1 The Chemistry of Acids and Bases

2 Acid and Bases

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5 Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. Have a bitter taste. Feel slippery. Many soaps contain bases. Bases

6 Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water þ Corrode metals þ Electrolytes þ React with bases to form a salt ( ionic compound) and water þ pH is less than 7 þ Turns blue litmus paper to red

7 Acid Nomenclature Review Binary  Ternary An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

8 Acid Nomenclature Flowchart

9 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue

10 Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)

11 Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H + ions in solution Bases – produce OH - ions in solution (problem: some bases don’t have hydroxide ions!)

12 Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

13 Acid/Base Definitions Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron! H +

14 A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor acid conjugate base base conjugate acid

15 ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID NH 3 is a BASE in water — and water is itself an ACID

16 Conjugate Pairs

17 Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O +

18 Acids & Base Definitions Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair Definition #3 – Lewis

19 The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

20 pH of Common Substances

21 Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

22 Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X M solution of Nitric acid

23 pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ] then - pH = log [H + ] - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = = 7.59 x M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

24 Strong and Weak Acids/Bases Generally divide acids and bases intoGenerally divide acids and bases into STRONG or WEAK ones.STRONG or WEAK ones. STRONG ACID: 100% dissociated in water. HNO 3 + H 2 O  H 3 O + (aq) + NO 3 - (aq) 6 strong acids, all others are weak. HNO 3, HCl, HBr, HI, HClO 4, H 2 SO 4

25 Weak acids are much less than 100% ionized/dissociated in water.Weak acids are much less than 100% ionized/dissociated in water. One of the best known is acetic acid = CH 3 CO 2 H (vinegar) Strong and Weak Acids/Bases

26 Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Group 1 and 2 hydroxides Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O --> Ca(OH) 2 (slaked lime) Ca(OH) 2 (slaked lime) CaO

27 Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

28 Weak Bases

29 pH testing There are several ways to test pHThere 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 base) –Universal indicator (multi-colored) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

30 pH meter Tests the voltage of the electrolyteTests the voltage of the electrolyte Converts the voltage to pHConverts the voltage to pH Very cheap, accurateVery cheap, accurate Must be calibrated with a buffer solutionMust be calibrated with a buffer solution

31 pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

32 ACID-BASE REACTIONS Titrations H 2 C 2 O 4 (aq) + 2 NaOH(aq)  Na 2 C 2 O 4 (aq) + 2 H 2 O(liq) acid base Chemical reaction between an acid and a base. Products are a salt (ionic compound) and water Salts can be neutral, acidic, or basic. Neutralization does not mean pH = 7.

33 Titration Titration you tube = Titration Technique using a buret. –Analytical method in which a standard solution( solution of known concentration, titrant ) is used to determine the concentration of an unknown solution( analyte ). standard solution unknown solution

34 Equivalence pointEquivalence point –Point at which equal amounts of H + and OH - have been added. endpoint) –Determined by… endpoint) »indicator color change »dramatic change in pH

35 Setup for titrating an acid with a base

36 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.

mL of NaOH is neutralized with 25.2 mL of M HCl by titration to an equivalence point. What is the concentration of the NaOH? LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.