Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq) acid base conjugate base conjugate acid conjugate acid-base pairs OH –(aq) + HCO3–(aq)  CO32–(aq) + H2O(l) base acid conjugate base conjugate acid conjugate acid-base pairs

HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq) acid base conjugate base conjugate acid conjugate acid-base pairs (b) CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq) base acid conjugate base conjugate acid (c) conjugate acid-base pairs H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq) acid base conjugate base conjugate acid conjugate acid-base pairs

HCO3–(aq) + S2–(aq)  HS–(aq) + CO32–(aq) acid base conjugate acid conjugate base conjugate acid-base pairs e) H2CO3(aq) + OH –(aq)  HCO3–(aq) + H2O(l) acid base conjugate base conjugate acid conjugate acid-base pairs f) H3O+(aq) + HSO3–(aq)  H2O(l) + H2SO3(aq) acid base conjugate base conjugate acid conjugate acid-base pairs g) OH –(aq) + HSO3–(aq)  H2O(l) + SO32–(aq) base acid conjugate acid conjugate base conjugate acid-base pairs

Will the following salts generate acidic, basic or neutral solutions: Constants: copper(II) hydroxide Kb = 4.8 x 10-13 acetic acid Ka = 1.75 x 10-5 ammonia Kb = 1.8 x 10-5 carbonic acid Ka = 4.2 x 10-7 Will the following salts generate acidic, basic or neutral solutions: a) LiI b) (NH4)2CO3 c) MgCl2 d) CsH2P e) Cu(C2H3O2)2 f) NH4ClO3 neutral lithium hydroxide and hydroiodic acid strong strong basic ammonia and carbonic acid weak weak acidic magnesium hydroxide and hydrochloric acid weak strong basic cesium hydroxide and hydrophosphic acid strong weak acidic copper (II) hydroxide and acetic acid weak weak acidic ammonia and chloric acid weak strong

pH There are many ways to consider acids and bases. One of these is pH. [H+] is critical in many chemical reactions. A quick method of denoting [H+] is via pH. By definition pH = – log [H+] The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of “6” is 10 as violent as a “5” Thus, the pH scale condenses possible values of [H+] to a 14 point scale Also, it is easier to say pH = 7 vs. [H+] = 1 x 10–7

Calculations with pH What is the pH if [H+]= 6.3 x 10–5? pH = – log [H+] (‘-’, ‘log’, ‘6.3’, ‘EE’, ‘(-)’, ‘5’) Ans: 4.2 What is the [H+] if pH = 7.4? [H+] = log–1(-pH) (’2nd’, ‘log’, ‘(-)’, ‘7.4’, ‘=‘) 3.98 x 10–8 M

Practice problems a) [H+] = 1x10–8 M b) [H+] = 1x10–7 M c) [H+] = 2.5x10–6 M d) [H+] = 1.3x10–4 M e) pH = 5.4 f) pH = 5.72

Practice problems a) pH = – log [H+] = – log [1x10–8] = 8.0 b) pH = – log [H+] = – log [1x10–7] = 7.0 c) pH = – log [H+] = – log [2.5x10–6] = 5.60 d) pH = – log [H+] = – log [1.3x10–4] = 3.89 e) [H+] = 10–pH = 10–5.4 = 3.98 x 10–6 mol/L f) [H+] = 10–pH = 10–5.72 = 1.9 x 10–6 mol/L

Find pH, pOH, [H+], and [OH-] It’s the same but different. By definition pOH = – log [OH-] pH + pOH = 14 [H+][OH-] = 1 x 10–14 Find pH, pOH, [H+], and [OH-] a) [OH-] = 1x10–6 M b) [H+] = 2.3x10–3 M c) pH = 1.7 d) pOH = 9.2 [H+] = 1 x 10-8 M pH= 8 pOH= 6 [OH-] = 4.34 x 10-12 M pH= 2.64 pOH= 11.36 [H+] = 2.0 x 10-2 M [OH-] = 5.0 x 10-13 M pOH= 12.3 [H+] = 1.6 x 10-5 M pH= 4.8 [OH-] = 6.31 x 10-10 M

Measuring pH Now that we know how to calculate pH of a solution, how do we measure it? There are several ways to test pH Blue litmus paper (red = acid) Red litmus paper (blue = basic) pH paper (multi-colored) pH meter (7 is neutral, <7 acid, >7 base) Universal indicator (multi-colored) Indicators like phenolphthalein Natural indicators like red cabbage, radishes

Choosing the Correct Indicator Not all indicators shift colors at pH 7. Many change colors over a wide range of pH values. When testing a sample for acidity or basicity it is best to choose an indicator that has a color change close to pH 7 Or use pH paper Or use a pH meter to get a digital reading

Sample Indicator pH Ranges Crystal Violet = yellow (pH 1) blue Cresol Red = red (pH 2) yellow (pH 8) red Thymol Blue = red (pH 3) yellow (pH 8) green/blue Bromophenol blue = yellow (pH 4) blue Methyl orange = red (pH 4.5) orange/yellow Bromcresol green = yellow (pH 4.5) green/blue Methyl red = pink (pH 5.5) yellow Bromcresol purple = yellow (pH 6) purple Alizarin = yellow (pH 6.5) red (pH 12) purple Bromthymol blue = yellow (pH 7 ) green/blue Phenol red = yellow (pH 7.2) red Phenolpthalein = clear (pH 8.3) pink Thymolphtalien = clear (pH 10) blue Alizarin yellow GG = orange (pH 10.5) red Universal Indicator = red (pH 4) orange (pH 6) yellow (pH 7) green (pH 8) blue (pH 9) purple

Acids and bases *Usually, but not always NaOH(aq) HCl(aq) Taste Bitter Sour Feel Slippery Sticky pH > 7 < 7 Litmus red turns blue blue turns red Phenolphthalein *Pink *Cloudy/ white Bromothymol *Blue *Yellow Magnesium NR Bubbles Sodium hydrogen carbonate NR Bubbles