Acids and BasesChapters 20-21

Properties of Acids• Sour taste

• Change the color of dyes known as acid-base indicators (turns litmus red)

• React with bases to produce a salt (ionic compound) and water

• Electrolytes (aqueous solutions will conduct electric current)

• Can react with active metals to give off hydrogen gas (H2)

Definitions of Acids

• Lewis: atom or molecule that is an electron-pair acceptor

Arrhenius (traditional): compound that contains hydrogen and ionizes in solution to form hydrogen ions (H(H++))

•Bronsted-Lowry: molecule or ion that is a proton (H(H++)) donor

Number of Protons in Acids

• Monoprotic acids can donate one H+ ion per molecule

Examples: HCl, HNOHCl, HNO33, HBr, HClO, HBr, HClO44

• Diprotic acids can donate two H+ ions per molecule

Examples: HH22SOSO44, H, H22SeSe

• Triprotic acids can donate three H+ ions per molecule

Example: HH33POPO44

• Polyprotic acids can donate more than one H+ ion per molecule H2SO4       H

+ + HSO4-

HSO4-       H+ + SO4

2-

Hydronium IonHydronium Ion

• The terms hydrogen ion (H+), proton (p+), and hydronium ionhydronium ion (H(H33OO++)) are used interchangeably

•Hydrogen ion (H+) in an aqueous solution (H2O) becomes HH33OO++

•HH33OO++ is known as a hydronium ionhydronium ion

Naming Acids (Review)

• OxyacidsOxyacids contains more than two elementstwo elements (H, O, and

33rdrd element) element) (a cation, H+, and a polyatomic anion with O)

•Binary AcidsBinary Acids

contain two elementstwo elements

(a cation, H+, and a monatomic anion)

hydro______ic acidhydro______ic acid

________ous acid________ous acid (-ite ion goes with –ous ending)(-ite ion goes with –ous ending)

________ic acid________ic acid (-ate ion goes with –ic ending)(-ate ion goes with –ic ending)

Oxyacid Naming Series

per______ic acid most oxygen’s

______ic acid goes with –ate anion

______ous acid goes with –ite anion

hypo______ous acid least oxygen’s

Properties of BasesProperties of Bases

• Bitter taste

• Change the color of dyes known as acid-base indicators (turns litmus blue)

• React with acids to produce a saltsalt (ionic(ionic compound)compound) and water and water

• Electrolytes Electrolytes (aqueous solutions will conduct electric current)

• Feel slipperyslippery to the skin

• Basic substances are referred to being “alkaline."

Definitions of Bases

• Lewis: atom or molecule that is an electron-pair donor

•Arrhenius (traditional): compound that contains hydroxide and dissociates in solution to form hydroxide ions (OH-)

•Bronsted-Lowry: molecule or ion that is a proton (H+) acceptor

Naming Bases (Review)• Name as ionic compound• Cation Cation named first, anionanion named second • Potassium Chloride KCl • All transition metals and PbPb and SnSn need

Roman numerals to denote their charge. (Zn, Ag, and Cd don’t need Roman (Zn, Ag, and Cd don’t need Roman numerals.)numerals.)

• Change ending of all nonmetals to –ide–ide to name their monatomic anion.monatomic anion.

• Polyatomic ionsPolyatomic ions must be memorized! Review them if you have forgotten.

Name the Following:

1. H3PO4

2. Ba(OH)2

3. HClO2

4. H3N5. Al(OH)3

6. HIO3

7. H2SO3

8. HBr9. Cu(OH)2

10. H2S

phosphoric acidbarium hydroxidechlorous acidhydronitric acidaluminum hydroxideiodic acidsulfurous acidhydrobromic acidcopper (II) hydroxidehydrosulfuric acid

Neutralization• Acid + Base Ionic Compound + H2O

• The ionic compound formed from the reaction of an acid and a base is known as a salt. It is formed from the cation of the base and the anion of the acid.

• The cation from the acid (H+) and the anion from the base (OH-) form the water

• Hydrolysis: reaction between water and ions of a dissolved salt; causes water to dissociate into H+ and OH- ions

Write balanced equations:

• barium hydroxide solution mixed with phosphoric acid

• aqueous sodium hydroxide neutralized with hydrochloric acid

• aluminum hydroxide solution mixed with chloric acid

• sulfuric acid reacted with aqueous magnesium hydroxide

Answers:

3 Ba(OH)2 (aq) + 2 H3PO4 (aq) Ba3(PO4)2 (s) + 6 H2O (l)

NaOH (aq) + HCl (aq) NaCl (aq) + H2O (l)

Al(OH)3 (aq) + 3 HClO3 (aq) Al(ClO3)3 (aq) + 3 H2O (l)

H2SO4 (aq) + Mg(OH)2 (aq) MgSO4 (aq) + 2 H2O (l)

Info for Hydrolysis Worksheet

• strong acids (ionize 100% in solution):

HClO4, HNO3, H2SO4, HI, HBr, HCl

• strong bases (ionize 100% in solution):

Hydroxides of Groups 1 and 2 on Periodic Table

• If they’re not strong, we assume they are weak!

Bronsted-LowryConjugate Acid-Base Pairs

Remember, B-L Acid: HAcid: H++ donor donor B-L Base: HBase: H++ acceptor acceptor

When an acid is dissolved in water, the acid (HA) donates a proton to water to form a new acid (conjugate acidconjugate acid) and a new base (conjugate (conjugate base)base)

HA (aq) + H2O (l) H3O+ (aq) + A- (aq) acid base conjugate acid conjugate base

H+ H+

Bronsted-Lowry Acid Conjugate Base

HA

HCl

HNO3

H2SO4

HSO4-

H3O+

H2O

A-

Cl-

NO3-

HSO4-

SO4-2

H2O

OH-

A few more items:

• Amphoteric: any species that reacts as either an acid or a base

• strong acids have weak conjugate basesweak conjugate bases• weak acids have strong conjugate basesstrong conjugate bases

• strong acids (ionize 100% in solution):

HClOHClO44, HNO, HNO33, H, H22SOSO4, 4, HI, HBr, HClHI, HBr, HCl

• strong bases (ionize 100% in solution): Hydroxides of Groups 1 and 2 on Periodic TableHydroxides of Groups 1 and 2 on Periodic Table

pH notespH notes• The pH scale ranges from 0 to 14. The pH scale ranges from 0 to 14.

• Any substance with a pH below 7pH below 7 is classified as an acidacid

• Any substance with a pH above 7 is classified as a base.base.

• Substances with a pH of 7pH of 7 are said to be neutral.

(Pure water has a pH of 7.)(Pure water has a pH of 7.)

• __________________________________________________________________________

• | | | | | | | | | | | | | | |

• 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

strong acid weak acid neutral neutral weak base strong base

Calculating pH

• See typed notes

Concentration Comparisons

• [H+] > [OH-]

• [H+] < [OH-]

• [H+] = [OH-]

neutral

basic

acidic

TitrationTitration• Titration is the method used to

determine the concentration of a solution (usually an acid or base).

• A solution of known concentration (the standard) is added to a measured amount of the solution of unknown concentration until an indicator signals the endpoint.

• The endpoint occurs when equivalent amounts of H+ and OH- have reacted in a titration, thus neutralizing the resultant solution.

Indicators• Acid-base indicators are dyes

used in titrations whose colors are sensitive to changes in pHchanges in pH, or hydronium ion concentrationhydronium ion concentration.

•There are many indicators, each indicative of a different pH range. For most titrations, a neutralization neutralization reaction is desired.

•For a strong acid and strong base, the chosen indicator will change near the neutral point at a pH of 7.

•Examples:Examples: phenolphthalein phenolphthalein (changes from clear in acid to pink in basepink in base) and bromothymol bluebromothymol blue (changes from yellowyellow in acid to blueblue in base)

Sample Titration

• 50. mL of 0.1 M HCl50. mL of 0.1 M HCl when titrated with • 0.1 M NaOH0.1 M NaOH should take just over 50. mL50. mL to cause

a color change • because it is a monoprotic strong acidmonoprotic strong acid being

neutralized by a group I hydroxide strong base.group I hydroxide strong base. • (For this titration, we would choose an indicator

that changed color at a pH of 7pH of 7 or neutral to indicate that the acid had been fully neutralized by the added base.)

• 0.1 M H0.1 M H22SOSO44 substituted in the above problem would have a different effect since the HH++ ion ion concentration would change for a diprotic aciddiprotic acid

Titration Equation

MMaaVVaa = M = MbbVVbb

• In titrations between acids and bases, neutralization is required so the [H[H++] = [OH] = [OH--]]

• In order to take this into account, our equation becomes

nbMaVa = MbVbna

# of H+ ions in base

# of OH- ions in acidMolarity

of acid

Molarity of base

volume of acid

volumeof base

AmphotericAmphoteric

Functions as an Base or Acid