Acids and Bases

Acids have a pH lower than 7. Bases have a pH higher than 7.

Pure water has a pH of exactly 7. All NEUTRAL solutions have a pH of 7.

Arrhenius Definition of Acids and Bases Svante Arrhenius was a scientist who defined acids and bases. This is the simplest definition of an acid and a base. He defined an acid as any substance which donates a hydrogen ion (H+). He defined a base as any substance which donates a hydroxide ion (OH-).

Brønsted-Lowry Definition of Acids and Bases Thomas Martin Lowry Brønsted and Lowry were two scientists that redefined acids and bases to include more compounds (primarily bases). They defined an acid as any substance which donates a hydrogen ion (H+). They defined a base as any substance which accepts a hydrogen ion (H+).

NH3 + H+  NH4 + Brønsted-Lowry Acids and Bases Why is ammonia (NH3) classified as a Brønsted-Lowry base but not an Arrhenius base? NH3 + H+  NH4 + ammonia hydrogen ion ammonium Because it accepts an H+ ion, but does not produce an OH- ion.

Strong Acid Weak Acid Images from The University of British Columbia When we talk about acids or bases being strong or weak, we are referring to how well they dissociate into ions. Strong acids and bases completely break apart! Weak acids and bases stay together!

The acidity of a solution is expressed as its pH. 3.372 3.60 2.09 4.72 5.0 2.64

The Ionization of Water Within any sample of water, some water molecules dissociate into a hydrogen ion and a hydroxide ion. For a pure sample of water, the concentration are shown below. [H+] = 0.0000001 M [OH-] = 0.0000001 M Notice that this is what makes the pH of water 7!

The Ionization of Water When acids or bases are dissolved in water, it affects how much the water breaks apart. However, it does this in a very predictable way. By knowing the ionization constant of water and the [OH-] of a solution, you can calculate the [H+] and figure out the pH

1.00 × 10-14 0.0033 = 3.0 × 10-12 M 11.52 1.00 × 10-14 0.000008 = 1.3 × 10-9 M 8.9 1.00 × 10-14 0.0000025 = 4.0 × 10-7 M 8.40 12.40 1.00 × 10-14 0.025 = 4.0 × 10-13 M 1.00 × 10-14 0.000125 = 8.0 × 10-11 M 10.10

When you dilute a solution, you make it less concentrated by adding more of the solvent. This is often referred to as “watering down” the solution when the solution is aqueous. When you are diluting acids you must be careful dissolving acids can release large amounts of heat.

Remember AAA: Always Add Acid When you are diluting acids you always add the acid to the water while stirring. AAA Remember AAA: Always Add Acid

Acids and bases must always be handled with care because they can be very corrosive. Because of this, they will always be labeled with the symbol above so that this fact is not forgotten.

Naming Acids: Important Facts 1. Binary acids ALWAYS begin with the prefix hydro- and end with the suffix -ic 2. If a polyatomic ion end with –ate, its acid will end with –ic. 3. If a polyatomic ion end with –ite, its acid will end with –ous.

Name the acids on your notes according to the rules you just reviewed. Sulfuric acid Hydrofluoric acid Perchloric acid Hypochlorous acid Hydriodic acid

Neutralization Reactions: Important Facts 1. The products of a neutralization reaction are WATER and a SALT. 2. The pH of a solution after the acids and bases have been neutralized is NEUTRAL (7). 3. You must find the charges of the ions before you can write the formula of the salt.

Determine the products of the neutralization reactions on your notes. H2O Na3PO4 H2O CaF2 H2O KCl H2O Ba(ClO3)2 H2O SrSO3 H2O NH4Br