pH scale The pH scale is used to measure the [H+] and [OH-] in solution. [H+] [OH-] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Water is neutral Water ionizes only slightly into equal concentrations of H+ and OH- ions. In 1.0L of water there are [H+] = 1.0x10-7 M and [OH-] = 1.0x10-7 M When multiplied together they give you the ion product constant for water!

Molarity is concentration

Practice problem #1 2 moles NaOH is dissolved in water to make a solution of 1000.0ml. What is the molar concentration of OH- and H+ ions in this solution? Step 1: do any conversions and determine given ion concentration Step 2: [OH-] x [H+] = 1.0 x 10-14

Practice problem #2 A 4.0g mass of KOH is dissolved in water to make a solution of 500ml. What is the molar concentration of H+ ions in this solution?

Practice problem #3 What are the concentrations of H+ and OH- if 9.50g of Lithium hydroxide is added to enough water to make a 2L solution?

pH numbers? pH = -log [H+] SØren SØrenson decided that expressing [H+] in scientific notation is tooooooo looooooooooooong It’s more convenient to express [H+] in terms of pH (0-14) pH = -log [H+]

If [H+] is given, find the log and take the absolute value LOGS If [H+] is given, find the log and take the absolute value That’s your pH If pH is given, find the antilog (10x) of the negative number That’s your [H+] What if [OH-] is given?

pH practice Find the pH for solutions having the following [H+] 0.0001 M 1 x 10-11 M Find [H+] & [OH-]given these pH 2 8 pH are not always whole numbers The pH of an unknown solution is 6.35, what is the [H+] & [OH-]?

pH practice (answers) Find the pH for solutions having the following [H+] 0.0001 M pH = 4 1 x 10-11 M pH = 11 Find [H+] & [OH-] given these pH 2 [H+]=0.01 [OH-]=10-12 8 [H+]=10-8 [OH-]=10-6 pH are not always whole numbers The pH of an unknown solution is 6.35, what is the [H+]= 4.47x10-7 [OH-] = 2.24x10-8

pH values less than 7 have high [H+] and are acidic (6, 5, 4 . . .) pH values greater than 7 have low [H+] and are basic (8, 9, 10 . . .) [H+] [OH-] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

AND…. Because pH numbers represent log values based on the power of 10 What pH is 10 times more acidic than pH 4? What pH is 100 times more acidic than pH 8? What pH is 10 times less acidic than pH 3? What pH is 10 times more basic than pH 12?

[H+] [OH-] What pH is 10 times more acidic than pH 4? 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 What pH is 10 times more acidic than pH 4? 3 What pH is 100 times more acidic than pH 8? 6 What pH is 10 times less acidic than pH 3? 4 What pH is 10 times more basic than pH 12? 13

Indicators & their colors… Approximate range of pH color change What colors IN BETWEEN????? litmus 4.5 - 8.3 Red to blue bromcresol green 3.8 - 5.4 Yellow to blue thymol blue 8.0 - 9.6 methyl orange 3.1 - 4.4 Red to Yellow bromthymol blue 6.0 - 7.6 Yellow to Blue phenolphthalein 8 - 9 Colorless to pink

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Methyl orange Bromthymol blue Bromcresol green Thymol blue litmus phenolphthalein Bromthymol blue 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

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