6. ACIDS AND BASES. Based on apparent properties, Robert Boyle classified the substance into acids and bases.

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1 6. AIDS AND BASES Synopsis: Bsed on pprent properties, Roert Boyle clssified the sustnce into cids nd ses. Acids Bses. Sour to tste Bitter to tste. Turn lue litmus to red Turn red litmus to lue. Neutrlise ses Neutrlise cids. Lierte H gs on rection with metls They re sopy to touch 5. Aqueous solutions re good conductors Aqueous solutions re good conductors 6. They decompose metl crontes nd icro-ntes to lierte O According to Lvoiser ll cids must contin oxygen. But dry proved tht ll cids must contin Hydrogen ut not oxygen. Eg: Hl, HBr, HI, HF etc,. The chemicl ehviour of cids nd ses is explined y following three theories. ) Arrhenius theory ) Brnsted - lowery theory ) Hewis theory Bronsted Lowery theory of Acids nd ses: This is lso clled protonic theory. Acid : which dontes proton Eg: Hl, H SO, HNO etc. Bse : which ccepts proton Eg: NH, PH, N H, R NH etc. Bronsted cid could e neutrl molecule, nion, ction. Neutrl molecule Hl, HNO, H SO etc. tions H O, NH Anions, HO, H PO, H( PO ), H ( ) PO HSO Bronsted se could e neutrl, ction or nion Neutrl NH, PH, N H etc. nions N, Br, I, OH etc. tions [Al(H O) 5 OH), [Fe(H O) 5 OH Neutrlistion : It involves trnsfer of proton from cid to se nd formtion of conjugte cid se pir. ) Hl H A O B HO B A l A ) NH H O NH OH B A ) NH Hl NH l B A B A B Amphoteric or Amphiprotic sustnce : The ct s oth cids nd se ecuse they donte proton nd ccept proton. Eg : H O

2 Acids nd Bses onjugte cid se pirs : The cid se pir which differs y proton is clled conjugted cid se pir. Acid H conjugte se Bse H conjugte cid Eg : Acid Bse Hl l H SO HSO HSO H S H H SO HS H H [ Al ( H ) O [ ( ) 6 Al HO 5 OH Fe ( ) Fe ( H O ) [ H H O 6 [ H e 5OH H In ny conjugte cid se pir, if the cid is stronger, the se is wek nd if se is stronger, the cid is wek. Eg:. Hl is strong cid, l is wek conjugte se.. H OOH is wek cid H OO is strong se. NH is wek se, NH strong cid. HlO is strongest cid, lo wek se List of conjugte cid se pirs in prticulr order of strength. Acid Bse [Decreses cidic strength. HlO lo. HI I. HBr Br. H SO HSO 5. Hl l 6. HNO NO 7. H O H O 8. HSO SO 9. H PO H PO 0. HF F. H OOH H OO. H O HO. HN N. NH NH 5. H O OH

3 NH 6. NH 7. OH O H Acids nd Bses 8. H Strength of ronsted cids nd ronsted ses will depend on the ility to donte or to ccept proton. Strong cids : which hve more ility to donte protons. Eg: HlO, Hl, H SO Wek cids : which hve less tendency to donte proton. Eg: HF, H OOH, H O, HN Among Hydrcids HN is the wekest cid Strong ses : which hve greter tendency to ccept protons Eg: OH, H OO, H etc. Wek ses which hve less tendency to ccept the proton. Eg: l, lo, Br, I, NH..etc. Levelling effect : The strength of stronger cids like HlO, H SO, Hl, HNO will ecome equl to the strength of H O ion in presence of H O. This is clled levelling effect HlO H SO Hl HNO H O Similrly the strength of stronger ses like NOH, OH, soh will ecome equl to the strength of OH ion in presence of H O NOH OH soh OH This levelling effect of cids is due to greter proton ccepting tendency of H O nd instntly conversion into H O therefore the rel strength cnnot e determined. The cids like HlO, H SO etc. cnnot e determined in levelling solvent like H O. Therefore the strongest cid tht cn exist in wter is H O nd the strongest se tht cn exist is OH ion. In solvent like glcil cetic cid, the rel strength of cids cn e determined ecuse of poor tendency to ccept protons. Therefore cetic cid is differentiting solvent nd the strongest cid tht cn exist in cetic cid solvent is HlO. In cetic cid, HlO > H SO > Hl > HNO Types of solvents: Bsed on proton donting or proton ccepting tendency, solvents re clssified into types y ronsted lowery solvents. ) Protophilic solvents : which ccept proton Eg : H O, NH, ether, H 5 OH etc. Protophilic solvents will increse cidic strength nd decrese the sic strength. ) Photogenic solvents : which donte H protogenic solvents will decrese the cidic strength nd increse the sic strength. ) Amphiprotic solvents : which dontes nd ccept proton Eg : H O, H 5 OH ) Aprotic solvents: which neither dontes nor ccepts proton. Eg : l, Hl, 6 H 6, Acetone Merits of Bronsted Lowery theory : ) It could explin cid se ehviour in non queous solvents lso. Eg: liquid SO, liquid NH ) It could explin the sic nture of sustnces like NH. ) It could explin the cidic nture of Hl gs.

4 Acids nd Bses ) It is more generlized thn Arrhenius theory. Limittions of Bronsted Lowery theory : ) This theory explins ehviour of cids only when there is se (or) It explins ehviour of se only when there is cid. (Acid se pirs must e present) ) It fils to explin the cidic nture of electron deficient compound like BF, All etc. Lewis theory of cids ses : Acid : which ccepts electron pir. All electrophiles re Lewis cids Lewis cid must contin suitle vcnt oritls. Eg: BF, Bl, All, H, Ag etc. Bse : which dontes e pir. All nucleophiles re Lewis ses Lewis se must contin or more lone pirs of electrons. Eg: NH,PH, R NH, NH NH,OH, l, H O Neutrlistion: It involves formtion of coordinte covlent ond y the trnsfer of e pir form se to cid. H N BF [H N BF H O H [ H O H or H N H [ H N H or [ l All All O H NH l or Al l Types of Lewis cids : ) All simple ctions : Eg : H, Ag, Li, u, o, Al etc. Ag [ Ag( ) NH NH ) Electron deficient molecules : Eg: BF, Bl, BBr, BI, All, Gl etc. BF < Bl < BBr < BI [ F B BF BF F F or ) Molecules which cn extend octet configurtion: Eg: SiF, Sil, Snl, SF, SFl, Tel etc. SiF F F F F S F F F or SiF 6 ) Molecules with multiple onds in etween toms of different electronegtivities

5 Acids nd Bses Eg : O, SO, SO, NO, N O 5, l O 7, P O 5 δ δ O O OH O O OH or HO 5) Molecules in which the centrl tom with sextet configurtion Eg : S, O, Se.. O S O SO O S O O SO SO Types of Lewis ses : All simple nions : Eg : l, P, Br, OH, N etc. Sil l Sil 6 Molecules with lone pirs : Eg : NH,P H,N H,R NH,R OH, H O, R O R, R S etc. N H H [H N H or NH Moleculr multiple onds in etween similr toms: Eg: H H, H H, pyridine, : NO, : O H H H Ag H Ag Drw cks of Lewis theory : ) It will not consider populr cids like HlO, HNO, H SO s they do not form co-ordinte covlent ond. ) It fils to explin the ctlytic ctivity of H. ) Lewis cid se neutrlistion is very slow s it involves formtion of co-ordinte covlent ond ut ctully neutrlistion rections re very fst. ) It fils to explin strength of cids nd ses. 5) It fils to explin the simple neutrlistion rections where H is involved. IONISATION OF AIDS AND BASES AND DEGREE OF IONISATION Acids which donte protons re generlly known s protonic cids. These re represented s HX The compounds which contin OH - ions re generlly known s ses nd represented y BOH When cids re dissolved in wter, they ionised into H nd X - HO HX H X - When ses re dissolved in wter they ionised into B nd OH - BOH - HO B This process in known s ionistion sme time referred to s dissocition 5

6 The extent of hydrolysis is more for strong cids nd strong ses ( 00% ionistion) The extent of hydrolysis is less for wek cids nd wek ses The process of ionistion is n equilirium process HO HX H X () HO BOH B OH () The dissocition constnt of cid [ [ H X (sed on the eqution()) [ HX The dissocition constnt of se or se ionistion constnt [ [ B OH (sed on the eqution()) [ BOH For ny wek cid: HX H X - ( - α ) α α α ( α). α. α /. H α. H H 5. P P log α degree of ioniztion of cid molr concentrtion of cid ionistion constnt of cid For ny wek se:. α. α /. OH α OH. OH 5. P P log H OH 6. P P α degree of ionistion of se molr concentrtion of se ionistion constnt of se Acids nd Bses 6

7 Acids nd Bses omprison of cid se theories : ) All Arrhenius cids re ronsted lowery cids ut ll ronsted lowery ses re not Arrhenius ses. Eg: Hl (q) It is Arrhenius cid s it gives H nd ronsted lowery cid s it dontes proton. NH It is ronsted lowery se ecuse it ccepts proton ut it is not Arrhenius se s it will not give OH. ) All ronsted lowery ses re Lewis se ut Lewis cids need not e ronsted lowery cids. Eg: NH It is Bronsted lowery se ecuse it ccepts proton nd it is Lewis se ecuse it dontes e - pir. BF It is Lewis cid s it ccepts electron pir ut it is not ronsted lowery cid s it will not donte proton. Ionic product of wter : Pure wter is wek electrolyte tht is just one molecule out of 556 millions of wter molecules will ionise. Ionistion of wter : H O H OH (or) H O O OH H By pplying lw of mss ction to the ove ionistion rection. [H [OH [HO [OH (or) [HO [HO since the molr concentrtion of [H O is prcticlly constnt nd therefore or ω [H [OH ω ionic product of wter. ω is defined s the product of molr concentrtion of H nd OH ions. At 5 0, ω 0 - mol / lit. with n increse in temperture the vlue of k ω increse s the extent of ionistion of wter increses At given temperture the vlue of ω remins constnt for ny given dilute queous solution. i.e. neutrl (or) cidic (or) sic. In pure wter (or) neutrl queous solution. [H [OH 0 7 mol/lit [H 0 7 mol/lit [OH 0 7 mol / lit ω x 0 mol/ lit In cidic solution : [H > [OH [H > 0 7 [OH < 0 7 ω 0 In sic solution [OH > 0 7 [H < 0 7 ω 0 At 90 0 the concentrtion of H O ions is 0 6 mole/ lit in pure wter. The vlue of w is 7

8 Pure H O [H O [OH x 0 6 x 0 6 w x 0 mol / lit p H of solutions: It ws introduced y Sorensen to clculte lower concentrtions of H ion. p H is ve logrithm of H ion concentrtion. p H is logrithmic reciprocl of H ion concentrtion. P H is the negtive power rised on ten in order to express H ion concentrtion. p H log[h p H log [H [H 0 ph Even OH ion concentrtion cn e expressed on p H scle. p OH log(oh ) [OH OH 0 P For ny dilute solution; [H [OH 0 mol / litre P w p H p OH Other similr expressions: p OH Similrly k log[oh p log k k p log k p k ω p k log p M log kω k log[m M metl ion concentrtion 8 Acids nd Bses p H scle cids 7 ses neutrl The mximum concentrtion of H ion tht could e expressed on p H scle is 0. M. When [H 0.; p H. If [H more thn 0. p H is less thn [no provision for less thn on scle The mximum concentrtion of OH ion tht could e expressed on p H scle is M. When [OH M; p OH 0; p H if [OH more thn M; p OH < 0 nd p H > [no provision for more thn on p H scle P H scle is pplicle for dilute solutions. With increse in the concentrtion of [H, p H vlue decreses, p OH vlue increses. With increse in the [OH the p H vlue increses, nd p OH vlue decreses. With increse in temperture p H vlue decreses. At higher temperture, the extent of ionistion increses nd H ion concentrtion increses. There fore p H vlue decreses. Similrly OH ion concentrtion lso increses nd p OH decreses nd thus the entire p H scle contrcts. If [H ion concentrtion is incresed y 0 n times p H vlue decreses y n units. If [H ion concentrtion is decresed y 0 n times p H vlue increses y n units. If cid solution is diluted y 0 n times, p H vlue increses y n units.

9 If sic solution is diluted y 0 n times, p H vlue decreses y n units. P H of wek cids nd wek ses : Ionistion of wek cid(ha) : HA H A 0 0 α α α α.α α α α ( α) ( α is very less) Acids nd Bses α ; α / α. V v c Ostwld s lw of dilution explins the vrition of degree of ionistion with concentrtion. The degree of ionistion is inversely proportionl to its squre root of its concentrtion (or) directly proportionl to squre root of its dilution. [H α [H k ; [H log [H log. log[h log log. Ostwld s lw of dilution is pplicle for wek electrolytes (wek cid nd wek se) it is not pplicle to strong electrolytes ecuse they completely ionise t moderte concentrtion. The ehviour of strong electrolytes is explined y Deye Huckel s theory. log [H log k log p H k p log Ionistion of wek ses (MOH) : MOH M OH 0 0 ( α) α α α x α α α ( α is very less) ( α) α ; α α α. v [OH α [ OH. log[ OH log v c log 9

10 OH p p p p H H k w w For wek cids : p OH p log log [. [ H α ; H Acids nd Bses α Κ For wek ses : [ OH α ; OH. α [ For strong cids ; [H N of cid For wek cids ; [H < N of cid For strong ses; [OH N of se For wek ses; [OH < N of se Buffers : The solutions which mintin constnt p H vlue on ddition of cid or se. Resisting chnge in p H vlue on dding cid or se to uffer is clled Buffer ction. Buffers posses reserve cidity nd reserve lklity. Reserve cidity will nullify the effect of dded se nd reserve sicity will nullify the effect of dded cid. Blood uffer is H O NHO. Types of uffers: ) Acid uffers: It is the mixture of wek cid nd it s slt of strong se. H OOH H OON H O NHO Tetr oric cid Borx [p H > 7 H PO NH PO The p H of cid uffers is usully less thn 7 ut not lwys. ) Bsic uffers: It is mixture of wek se nd its slt of strong cid. NH OH NH l Glycine Glycine hydro chloride ) Norml slt of wek cid nd its cidic slt N O NH O N PO N HPO ) Slt of wek cid nd wek se Eg : H OONH ; HOONH 5) Ampholytes Amino cids proteins : Which of the following cn ct s uffer Action of Acid uffers: Eg : H OOH H OON Acetic cid mostly remins s unionised nd sodium cette is lmost completely ionised. Therefore the components present in the ove uffer re 0

11 Acids nd Bses (H OOHH OO N ) If little strong cid (H ) is dded to the ove uffer, the dded strong cid will convert into wek cid. Thus the effect is nullified. H OO H H OOH If little strong se (OH ) is dded to uffer, the dded strong se is converted into wter (H O). Thus the effect of dded se is nullified. H OOH H H OO H O Thus cid uffer cn resist chnge in p H on ddition of little mount of cid or little mount of se. In the ove uffer the reserve cidity is due to H OOH nd reserve sisity is due to H OO. Action of Bsic uffer : Eg : NH OH NH l NH OH ionizes to very smll extent nd NH l eing slt ionizes completely. Therefore the components present in the ove uffer re [NH OH NH l The reserve cidity of the ove uffer is due to NH nd reserve scity is due to NH OH. If strong cid [H is dded to uffer, it is converted into H O H NH OH NH H O If strong se [OH is dded to uffer, it will convert into wek se NH OH NH OH Thus n cid uffer or sic uffer cn mintin constnt p H vlue y dding cid s well s se. P H of Buffers : [Henderson s eqution Deriving p H expression for Acid uffer : HA H A (wek cid) [H [A [HA [HA [ H [A Acid [ A Slt [ most of the A concentrtion comes from slt By pplying log on oth sides. Acid log[ H log log slt H Acid p p log slt H slt p p log cid Deriving p H expression for sic uffer : BOH B OH (wek se) [B [OH [BOH

12 [BOH [ OH [B se [ OH slt Acids nd Bses [ most of the B concentrtion come from slt By pplying log on oth sides se log[ OH log log slt OH se p p log slt OH slt p p log se H OH p p H ω p p p log H slt p p log cid OH slt p p log se Buffer cpcity : slt se [Henderson' s eqution It is the cpcity of uffer to resist chnge in p H y dding cid or se. A good uffer shows only slight chnge in p H on ddition of cid or se. Buffer cpcity is defined s the numer of moles of cid or se dded per litre of uffer to cuse the chnge in its p H y one unit (or) Buffer cpcity is the rtio of numer of moles of cid or se dded per litre of uffer to the chnge in p H Buffer cpcity no.of mole of cid or se dded per litre of uffer H chnge in p p H rnge of uffer : It is the rnge of p H vlues where uffer cn effectively resist the chnge in p H on dding cid or se. For n cid uffer the p H rnge. p H p ± For exmplep of H OOH H OON uffer is.5. Therefore it functions effectively etween p H vlues.5 nd 5.5. The p H rnge of sic uffer. OH p p ± Buffer cpcity will mximum if p H p :[slt [cid Buffer cpcity will e more if the components re tken in higher concentrtions. Any uffer hs definite p H vlues. The p H of uffer does not chnge on long stnding. The p H of uffer does not chnge on dilution.

13 Applictions of uffers : ) Buffers re used in vrious chemicl industries ) Buffers re used in vrious enzyme ctlyses rection. ) used in softening of hrd wter. ) used in vrious reserch progrmmes. 5) used in chemicl nlysis. [precipittion of rdicls Slt of Hydrolysis : Acid se neutrlistion slt hydrolysis slt H O Slt hydrolysis is endothermic ecuse t is reverse of neutrlistion. The rection of the slt with wter to produce cid or se or oth is clled slt hydrolysis. Slt hydrolysis is of three types. ) tionic hydrolysis : tion of the slt rects with wter to produce H ions. Acids nd Bses Eg: NH l, NH NO, [NH SO, All etc. In these slts ction is stronger ecuse it is the conjugte of wek se therefore they undergo ctionic hydrolysis. Eg: l NH : NH HO NH OH H ) Anionic Hydrolysis : Anion of the slt rects with wter to produce OH. Eg: H OON, HOO, N O, etc. In these slts nion is stronger s it is the conjugte of wek cid. Eg: H OON : H OO H O H OOH OH ) tionic nd Anionic hydrolysis : Both ction nd nion of the slt rect with wter to produce H nd OH ions. Therefore the solution is neutrl. Eg: H OONH, HOONH, Al(H OO) In these slts oth ction nd nion re stronger ecuse they re the conjugtes of wek se nd wek cid respectively. Eg: H OONH : H OO H O H OOH OH NH H O NH OH H there re four types of slts depending on the nture of cid nd se involved in the titrtions. Slt of strong cid nd wek se : Eg: NH l, NH NO, (NH ) SO, All, Mgl, Al (SO ) etc, These slts undergo ctionic hydrolysis to produce H ions. Their queous solution is cidic nd p H is less thn 7. Their queous solution will turn lue litmus to red nd they cn e used for titrting ginst ses. Eg: l NH Hydrolysis : NH H O NH OH H [NHOH [H [NH [H O [NHOH [H.[H O [NH

14 Acids nd Bses [NHOH[H h [NH Ionistion of NH OH : NH OH NH OH [NH [OH [NHOH Ion product of wter k ω [H [OH w [H [OH [NHOH [NH [OH w h The degree of hydrolysis of the slt is inversely proportionl to the squre root of its molr concentrtion. w α. [H α [H w. [H w. Appling log on oth sides log[ H log log log H w p p p log w Slt of wek cid nd strong se : Eg: H OON, HOO, N O, NHO, N PO, N HPO, N etc. Anionic hydrolysis : H OON H OO H O H OOH OH [HOOH[OH [H OO [H O [HOOH[OH [ HO [H OO [HOOH[OH h [HOO Ionistion of H OOH : H OOH H OO H [HOO [H [HOOH ionic product of wter : w [H [OH w [H [OH [HOOH [H OO [H

15 Acids nd Bses w h The degree o hydrolysis of these slts is lso inversely proportionl to the squre root of its concentrtion. k h α [ OH k w k. w w.. pplying log on oth sides log[ OH log w log log OH p p w p log queous solution of these slts re sic they undergo nionic hydrolysis ecuse the nion of the slt is stronger s it is the conjugte of wek cid. [OH is produced nd solution is sic. Slt of wek cid nd wek se : Eg: H OONH, HOONH, NH N, Al(H OO) etc The queous solution of these slts is ll most neutrl nd p H is ll most equl to 7. The nture of the slt solution ctully depends on nd vlues of cid nd se. i) If, solution is exctly neutrl. Eg: H OONH of H OOH of NH OH ii) If >, solution is cidic Eg: HOONH of HOOH > of NH OH iii) If <, solution is sic Eg: Mg(N) of Mg(N) > of HN These slts will undergo oth ctionic nd nionic hydrolysis to produce oth H nd OH ions. Eg: H OONH H OO H O H OOH OH NH H O NH OH H [HOOH [NHOH [H [OH [H OO [NH [H O [H O [HOOH [NHOH [H [OH [H OO [NH [HOOH [NHOH [H [OH h [HOO [NH The [H [OH they get cncelled mutully [HOOH [NHOH [H OO [NH h 5

16 ionic product of wter w [H [OH [H [H OO [H OOH [NH [OH [NH OH w.k ω.k [H [OH [HOOH[NHOH [H OO [H [NH [OH [HOOH [NHOH [H OO [NH 6 Acids nd Bses w. The degree of hydrolysis [α is independent of concentrtion of the slt ecuse oth ction nd nion of the slt re stronger s they re conjugte of wek se nd wek cid respectively. α h w. w w. [ H. α. pply - log on oth sides log[ H log log log H w p p p p [OH. α k w k w k k.k k pply log on oth sides log[ OH logk w logk logk Slt of strong cid nd strong se : OH kw k k p p p p Eg: Nl, NO, N SO, Bl, NlO, B(NO ), Sr.(NO ) etc. These slts do not undergo hydrolysis ecuse oth nion nd ction re wek s they re conjugtes of strong cid nd strong se respectively. Therefore their queous solutions re exctly neutrl nd p H is exctly. Soluility Product : - ( ) SP It is the product of the molr concentrtion of its ions in sturted solution of electrolyte. SP for slt chnges with temperture Soluility product of springly solule slt is given y y AB x x y xa yb y x y A. B x SP x y sp xs ys [ [

17 If soluility is known SP cn e clculted (or) vice vers. APPLIATIONS : Acids nd Bses ) The concept of soluility product helps the formtion of precipitte. ) Ionic product < SP, no ppt is formed (unsturted solution) ) Ionic product > SP, ppt is formed (super sturted solution) c) Ionic product SP, solution is sturted ) In predicting the soluility of springly solule slt. ) In qulittive nlysis, the sepertion nd identifi ction of vrious sic rdicls into different groups. ) In purifiction of common slts. 5) In slting out of sop. For inry slts like Agl, AgBr soluility S cn e clculted s S Pl, Mg OH, Ag ro For ternry slt like ( ) SP SP S (or) S For slt SP s : AB slt SP S : AB slt SP 7S 5 AB slt SP 08S ;Where SSoluility / SP OMMON ION EFFET :- The suppression of the dissocition of wek electrolyte y the ddition of strong electrolyte hving common ion is clled common ion effect. Ex : - A solution of Sodium Aectte is dded to solution of Acetic cid s result in the decrese in H OO ioniztion of cetic cid due to common ion is ( ) H OOH H OO H H OON H OO N common ions. According to Lechtlier principle H, decreses H P is increses nd equilirium shifts to left hnd side. APPLIATIONS : - ) It is used in the controlling the H ion concentrtion in Buffer solution. ) The concentrtion of S in the II Group or OH in III group of qulittive Anlysis is controlled y Hl nd NHOH on the sis of common ion effect. ) ommon ion effect is lso used in the purifiction of common slt y pssing dry Hl gs into impure slt solution 7

Which of the following describes the net ionic reaction for the hydrolysis. Which of the following salts will produce a solution with the highest ph?

Which of the following describes the net ionic reaction for the hydrolysis. Which of the following salts will produce a solution with the highest ph? 95. Which of the following descries the net ionic rection for the hydrolysis of NH4Cl( s)? A. NH4 ( q) Cl & ( q) NH4Cl( s) B. NH Cl & 4 ( s) NH4 ( q) Cl ( q) C. Cl ( q) H O & 2 ( l) HCl( q) OH ( q) D.