Solutions and mixtures

SOLUTIONS AND MIXTURES

QUICK REVIEW

• An element is a substance made up of atoms of one kind.

• A molecule is formed when atoms of the same elements combine.• Two atoms of oxygen combine to form a molecule of oxygen

[O2]• A compound is formed when atoms or molecules of

different elements combine chemically.• Hydrogen and oxygen are combined in a fixed proportion of

2:1 to form the compound water [H2O].• Mixtures are two or more substances that are mixed

together but not chemically joined.

PURE VS. MIXA pure substance: • cannot be separated into 2 or more substances by physical

means• has uniform composition throughout the whole sample

A mixture: • can be separated into 2 or more substances by physical or

mechanical means • displays the properties of the pure substances making it up • its composition can be varied by changing the proportion of

pure substances making it up • heterogeneous substances, ones with non-uniform

composition throughout the sample, are always mixtures

MIXTURES

• When a mixture’s components are easily recognizable, such as pizza, it is called a heterogeneous mixture.

• In a homogeneous mixture such as chocolate milk, the component particles cannot be distinguished, even though they still retain their original properties.

MORE ON MIXTURES

• Homogeneous – particles distributed evenly; the same throughout

• Heterogeneous – PARTICLES not evenly distributed; NOT THE SAME throughout

Type of Mixture Example

gas in gas The atmosphere is a mixture of gases, mostly nitrogen and oxygen.

liquid in liquid Wine is a mixture of mostly ethanol and water.

solid in solid Alloys, such as brass, are made up of a mixture of metals.

gas in liquid Soft drinks, such as cola, are mixtures of mainly carbon dioxide gas and water.

solid in liquid Sea Water is a mixture of salts dissolved in water.

solid in gas Smoke is mixture of tiny solid particles in atmospheric gases.

SOLUTION AKA HOMOGENOUS MIXTURE

• Solutions are composed of one or many solute(s) and only 1 solvent

• Solute: substance that dissolves into the solvent

• Solvent: substance that dissolves the solute(s)

A solution can exist in any of the 3 states of matter: (solid, liquid or gas) Solid Solutions

ex: brass = copper + zinc This is called an alloy. (solvent) (solute)

Gas Solutionsex: air = nitrogen + oxygen + argon + carbon

dioxide (solvent) (solutes)

Liquid Solutionsex: vinegar = acetic acid + water

(solvent) (solute)

P H Y S I C A L V S . C H E M I C A L C H A N G E S

TRANSFORMATION OF MATTER

What do you have left when you melt an ice cube?

Physical changes are those changes that do not result in the production of a new

substance. Chemical changes are changes that result

in the production of another substance.

PHYSICAL CHANGES

• Does not result in the formation of a new substance: the particles remain the same

• Physical changes are reversible

• Alters only non-characteristic properties of the substance:(size, shape, or state of matter)

CHEMICAL CHANGES

• A new substance is formed: it has different characteristic properties than the original substance

• Chemical changes are NOT reversible

• A chemical change has generally occurred if:• there is a color change• a gas is given off• a new substance is formed• heat or light is produced• a residue is formed

Physical• Phase change• Dissolution• Deformation

Chemical• Synthesis• Decomposition• Oxidation• Precipitation

PHYSICAL OR CHEMICAL CHANGE?

•Painting Wood•PHYSICAL

Physical or Chemical Change?

•Burning Paper•CHEMICAL


•Digestion of food•CHEMICAL


•Sugar dissolving in water

•PHYSICAL


•Iron turning red when heated•PHYSICAL


•Evaporation•PHYSICAL


•A pond freezing in winter

•PHYSICAL


•Melting ice•PHYSICAL


•Cutting wire•PHYSICAL


•Painting fingernails•PHYSICAL


•Cutting fabric•PHYSICAL


•Baking muffins•CHEMICAL


•Shattering glass•PHYSICAL


•Decomposition of old leaves

•CHEMICAL


•Wrinkling a shirt•PHYSICAL


•An old nail rusting•CHEMICAL

SOME EXAMPLES

PhysicalExamples:• water boiling• freezing cubes of ice• tearing paper• crushing a can• molding clay• butter melting on

warm toast

ChemicalExamples:• milk goes sour• jewelry tarnishes• a nail or screw forms

rust• fried egg• your stomach digesting

food• lighting a match

COMPOUNDS VS MIXTURES

Compounds Mixtures

Combine chemically forming molecules

Not chemically combined

Combine in set proportions Can combine in any proportion

Separated chemically Separated physically

SEPARATION TECHNIQUES

WHY WOULD WE WANT TO SEPARATE MIXTURES?

• to purify water so that it is safe to drink• to extract a mineral from rocks to be able to use

(example, quartz or gold)• to eliminate the pulp in freshly squeezed juice• to make soup broth

WHAT WE HAVE TO THINK OF WHEN WE SEPARATE MIXTURES…

We need to look for a difference between the parts of the mixture and then use a separation method that takes advantage of this difference.

These are some of the properties that can be used:•

1) The size of the particles 2) The density of a substance

3) The boiling point of a substance4) The solubility of a substance

WAYS TO SEPARATE MIXTURES

1) Sedimentation and decantationAKA : settling out and pouring out

When it works:•

- The size of the particles of a substance have to be large enough to settle to the bottom of the container.

- The larger the size of the particles the faster they will settle to the bottom of the container.- The liquid above the sedimented particles should be quite clear and can be poured off

easily.- This method only works for heterogeneous mixtures!When it doesn’t work:

- As the size of the particles get smaller , it may take too long for them to settle to the bottom of the container and the particles may also be easily stirred up if we try to pour off the liquid above the particles .

EXAMPLES OF S&D

• Examples:o noodles or vegetables in a soup settle to the bottomo muddy water (mud settles to the bottom)o orange juice that has pulpo salad dressing made of oil and vinegar


2) Filtration

When it works:•

- The size of the particles of a substance have to be too large to pass through the holes of a filter .

- This method only works for heterogeneous mixtures!

Downfall:- Filtration takes time and may take longer as the residue accumulates on the filter.

Vocabulary:- Residue: is what is left on the filter - Filtrate: is the liquid that passes though the filter

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FILTRATIONMixture ofsolid andliquid

Stirring rod

Filtrate (liquidcomponentof the mixture)

Filter papertraps solid

Funnel


3) Distillation

When it works:- The substance in the mixture with the lowest boiling point will evaporate first and will then

condense in another cooled container.- This method is the only one that works for SOLUTIONS! (homogeneous mixture)

When it Doesn’t work-This method cannot be used if 2 substances have the same boiling point

Vocabulary- Distillate: is the liquid that evaporates- Residue: is the substance left behind in the original container

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EXAMPLES OF DISTILLATION

Examples: o separating salt from saltwatero making distilled water in the labo commercially distilling alcohol (ethanol used for thermometers)

DISTILLATION

• Separates homogeneous mixture on the basis of differences in boiling point

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Solutions and mixtures