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. Mix A 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 Solutions ex: air = nitrogen + oxygen + argon + carbon dioxide (solvent) (solutes) Liquid Solutions ex: vinegar = acetic acid + water (solvent) (solute)

Transformation of Matter Physical vs. Chemical Changes

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

Phase change Dissolution Deformation Synthesis Decomposition Oxidation Physical Chemical Phase change Dissolution Deformation Synthesis Decomposition Oxidation Precipitation

Physical or Chemical Change? Painting Wood PHYSICAL

Physical or Chemical Change? Burning Paper CHEMICAL

Physical or Chemical Change? Digestion of food CHEMICAL

Sugar dissolving in water PHYSICAL Physical or Chemical Change? Sugar dissolving in water PHYSICAL

Iron turning red when heated PHYSICAL Physical or Chemical Change? Iron turning red when heated PHYSICAL

Physical or Chemical Change? Evaporation PHYSICAL

A pond freezing in winter PHYSICAL Physical or Chemical Change? A pond freezing in winter PHYSICAL

Physical or Chemical Change? Melting ice PHYSICAL

Physical or Chemical Change? Cutting wire PHYSICAL

Physical or Chemical Change? Painting fingernails PHYSICAL

Physical or Chemical Change? Cutting fabric PHYSICAL

Physical or Chemical Change? Baking muffins CHEMICAL

Physical or Chemical Change? Shattering glass PHYSICAL

Decomposition of old leaves CHEMICAL Physical or Chemical Change? Decomposition of old leaves CHEMICAL

Physical or Chemical Change? Wrinkling a shirt PHYSICAL

Physical or Chemical Change? An old nail rusting CHEMICAL

Some Examples Physical Chemical Examples: water boiling freezing cubes of ice tearing paper crushing a can molding clay butter melting on warm toast Examples: milk goes sour jewelry tarnishes a nail or screw forms rust fried egg your stomach digesting food lighting a match

Compounds vs Mixtures Mixtures Compounds 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:   The size of the particles The density of a substance The boiling point of a substance The solubility of a substance

Ways to Separate Mixtures Sedimentation and decantation AKA : 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: noodles or vegetables in a soup settle to the bottom muddy water (mud settles to the bottom) orange juice that has pulp salad dressing made of oil and vinegar

Ways to Separate Mixtures 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

Filtration Mixture of solid and liquid Stirring rod Funnel Filtrate (liquid component of the mixture) Filter paper traps solid Funnel

Ways to Separate Mixtures 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  

Examples of Distillation separating salt from saltwater making distilled water in the lab commercially distilling alcohol (ethanol used for thermometers)

. DIstillation Separates homogeneous mixture on the basis of differences in boiling point