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pH Scale

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  1. [H+] pH 10-14 14 10-13 13 10-12 12 10-11 11 10-10 10 10-9 9 10-8 8 10-7 7 10-6 6 10-5 5 10-4 4 10-3 3 10-2 2 10-1 1 100 0 1 M NaOH Ammonia (household cleaner) 7 Acid Base 0 14 Blood Pure water Milk Acidic Neutral Basic Vinegar Lemon juice Stomach acid 1 M HCl pH Scale Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 515

  2. pH of Common Substances water (pure) 7.0 vinegar 2.8 soil 5.5 gastric juice 1.6 carbonated beverage 3.0 drinking water 7.2 bread 5.5 1.0 M NaOH (lye) 14.0 blood 7.4 potato 5.8 orange 3.5 1.0 M HCl 0 milk of magnesia 10.5 urine 6.0 apple juice 3.8 detergents 8.0 - 9.0 bile 8.0 lemon juice 2.2 milk 6.4 tomato 4.2 ammonia 11.0 seawater 8.5 bleach 12.0 coffee 5.0 13 11 12 14 1 6 9 10 0 2 3 4 7 5 8 basic neutral acidic [H+] = [OH-] Timberlake, Chemistry 7th Edition, page 335

  3. pH of Common Substance pH [H1+] [OH1-] pOH 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5 8 1 x 10-8 1 x 10-6 6 6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14 NaOH, 0.1 M Household bleach Household ammonia Lime water Milk of magnesia Borax Baking soda Egg white, seawater Human blood, tears Milk Saliva Rain Black coffee Banana Tomatoes Wine Cola, vinegar Lemon juice Gastric juice More basic 7 1 x 10-7 1 x 10-7 7 More acidic

  4. Acid – Base Concentrations 10-1 pH = 3 pH = 11 OH- H3O+ pH = 7 10-7 concentration (moles/L) H3O+ OH- OH- H3O+ 10-14 [H3O+]<[OH-] [H3O+]>[OH-] [H3O+]=[OH-] acidic solution neutral solution basic solution Timberlake, Chemistry 7th Edition, page 332

  5. pH pH = -log [H1+] Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285

  6. pH Calculations pH [H3O+] pH = -log[H3O+] [H3O+] = 10-pH pH + pOH = 14 [H3O+] [OH-] = 1 x10-14 pOH [OH-] pOH = -log[OH-] [OH-] = 10-pOH

  7. 10x log 2nd antilog pH = - log [H+] Given: determine the [hydronium ion] pH = 4.6 choose proper equation pH = - log [H+] substitute pH value in equation 4.6 = - log [H+] multiply both sides by -1 - 4.6 = log [H+] take antilog of both sides - 4.6 = log [H+] [H+] = 2.51x10-5M Recall, [H+] = [H3O+] You can check your answer by working backwards. pH = - log [H+] pH = - log [2.51x10-5M] pH = 4.6

  8. Acid Dissociation pH = ? pH = - log [H+] H1+(aq) + A1-(aq) HA(aq) monoprotic 0.03 M 0.03 M 0.03 M pH = - log [0.03M] e.g. HCl, HNO3 pH = 1.52 pH = - log [H+] 2 H1+(aq) + A2-(aq) H2A(aq) diprotic 0.3 M 0.6 M 0.3 M pH = - log [0.6M] e.g. H2SO4 pH = 0.22 Given: pH = 2.1 3 H1+(aq) + PO43-(aq) polyprotic H3PO4(aq) e.g. H3PO4 ? M x M find [H3PO4] assume 100% dissociation

  9. - 2.1 = log [H+] 2nd log 2nd log 7.94 x10-3M 3 Given: pH = 2.1 3 H1+(aq) + PO43-(aq) H3PO4(aq) XM 0.00794 M find [H3PO4] assume 100% dissociation Step 1) Write the dissociation of phosphoric acid Step 2) Calculate the [H+] concentration pH = - log [H+] [H+] = 10-pH 2.1 = - log [H+] [H+] = 10-2.1 - 2.1 = log [H+] [H+] = 0.00794 M 7.94 x10-3M [H+] = 7.94 x10-3M Step 3) Calculate [H3PO4] concentration Note: coefficients (1:3) for (H3PO4 : H+) = 0.00265 M H3PO4

  10. How many grams of magnesium hydroxide are needed to add to 500 mL of H2O to yield a pH of 10.0? Mg2+ OH1- Step 1) Write out the dissociation of magnesium hydroxide Mg(OH)2 Mg(OH)2(aq) Mg2+(aq) + 2 OH1-(aq) 0.5 x10-4 M 5 x10-5 M 1 x10-4 M pH + pOH = 14 Step 2) Calculate the pOH 10.0 + pOH = 14 pOH = 4.0 pOH = - log [OH1-] Step 3) Calculate the [OH1-] [OH1-] = 10-OH [OH1-] = 1 x10-4 M Step 4) Solve for moles of Mg(OH)2 x = 2.5 x 10-5 mol Mg(OH)2 Step 5) Solve for grams of Mg(OH)2 58 g Mg(OH)2 x g Mg(OH)2 = 2.5 x 10-5 mol Mg(OH)2 = 0.00145 g Mg(OH)2 1 mol Mg(OH)2