Cracking the AP Chemistry Exam

Part IV

Content Review for the AP Chemistry Exam

Chapter 8

Big Idea #6: Equilibrium, Acids and Bases, Titrations, and Solubility

pH

Many of the concentration measurements in acid-base problems are given to us in terms of pH and pOH.

p (anything)=−log (anything)

pH=−log [H⁺]

pOH=−log [OH⁻]

pK_a=−log K_a

pK_b=−log K_b

In a solution

· when [H⁺]=[OH⁻], the solution is neutral, and pH=7

· when [H⁺] is greater than [OH⁻], the solution is acidic, and pH is less than 7

· when [H⁺] is less than [OH⁻], the solution is basic, and pH is greater than 7

It is important to remember that increasing pH means decreasing [H⁺], which means that there are fewer H⁺ ions floating around and the solution is less acidic. Alternatively, decreasing pH means increasing [H⁺], which means that there are more H⁺ ions floating around and the solution ismore acidic.