3. Starting with…  All About Acids

4. Look at some examples, and see if you can figure out what an acid is… HCl (Hydrochloric acid) HNO 3 (Nitric acid) H 2 SO 4 (Sulfuric acid) What do these formulas have in common?

5. Acids all have hydrogen in their formulas.  Acids are defined as compounds that give away hydrogen ions: HCl  H + + Cl - HNO 3  H + + NO 3 - H 2 SO 4  H + + HSO 4 -

6. Definition 1: Arrhenius Definition An acid is a substance that produces H + in water: Official Acid definitions (Unfortunately, there’s more than one.) HCl (aq)  H + (aq) + Cl - (aq) Remember: “aq” means “dissolved in water.”

7. Definition 1: Arrhenius Definition An acid is a substance that produces H + in water: Official Acid definitions HCl (aq)  H + (aq) + Cl - (aq) Important note: H + ions in water don’t last very long. They immediately bond to a water molecule to form H 3 O +. A more realistic version of the equation above is: HCl + H 2 O  H 3 O + + Cl - To a chemist, those equations say the same thing. The terms “hydrogen ion (H + ) and hydronium ion (H 3 O + )” are used interchangeably and are considered to be the same thing.

8. Because acids give away hydrogen ions, chemists write formulas for most acids with the H in front: HCl (Hydrochloric acid) HNO 3 (Nitric acid) H 2 SO 4 (Sulfuric acid)

9. Definition 1: Arrhenius Definition An acid is a substance that produces H + in water. (Actually produces H 3 O + ) Official Acid definitions The Arrhenius definition is a little narrow: Can an acid only be an acid when it’s in water?

10. Definition 2: Bronsted-Lowry definition : (broader definition) Acids are substances that donate hydrogen ions. (No water required!) Example: HCl gives away hydrogen to NH 3 : HCl + NH 3  NH 4 + + Cl- Memory hint: Br onsted is br oader: The acid doesn’t have to be in water.

11. Acids give away H ions.  Using the periodic table, draw a H + ion. What does it consist of?

12. A hydrogen ion is simply a proton. Acids are also called “proton donors.” H + donor = proton donor

13. Which is the acid in these reactions? (Hint: Which compound gave away hydrogen? HF + HCO 3 -  F - + H 2 CO 3 H 2 0 + HNO 2  H 3 0 + + NO 2 -

14. Some Properties of Acids þ Produce H + ions in water þ Taste sour þ Electrolytes þ React with bases to form a salt and water þ React with metals to produce H 2 gas

15. Organic Acids  Acetic acid is an organic acid: it has carbon in it. The part in red makes it an organic acid. The H that can be donated is the one in red. Another organic acid:

16. Strong Acids and Weak Acids

17. Strong acids are assumed to be 100% ionized in solution (good H + donors). Weak acids are usually less than 5% ionized in solution (poor H + donors).

18. HA Let’s examine the behavior of a generic acid, HA, in water: What happens to the HA molecules in solution?

19. HA H+H+ A-A- Strong Acid Strong acids ionize completely. Every molecule gives away H + : Would this solution conduct electricity?

20. HA H+H+ A-A- Strong Acid Strong acids are strong electrolytes because they produce a lot of ions:

21. HA H+H+ A-A- Weak Acid Weak acids only partially ionize. Most molecules stay together; only a few give away H + : Would this solution conduct electricity?

22. HA H+H+ A-A- Weak Acid Weak acids are weak electrolytes because they produce only a few ions.

23. Naming acids Rule #1: If the acid does not have oxygen in it, then name it… hydro + second element + ic Example: HCl is hydrochloric acid. What would HF be? H 2 S?

24. Naming acids Rule #2: If the acid comes from a polyatomic ion that ends in “ate,” the acid is named ____-ic. H 2 SO 4 : sulfuric acid (from sulfate) HNO 3 : nitric acid (from nitrate) What is the name of H 3 PO 4 ? If you need to name an acid, use your list of polyatomic ions!

25. Naming acids Rule #3: If the acid comes from a polyatomic ion that ends in “ite,” the acid is named ____-ous. H 2 SO 3 : sulfurous acid (from sulfite) HNO 2 : nitrous acid (from nitrite)

26. Acid Practice Questions: 1.A H + ion is the same thing as a – a.an electron b.a proton c.an acid d.a base

27. Acid Practice Questions: 2.Which acid is a strong acid?

28. 3. An Arrhenius acid is a.any substance that can donate a H + ion b.any substance that ionizes in water to form H + ions

29. 4. An element common to all acids is – a. chlorine b. hydrogen c. oxygen d. sodium

30. 5. Name the following acids: a.HNO 3 b.HBr c.H 3 PO 4 d.HC 2 H 3 O 2

31. Bases Just like we had two definitions of acids, we have two definitions of bases.

32. (Review) Arrhenius acid is a substance that produces H + in water: Arrhenius base is a substance that has hydroxide in the formula, and produces OH - in water: Acid/Base definitions Definition 1: Arrhenius HNO 3 (aq)  H + (aq) + NO 3 - (aq) NaOH (aq)  Na + (aq) + OH - (aq) Ca(OH) 2 (aq)  Ca 2+ (aq) + 2 OH - (aq)

33. Strong and Weak Bases  Like strong acids, strong bases produce a lot of ions in water. Weak bases produce only a few ions in water. In this diagram, which is the strong base and which is the weak base?

34. Strong bases  Like strong acids, strong bases are good electrolytes because they make lots of ions.

35. Neutralization reactions: If you combine an acid with an Arrhenius base you can make water: HCl + NaOH  ?

36. If you combine an acid with a base… HCl + NaOH  H 2 O + NaCl This is called a neutralization reaction because the acid and base neutralize each other.

37. If you combine an acid with a base… HCl + NaOH  H 2 O + NaCl The products of any neutralization reaction are water and a salt. Salt? Salt? (In chemistry, salt is not just NaCl. A salt is defined as the product of a neutralization reaction between an acid and a base.)

38. Acid/Base reactions: Produce water and a salt. Hint: concentrate on the water first. Remember, water has the formula HOH. Complete and balance the following: HCl + KOH  HCl + Ca(OH) 2  HOH + KCl HOH + CaCl 2

39. Acid/Base Definitions  Definition #1: Arrhenius definition A base produces hydroxide ions in water. Once again, the Arrhenius definition is narrow.  Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor

40. An acid is a proton donor A base is a proton acceptor acid base NH 3 is a Bronsted-Lowry base because it accepts protons, but not an Arrhenius base because it doesn’t have hydroxide in the formula.

41. Practice: Identify the acid and base in these reactions: 1. NH 4 + + OH -  NH 3 + H 2 O 2. HSO 4 - + H 2 O  H 3 O + + SO 4 2-

42. Summary of the definitions: ArrheniusBronsted-Lowry AcidHas hydrogen in the formula, and donates H + in water Proton donor BaseHas hydroxide in the formula, and donates hydroxide in water Proton acceptor

43. Some Properties of Bases  Produce OH - ions in water  Taste bitter  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water

44. Practice Question Given the balanced equation representing a reaction: HSO 4 - (aq) + H 2 O (ℓ) → H 3 O + (aq) + SO 4 2- (aq) The H 2 O molecules act as a. an acid because they accept H ions b. a base because they donate H ions c. a base because they accept H ions d. an acid because they donate H ions