Chapter 14. Acid and Bases. What is an Acid? Acids & Bases. Acids & Bases

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1 hpter 1 Acids & Bses Acid nd Bses Acid nd Bses Acid nd Bses Wht is n Acid? YS NO Acids & Bses There re mny different wys of defining cids nd ses. There is no cler consensus s to the proper definitions for the terms cid nd se. Nor is ny single definition est for ll situtions. There re 7 common different cid se theories. We will only e discussing of those.

2 Usnovich Bronsted Lowry Lewis onotropic Arrhenius LuFlood Solvent System Arrhenius n 19, Lewis Bronsted in 1887 nd first proposed Lowry defined tht defined the n cids terms is s cid n hydrogen electron nd ion se. pir donors cceptor nd nd ses They is re s n defined hydrogen electron ion s pir n cceptors. donor. cid eing hydrogencontining species tht dissocites in wter to give, H, nd se s hydroidecontining species tht dissocites in wter to give OH. Arrhenius Limits cidse chemistry to queous solutions. Rections in the gs nd solid phses nd in solvents other thn wter re ecluded. The sic rection tht is discussed is the neutrliztion rection. This cn e roken down in to two different ctegories. Neutrliztion Gs Forming Acid Bse wter common slt A slt is ny ionic compound whose ction comes from se nd whose nion comes from n cid BronstedLowry The theory y Bronsted nd Lowry rodens the definition given y Arrhenius An cid is ny sustnce tht cn donte proton to ny other sustnce A se is sustnce tht cn ccept proton from ny other sustnce This theory is not restricted to compounds in wter Bronsted Acids n e moleculr compounds HNO (q) H O(l) NO (q) H O (q) cid n e ctions NH (q) H O(l) NH (q) H O (q) cid n e nions H PO (q) H O(l) HPO (q) H O (q) cid Bronsted Bses n lso e moleculr compounds NH (q) H O(l) NH (q) OH (q) se n e nions O (q) H O(l) HO (q) OH (q) se n e ctions Al(H O) (OH) (q) H O(l) Al (H O) 6 (q) OH (q) se mple of Bronsted Acid H O Hl [H O] [l] Proton Donor Proton Acceptor Hydronium on

3 Generl Dissocition of n Acid Generic cid dissocition HA H O H O A HA Acid H O Bse H O onjugte Acid The species formed when proton is dded to se. A onjugte Bse Wht remins of n cid molecule fter proton is lost Why cn wter pull off tht proton? onjugte AcidBse Pirs A pir of compounds tht differ y the presence of one H ion is clled conjugte cidse pir Acid quilirium Since there is n equilirium, we need to use K eq somehow. The trick is it is no longer clled K eq. We cll if K cid dissocition constnt. HA H O H O A [HO ][A ] [H ][A ] K [A] [HA] Why is wter removed? But rememer wter s very importnt it is cusing the cid to ionize (dissocite) mples of K Note tht K is lwys written so tht the proton is lwys removed from HA to form the conjugte se (A ). Write the K for the following: Hl Hl H l H OOH H OOH H H OO NH NH H NH 6 H NH 6 H NH H 6 H NH [Al(H O) 6 ] [Al(H O) 6 ] H [Al(H O) (OH)] Gs Phse BronstedLowry cn lso e used in the gs phse. NH Hl [NH ] [l] Acid Strength Defined y the equilirium position or K Strong Acids quilirium lies fr to the right Wek Acids quilirium lies fr to the left

4 Strong nd Wek Acids/Bses HNO, Hl, H SO nd HlO re mong the only known strong cids. Strong nd Wek Acids/Bses Wek cids re much less thn % ionized in wter. One of the est known is cetic cid H O H Strength vs. onjugte Strong cids produce wek conjugte ses. Wek cids produce strong conjugte ses. mples of Strong Acids H SO diprotic Hl monoprotic HNO monoprotic HlO monoprotic mples of Wek Acids H PO HNO HOl Orgnic cids OyAcids the cidic proton is ttched to n oygen Monoprotic nd Polyprotic Acids Monoprotic cids re cple of donting one proton e.g., HF, Hl, HNO : ll cn donte one proton Polyprotic cids re cple of donting two or more protons H SO : cn donte two protons H SO (q) H O (l) HSO (q) H O (q) HSO (q) H O (l) SO (q) H O (q) mple Wht is the order of strength of the following ses? F, l, NO, N Rememer the stronger the cid the weker the se. l < F < NO < N Amphiprotic Forms Some molecules cn ehve s either Bronsted cid OR Bronsted se: they re clled mphiprotic mple: hydrogen phosphte ion HPO (q) H O(l) H O (q) PO (q) cid HPO (q) H O(l) H PO (q) OH (q) se

5 Wter is Amphoteric n e seen y the utoioniztion of wter H O(l) H O (q) OH (q) K [H O ][OH ] [H ][OH ] Now know s K w From eperiment we cn determine t [H ] [OH ] 1. 7 M K w [H ][OH ] (1. 7 M) 1. 1 M Rememer K w chnges with temperture! More Aout Wter H O cn function s oth n AD nd BAS. n pure wter there cn e AUTOONZATON wter_utoioniztion.mov quilirium constnt for utoion K w [H O ] [OH ] 1. 1 t o K w Think ph nd mple No mtter the product of [H ][OH ] 1. 1 Think out ph Wht is the highest ph vlue? [H ] [OH ] neutrl [H ] > [OH ] cidic [H ] < [OH ] sic lculte [H ] or [OH ]: ) 1. M OH ) 1. 7 M OH c) M H Acidic or Bsic? ph Scle s milk cid or sic? ph log [H ] poh log [OH ] ph poh 1 K w [H ][OH ] p is just function [H O ], [OH ] nd ph f the ph of oke is.1, it is. Becuse ph log [H O ] then log [H O ] ph Tke ntilog nd get [H O ] ph [H O ] M mple ph of humn lood is 7.1. Wht is: poh ph poh poh 1 poh 6.9 [H ] ph log [H ] 7.1 log [H ] 7.1 [H ].89 8 M [OH ] poh log [OH ] 6.9 log [OH ] 6.9 [OH ].7 7 M

6 mple lculte the ph of:. M HNO ph log [H ] ph log. ph 1 1. M Hl ph log [H ] ph log 1. ph (But tht is BAS!) Rel nswer is ph 7. Since [Hl] is so low it does not chnge the ph of wter. quiliri nvolving Wek Acids nd Bses Aspirin is good emple of wek cid, K. ph of wek cids Since wek cids do not fully dissocite You know tht K must chnge the ph But HOW?! Wht type of tle might we use to help us out in such predicment? mple Wht is the ph of 1. M solution of HF? K Which is more importnt? HF(q) H (q) F (q) K 7. H O(l) H (q) OH (q) K w TABL HF 1 1 H F K is so smll don t worry out 1 K [H ] ph log [H ] ph log.68 ph.7 Another mple ph of. M HOl K. 8 HOl K.. 8 [H ] H Ol ph log [H ] log.916.

7 ph when you hve mitures How do determine the ph of miture of different cids? Mke life esy consider K. HNO H NO ph of miture of 1. M HN nd. M HNO? K (HN) 6. K (HNO ). K w 1. 1 K..7 [H ] ph log [H ] log.7 1. K K Now, lculte [N ] [H ][N ] [HN] (. 1 M )() Percent Dissocition Amount Dissocited (M) Percent Dissocition nitil oncentrion (M) For emple, we found erlier tht in 1. M solution HF [H ] eq.7 M.7 Percent Dissocition 1..7% mple lculte the % dissocition of cetic cid (K 1.8 ) for. M solution. H OOH H H OO.. K Percent Dissocition 1.%. 1. M [H ] mple in Reverse K from % dissocition n. M solution of lctic cid is.7 % is dissocited. H H O (q) H (q) H O (q) K H H O.. [H ][HO ] [H H O ] H H O

8 Percent Dissocition [H H O.7% ] Percent Dissocition.7%. H H O H M.7.7 H O.7.7 K [H ][HO ] [H H O ] (.7 )(.7 ) K 1.. Bses Bses Arrhenius A sustnce tht produces OH ion in queous solution. BronstedLowry A proton cceptor Strong Bses ompletely dissocite Wek Bses Do not completely dissocite Alkli Metl Hydroides Strong ses NOH nd KOH common l ses LiOH, ROH, nd soh re not ecuse they re so epensive Alkline rth Hydroides Strong ses But tend not to dissolve in wter very esily We cn use this fct in ntcids Suspensions of metl hydroides re used so tht the OH does not dmge the soft internl tissue But still rects with stomch cid mple lculte the ph of. M NOH. would clculte poh first poh log [OH ] poh log. 1. poh ph 1 1. ph 1 ph 1.7 Proton Acceptor But rememer we think of n se s proton cceptor. So, we hve to look t se dissocition constnt. B(q) H O(l) BH (q) OH (q) [BH ][OH ] [B] K K lwys refers to the rection of se with wter to form the conjugte cid nd the hydroide ion

9 mple lculte the ph for 1. M solution of NH (K 1.8 ) would clculte poh first Wht is more importnt? NH (q) H O(l) NH (q) OH (q) H O(l) H (q) OH (q) NH (q) 1 1 H O(l) NH (q) OH (q) NH (q) H O(l) NH (q) OH (q) 1 1 K 1.8 [NH ][OH ] ()() [NH ] ph 1. poh log [OH ] poh log 1.6 [OH ] Do this One Determine the ph of 1. M solution of methylmine (K.8 ). Methylmine H NH [HNH ][OH ] ()() K.8 [H NH ] ph 1. poh log [OH ] poh log.1 [OH ] 1.68 Polyprotic Acids hve mentioned tht there re cids tht hve the ility to donte more thn one proton. ch time this polyprotic cid dontes proton, we must consider ech cid dissocition constnt. For emple, clculte the ph of. M H PO solution. K 1 7. [H ][HPO [H PO ] ] ()().. H H PO (q) (q) H PO (q) ph log [H ].7 K [H [H ][HPO ] [H PO ] ] (.19)().19 only [HPO M of H PO ] hs dissocited

10 K.8 only [H ][PO ] (.19)() 8 [HPO ] [PO M of HPO ] hs dissocited mple lculte the ph of 1. M H SO? Very little HPO nd H PO hs dissocited so we don t hve to worry out the mount of H from them. Slt s Acids/Bses Wht is slt? Slt is generic nme tht chemist give for ionic compounds. Usully solule in wter. When slts dissocite, it my e possile to crete wek cid or wek se. The wek cid or wek se my then further go on nd chnge the ph of the system. Types of Slts There re relly not different types of slts, ut we cn think of three different possiilities tht cn tke plce when slt dissocites. 1. Does not chnge the ph Usully slts tht hve high soluility. : l, NO, N, K. Mkes it Bsic. Mkes it Acidic Slts tht re Bsic Tke for emple NH OO dissolving in wter. N nd H OO is creted (rememer your soluility tles) H OO H O H OOH OH [OH ][HOOH] [H OO ] K How to determine K? K (cetic cid) 1.8 How to get K from K? H OOH H O H OO H K 1.8 [H K K [H OOH] ][HOO ] (1.8 [H ][HOO ] [H OOH] K K [H][OH] K K.6 [OH ][H OOH] )K 1 [HOO ] w 1

11 SO lculte the ph of. M NF solution. K 7. NF fully dissocites F H O HF OH K K 1. (7. [OH ][HF] K [F ] K )K 1. 1 F.. H O(l) [OH ][HF] K [F ] K. 6. [OH ] poh.69 ph 8.1 HF(q) OH Slts tht re Acidic onsider. M NH l solution. NH H O NH H O K (NH K (NH ) 1.8 ).6 setup tle [H ] ph.1 [NH ][H ] [NH ] Those re the esy ones mple: Predict if the following solutions will e sic, cidic, or neutrl ompound NH H O NH N Al (SO ) K.6 (NH ).6 (NH ) 1. (Al(H O 6 ) ) K.6 ( H O ) 1.6 (N ) 8. 1 (SO )? Why? Why re some compounds cids? Why re some compounds ses? Why do cids nd ses vry in strength? n we predict vritions in cidity or sicity?

12 Why is H O H n Acid? 1. The electronegtivity of the O toms cuses the H ttched to O to e highly positive.. The O H ond is highly polr.. The H tom of O H is redily ttrcted to polr H O. Acetic cid Trichlorocetic cid K 1.8 K. Trichlorocetic cid is much stronger cid owing to the high electronegtivity of l, which withdrws electrons from the rest of the molecule. This mkes the O H ond highly polr. The H of O H is very positive. Bsicity of Oonions NO O These ions re BASS. They ecome more nd more sic s the negtive chrge increses. As the chrge goes up, they interct more strongly with polr wter molecules. PO Structure nd its ffect on AcidBse Properties So, we re sying we hve to look t the Lewis structure of the compound we re considering. Look t the difference etween HlO HlO HlO HlO Drwing Lewis Dot Structures 1. Determine the totl numer of vlence electrons ville. Set this numer equl to T.. Drw the skeleton of the compound. The centrl tom is usully the one with the lowest electron ffinity.. ount up the numer of onding electrons used nd sutrct tht from T. Set the numer you get equl to R.. ount up the numer of electrons needed to fill the octet rule for ll of the toms. Set this numer equl to N.. f N R then fill in the remining electrons 6. f N > R then you need t dd multiple onds. (NR) the numer of onds to dd. 7. f N < R then you need to dd electrons to the centrl tom (mke sure the centrl tom is rd period or greter tom).

13 Lewis The theory developed y Lewis ws more generl thn either the Bronsted Lowry theory or the Arrhenius theory A Lewis cid is sustnce tht cn ccept pir of electron from nother tom to form new ond A Lewis se is sustnce tht cn donte pir of electron from nother tom to form new ond LewisAcid Bse Model BronstedLowry cidse rections re encompssed y the Lewis model. (Proton donorproton cceptor rections) The Lewis model for cids nd ses covers mny rections tht do not involve BronstedLowry cids. i.e the gsphse rection etween oron trifluoride nd mmoni Three Models for Acids nd Bses Arrhenius BronstedLowry Lewis Model Definition of Acid H producer H donor lectronpir cceptor Definition of Bse OH producer H cceptor lectronpir donor Lewis Acids & Bses Lewis cid sustnce tht ccepts n electron pir Lewis se sustnce tht dontes n electron pir Rection of Lewis Acid nd Lewis Bse New ond formed using electron pir from the Lewis se. oordinte covlent ond Notice geometry chnge on rection. Lewis Acids & Bses Formtion of hydronium ion is lso n ecellent emple. H AD O H H BAS lectron pir of the new OH ond origintes on the Lewis se. H O H H

14 Lewis Acid/Bse Rection Lewis Acids & Bses Other good emples involve metl ions. o AD O H o H BAS O H H Lewis Acids & Bses The comintion of metl ions (Lewis cids) with Lewis ses such s H O nd NH > OMPLX ONS Rection of NH with u (q) Lewis AcidBse nterctions in Biology Heme group The heme group in hemogloin cn interct with O nd O. The Fe ion in hemogloin is Lewis cid O nd O cn ct s Lewis ses Lewis Acids & Bses Mny comple ions contining wter undergo HYDROLYSS to give cidic solutions. [u(h O) ] H O > [u(h O) (OH)] H O

15 Lewis Acids & Bses Amphoterism of Al(OH) This eplins why wter solutions of Fe, Al, u, P, etc. re cidic. This interction wekens this ond Another H O pulls this H wy s H Lewis Acids & Bses This eplins AMPHOTR nture of some metl hydroides. Al(OH) (s) H > Al H O Here Al(OH) is Brønsted se. Al(OH) (s) OH > Al(OH) Here Al(OH) is Lewis cid. Al O H