The pH scale and strong acids

• pH is a simple numerical scale for measuring hydrogen ion concentration
• What is the strength of Sorensen's pH scale?

  It simplicity and ease of use - for any solution at 25 degrees:

  1. pH less than 7 shows decreasing acidity
  2. pH greater than 7 shows increasing alkalinity
  3. pH 7 is neutral
• pH meters are used for measuring pH accurately and are based on the same principle
• pH - a logarithmic scale
• A low value of [H+] matches a high value of pH
• A high value of [H+] matches a low pH
• pH = -log[H+(aq)]
• [H+(aq)] = 10^-pH
• As a logarithmic scale, a change of one pH number is equal to a 10 times difference in [H+(aq)].
• A pH of 1 has 10x the concentration of [H+] ions as a solution with a pH of 2
• To dilute a solution from a pH 1 to a pH of 4 would require dilution by 10x10x10 = 1000 times
• A solution with a pH of 1 contains 10^13 x more H+ ions as a solution with a pH of 14
• Comparing 1 with 14 is more manageable than comparing 1x10^-1 with 1x10^-14
• In aqueous solutions, a strong monobasic acid, completely dissociates: HA (aq) = H+ (aq) + A- (aq)

  1 mol 1 mol
• So for a strong acid, [H+(aq)] is equal to the concentration of the acid [HA(aq)]
• [H+(aq)] = [HA(aq)]
• The pH of a strong acid can be calculated directly fom the concentration of the acid