Acids and bases play a central role in chemistry because, with the exception of redox reactions, every chemical reaction can be classified an as acid-base reaction. Our understanding of chemical reactions as acid-base interactions comes from the wide acceptance of the Lewis definition of acids and bases, which supplanted both the earlier Bronsted-Lowry concept and the first definition--the Arrhenius model. Arrhenius first defined acids as proton (H) producers in aqueous solution and bases as hydroxide (OH) producers. Although this model is intuitively correct, it is limited to substances that include proton and hydroxide groups. Lewis gave us the more general definition of acids and bases that we use today. According to Lewis, acids are electron pair acceptors and bases are electron pair donors. Any chemical reaction that can be represented as a simple exchange of valence electron pair to break and form bonds is therefore an acid-base reaction.
What do you think is worse for you an acid or base? Consider the question and then we will return to the question after the demonstration. .
Yvette will now demonstrate some substances to determine if they are an acid or a base.
(While Yvette is demonstrating, write equations on the board and the color guide that determines if it is an acid, base, or neutral).
Substances are:.
Acids.
Vinegar - an acidic acid CH3COOH.
Soda (coke) - acidic and carbonic acid (H2CO3).
Neutrals.
Water - H20.
Bases.
Clorox - NaOCl.
Ammonia - NH3 (weak base).
Baking Soda/Water - Na2CO3 + H2O.
COLOR GUIDE .
(Included on Board).
DEEP RED = STRONG ACID.
PINK = WEAK ACID DARK GREEN = STRONG BASE .
YELLOW = WEAK BASE .
NO CHANGE = NEUTRAL.
So going back to our question, What do you think is worse for you an acid or base? Consider orange juice is an acid and drain cleaner is a base.
Acid-base chemistry is important to us on a practical level as well, outside of laboratory chemical reactions.