•The strength of an acidic or basic solution can be measured numerically on the pH scale. •pH scale usually applied over a range of 1 to 14. •Neutral solution: pH = 7 •Acidic solution: pH < 7 •Basic solution: pH > 7 •pH is a measure of the concentration of hydronium ions, H30+
pH = - log 10 [H30+]
[H30+] = 10^-pH pH calculations pH of a monoprotic acids (1 proton): Sample Problem: 0.01 M solution of HNO3 is prepared by adding water. Calculate pH of solution.
Calculating pH of dilution: Sample Problem: •50 mL of a solution of HCl of pH 2 is diluted so that a new pH is 5. •What volume of water was added?
Solution: Step 1: Convert pH into [H30+ ]. •pH = 2 so [H30+] = 10-2 M •pH = 5 so [H30+] = 10-5 M •Step 2: List Data •C1 = 10-2 M C2 = 10-5 M •V1 = 50 ml = 0.050 L V2 = ?
Solution: Step 3: Calculate Final Volume (V2) •Dilution use C1V1 = C2 V2 •C1V1 = C2 V2 •10-2 x 0.050 = 10-5 x V2 •V2 = 10-2 x 0.050 / 10-5 = 50 L = 50000 mL Step 4: Calculate Volume of water added. = Final Volume – Initial Volume = 50 000 – 50 = 49 950 mL= 49.95 L
The ionic product of water •Pure water is neutral and has a pH of 7 at 25OC. •The ionic product of water shows a direct relationship between levels of H30+ and OH- in aqueous solutions using the following equation: [H30+] x [OH-] = 10-14 M2 at 25OC. Using the ionic product to find pH of a basic solution : Sample Problem: •The concentration of [OH-] in a cleaning product is found to be 10-3 M. •Find the pH of the solution. Solution: Step 1: Calculate [H30+ ]. •[H30+] x [OH-] = 10-14 •[H30+] x [10-3] = 10-14 •[H30+] = 10-14 / 10-3 = 10-11 M Step 2: Calculate pH •pH = - log 10 [H30+] = - log 10 [10-11] = 11
pH scale courtesy of By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons