The pH Scale

What does the pH Scale Measure? The pH scale is used to measure the degree of acidity or basicity of a solution. The pH scale runs from 0 (very acidic) to 14 (very basic), while a neutral substance has a pH of 7. The pH level is linked to the concentration of hydrogen ions found in the solution as indicated in the table below.pH ValueH3O+ ConcentrationExample01Battery acid1.1Concentrated sulfuric acid2.01Lemon juice, vinegar3.001Orange juice, soda4.0001Tomato juice, acid rain5.00001Black coffee, bananas6.000001Milk, urine7.0000001Water8.00000001Sea water, eggs9.000000001Baking soda10.0000000001Milk of magnesia11.00000000001Ammonia12.000000000001Soapy water13.0000000000001Bleach, oven cleaner14.00000000000001Liquid drain cleaner Use the information above to answer the following questions. 1. What pH has the highest concentration of H3O+? pH = 02. What pH has the lowest concentration of H3O+? pH = 143. Would a pH of 5 or 6 have more hydronium ions? pH of 55. Would a pH of 6 or 7 have more hydronium ions? pH of 66. A change in 1 pH unit is equal to a change in 10 times the hydronium ions.7. When the pH increases (increases or decreases) the amount of hydronium ions decreases.8. For each question, the two pH values are being compared. Determine how many times stronger or weaker the hydronium ion concentration is in the second solution. a. pH 4 → pH 3 The amount of hydronium increases (increases or decreases) by 10. b. pH 8 → pH 6 The amount of hydronium increases (increases or decreases) by 100. c. pH 12 → pH 14 The amount of hydronium decreases (increases or decreases) by 100. d. pH 2 → pH 5 The amount of hydronium decreases (increases or decreases) by 1000. Classify each of the following as acid, base, or neutral. Acid pH below 7 [H+] > [OH-] lemon juice HCl [H+] = .1 and [OH-] = 1x10-13 Base pH above 7 ammonia drain cleaner [H+]<[OH-] [OH-] = .1 and [H+] = 1x10-13 More OH- Neutral pH = 7 [H+] = [OH-] water pH Indicators Indicators are compounds which turn different colors when H+ is added and taken away. For example, phenolphthalein appears pink in basic solutions because the extra H+ has been removed. When in acid, the solution is clear because the H+ is present. Because the H+ can be easily removed or returned, this indicator can change back and forth from pink to clear a limitless number of times. The equilibrium reaction for phenolphthalein is as follows. HIn (aq) + H2O (l) ↔ H3O+ (aq) + In- (aq) Colorless PinkTable M: Table M 1. Look at Table M in your reference tables. What pH range is phenolphthalein colorless? 0-82. When an acid is added, the amount of H3O+ is increased and the reaction shifts left turning the phenolphthein colorless.3. Look at Table M in your reference tables. What pH range is phenolphthalein pink? 9-144. Bases have hydroxide ions that remove H3O+ from solution. When adding a base the reaction will shift right turning the phenolphthalein pink.