: measures acidity/basicity pH scale : measures acidity/basicity ACID BASE 10x 100x 10x 10x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NEUTRAL pH Scale - provides a convenient way of expressing the hydrogen ion (H+) concentration of a solution and describes acidity or basicity in quantitative terms Pure liquid water contains extremely low but measurable concentrations of H3O+ and OH– ions produced by an autoionization reaction in which water acts as an acid and as a base. Concentration of hydrogen ions and hydroxide ions in pure water is 1.0 x 10-7 M; thus, pure water is a neutral solution. Measurement of pH 1. pH paper impregnated with acid-base indicators, intensively colored organic molecules whose colors change dramatically depending on the pH of the solution. Place a drop of the solution on a strip of pH paper and compare its color with standards to give the solution’s pH. 2. pH meter — more accurate and makes use of a glass electrode, a device whose voltage depends on the hydrogen ion concentration. Each step on pH scale represents a factor of 10. pH 5 vs. pH 6 (10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different)

: measures acidity/basicity pH scale : measures acidity/basicity Søren Sorensen (1868 - 1939) ACID BASE 10x 100x 10x 10x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NEUTRAL pH is defined as the negative base-10 logarithm of the hydrogen ion concentration pH = – log [H+] or [H+] = 10-pH Hydrogen ion concentration in pure water is 1 x 10-7 M at 25ºC; the pH of pure water is – log [1.0 x 10-7] = 7.00. pH decreases with increasing [H+] — adding an acid to pure water increases the hydrogen ion concentration and decreases the hydroxide ion concentration. Adding a base to pure water increases the hydroxide ion concentration and decreases the hydrogen ion concentration—pH increases with decreasing [H+]. pH scale runs from pH = 0 (corresponding to 1 M H+) to pH 14 (corresponding to 1 M OH–). Relationships between acidity, basicity, and pH: If pH = 7.0, the solution is neutral. If pH < 7.0, the solution is acidic. If pH > 7.0, the solution is basic. A change of 1,0 in the pH of a solution corresponds to a tenfold change in the hydrogen ion concentration because the pH scale is logarithmic. Each step on pH scale represents a factor of 10. pH 5 vs. pH 6 (10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different)

Richter Scale - Earthquakes 6 5 7 Area Radius Richter Scale Diameter pH [H+] 1000000 564 7 1128 mm 1 0.1 M 100000 178.4 6 356.8 2 0.01 M 10000 56.4 5 112.8 3 0.001 M 1000 17.8 4 35.6 4 0.0001 M 100 5.64 3 11.28 5 0.00001 M 10 1.784 2 1.128 6 0.000001 M 1 0.564 1 ------ 7 0.0000001 M . 4 3 2 1

pH = -log [H1+] Acid Base pH = 7 [H+] Acidic Basic [OH-] Neutral

radius = 112.8 cm radius = 35.7 cm radius = 11.3 cm radius = 3.6 cm pH = 2 pH = 3 pH = 1 Area Radius Richter Scale Diameter pH 1000000 564 7 1128 mm 1 100000 178.4 6 356.8 2 10000 56.4 5 112.8 3 1000 17.8 4 35.6 4 100 5.64 3 11.28 5 10 1.784 2 1.128 6 1 0.564 1 ------ 7 . pH = 4 5 6