Unit 7 Acids and Bases

1. Unit 7 Acids and Bases Properties of Acids and Bases What are some characteristics of Acids and Bases? 1. Acids taste Sour while Bases taste Bitter* and feel slippery. * Never Taste Laboratory Chemicals!! 2. Acids and Bases can be corrosive: Can dissolve some metals and damage living tissue. 3. Acids and Bases produce Ions and are Electrolytes. 4. Acids have a pH below 7 and Bases have a pH above 7.

2. Acid Base Theory What is an Early Explanation for Acid and Base Properties? Arrhenius (1887) Described Acids as substances that yield H+(aq) as the only positive ion. Bases produce OH-(aq) as the only negative ion. How does Water fit these definitions? Water has a very slight tendency to ionize: H2O H+ + OH- Thus, Water can act as a very weak acid and as a very weak base. Water is Neutral because [H+] = [OH-] How does [H+] relate to [OH-]? (Hint: Apply LeChatelier’s Principle) “If one increases, the other one must decrease.” If [H+] decreases, then [OH-] will increase. What is a More Recent Theory of Acids and Bases? Bronsted-Lowry (1920’s) Described Acids as Proton (H+) Donors and Bases as Proton Acceptors. How is Ammonia, NH3 a Bronsted-Lowry Base, but not an Arrhenius Base? Ammonia can Accept H+ by making a bond with its Lone Pair of Electrons forming NH4+ When [H+] decreases [OH-] Increases!

3. Hydrogen Ion or Hydronium Ion? Do Acids produce Hydrogen ions (H+) or Hydronium ions (H3O+)? Yes! When H+ (a proton) is produced by an acid it will form a Coordinate* Covalent Bond with one of the Lone Pairs on the Oxygen of a water molecule forming a Hydronium ion. H+ is equivalent to H3O+ Click the picture  *Shared electrons are both from the same atom. Not a typical “BYOE” Bond. Describe how Water can be a Proton Donor and a Proton Acceptor. HOH + HOH  OH- + H3O+See Hyperlink Identify the Acids and the Bases in the following: HS- + NH3= NH4+ + S2- HSO4- + H2O = OH- + H2SO4 Acid Base = Acid Base Base Acid = Base Acid CO32- + H2O = HCO3- + OH- HCO3- + H3O+ = H2CO3 + H2O Base Acid Acid Base Base Acid Acid Base

4. Strong Acids vs. Weak Acids How are Strong Acids different from Weak Acids? Strong Acids Ionize Completely (100%) to produce H+ while Weak Acids Ionize only slightly. See Hyperlink. What other factors determine the Acidity of a sample? The Concentration of the sample: A Dilute solution of a Strong Acid may be only slightly acidic. A Concentrated solution of a Weak Acid may also be only slightly acidic. Common Acids and Bases Strong Acids Weak Acids Only Soluble Metal Hydroxides are Strong Bases. Ref. Tbl. F

5. Acidity, Alkalinity and pH How does the pH Scale indicate how Acidic or how Alkaline (Basic) a sample is? [H+] = 10-pH What does pH = 7 Really mean? pH = 7 means: [H+] and [OH-] both are 10-7 and sample is Neutral. [H+] [OH-] = 10-14 Explain a change to pH = 4 [H+] has Increased to 10-4 and [OH-] has Decreased to 10-10 How does a change in pH units compare with a change in acidity or [H+]? When the pH Decreased from 7 to 4 the [H+] or acidity Increased by 103 or 1,000 times!! Compare the acidity of Solution A pH = 8 with Solution B pH = 3 Solution A is Alkaline and B is Acidic. Since 8 – 3 = 5, Solution B is 105 or 100,000 times more acidic than A. Solution A [H+] = 10-8 and [OH-] = 10-6 For B [H+] = 10-3 and [OH-] = 10-11

6. Examples of Acids and Bases Compare the Acidities of the following: Vinegar vs. Seawater Vinegar is 105 or 100,000 times more acidic. Coffee vs. Distilled Water Coffee is 100 times more acidic. Household Bleach vs. Household Ammonia Bleach is 10 times more alkaline than Ammonia Battery Acid vs. Lemon Juice Battery Acid is more than 100 times more acidic. Milk of Magnesia vs. Blood Milk of Magnesia is 1,000 times more alkaline.

7. Acid-Base Indicators How can Acid-Base Indicators be used to test Acidity-Alkalinity? Acid-Base Indicators show different colors at different pH’s. What color is methyl orange if the solution has a pH of 2.5? Methyl orange would be Red. What color is bromcresol green in a basic solution? It would be Blue. How would the color of litmus change if the pH of a sample changed from 4 to 9? Litmus would change from red to blue. What would be a good indicator to show that an acid with pH = 5 had become a base with pH = 9? What change would be observed? Bromthymol blue would change from yellow to blue. Phenolphthalein would change from colorless to pink. Litmus may change from red to blue.

8. Neutralization and Titration Complete the following reaction between an Acid and a Base: HCl (aq) + NaOH (aq) H+ + Cl- + Na+ + OH- H2O + NaCl (aq) Describe the General Products of every Neutralization reaction. The Products of Neutralization are Water and a Salt. What is an Acid-Base Titration? An Acid-Base Titration is an experimental method to determine the unknown concentration of an acid (or base) by neutralization with a base (or acid) of known concentration. Click the Flask Revise the formula to: (#H’s) x MA VA = MB VB x (#OH’s)

9. Practice with Titration Problems 1. What is the concentration of an HCl sample if 25.4 mL of 0.050 M NaOH is required to titrate 10.0 mL of the acid to end point? (#H’s) x MA VA = MB VB (#OH’s) 1 x MA x 10.0mL = 0.050 M x 25.4 mL x 1 X = 0.127M 2. How many mL of 0.25 M KOH are required to neutralize 15.0 mL of 0.33 M H2SO4? (#H’s) x MA VA = MB VB (#OH’s) 2 x 0.33 x 15.0 = 0.25 x VB x 1 X = 39.6 mL of KOH 2 x MA x 12.0 = 0.16 x 36.0 x 1 X = 0.24M