ACIDS AND BASES

OPERATIONAL DEFINITIONS

A. Classification of a substance based on its observable properties

B. Operational definitions of acids

1. Aqueous solutions of acids conduct electricity

a. Strong acids are good conductors of electricity

• Therefore they must break up into many ions

• They are strong electrolytes

• They cause the bulb of a conductivity tester to glow brightly

b. Weak acids are poor conductors of electricity

• Therefore they must break up into few ions

• They are weak electrolytes

• They cause the bulb of a conductivity tester to glow faintly

2. Acids react with metals to produce hydrogen gas(H2)

a. Reference Table J

b. All metals found above hydrogen on the table react with acids to produce hydrogen gas (H2)

3. Acids cause acid-base indicators to change color

a. indicators- substances which have different colors in acid and base

b. examples: litmus: red in acid, blue in base

phenolphtalein is clear in acid, pink in base

c. Table M

4. Acids react with bases (hydroxides (OH)) to form a salt and water

a. Called a neutralization reaction

b. Example: HCl + NaOH NaCl + HOH

c. Referred to as a titration

5. Dilute aqueous solutions of acids have a sour taste

a. Examples: vinegar-acetic acid

Lemons- citric acid

6. Names and formulas of some common acids are found on table K

C. Operational definitions of bases

1. aqueous solutions of bases conduct electricity

a. Strong bases are good conductors of electricity

• Therefore they must break up into many ions

• They are strong electrolytes

• They cause the bulb of a conductivity tester to glow brightly

•

b. Weak bases are poor conductors of electricity

• Therefore they must break up into few ions

• They are weak electrolytes

• They cause the bulb of a conductivity tester to glow faintly

2. Bases cause acid-base indicators to change color

a. litmus turn blue in base

b. phenolpthalien turns pink in base

c. Table M

3. Bases react with acids to form salt and water- neutralization reaction

a. HCl + NaOH NaCl + HOH

b. Known as a titration

4. Bases are caustic and have a slippery or soapy feeling

5. Names and formulas of some common bases are found on table L.

CONCEPTUAL DEFINITIONS

A. Stated in terms of inferences or interpretations of observed facts

B. Conceptual definitions of acids and bases

1. Theory 1: Arrhenius Theory

a. Arrhenius Acid

Substance whose water solution

contains hydrogen ions (H+) as the only positive ions in the solution

• Sometimes instead of H+ a problem will state that H3O+ or the hydronium ion is present.

• ALL FORMULAS FOR ACIDS CONTAIN AN “H” IN THE BEGINNING OF THE COMPOUND OR A –COOH GROUP AT THE END.

• Examples: HCl, HNO3, H2SO4, H3PO4

HCl (l) H+ (aq) + Cl- (aq)

H2SO4 (l) 2H+ (aq) + SO4 -2 (aq)

• Table K – has a list of some common

Arrhenius acids

b. Arrhenius base

• Substance whose water solution yield hydroxide ions(OH-) as the only negative ions in aqueous solution

• ALL BASES HAVE AN (OH) IN THEIR FORMULA EXCEPT NH3

• Examples: NaOH, KOH, NH4OH

NaOH(s) Na+ (aq) + OH- (aq)

• Table L has a list of some common Arrenius Bases

2. Theory 2: The alternate theory of acids and bases AKA:Bronsted-Lowry Theory-a.

Alternate Theory Acid orBronsted-Lowry Acid

1. Defined as a proton (H+) donor

Alternate Theory Base or Bronsted-Lowry Base

2. Defined as a proton (H+) acceptor

Bronsted-Lowry Reactions

1. Each reaction contains two acid-base pairs.

2. A pair differs only by a hydrogen,”H”

3. In the pair the species with the extra “H” is the B-L acid the other is B-L base

Examples:

HCl + H2O H3O+ + Cl-

NH3 (g) + H2O ↔ NH4+ (aq) + OH-(aq

AMPOHIPROTIC OR AMPHOTERIC SUBSTANCES

A. Definition: Substances that act as either an acid or a base depending on the chemical environment

B. Examples:

H2O + NH3↔ NH4+ + OH–

Water donates a proton and is acting as an acid

H2O + HNO3 ↔ H3O+ + NO3-

Water is accepting a proton and is acting as a base

Other Examples HSO4- , OH-, H2PO4

-, H2O,

HPO4-2

ACID-BASE REACTIONS IN AQUEOUS SOLUTIONS

A. Neutralization

1. A reaction in which equal molar quantities of acid and base are mixed

2. Acid + Base Salt + Water

• Salt is another name for an ionic compound

• The water is formed when the H+ from the acid combines with the OH- from the base

• What is left combines to form the salt

• Look for the word titration to indicate a neutralization reaction.

B. Acid-Base Titrations

1. Volumetric analysis performed by adding measured volumes of a base of known molarity to an acid of unknown molarity. (or vice versa)

2. The acid or base of known molarity is called the standard solution

3. The endpoint (when neutralization is complete) occurs when moles of H+ equals moles of OH- . It is where the indicator changes color

• Calculating the Unknown molarity

• MaVa = Mb Vb

• Table T

• Ma=Molarity of H+ (Usually of acid)

• Va=Volume of Acid

• Mb= Molarity of (OH)- (Usually of base)

• Vb=Volume of base

5. Classification of acids

• Monoprotic acids have one H+ so Ma is the same as the concentration of the acid

Ex: HCl

• Diprotic acids have two H+ so Ma is twice the concentration of the acid

Ex: H2SO4

• Triprotic acids have three H+ so Ma is three times the concentration of the acid

• Ex: H3PO4

6. Examples:

a. You are titrating 62.00 ml of HCl with a 1.0M standard NaOH solution and the following data is obtained

Initial reading: 1.00 ml

Final reading: 45.62 ml

b. 25.0 ml of .25M H2SO4 is titrated with 35.0ml of NaOH solution of unknown concentration. Calculate the concentration of the NaOH solution

pH

1. Def: indicates the concentration of hydrogen ions (acid strength) in a solution

2. pH = -log[H+]

3. pH = 7 neutral [H+] = [OH-]

4. pH < 7 acidic [H+] > [OH-]

5. pH > 7 basic [H+] < [OH-]

6. [H+][OH-] =1X10-14

What is the pH of a solution of HCl with an [H+]of 1.0 x 10-13 M?

.pH = -log(1.0 x 10-13) hit 1.0 x 10-13 into your calculator then hit log button then take the negative of the answer

.pH = 13

What is the [H+] of an HCl solution with a pH of 5?

What is the [H+] and the pH of a solution whose [OH-] is 1 x 10-5?

7. A change of:

one pH unit represents a 10 fold change.

Two pH units represents a 100 fold change

Three pH units represents a 1000 fold change

Four pH units represents a 1000 fold change.

Example: If the pH decreases from 5 to 3 the substance has become 100 times more acidic.

• If the pH increases from 7 to 9 it has become 100 times less acidic or 100 times more basic

How to use Table M

If the pH is below the lower limit then the solution is the first color, if the pH is within the range the it is a mix of the two colors and if the pH is greater than the upper limit the color of the solution if the second color listed