Acids, Bases, & Chemical Changes

Physical Change A change in matter in which the appearance or state (solid, liquid, or gas) of the matter is altered, but the matter is NOT converted into a new substance Chopping wood Chopping wood Shaping clay Shaping clay Melting ice Melting ice

Chemical Change (chemical reaction) A change in matter resulting in the formation of one or more new substances that are chemically different from the original substances. Iron rusting Wood burning Vinegar and baking soda reacting and giving off a gas Burning magnesium metal

Chemical Reaction Indicators A chemical reaction has possibly taken place if…  The temperature changes  A light is given off  The color changes  A gas is given off  A precipitate is formed

What is happening?

Endothermic Reaction Any chemical reaction in which heat is absorbed during the reaction. This may make the container feel cool to the touch. The temperature goes down.

Exothermic Reaction Any chemical reaction in which heat is given off during the reaction. This may make the container feel warm or hot to the touch. The temperature goes up.

PROOF… The only definite proof that a chemical reaction has taken place is the formation of new substances. The old stuff is GONE The new stuff has been made

Compound A substance made of two or more elements chemically combined. Example: Sodium chloride (NaCl) is a compound formed when the element sodium (Na) combines with the element chlorine (Cl). Sodium chloride is table salt. +  Cl NaCl

Chemical Formula A combination of symbols that represent a compound. NaCl (Sodium Chloride) H 2 0 (Water) C0 2 (Carbon Dioxide)

Chemical Equation The use of chemical formulas and other symbols instead of words to summarize a chemical reaction. 2H  2H 2 0 2H  2H 2 0 (Hydrogen combines with oxygen to make water.)

Reactants and Products at the beginning of a chemical reaction REACTANTS are substances you have at the beginning of a chemical reaction when a chemical reaction is complete PRODUCTS are substances you have when a chemical reaction is complete REACTANT + REACTANT  PRODUCT + PRODUCT

Types of Chemical Reactions Synthesis Reaction Decomposition Reaction Replacement Reaction

Synthesis Reaction A chemical reaction in which two or more elements or compounds combine to make one more complex substance. Synthesis reactions have one product. Pattern: A + B  AB Pattern: A + B  AB Example: 2Na + Cl 2  2NaCl Example: 2Na + Cl 2  2NaCl

Decomposition Reaction A chemical reaction in which a compound is broken down into simpler products. Decomposition reactions have one reactant. Pattern: AB  A + B Pattern: AB  A + B Example: CaCO 3  CaO + CO 2 Example: CaCO 3  CaO + CO 2

Replacement Reaction A chemical reaction in which one element replaces another in a compound, or two elements trade places. Pattern: A + BC  B + AC Pattern: A + BC  B + AC Example: C + 2Cu 2 O  4Cu + CO 2 Example: C + 2Cu 2 O  4Cu + CO 2 Pattern: AB + CD  AD + CB Pattern: AB + CD  AD + CB Example: FeS + 2HCl  FeCl 2 + H 2 S Example: FeS + 2HCl  FeCl 2 + H 2 S

Describing Chemical Reactions Types of Reactions What is each type of reaction represented?

Acids Substances that produce hydrogen ions (H + ) in water. Taste sour React with metals and carbonates Turn litmus paper red Have a pH less than 7

Common Acids

Bases Substances that produce hydroxide ions (OH - ) in water. Taste bitter Feel slippery Have no reaction with metals or carbonates Turn litmus paper blue Have a pH greater than 7

Common Bases

pH Scale The pH scale is a range of values from 0 to 14 that expresses the amount of hydrogen ions in solution. Strong acids have a pH close to 0 while strong bases have a pH close to 14. Substances with a pH of 7 or close to 7 are neutral (not an acid or a base).

Indicators An indicator is any substance that changes color in the presence of an acid or a base. Below are some common indicators and the colors they change when in the presence of an acid or a base. Cabbage juice indicator