Bases

1. Acids and Bases

2. Objectives • Properties of acids and bases • The pH scale • Distinguish between strong and weak acids and list the uses of these acids • Distinguish between strong and weak bases and list the uses of these bases • Understand neutralization and applications of neutralization

3. An acid (from the Latin acidus meaning sour) is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. • In chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals.

4. Acids and Bases Solutions can be sorted by whether they are: acid, basic (alkali) or neutral. When a substance dissolves in water it makes a solution.

5. Acids & Bases Acids Taste sour Turns litmus red Neutralizes bases Acids are made of one or more H+ ions and one negative ion Ex. HCl Produces H+ ions when dissolved in water Are corrosive Bases Taste bitter Turns litmus blue Neutralizes acids Bases are made of metals combined with hydroxide ions (OH-) Ex. NaOH Produces OH-when dissolved in water Feel slippery or “soapy” Are corrosive

6. ACIDS Taste sour Turn litmus React with active metals – Fe, Zn React with bases BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids General properties blue to red red to blue

7. Definitions • Acids – produce H+ • Bases - produce OH- • Acids – donate H+ • Bases – accept H+ Arrehenius only in water Bronsted-Lowry any solvent

8. Neutralization In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH)2 H2SO4 + NaHCO3

9. Acids & Bases STRONG vs WEAK _ completely ionized _ partially ionized _ strong electrolyte _ weak electrolyte Strong Acids:Strong Bases: HClO4LiOH H2SO4NaOH HIKOH HBr Ca(OH)2 HClSr(OH)2 HNO3Ba(OH)2

10. Examples Strong Acids:Strong Bases: HClO4LiOH H2SO4NaOH HIKOH HBr Ca(OH)2 HClSr(OH)2 HNO3Ba(OH)2

11. Let’s examine the behavior of an acid, HA, in aqueous solution. HA What happens to the HA molecules in solution?

12. 100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

13. Partial dissociation of HA HA H+ Weak Acid A- Would the solution be conductive?

14. Marieb, Fig 26.11

15. Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HClNaOH HNO3KOH H2SO4 Weak acids/bases – partial dissociation, both ions and molecules CH3COOHNH3

16. acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area pH 0-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12 acidic (H+) > (OH-) neutral @ 25oC (H+) = (OH-) distilled water basic or alkaline (H+) < (OH-) normal rain (CO2) pH = 5.3 – 5.7 fish populations drop off pH < 6 and to zero pH < 5 natural waters pH = 6.5 - 8.5

17. On the pH scale, values below 7 are acidic, a value of 7 is neutral, and values above 7 are basic. Marieb, 2.12

18. Increasing acidity pH of Rainwater across United States in 2001 air masses You are here! Why is the eastern US more acidic? http://nadp.sws.uiuc.edu/isopleths

19. What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O  H2CO3H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O …  HNO3 both strong acids SO2, SO3 + H2O …  H2SO4 pH < 5.3

20. Vocabulary • Hydronium ion -is the common name for the aqueous cation H3O+ • Hydroxide ion – common name for the aqueous anion OH- • Indicator –is a chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. • Buffers - make the pH of the solution change very little when a small amount of strong acid or base is added to it.

21. Vocabulary • Soaps -a cleansing agent created by the chemical reaction of a fatty acid with an alkali metal hydroxide. (KOH) • Detergents -developed in response to the shortage of the animal and vegetable fats used to make soap during World War I and World War II. Detergents are primarily surfactants, which could be produced easily from petrochemicals. • Titration -one solution (solution #1) is added to another solution (solution #2) until a chemical reaction between the components in the solutions has run to completion.

22. What does pH stand for? • Define acid. • Define base. • List the properties of acids • List the properties of bases • Define indicator • Define soap (how are they made) • What do we mean by neutralization

23. pH Calculations pH [H+] pH = -log[H+] [H+] = 10-pH pH + pOH = 14 [H+] [OH-] = 1.0 x10-14 pOH [OH-] pOH = -log[OH-] [OH-] = 10-pOH

24. pH and pOH calculations What is the pOH of a solution whose pH is 3.45? What is the [OH-] of a solution whose pOH = 2.86 ? The pH of a softdrink is determined to be 4.0. What is the [OH-] of the drink? What is the pOH of a solution whose [H+] is 2.75 x 10-4 M? What is the [H+] of a solution whose pOH = 2.86 ? What is the pH of a solution whose pOH is 11.09? What is the [H+] of an acid solution that has a pH of 3?