IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents*For centuries people had known that vinegar, lemonjuice,apple and many other food items taste sour. But they didn’tknow that their sourness comes from their specific acids. The termacid comes from the Latin word “acere” ,which means sour. In the17thcentury,the English Chemist Robert Boyle grouped substances aseither acids or bases, but he couldn’t explain their behavior. Thefirst logical definition wouldn’t be coined until 200 years later.In this presentation ,we will focus on acid-base reactions inaqueous solutions. such solutions play important roles in our dailylives.The Authors
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsContent1. Acid-Base Theories1.a. The Arrhenius Acid-Base Theory1.b. The BrФnsted-Lowry Acid-Base Theory1.c. The Lewis Theory1.d. General Properties of Acids1.e. General Properties of Bases2. Ionization of Water3. The pH Scale4. Strength of Acids and Bases4.a. Acid Strength4.b. Base Strength5. Neutralization
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1. Acid-Base Theories1.a. The Arrhenius Acid-Base TheoryIn 1884, Swedish chemist SvanteArrhenius defined acids as compoundsthat produce H+ ions in aqueoussolutions,and base as compounds thatproduce OH-- ions in aqueous solutions.For example,HCL and are HNO3 Arrheniusacids.HCL(aq) ------------→ Cl - (aq) + H+ (aq)HNO3 (aq) ---------- → NO 3- (aq) + H+ (aq)
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1. Acid-Base TheoriesNaOH and Ba(OH)2 are example ofArrhenius bases. These basesrelease OH-- ions in aqueous media.NaOH(aq) ------------→ Na+(aq) + OH - (aq)Ba(OH)2 (aq) ----------→ Ba2+(aq) + 2OH - (aq)In water, the H+ ion of acid isattracted to a water(H2O) moleculeto produce hydronium ion (H3O+ )
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1. Acid-Base Theories• The Arrhenius acid-base theory isinsufficient to explain the acidicor basic properties of somesubstances,such as SO2 and NH3since these don’t have H + andOH- ions in their structures. Forthese molecules,another theorymust be applied,since theArrhenius acid-base theory canonly be applied to aqueoussolutions.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1.Acid-Base Theories1.b. The The BrФnsted-Lowry Acid-Base TheoryIn 1923,Johannes BrФnsted and his English counterpart Thomas Lowryindependently developed a more general acid-base theory. According to theBrФnsted-Lowry model,an acid is a proton donor and a base is a proton acceptor.Each proton donor(acid) has its pair(conjugate) proton acceptor base.For example:NH3(Base 1)H2O(Acid 2)OH-(Base 2)NH4+(Acid 1)Conjugate acid-base pairConjugate acid-base pair
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsExampleSolution:H2S give H+ (proton) to H2O (proton accceptor), so itis an acid. In the same way, H2O accepts one H+(proton) from H2S (proton donor). Thus it is abase.H2S (g) + H2O (l) ↔ H3O+ (aq) + HS- (aq)find the conjugate acid-base pairs for the abovereaction.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1.Acid-Base TheoriesNH3 and NH4+ form a conjugate acid-base pair,where NH3 is the conjugate base ofNH4 (NH4+ is the conjugate acid of NH3). Similarly, H2O and OH- are conjugates ofeach other.A model of Acid-Base reaction between NH3 and H2OHOHHNHHHOHNHHH
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1.Acid-Base Theories1.c. The Lewis Acid-Base Theoryin 1923, American chemist,Gilbert N.Lewis definited acid and base considered tochemical bond theory. According to Lewis opinion that acid is compound thataccept the pair of free electron. And base is compound that donor the pair of freeelectron.the example of The Lewis Acid-Base theory:B BFFFFFFFF
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1.Acid-Base Theories1.d. General Properties of AcidsThe General properties of Acids can be summarized as:1.The aqueous solutions of acids conduct electricity2. Acids change the color of litmus paper to red3. Acids have a sour taste (such as vinegar and lemon)4. Acids are corrosive substances.5. Acids react with active metals and produce hydrogen gas.For example:2Al(s) + 3H2SO4(aq) → Al2(SO4)3 (aq) + 3H2(g)Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2 (g)
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents6. Acids react with bases to produce salt and water,this reaction is called aneutralization reaction.For example:NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)7.Inert metals (Cu,Hg,Ag,Pt,Au) do not react with binary acids(HCl,HBr,…).Cu,Hg,and Ag can react with strongoxyacid such as HNO3 and H2SO4.For example:3Cu(s) + 8HNO3(aq) →(dilute) → 3Cu(NO3)2 (aq) + 2NO (g) + 4H2O(l)8. Acids react with carbonate salts of metal.For example:MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l)
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents1.Acid-Base Theories1.e. General Properties of BasesThe General properties of Bases can be summarized as:1.The aqueous solutions of Bases conduct electricity2. Bases change the color of litmus paper to blue3. Bases have a bitter taste4. Strong bases are corrosive5. Basic solutions cause slippery skin6. Bases do not react with most metals. However, strong bases(KOH,NaOH)react with amphoteric metals such as aluminium(Al), zink(Zn),and producehydrogen gas.For example:2Al(s) + 6NaOH(aq) → 2Na3AlO3(aq) + H2(g)Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2 (g)
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents2. Ionization of WaterSome molecules and ions act as acids or bases depending on the conditionsof the reaction are called amphoteric.A water molecule acts as an acid when it donates a proton, and acts as abase when it accepts a proton, as given below:H2O(l) +H2O(l) ↔ H3O+(aq) + OH-(aq)OHOHOHOHHHHH
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents2. Ionization of WaterThe equilibrium sconstan expression for the reaction is:Kw is the equilibrium constant used in equations to refer to ionization of water.Kw= 1,0 . 10-14 at 250C[H3O+ ] = [OH-] for the neutral medium. Then,1 . 10-14 = [H3O+ ] 21. 10-7 = [H3O+ ][H3O+ ] = [OH-] = 1. 10-7 MKw = [H3O+ ] [OH-]
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents3. The pH ScaleThe acidity or basicity of a solution can be described in terms of its H3O+ or OH- ionconcentrations.These concentrations are usually small. For example,H3O+ ion concentration is 1.10-7 Min the neutral solution. Thus,the concentration of H3O+ is generally expressed asthe negative logarithm. This is known as pH. From now on, for simplicity H+ will beused instead of H3O+andIn a similar,the way negative logarithm of [OH-] is pOHandpH = -log [H+]pOH= -log[OH-] [OH-] = 10-pOH[H+] = 10-pH
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsFor pure water at 250C,[H+] = 1. 10-7 [OH-] = 1. 10-7pH = - log (1. 10-7) pOH = - log (1. 10-7)pH = 7 pOH = 7Since [H+] [OH-] = 1. 10-14 aThe pH value of a solution gives an idea about the condition of a solution as follows:If pH < 7,0If pH = 7,0 solution is neutralIf pH > 7,0pH + pOH = 14Solution is acidicSolution is basic
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentspH is measured by using a pH meter. A pH meter translates H+ionconcentrations in solutioninto an electrical signal that is converted into a digitaldisplay0 1 2 3 4 5 6 7 8 9 10 11 12 13 14pure water baking powderAcid in stomach vinegar coffe rain water blood soap householdlemon juice tomato bread milk sea water amonniajuicepH scaleH+ CONCENTRATION, [H+] in mol/L100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsA less accurate way to mesure pH is to use indicators. An indicator is acompound such as phenolphthalein or methyl orange, that is changes colorreversibility at different pH values. For exampe, phenolphthalein is a colourlesssubstance in any solution with a pH value smaller than 8,3 it turns red-violet insolution with a pH value greater than 8,3.Indicator Acidic BasicPhenolphthalein Colorless Red-violetMethyl orange Red Orange-yellowLitmus Red Blue
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents4. Strength of Acids and Bases4.a. Acid StrengthAcids are classified as strong and weak, depending upon theirdegree of ionization inwater. A weak acidionizes in water reversibly to form H3O+ions. A weak acid is a weakelectrolyte and its aqueous solution does not conduct electricity well. The dissociationreaction occurs to very small extent; usually,fewer than 1 percent of the HA molecules areionized. The ionized of a weak acid is shown as follows:HA(aq) + H2O(l) ↔H3O+(aq) + A-(aq)weak acid conjugate baseThe dissociation constant Ka,of a given acid iswritten as ;Ka refers to the acid dissociation constant which is measure of an acid’s strength. Somereferences call Ka the acid ionization constantIf Ka < 10-3, acid is generally said to be weakIf Ka = 1 to 10-3, acid is accepted as moderateIf Ka > 1 acid is strong.Ka=[H3O+] [A-] / [HA]
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsSome Ka values of acids are given in Table below.Name of acid Formula KaHydrochloric acid HCL 1.107Nitric acid HNO3 1.103Sulfuric acid H2SO4 22Oxalic acid (COOH)2 6,5 .10-2Phosphoric acid H3PO4 7,5 . 10-3Lictic acid C2H5OCOOH 1,38 .10-4Formic acid HCOOH 1,8.10-4Nitrous acid HNO2 4. 10-4Hydroflouric acid HF 7,2 .10-4Acetic acid CH3COOH 1,8 . 10-5
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents4. Strength of Acids and Bases4.2 Base StrengthThe dissociation of a weak base in water is illustrated as follows ;B(aq) + H2O(l)↔ BH+(aq) + OH-(aq)The equilibrium expression for the above weak base isKb is the base dissociation constant or baseionization constant, that measure a base’s strength.Kb= [BH+] [OH-] / [B]
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsSome Kb values of bases are given in Tablebelow.Name of base Formula KbPotassium hydroxide KOH 158,5Sodium hydroxide NaOH 10Methylamine CH3NH2 4,38 . 10-4Ethylamine C2H5NH2 5,6 . 10-4Ammonia NH3 1,8 . 10-5Pyridine C5H5N 1,7 . 10-9Aniline C6H5NH2 3,8 . 10-10
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents4. Strength of Acids and Bases4.c. Relationship between Ka and KbDissociation constants of weak acids and basescan be determined in the laboratory. However, itis easy to find the Ka or Kb values of acids orbases by using a simple mathematicalexpression between Ka and Kb of conjugate acid-base. The multiplication of Ka and Kb ofconjugate acid-base is Kw.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents4. Strength of Acids and BasesKw = Ka . Kb = Kb . Ka = 1 . 10-14For example NH4+ - NH3 is a conjugate acid base.I. NH3 + H2O ↔ NH4+ + OH- K1 = Kb of NH3II. NH4+ + H2O ↔ NH3 + H3O+ K2 = Ka of NH4+2H2O ↔ H3O+ + OH- Kw = K1 . K2
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsExampleWhat is the Ka value of NH4+ if the Kb of NH3 is1.8 x 10-5 ?Solution:NH3 + H2O ↔ NH4+ + OH-NH4+ is the conjugate acid of NH3Kb for NH3 is 1,8 x 10-5
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContents5. NeutralizationThe reaction of an acid and a base solution to form saltand water is called a neutralization reaction. Indeed,aneutralization reaction is a reaction hydrogen(H+) ions andhydroxide(OH-) ions to form water. In neutralization,all H+ andOH- ions coming from acid and bases turn into H2O. Thereaction between HCl(aq) and NaOH(aq) is an example of aneutralization reaction.HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)The net ionic equation for this reaction isH+(aq) + OH- (aq)→ H2O (l)
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsThe nature of the particular acid and base involved in a reaction determines theacidity or basicity of the resulting solution.1 .Neutralization of a strong acid and strong base gives a neutral solution.HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)The resulting NaCl salt is neutral2. Neutralization of a strong acid and a weak base gives a acidic solution.HCl(aq) + NH3(aq) → NH4Cl(aq) + H2O(l)NH4Cl is called acidic salt3. Neutralization of a weak acid and a strong base gives a basic solution.CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)CH3COONa is called basic salt4. Neutralization of a weak acid and a weak base gives a complex type of acid-basesolution. If weak acid and weak base have the same strength,the solution isneutral. If the strength of an acid and base are not equal,the solution will be eitheracidic or basic,depending on the strength of either.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsSupplementary Questions2. What is the pH of a solution prepared bydissolving 0.8 g NaOH in water to make 200mL solution ?3. How many moles of HCl are found in 500 mLof HCl solution, whit a pH of 3 ?4. How many millilitres of 0.01 M NaOH arerequired to neutralize 50 mL of 0.02 M HCl ?
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsSupplementary Questions5.I IIafter mixing the solutions, what would bethe pH of the final solution ?
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossaryAcid : A substance that produces hydrogen ionsin solution. A proton donor substance.Acid dissociation constans (Ka) : The equilibriumconstant for weak acids.Aqueous solutions : solutions in which water isthe solvent.Arrhenius concept : A concept stating that acidsproduce hydrogen ions and bases produchydroxide ions in aqueous solution.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossaryBase : A substance that produces hydroxide ionsin aqueous solution. A proton acceptor substanceBase dissociation constans (Kb) : the equilibriumconstans for the reaction of a base with water toproduce the conjugate acid and hydroxide ion.Chemical bond : The force, or energy, that holdsatoms together in a compound.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossaryConjugate acid : The specie formed when aproton is added to a base.Conjugat acid-base pair : two species related toeach other by donating and accepting of a singleproton.Conjugat base : What remains of an acidmolecule after a proton is lost.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossaryEquilibrium : The position where the rate offorwad and reverse reaction becomes equal.Indicator : A chemical that changes color and isused to mark the end-point of a titration.Ion-product constant (Kw) : the equilibriumconstant for water.Lewis acid : An electron-pair acceptor
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossaryPolyprotic acid : an acid with more than oneacidic proton. It dissociates in a stepwisemanner, one proton at a time.Salt brige : A U-shaped tube containing anelectrolyte that connects the two compartmentsof a galvanic cell without extensive mixing of thedifferent solutions.
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsGlossarySolution : A homogeneous mixture.Strong base : A metal hydroxide salt thatcompletely dissociates into its ions in water.Weak acid : An acid that dissociates only slightlyin aqueous solution.Weak base : A base that reacts with water toproduce hydroxide ions to only a slight extentain aqueous solution.
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IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsReferences• Ratcliff B., Eccles H., and others, AS Level andA level Chemistry. Cambridge UniversityPress, UK : 2005• Oxtoby, D.W., Nachtrieb, N.H., Principals ofModern Chemistry. 3rd Ed., Saunders CollagePublising, USA : 1996
IntroductionGlossary ReferencesSupplementaryQuestionsMaterialContentsReferences• Sevenair, J.P., Burkett, A.R., IntroductoryChemistry. Investigating the MolecularNature of Matter. WBC Publishers, USA :1997• Prescott, C.N., Chemistry A Course for “0”Level. Times Media Privat Limited, Singapore :2000