture through a porous material such as a type of filter.

• Works by letting the fluid pass through but not the solid.

• Examples of filters: coffee filter, cloth, oil filter, even sand!

Example of filtration:

• Using a coffee filter to separate the coffee flavor from the coffee beans.

Sifting or sieving

• Used to separate a dry mixture which contains substances of different sizes by passing it through a sieve, a device containing tiny holes.

Example of sifting/sieving:

• Using a sieve to separate sand from pebbles.

Extraction

• Used to separate an insoluble solid (something that doesn’t dissolve in a liquid) from a soluble solid (something that DOES dissolve in a liquid). Done by adding a solvent (liquid that does the dissolving) to the mixture. Then pouring the liquid through a filter.

Example of extraction

• With a mixture of sugar and sand, pouring water in the mixture which causes the sugar to dissolve. Then pouring the solution through a filter, causing the sand to separate from the sugar water.

Evaporation

• Allowing the liquid to evaporate, leaving the soluble solid behind.

• Example: heating sugar water. The water evaporates and the sugar crystals are left behind.

Example of using extraction and evaporation together:

• Using water to dissolve sugar, then letting the water evaporate, leaving the sugar behind.

Chromatography

• Used to separate dissolved substances in a solution from each other.

Stationary Phase Separation Mixture Mobile Phase Components

Example of chromatography:

• Using chromatography paper to separate ink into it’s original components.