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]

pKa=−log Ka

pKb=−log Kb

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.