Acids and Bases Chapters 20-21
Mar 26, 2015
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