Acids and Bases. Acid and Base Definitions 19.1 Acid Properties Water solutions of acids conduct...
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Transcript of Acids and Bases. Acid and Base Definitions 19.1 Acid Properties Water solutions of acids conduct...
Acid PropertiesAcid Properties Water solutions of acids conduct electricityWater solutions of acids conduct electricity Acids often react with metal to produce Acids often react with metal to produce
hydrogen gashydrogen gas Acids change color indicatorsAcids change color indicators Acid + Base Acid + Base → Salt + Water→ Salt + Water Acids have sour taste—don’t try thisAcids have sour taste—don’t try this Acids react with carbonates to produce Acids react with carbonates to produce
carbon dioxidecarbon dioxide Acids sting skinAcids sting skin
BasesBases
Water solutions of bases conduct Water solutions of bases conduct electricityelectricity
Bases change color indicatorsBases change color indicators Acid + Base Acid + Base → Salt + Water→ Salt + Water Bases have a bitter taste—don’t try thisBases have a bitter taste—don’t try this Bases react with fat to make soapBases react with fat to make soap Bases have slippery feelBases have slippery feel Strong bases are caustic to skinStrong bases are caustic to skin
The pH scale.The pH scale.pH = -log [H+]pH = -log [H+]
Examples:Examples:
1.1. Find the pH of a solution if Find the pH of a solution if the hydrogen ion the hydrogen ion concentration is 0.027M.concentration is 0.027M.
2.2. Find the pH of a solution Find the pH of a solution where 0.03 moles of HCl is where 0.03 moles of HCl is dissolved into 0.2 liters of dissolved into 0.2 liters of water.water.
1313 Oven Cleaner/DranoOven Cleaner/Drano
12 12 Hair removerHair remover
11 Ammonia11 Ammonia
10 Soap10 Soap
99 Baking Soda, bleach, antacidsBaking Soda, bleach, antacids
88 ShampooShampoo
77 Water, blood, eggs, baby shampooWater, blood, eggs, baby shampoo
66 Urine, milk, salivaUrine, milk, saliva
55 Coffee, bread, rainwaterCoffee, bread, rainwater
44 TomatoesTomatoes
33 Vinegar, soda, beerVinegar, soda, beer
22 Stomach acid, lemon juiceStomach acid, lemon juice
11 Battery acidBattery acid
pHpH of Various solutions
Acid & Base StrengthAcid & Base Strength
Strong acids and bases completely Strong acids and bases completely ionize (separate) in solutionionize (separate) in solution• Acids: Nitric, sulfuric, hydrobromicAcids: Nitric, sulfuric, hydrobromic• Bases: sodium hydroxide, potassium Bases: sodium hydroxide, potassium
hydroxide hydroxide Weak acids and bases slightly ionizeWeak acids and bases slightly ionize
• Acids: Acetic, carbonic, hydrofluoricAcids: Acetic, carbonic, hydrofluoric• Bases: Ammonium hydroxideBases: Ammonium hydroxide
Acid and Base TypesAcid and Base Types Monoprotic acidsMonoprotic acids
• HClHCl Monobasic basesMonobasic bases
• NaOHNaOH Diprotic AcidDiprotic Acid
• HH22SOSO44,,HH22COCO33
Triprotic AcidTriprotic Acid• HH33POPO44
Dibasic BasesDibasic Bases• Ca(OH)Ca(OH)22, Mg(OH), Mg(OH)22
“polyprotic”
© 2009, Prentice-Hall, Inc.
Some DefinitionsSome Definitions ArrheniusArrhenius
• An acid is a substance that, when An acid is a substance that, when dissolved in dissolved in water, increases the water, increases the concentration of hydrogen ions.concentration of hydrogen ions.
HCl → HHCl → H++ + Cl + Cl--
• A base is a substance that, when A base is a substance that, when dissolved in water, increases the dissolved in water, increases the concentration concentration of hydroxide ions.of hydroxide ions.
NaOH → NaNaOH → Na++ + OH + OH--
© 2009, Prentice-Hall, Inc.
Brønsted-Lowry Theory of Acids Brønsted-Lowry Theory of Acids and Basesand Bases
An acid is a proton donor.An acid is a proton donor. A base is a proton acceptor.A base is a proton acceptor.
HCl + HHCl + H22O → HO → H33OO++ + Cl + Cl--
HCl is an acid because it donates a HCl is an acid because it donates a proton to water.proton to water.
Hydronium Ion: HHydronium Ion: H33OO++ • This is a hydrated protonThis is a hydrated proton
Brønsted-Lowry Theory of Acids Brønsted-Lowry Theory of Acids and Basesand Bases
An acid is a proton donor.An acid is a proton donor. A base is a proton acceptor.A base is a proton acceptor. NaNa22COCO33 is a Bronsted-Lowry base because the is a Bronsted-Lowry base because the
carbonate ion accepts a proton from water.carbonate ion accepts a proton from water. Water is an acid because it donates a proton Water is an acid because it donates a proton
to the carbonate ion.to the carbonate ion.
COCO332-2- + H + H22O ↔ OHO ↔ OH-- + HCO + HCO33
--
Notice that we ignore the sodium ion because Notice that we ignore the sodium ion because it is neutral.it is neutral.
© 2009, Prentice-Hall, Inc.
Brønsted-Lowry Acids and Brønsted-Lowry Acids and BasesBases
A water molecule that gains a hydrogen ion A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion becomes a positively charged hydronium ion (H(H33OO++).).
19.1
© 2009, Prentice-Hall, Inc.
Lewis AcidsLewis Acids
Lewis acids are defined as electron-pair Lewis acids are defined as electron-pair acceptors.acceptors.
Atoms with an empty valence orbital can be Atoms with an empty valence orbital can be Lewis acids.Lewis acids.
© 2009, Prentice-Hall, Inc.
Lewis BasesLewis Bases
Lewis bases are defined as electron-pair Lewis bases are defined as electron-pair donors.donors.
Anything that could be a Brønsted-Lowry Anything that could be a Brønsted-Lowry base is a Lewis base.base is a Lewis base.
Lewis bases can interact with things other Lewis bases can interact with things other than protons, however.than protons, however.
•A A conjugate acid-base pairconjugate acid-base pair consists of consists of two substances related by the loss or two substances related by the loss or gain of a single hydrogen ion.gain of a single hydrogen ion.
19.1
Conjugate Acid-Base PairsConjugate Acid-Base Pairs
Conjugate Acids and Bases
The species that remains after a Brønsted-Lowry acid has given up a proton is the conjugate base of that acid.
aq + l aq + aq–2 3HF( ) H O( ) F ( ) H O ( )
Chapter 14
acid conjugate base
Conjugate Acids and Bases, continued
Brønsted-Lowry acid-base reactions involve two acid-base pairs, known a conjugate acid-base pairs.
aq + l aq + aq–2 3HF( ) H O( ) F ( ) H O ( )
Chapter 14
acid1 base2 base1 acid2
Conjugate Acids and Bases, continued
Strength of Conjugate Acids and Bases• The stronger an acid is, the weaker its
conjugate base
• The stronger a base is, the weaker its conjugate acid
g + l aq + aq–2 3HCl( ) H O( ) H O ( ) Cl ( )
Chapter 14
strong acid base acid weak base
Conjugate Acids and BasesStrength of Conjugate Acids and Bases
Proton transfer reactions favor the production of the weaker acid and the weaker base.
aq + l aq + aq–4 2 3 4HClO ( ) H O( ) H O ( ) ClO ( )
aq + l aq + aq–3 2 3 3CH COOH( ) H O( ) H O ( ) CH COO ( )
Chapter 14
stronger acid stronger base weaker acid weaker base
The reaction to the right is more favorable
weaker acid weaker base stronger acid stronger base
The reaction to the left is more favorable
Amphoteric Compounds
Any species that can react as either an acid or a base is described as amphoteric.
example: waterwater can act as a base
aq + l aq + aq–2 4 2 3 4H SO ( ) H O( ) H O ( ) HSO ( )
g + l aq aq–3 2 4NH ( ) H O( ) NH ( ) OH ( )
acid1 base2 acid2 base1
water can act as an acid
base1 acid2 acid1 base2
pHpH
pH = -log [HpH = -log [H++]] (acid concentration)(acid concentration) pOH = -log [OHpOH = -log [OH--] ] (base concentration)(base concentration)
For aqueous solutions at 25 For aqueous solutions at 25 °C:°C:• [H[H++] [OH] [OH--] = 1.0 x 10] = 1.0 x 10-14 -14 = K= Kww
This is called the “ion product constant” for This is called the “ion product constant” for waterwater
• pH + pOH = 14pH + pOH = 14
Amphoteric Compounds, continued–OH in a Molecule
• The covalently bonded IOH group in an acid is referred to as a hydroxyl group.
• Molecular compounds containing —OH groups can be acidic or amphoteric.
• The behavior of a compound is affected by the number of oxygen atoms bonded to the atom connected to the —OH group.
Section 3 Acid-Base Reactions
Other Acid Base FactsOther Acid Base Facts
Water is able to self ionizeWater is able to self ionize
HH22O + HO + H22O O H H33OO++ + OH + OH--
When H+ ion are in solution, they When H+ ion are in solution, they always join with a water molecule to always join with a water molecule to form a hydronium ionform a hydronium ion
HH++ + H + H22O O H H33OO++
KKaa Acid Ionization Constant Acid Ionization Constant
KKaa = [H = [H++] [A] [A--]]
[HA] [HA]A 0.1M solution of ethanoic acid is found to have A 0.1M solution of ethanoic acid is found to have [H+]=4.2 x 10[H+]=4.2 x 10-3-3. Calculate the acid dissociation . Calculate the acid dissociation constant.constant.
KKaa = [H = [H++] [A] [A--]] [HA] [HA]
KKa a = (4.2 x 10= (4.2 x 10-3-3)(4.2 x 10)(4.2 x 10-3-3) = 1.8 x 10) = 1.8 x 10-4-4
0.1 - 4.2 x 100.1 - 4.2 x 10-3-3
Buffer SolutionsBuffer Solutions Solutions that resist change in pH when acids or Solutions that resist change in pH when acids or
bases are added to them.bases are added to them. Formed by mixing a weak acid and its saltFormed by mixing a weak acid and its salt
• HCHC22HH33OO22 + NaC + NaC22HH33OO22
When NaOH is added to the solution, HCWhen NaOH is added to the solution, HC22HH33OO2 2
reacts and consumes the OHreacts and consumes the OH-- ions ions When HCl is added to the solution, the HWhen HCl is added to the solution, the H++ ions ions
react with the acetate ions from the saltreact with the acetate ions from the salt
Results: buffer solution resist changes in pH!Results: buffer solution resist changes in pH! Buffer solutions are important in maintaining Buffer solutions are important in maintaining
blood pH.blood pH.
Amphoteric SubstancesAmphoteric Substances
Substances that can act as acids or basesSubstances that can act as acids or bases• Remember:Remember:
Acids are proton donorsAcids are proton donors Bases are proton acceptorsBases are proton acceptors
Ex. Bisulfate ion: HSOEx. Bisulfate ion: HSO44--
HSOHSO44- - ++ HH+ + →→ H H22SOSO44
HSOHSO44- - ++ OHOH- - →→ H H22O + SOO + SO44
2-2-
TitrationTitration
Titration is the process of determining the Titration is the process of determining the concentration of an unknown solution concentration of an unknown solution through volumetric analysisthrough volumetric analysis
When an acid and base are mixed, for When an acid and base are mixed, for neutralization to occur:neutralization to occur:
nnAA=n=nBB
MMacidacid x V x Vacid acid = M = Mbasebase x V x Vbasebase
Microscopic viewMicroscopic viewof the solutions of the solutions
in the titration of in the titration of 0.200 0.200 MM HNO HNO33
with 0.100 with 0.100 M M NaOH.NaOH.
End point is when the color change occurs
Macid x Vacid = Mbase x Vbase
0.2M x 50mL = 0.1M x Vbase
Vbase = 100mL
The pH curve for the titration of 50.0 mL of The pH curve for the titration of 50.0 mL of 0.200 0.200 MM HNO HNO33 with 0.100 with 0.100 M M NaOH.NaOH.
Titration ProblemsTitration Problems
A solid mixture contains NaOH and A solid mixture contains NaOH and NaCl. If 10 ml of 0.1 M HCl is required NaCl. If 10 ml of 0.1 M HCl is required to titrate a 0.1 g sample of this to titrate a 0.1 g sample of this mixture to its end point, what is the mixture to its end point, what is the percent NaOH in the sample? percent NaOH in the sample?
1 mole of HCl neutralizes 1 mole of 1 mole of HCl neutralizes 1 mole of NaOHNaOH
How many moles of HCl are How many moles of HCl are required to complete titrationrequired to complete titration
Titration ProblemsTitration Problems
20 ml of an aqueous base Ca(OH)20 ml of an aqueous base Ca(OH)22 is used is used in titration with a color indicator. If 25 ml in titration with a color indicator. If 25 ml of 0.05M HCl is required to reach the end of 0.05M HCl is required to reach the end point, what is the concentration of the point, what is the concentration of the Ca(OH)Ca(OH)22??
Balance Equation:Balance Equation:2HCl + Ca(OH)2HCl + Ca(OH)2 2 → CaCl→ CaCl22 + 2H + 2H22OO
moles of acid = 2 x moles of basemoles of acid = 2 x moles of base• Therefore Therefore MMacidacid x V x Vacid acid = 2 x M = 2 x Mbasebase x V x Vbasebase