Chapter 2
Heterogeneous Mixture Matter Substance Element Compound Mixture Heterogeneous Mixture Colloid Suspension Homogeneous Mixture
Matter Definition: Anything that has mass and volume Chemistry is the study of matter and the transformations it undergoes Everything can be classified as matter, energy, or space
Transformations of Matter Physical changes Some properties of matter change but the composition remains constant Chemical changes The composition of matter changes
Types of Properties Intensive properties Extensive properties Based upon the composition of matter Include Melting point Color Hardness Extensive properties Based upon the quantity of matter Mass Volume
Chemical Changes Chemical changes change the composition of matter. When matter changes it is called a chemical reaction during which one or more substances are changed to one or more new substances there are several indications a chemical reaction has occurred.
Indicators of a Chemical Reaction Formation of a precipitate Transfer of Energy Change of color Production of a gas
Chemical Reaction Fe2O3 + 2Al → 2Fe + Al2O3 + heat Reactants Products Fe2O3 + 2Al → 2Fe + Al2O3 + heat Chemical reactions take advantage of the chemical properties of a substance to alter its composition. Above is an example of a chemical reaction between iron and aluminum. This specific reaction is known as the thermite reaction and reaches temperatures of over 2500°C.
Chemical Properties Definition: The ability of a substance to undergo a specific chemical change Mixtures do not have chemical properties, but the substances in mixtures do have chemical properties. Mixtures can be separated based upon chemical properties and compounds (a type of substance) can be separated based on chemical properties
Physical changes There are two types of physical changes Reversible Irreversible Reversible changes are most often changes of physical state Irreversible changes are most often mechanical changes
Mechanical Changes Mechanical changes are usually described as irreversible physical changes. Some of these changes include: Grinding Cutting Breaking Crushing All of these actions change the physical nature of matter yet do not change the state or composition of the matter.
Physical States Matter exists in 3 major states Solid Liquid Gas Changes between these three states are always reversible and do not change the composition of the matter Ex. Icewatersteam (all states of water)
Energy Energy is the potential to do work or produce heat It is easy to confuse energy with sources of energy. The sun produces light and heat which are both forms of energy but the sun itself is made up of matter.
Elements Definition: Simplest form of matter that has unique chemical properties Elements are homogeneous substances in which every atom of the substance is exactly the same. 94 elements occur naturally on the earth. Elements are represented by chemical symbols
Chemical Symbols A one or two letter abbreviation for the chemical The first letter is always capitalized the second is always lower case
Compounds Definition: a substance that contains two or more elements chemically combined in a fixed proportion. Like elements compounds have unique properties and cannot be broken down by physical means, however unlike elements, compounds can be broken down chemically.
Fixed Proportions Fixed proportions means that the ratio of each type of element in a compound must be the same. Example H2O is a compound called water HO is a compound called hydroxide H2O2 is a compound called peroxide All of these compounds are made of the same elements but their chemical properties differ greatly
Substances Definition: Substances have uniform and definite composition Uniform composition means that at any given point in the sample of matter the type of matter present will be exactly the same as any other given point Definite composition means there is only one way the substance can be made. A molecule of water can only be made with 2 Hydrogen atoms and 1 oxygen atom.
Mixtures Definition: A physical blend of two or more components Matter is classified as a mixture if it fails to meet one or more of the two requirements to be a substance (uniform and definite composition)
Homogeneous Mixture (Solutions) Definition: a mixture in which the composition is uniform throughout Homogeneous mixtures will have only one phase Despite only having one phase a mixture is able to be separated by physical processes
Phase Definition – A portion of matter that has uniform composition and properties but not necessarily definite composition Phases appear homogeneous to the naked eye
Heterogeneous Mixture Definition: A mixture in which the composition is not uniform throughout Heterogeneous mixtures have 2 or more phases The components of a heterogeneous mixture are able to be separated by physical means
Colloids Description: solute particles are small enough to remain mixed and pass through filter paper, but they are visible in a Tyndall test Often colloids have cloudy or milky appearances Colloids are in a gray area between homogeneous and heterogeneous but for this class they will be considered heterogeneous
Suspensions Description: have larger particles which settle out over time and can be filtered out of the mixture Classified as a heterogeneous mixture
Tyndall test They Tyndall effect (Tyndall Test) occurs when a beam of light is passed through a mixture. If the light is scattered as it passes through the mixture it tests “positive” for the Tyndall effect A positive result indicates a colloid Light scattering gives mixtures the appearance of glowing