Chemistry: Matter and Change   Chapter 3

water, ammonia, sucrose, gold, oxygen Chemistry is the study of matter and the changes it undergoes Matter is anything that occupies space and has mass. A substance is a form of matter that has a definite composition and distinct properties. water, ammonia, sucrose, gold, oxygen 1.4

Heterogeneous mixture – composition is not uniform throughout. A mixture is a combination of two or more substances in which the substances retain their distinct identities. Homogenous mixture – composition of the mixture is the same throughout. soft drink, milk, solder Heterogeneous mixture – composition is not uniform throughout. cement, iron filings in sand 1.4

Physical means can be used to separate a mixture into its pure components. distillation magnet 1.4

116 elements have been identified An element is a substance that cannot be separated into simpler substances by chemical means. 116 elements have been identified 92 elements occur naturally on Earth gold, aluminum, lead, oxygen, carbon 34 elements have been created by scientists technetium, americium, seaborgium 1.4

A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions. Compounds can only be separated into their pure components (elements) by chemical means. Water (H2O) Glucose (C6H12O6) Ammonia (NH3) 1.4

Kinetic Nature of Matter Matter consists of atoms and molecules in motion.

STATES OF MATTER SOLIDS — have rigid shape, fixed volume. External shape can reflect the atomic and molecular arrangement. Reasonably well understood. LIQUIDS — have no fixed shape and may not fill a container completely. Not well understood. GASES — expand to fill their container. Good theoretical understanding.

OTHER STATES OF MATTER PLASMA — an electrically charged gas; Example: the sun or any other star BOSE-EINSTEIN CONDENSATE — a condensate that forms near absolute zero that has superconductive properties; Example: supercooled Rb gas

Physical or Chemical? A physical change does not alter the composition or identity of a substance. ice melting sugar dissolving in water A chemical change alters the composition or identity of the substance(s) involved. hydrogen burns in air to form water 1.6

Extensive and Intensive Properties An extensive property of a material depends upon how much matter is is being considered. mass length volume An intensive property of a material does not depend upon how much matter is is being considered. density temperature color 1.6

Law of Definite Proportions A compound is always composed of the same elements in the same proportions by mass, no matter how large or small the sample. Examples: Water 2 hydrogens and 1 oxygen It is always the ratio for H to O to make water.

Law of Multiple Proportions When two different compounds are formed rom the same elements, different masses of the elements combined in different ratios. Example: water and hydrogen perioxide

Classification of Mixtures homogeneous = mixture that has uniform composition throughout Every piece of a sample has identical characteristics, though another sample with the same components may have different characteristics. atoms or molecules mixed uniformly heterogeneous = mixture that does not have uniform composition throughout contains regions within the sample with different characteristics atoms or molecules not mixed uniformly 18 18

Changes in Matter Changes that alter the state or appearance of the matter without altering the composition are called physical changes. Changes that alter the composition of the matter are called chemical changes. During the chemical change, the atoms that are present rearrange into new molecules, but all of the original atoms are still present. 19 19

Solution a mixture of two or more substances that is identical throughout can be physically separated composed of solutes and solvents Salt water is considered a solution. How can it be physically separated? the substance in the smallest amount and the one that dissolves in the solvent the substance in the larger amount that dissolves the solute Iced Tea Mix (solute) Water (solvent) Iced Tea (solution) Colloids (milk, fog, jello) are considered solutions

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.

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!

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. Mixture Components Separation Stationary Phase Mobile Phase

Example of chromatography: Using chromatography paper to separate ink into it’s original components.

Percent Composition (mass) Sometimes it’s useful to know the composition of a compound in terms of what percentage of the total is each element Percent “Parts per 100” The number of specific items per a group of 100 items 50% of $100 is $50 (50 items/100 total items) The number of items of a specified type in a group of 100 items

Percent Example You have 4 oranges and 5 apples. What percent of the total is oranges? In “parts per 100”

Percent Composition It is the percent by mass of each element in a compound Can be determined By its chemical formula Molar masses of the elements that compose the compound The percent of each element contributes to the mass of the compound The formula of carbon dioxide indicates it is composed of one atom of carbon and two atoms of oxygen. Now we will express it in terms of mass percent

Calculating Percent Composition Example What is the percent composition of each element in NH4OH? Determine the contribution of each element Molar mass On a per mol basis

We will talk about this section later.