Acids and Bases

Electrolytes

• Substance that conducts electricity when dissolved in water

• Ionizes in water

Examples: aqueous ionic solutions, acids, bases

Properties of Acids

• Acids have a pH less than 7.0• Acids will burn your skin• Dilute acids have a sour taste• Strong acids are good conductors of electricity• Acids react with bases to form water and a salt

(neutralization reaction)• Acids react with certain metals to produce

hydrogen gas– Metals above H2 will react with acids to produce H2(g)

Properties of Bases

• Bases have a pH greater than 7.0

• Bases have a slippery or soapy feeling

• Dilute bases have a bitter taste

• Strong bases are good conductors of electricity

• Bases react with acids to form water and a salt (neutralization reaction)

Common Acids and Bases

pH Scale

• Scale ranges from 0-14

• Acids = pH less than 7

• Bases = pH greater than 7

• Neutral = pH = 7

pH of common substances

• Common indicators are listed in Table M

Examples:

1. What color will thymol blue be in a solution with a pH of 6.5?

2. What color will methyl orange turn if a solution has a pH of 7.0?

3. What color will phenolphthalein turn in an acid?

Indicators

Arrhenius Theory

• Definition of acids and bases• Acids – substances whose water solution

contain hydrogen ions (H+), ionize to produce H+

• Bases – substances whose water solutions contain hydroxide ions (OH-), ionize to produce OH-

• Properties of acids and bases are due to an excess of H+ or OH- ions

Hydrogen/Hydronium

• H+ cannot exist unbonded in a system; instead it is bonded with a water molecule to make the hydronium ion (H3O+)

• H+ and (H3O+) are both used to indicate the presence of an acid

Bronsted-Lowry Theory

• Acids – donate/lose H+

• Bases – gain H+

Example: NH3 + H2O NH4+ + OH-

• H2O is the

• NH3 is the

Strength of Acids/Bases

• Strength is proportional to the degree to which it ionizes in solution

• Greater dissociation (more ions), stronger

Ionization Constant for Water Kw

• For pure water, at 25oC– Kw = 1.0 x 10-14 = [H+][OH-]

• Kw is a constant– therefore [H+][OH-] = 1.0 x 10-14

• Examples:1. Find the [OH-] concentration if [H+] = 10-8

2. Find the [H+] concentration if [OH-] = 10-3

3. Find the [OH-] concentration if [H+] = 10-7

* Exponents add up to -14

Hydrogen Ion Concentration (pH)

• used for convenience• pH = -log [H+]• Examples:

1. [H+] = 1.0 x 10-7, pH = 2. 2. [H+] = 1.0 x 10-3.5, pH =

• Acids: pH is lower than 7, [H+] is greater than [OH-]

• Bases: pH is greater than 7, [H+] is less than [OH-]

Hydroxide Ion Concentration (pOH)

• pOH = -log [OH-]

• Since [H+][OH-] = 1.0 x 10-14

• pH + pOH = 14

• Examples: 1. Find the pOH of a solution with a pH = 8. Is

this solution acidic or basic?

2. Find the pH of a solution with a pOH = 12. Is this solution acidic or basic?

Concentration and pH

• A change of 1 in pH is a tenfold increase in acid or base strength– A pH of 4 is 10 times more acidic than a pH of

5– A pH of 12 is 100 times more basic than a pH

of 10

Mono/Di/Triprotic

• Monoprotic acids – produce a single hydrogen ion– Examples: HCl, HBr

• Diprotic aicds – produce two hydrogen ions– Examples: H2SO4, H2S

• Triprotic acids – produce three hydrogen ions– Examples: H3PO4

Neutralization Reactions

• An acid and a base react together to form water and an ionic salt

Examples:

1. HCl + NaOH H2O + NaCl

2. H2SO4 + Ca(OH)2 2H2O + CaSO4

3. HNO3 + Ca(OH)2

Acid-Base Titrations

• Process of adding a measured volume of an acid (or a base) of known molarity to a base (or an acid) of unknown molarity until neutralization occurs– Standard Solution – acid or base of known

molarity– End Point – point of neutralization

• Unknown molarity is calculated using the titration formula

Titration

• MAVA = MBVB equation• MA = Molarity of H+

• MB = Molarity of OH-

• Moles of acid = moles of base (moles = molarity x liters)

Titration Examples

1. What volume of 1.0M sulfuric acid can be neutralized by 50.0mL of 3.0M sodium hydroxide?

2. 50.0mL of a 0.250M KOH are needed to neutralize 20.0mL of a HCl solution of unknown concentration. What is the concentration of the HCl?