Acids, Bases, and the pH Scale An Introduction
General Properties of Acids and Bases • Acids Have a sour taste • Acetic acid is found in vinegar and citric acid is found in citrus fruit • Acids produce H+ ions in water • Bases have a bitter taste and feel slippery or waxy to the touch. Soaps often contain bases. • Bases produce OH- ions in water
+ H H O O [ ] + + - H H H O H O H H H2O (l) H+(aq) + OH-(aq) Acid-Base Properties of Water autoionizationof water Water is amphoteric… which means it can act as both an acid and a base under the proper conditions.
[H+][OH-] [H2O] H2O (l) H+(aq) + OH-(aq) The Ion Product Constant of Water Keq= Since the equilibrium constant for water Is special… it is given a special symbol, Kw. At 25C Kw Is equal to 1.0 x 10-14. This can be used to Determine the pH of certain solutions. Kw =[H+][OH-]= 1.0 x 10-14
What is the concentration of OH- ions in an HCl solution having a hydrogen ion concentration of 1.3 M?
pH- a measure of acidity pH= -log [H+] Solution Is At 250C neutral [H+] = [OH-] [H+] = 1 x 10-7 pH [H+] > 1 x 10-7 pH acidic [H+] > [OH-] basic [H+] < [OH-] [H+] < 1 x 10-7 pH
Strong vs. Weak Frequently, you will see acids and bases described as strong and weak. This has simply to do with their ionization/dissociation constant. You will not be expected to calculate Ka or Kb, however it would be a wise idea to memorize the list of strong acids and bases found below. If you don’t see it on this list, then it is a weak acid or base and there is a different process for finding the pH of these substances.
Strong Acids Perchloric Acid HClO4 ChloricAcid HClO3 Hydrochloric Acid HCl Hydrobromic Acid HBr Hydroiodic Acid HI Nitric Acid HNO3 Sulfuric Acid H2SO4 Strong Bases Group 1A metal hydroxides LiOH, NaOH, KOH, RbOH, CsOH Heavy group 2A metal hydroxides Ca(OH)2, Sr(OH)2, Ba(OH)2
pHs of some common fluids pOH=-log[OH-] pH+pOH=14 [H+]=10-pH [OH-]=10-pOH
Practice Problems and Examples What is the pH of a solution of HNO3 having a molarity of 4.675? What is the pH of a solution with a volume of 475mL containing a total of 1.20g HCl?
The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?