Compounds, Mixtures, and Reactions Unit II-Part 5

Classifying Matter Matter Pure SubstancesMixtures ElementsCompounds HomogeneousHeterogeneous Fe, OH 2 O, CO 2 milk, tea Rocky Road ice cream, muddy water

What is a Pure Substance? A pure substance cannot be separated by physical means. It is a classification of matter that includes both elements and compounds

Elements We have already studied elements − An element is made of one kind of atom − Found on the periodic table

What Is A Compound? A compound is a pure substance that is created by 2 or more elements chemically reacting and joining together − Ex: NaCl, H 2 O, CO 2, NH 3, NaHCO 3, and C 6 H 12 O 6 Notice that elements combine in many ways to make compounds − Ex: H 2 O, H 2 O 2, CO, and CO 2

Why Do Compounds Form? Compounds form to allow elements to become more stable − Na is flammable when it comes in contact with H 2 O, and Cl 2 is a toxic gas − NaCl is a very stable compound that is neither flammable nor toxic (in normal quantities)

Can a compound be reversed? bQ-2whttp:// bQ-2w “Breaking Down Water” -Anode: The anode of a device is the terminal where current flows in from outside. -Cathode: The cathode of a device is the terminal where current flows out.

How Do Compounds Form? Compounds form by the interaction between the nuclei and valence electrons of 2 or more elements THE OCTET RULE: an element is most stable with 8 valence electrons − Elements will join chemically to get 8 valence electrons

What Do Compounds Have To Do With My Life? Compounds are the substances that make up ALL living and non-living things Examples: Where would you be without: − H 2 O—water − NaCl—table salt − C 3 H 8 O—rubbing alcohol − C 55 H 98 O 6 —an example of an unsaturated fat

What Is A Mixture? A mixture is the physical combination of 2 or more substances It is important to understand that a mixture is not chemically combined Mixtures can be separated by physical means such as filtration, distillation, and chromatography Mixtures can be divided into 2 groups − Homogenous mixtures − Heterogeneous mixtures

What Is a Homogenous Mixture? A homogeneous mixture is a mixture that is evenly distributed Homogeneous mixtures are commonly called solutions. − Solution = Solute + Solvent Solute: “stuff” being dissolved Solvent: liquid it is dissolved into The solvent is present in greater quantity The solute is present in the lesser quantity − Ex: Salt water: Salt=solute, Water=solvent

What Is a Heterogeneous Mixture? A heterogeneous mixture is a mixture that is unevenly distributed. Examples: − Iced tea: The ice is floating at the top and therefore is not evenly distributed throughout the tea − Chex Mix: You may find a different number of pretzels or Chex cereal in each handful; therefore, the mixture is unevenly distributed

How Are Mixtures Important To My Life ? We encounter mixtures everywhere in our lives Where would you be without: − Ice cream − Kool-aid − Shampoo − Soup − Milk − Orange juice

How Can We Change Matter Into New Substances? Chemical reaction (also known as a chemical change) is a change in a substance or substances that results in a totally new substance − Ex: 2H 2 (g) + O 2 (g)  2H 2 O(g) Notice that the reactants (the substances you start with) combine to form a new substance (the product)

How Do I Know If A Chemical Reaction Has Occurred? There are 5 indicators of a chemical reaction. 1.Evolution of a gas 2.Evolution of light 3.Evolution of heat 4.Color change 5.Evolution of a precipitate Precipitate: an insoluble substance that is produced as result of a chemical reaction.

Why Do Chemical Reactions Occur? Chemical reactions occur to produce a more stable product than the existing reactants − Ex: 2Na(s) + Cl 2 (g)  2NaCl(s) *The sodium is highly unstable and the chlorine gas is somewhat unstable. The resulting Sodium Chloride is VERY stable. **It is important to understand that the products have totally different properties than the reactants

Where Does The Matter Go? It is important to understand that when matter undergoes a chemical reaction (chemical change) it does not disappear or appear − The atoms are rearranged and form new bonds, but no matter is lost nor gained This is called the Law of Conservation of Matter

What Kind of Chemical Reactions Do I Experience? The acidic milk and basic baking soda that produce CO 2 gas when a cake bakes Paper burning to produce ashes, CO 2, and H 2 O vapor Hydrogen peroxide decomposing to produce water and oxygen gas