Acids/Bases Svante Arrhenius, a Swedish chemist, proposed the following definition: Acids form hydronium ions in aqueous solutions, while bases form hydroxide ions. Acids give off H+ Bases give off OH-

Properties of acids Give foods a tart or sour taste Electrolytes React with hydroxide ions to form water and a salt HCl + NaOH --> NaCl + H2O

Properties of bases React with acids to form water and salt Have a bitter taste Have a slippery feel Electrolytes Milk of Magnesia (Magnesium Hydroxide) is a base used to treat excess stomach acid problems.

Hydrogen Ions from Water This is the basis to start understanding pH Water is considered neutral Collision between water molecules can cause a hydrogen ion to transfer from one molecule to another. H2O H2O H3O+ OH- hydronium ion hydroxide ion

Self-Ionization of Water Water self ionizes to the concentration of 1.0 x 10-7 mol/L. When the concentration of each ion equals 1.0 x 10-7 mol/L the solution is said to be neutral Therefore, since water is considered neutral the concentrations of the ions can be calculated through the Ion product constant.

The Ion-Product Constant Kw Notation [H+] - concentration of hydrogen ions Or hydronium ions [OH-] - concentration of hydroxide ions When [H+] and [OH-] are multiplied we get the ion-product constant. Kw = [H+] x [OH-] = 1.0 x 10-14 (mol/L)2 or M2 This is an inverse relationship. One goes up, the other goes down.

The Ion-Product Constant Kw example problem If [H+] = 1.0 x 10-5 mol/L, is the solution acidic, basic, or neutral? What is the [OH-] of this solution? Answer Acidic - the [H+] is greater than 1.0 x 10-7 mol/L 1.0 x 10-5 mol/L x [OH-] = 1.0 x 10-14 M2 [OH-] = 1.0 x 10-9 mol/L

The Ion-Product Constant Kw example problem If [OH-] = 2.8 x 10-8 mol/L, is the solution acidic, basic, or neutral? What is the [H+] of this solution? Answer acidic - the [OH-] is less than 1.0 x 10-7 mol/L [H+] x 2.8 x 10-8 mol/L = 1.0 x 10-14 M2 [H+] = 3.5 x 10-7 mol/L