Classification of Matter • Mixtures • Chemical and Physical Properties & Changes • Separation Techniques • Endothermic & Exothermic Energy
Pure Substances These things have a constant composition throughout. A sample can be taken from any part of the object and it will always have the properties. Ex: hydrogen gas, water, any element from the periodic table
Elements • An element is a substance that cannot be broken down into simpler substances. • An element has a fixed composition because it contains only one type of atom.
Compounds A pure substance composed of two or more elements joined in a fixed proportion. Compounds can only be broken apart by some chemical means. Someone cannot pour two glasses of water from the same pitcher of water and have hydrogen in one glass and oxygen in the other glass.
Mixtures A mixture is a combination of substances that combine and keep their own properties. The substances can be taken apart by physical means. The properties of mixtures can vary because the composition of a mixture is not fixed.
Mixtures There are two types of mixtures • Homogeneous • Heterogeneous
Homogeneous Mixtures Homo meaning “same” reminds us that homogeneous mixtures are the same elements and compounds throughout the mixture. One can take a sample from anywhere in the mixture and get the same results. Ex: Salt water (liquid); Brass (Cu and Zn)
Heterogeneous Mixtures Hetero meaning “different” reminds us that heterogeneous mixtures have different elements and compounds scattered throughout the substance. When a sample is taken from different locations within a mixture different elements and compounds can be found. Ex: pizza , concrete
Putting it all Together Matter Has mass and takes up space Pure Substance Definite Composition Mixture Variable Composition Compound 2 or more kinds of atoms Element One kind of atom Homogeneous Evenly mixed Heterogeneous Unevenly mixed Return to Home Page
Solutions, Suspensions, & Colloids • Solution ~ when substances dissolve and form a homogeneous mixture Ex: water and salt • Suspension ~ heterogeneous mixture that separates into layers over time Ex: sandy water • Colloids ~ some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension; don’t separate into layers. Ex: fog
Physical Properties Properties of a compound or element that can be tested or observed without changing the identity of the substance.
Physical Changes A change in size, shape, or state of matter. The changes do not alter the substances in the material. Ex: when you drop a piece of chalk and it breaks, you change the size of the chalk but you still have chalk.
Using Physical Properties & Changes When a scientist is given a sample of a white powder and asked to identify it the physical changes and properties will help to do so. He/she would not want to alter the powder with chemical changes and therefore test for physical properties and changes of substances that are known to be white powders. Ex: distinguishing between baby powder, flour, and powdered sugar Return to Home Page
Separation Techniques When different elements and compounds are mixed together, its not always a good thing. Scientists want to separate the elements or compounds from one another. In order to do so, they have to perform certain separation techniques based upon chemical and physical properties of the substances.
Density When objects have different densities they can be separated layer by layer. Water is more dense than oil and it settles on the bottom of the container. An oil layer forms on the top of the container. Oil can then be suctioned off of the layer of water. Oil Water
Particle Size (Filtration) Just like playing in the sand at the beach, a sifter can be used to separate particles based upon their size. The bigger particles remain in the sifter while the smaller particles fall through the holes.
Solubility Different compounds are soluble in different solutions. Mixing the compounds in the liquid will create a solution and allow one compound to be rinsed from the unknown. Water is often the liquid used for this process.
Boiling and Melting Points When two liquids are mixed together one way to separate them is to either freeze them. If one has a higher freezing point than the other, it will begin freezing leaving the other liquid behind. The same holds true for two solids. If one has a lower melting point, it will begin melting leaving the other substance as a solid. This is known as distillation.
Chemical Properties A characteristic of a substance that indicates if it can undergo a certain chemical change. Examples of Chemical Properties: • Flammability – a material’s ability to burn in the presence of oxygen. • Reactivity – how easily a substance combines chemically/reacts with another substance.
Questions to Check for Chemical Properties 1. Does it burn in air? 2. Does it decompose when heated? 3. What happens when it is placed in acid? 4. What other chemicals will it react with? 5. What substances are obtained from a reaction?
Chemical Changes A change of one substance in a material to a different substance. A distinct odor is produced when these changes occur. Ex: fireworks exploding, matches burning, metal rusting
Signs of Chemical Changes • Production of a gas - The foaming of an antacid tablet in a glass of water. • A Change in color - Rusting iron on a car. • Formation of a Precipitate – adding vinegar to milk.
Endo- & Exothermic Reactions When a chemical or physical change occurs there is energy present. The energy is either absorbed or given off as the change occurs.
Endothermic Changes Endothermic- heat energy is taken in or absorbed during a reaction. Ex: Photosynthesis - a plant’s food process Energy + H2O + CO2 Sugar + O2
Exothermic Changes Exothermic- reaction that releases heat Ex: Metabolism releases energy when food is used by living cells Sugar + O2 H2O + CO2 + Energy Return to Home Page