1. Acids and Bases Dr. Ron Rusay Spring 2004 © Copyright 2001-2004 R.J. Rusay

2. Introduction to Aqueous Acids & Bases  Acids: taste sour and cause certain dyes to change color.  Bases: taste bitter, feel soapy and cause certain dyes to turn color.

3. Electrolytes  Aqueous solutions can be categorized into 3 types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct electricity.  A solution must have ions to conduct.  Pure Water does not conduct.  Aqueous solutions can be tested for conductivity which will determine the degree of ionization of the solutes.  It is possible to have full or partial ionization. © Copyright 1995-2000 R.J. Rusay

4. Solution Test Apparatus for Electrolytes

5. Electrolytes  Almost all ionic compounds and a few molecular compounds are strong electrolytes.  Most molecular compounds are non-conductors.  Conductivity is directly related to the amount of ionization, i.e. ions in solution. Table salt, sodium chloride, is completely ionized: NaCl (s) + H 2 O (l) ---> NaCl (aq) ---> 0.10molNa + (aq) + Cl - (aq) © Copyright 1995-2000 R.J. Rusay 0.00mol 0.10mol 0.10mol

6. Strong vs. Weak Electrolytes

7. Sugar is non-ionized in water and does not conduct.

8. What is an acid and how strong is it?  Acids have a proton, eg HCl(aq).  Acids have a proton, H +, eg HCl(aq).  A strong acid is 100% ionized. For example nitric acid, HNO 3. Other common strong acids are sulfuric, H 2 SO 4 (aq) and hydrochloric, HCl (aq) which also produce.  A strong acid is 100% ionized. For example nitric acid, HNO 3, produces 100% H + (aq). Other common strong acids are sulfuric, H 2 SO 4 (aq) and hydrochloric, HCl (aq) which also produce 100% H + (aq). Acids & Strong Acids:

9. Dissociation of Strong and Weak Acids A weak acid does not dissociate 100%, eg. Acetic acid in vinegar.

10. Acid Strength (continued)  A weak acid is not 100% ionized. For example acetic acid, CH 3 COOH,. Most acids, particularly organic acids, are weak acids.  A weak acid is not 100% ionized. For example acetic acid, CH 3 COOH, produces <100% H + (aq). Most acids, particularly organic acids, are weak acids. Weak Acids :

11. Strong or weak acids?

13. A scale to relate acidities.

14. Aqueous Bases  Any compound that accepts a proton is a base.  The common bases are group IA & IIA metal hydroxide compounds. “Strong” and “weak” are used in the same sense for bases as for acids.  Strong = complete dissociation (100% hydroxide ion is supplied to the solution) An example of a weak base is ammonia. NH 3 (g) + H 2 O (l) NH 3 (aq) NH 4 + (aq) + OH - (aq) © Copyright 1995-2001 R.J. Rusay

15. Bases (continued)  Weak bases have very little dissociation (or reaction with water), eg. methyl amine has <100% hydroxide ion in aqueous solution. H 3 CNH 2 (aq) + H 2 O(l)  H 3 CNH 3 + (aq) + OH  (aq)  Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular decomposition) and morphine (narcotic pain killer) are weak bases.

16. Strong or weak bases?

20. Water as an Acid and a Base  Water is amphoteric (it can behave either as an acid or a base). H 2 O + H 2 O  H 3 O + + OH  conj conj conj conj acid 1 base 1 acid 2 base 2 acid 1 base 1 acid 2 base 2  K w = 1  10  14 at 25°C

21. Water: Self-ionization

22. The pH Scale  pH   log[H + ]  log[H 3 O + ]  pH in water ranges from 0 to 14. K w = 1.00  10  14 = [H + ] [OH  ] pK w = 14.00 = pH + pOH  As pH rises, pOH falls (sum = 14.00). There are no theoretical limits on the values of pH or pOH. (e.g. pH of 2.0 M HCl is -0.301, the pH at Iron Mountain is ~ -2 to -3)

26. The pH of Some Familiar Aqueous Solutions [H 3 O + ] [OH - ] [OH - ] = KWKW [H 3 O + ] neutral solution acidic solution basic solution [H 3 O + ]> [OH - ] [H 3 O + ]< [OH - ] [H 3 O + ] = [OH - ]

27. Natural Indicators

29. The pH Scale 1 1 1.0 12.0 1 x 10 -11 3 1 x 10 -4 4 1 x 10 -1

30. Neutralization Reactions

31. Aqueous Reactions: Neutralization Net Ionic Equations HCl (aq) + NaOH (aq) ---> NaCl (aq) + H 2 O (l) ___________________________________________________   HCl (aq) ---> H + (aq) + Cl - (aq)   NaOH (aq) ---> Na + (aq) + OH - (aq)   NaCl (aq) ---> Na + (aq) + Cl - (aq) ________________________________________________ Na + (aq) + OH - (aq) + H + (aq) + Cl - (aq) ---> Na + (aq) + Cl - (aq) + H 2 O (l) _______________________________________________________ © Copyright 1995-2000 R.J. Rusay H + (aq) + OH - (aq) ---> H 2 O (l)

32. Acid-Base Titration

35. Stomach Chemistry

36. Buffers