Acids, Bases, &Chemical Changes

Physical ChangeA 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 Shaping clay 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 rustingWood burningVinegar and baking soda reacting and giving off a gasBurning 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

CompoundA 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)

H20 (Water)

C02 (Carbon Dioxide)

Chemical Equation

The use of chemical formulas and other symbols instead of

words to summarize a chemical reaction.

2H2 + 02 2H20

(Hydrogen combines with oxygen to make water.)

Reactants and Products

REACTANTS are substances you have at the beginning of a chemical reaction

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

Example: 2Na + Cl2 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

Example: CaCO3 CaO + CO2

Replacement Reaction

A chemical reaction in which one element replaces another in a

compound, or two elements trade places.

Pattern: A + BC B + AC

Example: C + 2Cu2O 4Cu + CO2

Pattern: AB + CD AD + CB

Example: FeS + 2HCl FeCl2 + H2S

Describing Chemical Reactions

Types of ReactionsWhat 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).

IndicatorsAn 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