1. 1 The Chemistry of Acids and Bases

2. 2 Acids and Bases

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5. 5 Some Properties of Acids þ Produce H + ions in water þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red ACID”

6. 6 Some Common Acids HNO3Nitric Acid HCLHydrochloric Acid H2SO4Sulfuric Acid H3PO4Phosphoric Acid H2CO3Carbonic Acid

7. 7 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 “Basic Blue”

8. 8 Some Common Bases NaOHsodium hydroxide KOHpotassium hydroxide Ba(OH) 2 barium hydroxide Mg(OH) 2 magnesium hydroxide Al(OH) 3 aluminum hydroxide Al(OH) 3 aluminum hydroxide

9. 9 Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H + ions HCl → H + (aq) + Cl - (aq) Bases – produce OH - ions NaOH → Na + (aq) + OH - (aq)

10. 10 Acid/Base Definitions Definition #2: Brønsted – Lowry Acids – proton (hydrogen ion H + ) donor HNO 3 + H 2 O → H 3 O + (aq) + NO 3 - (aq) Bases – proton acceptor NH 3 + H 2 O → NH 4 + (aq) + OH - (aq)

11. 11 Brønsted-Lowry Model According to the B-L model, the reaction can be represented as an acid (HA) donating a proton to a water molecule to form a new acid (the conjugate acid) and a new base (a conjugate base). Conjugate representing how the species reacts in the reverse reaction. –HA (aq) + H 2 O → H 3 O + (aq) + A - (aq)

12. 12 Conjugate Pairs

13. 13 Strong vs. Weak Acids/Bases The term strong vs. weak for acids and bases does not refer to concentration or danger. A strong acid or base completely ionizes in water. A weak acid or base partially ionizes in water.

14. 14 ACID-BASE THEORIES The Brønsted definition means H 2 O is both an acid and a base.The Brønsted definition means H 2 O is both an acid and a base. It is called Amphoteric; a substance that can behave as an acid or base.It is called Amphoteric; a substance that can behave as an acid or base. H 2 O + H 2 O → H 3 O + (aq) + OH - (aq)

15. 15 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

16. 16 Calculating the pH pH = - log [H+] (Remember that the [ ] means Molarity) Example: If [H + ] = 1 X 10 -10 pH = - log 1 X 10 -10 pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X 10 -5 pH = - log 1.8 X 10 -5 pH = - (- 4.74) pH = 4.74

17. 17 Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10 -7 M solution of Nitric acid

18. 18 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 + ] = 10 -3.12 = 7.6 x 10 -4 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

19. 19 pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) 10 -8.5 = [H + ] 3.16 X 10 -9 = [H + ] pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) 10 -8.5 = [H + ] 3.16 X 10 -9 = [H + ]

20. 20 More About Water H 2 O can function as both an ACID and a BASE. In pure water there can be AUTOIONIZATION Equilibrium constant for water = K w K w = [H 3 O + ] [OH - ] = 1.00 x 10 -14 at 25 o C

21. 21 In a neutral solution [H 3 O + ] = [OH - ] so K w = [H 3 O + ] 2 = [OH - ] 2 and so [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M Autoionization

22. 22 pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

23. 23 The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H + ion concentration of the rainwater? The OH - ion concentration of a blood sample is 2.5 x 10 -7 M. What is the pH of the blood?

24. 24 HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION.

25. 25 Strong and Weak Acids/Bases Generally divide acids and bases into STRONG or WEAK ones.Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO 3 (aq) + H 2 O (l) ---> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water.

26. 26 Weak acids are much less than 100% ionized in water.Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

27. 27 Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) 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 HONORS ONLY!

28. 28 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

29. 29 Weak Bases

30. 30 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

31. 31 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. –Take 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 and 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.

32. 32 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