Slide 1

Slide 2 Ch. 18/19 Slide 3 Slide 4 Properties of Acids Formulas begin with H (HCl) React with metals to produce hydrogen gas Turns blue litmus paper to red Blue to Red A-CID Conduct electricity in water Electrolytes React with bases to form a salt and water Taste sour pH is less than 7 Slide 5 Common Acids Sulfuric AcidH 2 SO 4 Nitric AcidHNO 3 Phosphoric AcidH 3 PO 4 Hydrochloric AcidHCl Acetic AcidCH 3 COOH Carbonic Acid H 2 CO 3 Battery acid Used to make fertilizers and explosives Food flavoring Stomach & pool acid In Vinegar Carbonated water Slide 6 Slide 7 Slide 8 Slide 9 Some Properties of Bases Formulas end in OH - Turns red litmus paper to blue Basic Blue Are electrolytes React with acids to form salts and water Feel soapy, slippery pH greater than 7 Taste bitter, chalky Slide 10 Some Common Bases NaOHsodium hydroxide lye KOHpotassium hydroxide liquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide Milk of magnesia Al(OH) 3 aluminum hydroxide Maalox (antacid) Al(OH) 3 aluminum hydroxide Maalox (antacid) Slide 11 Slide 12 Self-Ionization of Water As you know, water molecules are very polar, they constantly move, & collide with each other. Sometimes, when they hit, H + s are transferred from one molecule to another forming hydroxide ions (-OH -) & hydronium ions (H 3 O + ) H 2 O + H 2 O H 3 O + + OH - Slide 13 Self-Ionization of Water Slide 14 In pure water: [H 3 O + ] = 1 x 10 - 7 M and [OH - ] = 1 x 10 -7 M K w = [H 3 O + ][OH - ] K w = (1 x 10 -7 M)(1 x 10 -7 M) = 1 x 10 -14 M 2 K w = ion product constant for water If [H 3 O + ] > 10 -7 then [OH - ] < 10 -7 If [H 3 O + ] 10 -7 If we know one, we can determine the other. Ex. If [H 3 O + ] = 10 -4 whats the [OH - ] ? K w = [H 3 O + ][OH - ] so [OH - ] = K w / [H 3 O + ] [OH - ] = 1 x 10 -14 M 2 = 1 x 10 -10 (1 x 10 -4 M) Inverse Proportion! Slide 15 VERY HANDY TIP!!! *if the 1st factor is a 1, just subtract the exponent from -14 ! - 14 - 4 = - 10 So, [OH - ] = 10 -10 Ex. If [OH - ] = 10 -8 whats the [H 3 O + ] ? Ans. 10 -6 Ex. If [H 3 O + ] = 10 -5 whats the [OH - ] ? Ans. 10 -9 Slide 16 If we add something to water to make the [H+] > 10 -7 (and [OH-] < 10 -7 ) The Solution is Acidic If [H+] 10 -7 ) The Solution is Basic Ex. If [OH - ] = 10 -3 M, whats the [H 3 O + ] ? Is it acidic, basic, or neutral? Ans. [H 3 O + ] = 1 x 10 -11 M Basic Scientists dont like working with sci. notation any more than you do, so Slide 17 Soren Sorensen (1868 - 1939) pH Scale Slide 18 The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10x100 17 pH scale ranges from 0 -14 pH 7 is neutral; pH >7 is Basic pH < 7 is Acidic Slide 19 Calculating pH & pOH pH = -log [H 3 O + ] Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH pOH = -log [OH-] Slide 20 Calculating pH pH = -log [H 3 O + ] Ex. If [H 3 O + ] = 1 x 10 -5 M pH = -log (1 x 10 -5 ) pH = -((log 1) + (log 10 -5 )) pH = - (0 + -5) pH = 5 BIG HINT!!! If the first factor is a one, the pH is just the positive exponent! So what is the pH of a solution with a [H 3 O + ] = 1 x 10 -6 QUICK!!!! Thats Right! 6 is it acidic, basic, or neutral? acidic Slide 21 What if the first exponent isnt a one?! Ans: 4.2 You will need the log button on your calculator! Q: What is the pH if [H + ]= 6.3 x 10 5 ? pH = log [H + ] = - log (6.3 x 10 5 ) What if youre given pH & asked to find [H 3 O + ]? Ex. What is the [H 3 O + ] of a solution with a pH of 9? If the pH is a whole number, just use it as the negative exponent! So [H 3 O + ] = 1 x 10 -9 M Slide 22 What if youre given a pH that is not a whole number! - pH 2 nd log 10 x (antilog) Ex. Determine the hydronium ion concentration of a solution with a pH of 4.6. *You can check your answer by working backwards. pH = - log [H + ] pH = - log [2.51x10 -5 M] pH = 4.6 *if it was 1 x 10 -5 the pH would be 5 so, is it reasonable ? or 10 -pH 10 -4.6 = [H+] = 2.51 x 10 -5 M Slide 23 Q: What is the [H+] if pH = 7.4? [H+] = 10 pH mol/L [H+] = 10 7.4 mol/L 3.98 x 10 8 M Slide 24 pH Calculations pH pOH [H 3 O + ] [OH - ] pH + pOH = 14 pH = -log[H 3 O + ] [H 3 O + ] = 10 -pH pOH = -log[OH - ] [OH - ] = 10 -pOH [H 3 O + ] [OH - ] = 1 x10 -14 Slide 25 pH Scale Slide 26 ACID BASE THEORIES There are 3 main acid-base theories. We will look at the two earliest ones! (In chronological order) More recent theories do not negate earlier ones they just expand on them so they include more substances! Slide 27 Svante Arrhenius Arrhenius Acids - produce hydrogen ions in aqueous solution. HCl H + + Cl - Arrhenius Bases - produce hydroxide ions when dissolved in water. KOH K + + OH - Slide 28 Polyprotic Acids Some compounds have more than 1 ionizable hydrogen. HNO 3 nitric acid - monoprotic - 1 H + H 2 SO 4 sulfuric acid - diprotic - 2 H + H 3 PO 4 phosphoric acid - triprotic 3 H + Slide 29 Bronsted-Lowry Acids & Bases A B-L Acid is a proton (H + ) donor A B-L Base is a proton (H + ) acceptor. These acids and bases always come in pairs in an entire equation! Ex. HCl(g) + H 2 O(l) H 3 O + + Cl - acid base Slide 30 NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Identify the acid & the base in this equation 1.Find the look-a-likes & connect them 2. Decide what happens to each reactant (Lose an H? Gain an H?) Acid Base 3. Do the same for the products. These are labeled the conjugates base acid conjugate baseconjugate acid Slide 31 What do you notice about water in the two examples we just did? thats right! In the first, it acted like a base, and in the second it acted like an acid! (How fickle!) Water is Amphoteric it can act as either an acid or a base depending on what you put it with! Slide 32 Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l) C 2 H 3 O 2 (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH (aq) + HCO 3 (aq) CO 3 2 (aq) + H 2 O (l) conjugate acid-base pairs Slide 33 acidbase conjugate acidconjugate base HF (aq) + SO 3 2 (aq) F (aq) + HSO 3 (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2 (aq) + HC 2 H 3 O 2 (aq) C 2 H 3 O 2 (aq) + HCO 3 (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl (aq) H 2 PO 4 (aq) + HOCl (aq) conjugate acid-base pairs (a) (b) (c) Slide 34 Slide 35 Acid-Base Reactions Neutralization Reaction - a reaction in which an acid and a base react in an aqueous solution to produce a salt and water: Acid + Base Water + Salt HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) H 2 SO 4(aq) + 2KOH (aq) K 2 SO 4(aq) + 2 H 2 O (l) Slide 36 Question: Write the chemical reaction when lithium hydroxide is mixed with carbonic acid. Step 1: write out the reactants LiOH (aq) + H 2 CO 3 (aq) Step 2: determine products -H 2 O and Li +1 (CO 3 ) -2 LiOH (aq) + H 2 CO 3 (aq) Li 2 CO 3 (aq) + H 2 O (l) Step 3: balance the equation 2LiOH (aq) + H 2 CO 3 (aq) Li 2 CO 3 (aq) + 2H 2 O (l) lithium hydroxide + carbonic acid lithium carbonate + water Writing neutralization equations NaOH + HCl H 2 O + NaCl Ca(OH) 2 + H 2 SO 4 2H 2 O + CaSO 4 Slide 37 Strengths of Acids & Bases (strong does not mean concentrated!) Strong acids and bases completely ionize in solution (about 99%) Ex. Strong acids: HCl, H 2 SO 4, HNO 3 Weak acids and bases dont completely ionize. (about 1%) Ex. Weak base: NH 3 (NH 4 OH) Slide 38 Representation of the behavior of acids of different strengths in aqueous solution. Slide 39 Marieb, Fig 26.11 Slide 40 Salt Hydrolysis We saw that a salt, for example NaCl, is formed in a neutralization reaction. the anion of the salt comes from the acid Cl - from HCl and the cation comes from the base Na + from NaOH some salt solutions are neutral; some are acidic or basic Salt hydrolysis- salt reacts with water to produce an acidic or basic solution Slide 41 Salt Hydrolysis To see if the resulting salt is acidic or basic, check the parent acid and base that formed it: 1. NaCl HCl + NaOH 2. (NH 4 ) 2 SO 4 H 2 SO 4 + NH 4 OH 3. KC 2 H 3 O 2 HC 2 H 3 O 2 + KOH Slide 42 Hydrolyzing salts usually made from: strong acid + weak base = slightly acidic weak acid + strong base = slightly basic (Whose the dominant parent?!!) strong acid + strong base = neutral NaCl OH H Slide 43 Titration is the process of adding a known amount of solution of known concentration to determine the concentration of another solution Slide 44 The concentration of acid (or base) in solution can be determined by performing a neutralization reaction An indicator is used to show when neutralization has occurred Often use phenolphthalein- colorless in neutral and acid; turns pink in base Slide 45 #1. A measured volume of an acid of unknown concentration is added to a flask #2. Several drops of indicator added #3. A base of known concentration is slowly added, until the indicator changes color; measure the volume Slide 46 The solution of known concentration is called the standard solution added by using a buret Continue adding until the indicator changes color called the end point of the titration Slide 47 TitrationTitration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3.Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION. This is called NEUTRALIZATION. Simulation Slide 48 Setup for titrating an acid with a base Slide 49 pH testing There are several ways to test pHThere are several ways to test pH Blue litmus paper (red = acid)Blue litmus paper (red = acid) Red litmus paper (blue = basic)Red litmus paper (blue = basic) pH paper (multi-colored)pH paper (multi-colored) pH meter (7 is neutral, 7 base)pH meter (7 is neutral, 7 base) Universal indicator (multi-colored)Universal indicator (multi-colored) Indicators like phenolphthaleinIndicators like phenolphthalein Natural indicators like red cabbage, radishesNatural indicators like red cabbage, radishes Slide 50 Paper testing Paper tests like litmus paper and pH paperPaper tests like litmus paper and pH paper Put a stirring rod into the solution and stir.Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paperTake the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read anRead an d record the color change. Note what the color indicates.d record the color change. Note what the color indicates. You should only use a small portion of the paper. You can use one piece of paper for several tests.You should only use a small portion of the paper. You can use one piece of paper for several tests.