Strong acids and bases. Strong acids and bases. Systematic Treatment of Equilibrium & Monoprotic Acid-base Equilibrium.

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1 Strong cids nd bses Systemtic Tretment of Equilibrium & Monoprotic cid-bse Equilibrium onc. (M) p Strong cids nd bses onc. (M) p ? We hve to consider utoprotolysis of wter: O w O - hrge Blnce The sum of the positive chrges in solution equls the sum of the negtive chrges in solution. tion n ii i j n j nion j n > chrge, >concentrtion Mss Blnce Mteril blnce. The quntity of ll species in solution contining prticulr tom (or group of toms) must equl the mount of tht tom (or group) delivered to the solution. Systemtic Tretment of Equilibrium - Strong cids nd bses hrge blnce. O - l - Mss blnce. l M O - - ( M) w O - ( ( M)) ( ) w M, M p 6.98 O w O - When the (strong) cid or bse concentrtion is round ~ M, we hve to be concerned with utoprotolysis. For etremely low strong cid or bse concentrtion (<0-8 ), p 7.00 Problem: Wht is the po, nd p of M solution of NO? NS: 6.55; 7.5

2 Systemtic Tretment of Equilibrium - Wek cids nd bses Wek cid: cid dissocition constnt () O - O - O Wek Bse, hydrolysis rection: bse hydrolysis constnt (b) B O b B O - B O b B Reltionship between nd b for conjugte cid/bse pirs: w b O O O 0 typicl wek-cid problem Emple: lculte the p of L solution prepred by dissolving 0.0 moles of cetic cid? c c w O O - c 5 c w O hrge Blnce: O - c Mss Blnce: c c typicl wek-cid problem Emple: lculte the p of L solution prepred by dissolving 0.0 moles of cetic cid? Simplifying ssumptions c c c Solve the qudrtic Eq. - c M nd.750-5,. 0 - M typicl wek-cid problem Emple: lculte the p of L solution prepred by dissolving 0.0 moles of cetic cid? Frction of dissocition () For monoprotic wek cid: c c c c c ( c ) ( ) α c α typicl wek-bse problem Emple: Find the p of 0.0 M mmoni. N b O N O b O N N w O O - w O hrge Blnce: O - N Mss Blnce: N N 0.0 typicl wek-bse problem Emple: Find the p of 0.0 M mmoni. Simplifying ssumptions O N b N O N O O O Solve the qudrtic Eq. b - c b M nd.760-5,. 0 - M

3 typicl wek-bse problem Emple: Find the p of 0.0 M mmoni. Frction of dissocition () For monoprotic wek bse: N N α N N N ( ) ( ) α Buffers buffer solution resists chnges in p when cids or bses re dded or when dilution occurs. buffer solution generlly consists of miture of n cid nd its conjugte bse. enderson-sselblch Eqution O B b B For buffer solution contining wek cid nd its conjugte bse: p p log For buffer solution contining wek bse nd its conjugte cid, enderson-sselblch Eqution p p - For every power of 0 chnge in the rtio of - /, the p chnges by one unit. p p log p p B log B or po p b B log B s the cid increses, the p goes down. Effect of dding cid to buffer Emple. lculte the p of buffer prepred by dding 0.00 ml of 0.0 M cetic cid nd 0.00 ml of 0.0 M sodium cette. p p 0.00*0.0 / 0.00 log.76 log *0.0 / 0.00 Emple. Wht is the p if 0.00 ml of M l is dded to the bove buffer solution? p p (0.00* *0.00) / 0.00 log.76 log 5.0 (0.00* *0.00) / 0.00 Buffer pcity β db dp d dp mesure of how well solution resists chnges in p when strong cid or bse is dded. Buffer cpcity is mimum when p p Best to chose buffer system whose p is within ± p unit of your desired p

4 Diprotic Buffers For, we cn write two enderson-sselblch equtions: p p log p p log Polyprotic cid-bse Equilibrium E: Wht is the p of solution prepred by dissolving.0 g P (FW: 0. g/mol) nd.0 g N P (FW: 0.09 g/mol) in 50.0 ml wter (p.950, p 5.08)? p P log P.0g / 0.09g / mol 5.08 log.00g / 0.g / mol p 5.7 Diprotic cids/dibsic bses Polyprotic cids/polybsic bses - - -, PO PO PO - PO PO - PO mino cid n mino cid hs n cidic crboylic cid group, bsic mino group, nd vrible substituent designted R. Its nonionized form rerrnges spontneously to the zwitterion. zwitterion: molecule with both positive nd negtive chrges Leucine L (cidic form) Wht s the p of M solution of L nd Diprotic cid: L L L L - Diprotic bse: L O L O L O L O bw/ bw/ ssume tht L cts s monoprotic cid L L Solve for with the qudrtic eqution..0 - M, p.88

5 L (cidic form) Wht s the p of M solution of L? ssume tht L cts s monoprotic cid L L.0 - M, p.88 heck our ssumption by clculting L - L L L L M L - (Bsic form) Wht s the p of M solution of L -? The reltions between cid nd bse equilibrium constnts for diprotic cid/bse: b b w w L L L L - L O L O bw/ L O L O bw/ L - (Bsic form) Wht s the p of M solution of L -? L O L O bw/ L O L O bw/.0 - ssume tht L - cts s monobsic species with bb O L b L.60 - M, w/ M, p. L - (Bsic form) Wht s the p of M solution of L -? L O L O bw/ L O L O bw/.0 - ssume tht L - cts s monobsic species with bb O L b L.60 - M, w/ M, p. heck our ssumption by clculting L L O b L b L b. 0 L O M L (Intermedite Form) Wht s the p of M solution of L? L is mphiprotic, mening it cn both donte nd ccept proton L L L L L O L O bw/ L O L O bw/.0 - We hve to use the systemtic tretment to determine p. L (Intermedite Form) Wht s the p of M solution of L? L L L O L O bw/.0 - hrge blnce: L L - O - Equilibrium onstnts: 5

6 6 L (Intermedite Form) Wht s the p of M solution of L? L L L O L O bw/.0 - L L (Intermedite Form) Wht s the p of M solution of L? L L L O L O bw/.0 - L heck our ssumptions: L (Intermedite Form) Wht s the p of M solution of L? L L L O L O bw/.0 - Simplified lcultion for the Intermedite form: If >>w, thn the nd term in the numertor cn be dropped nd if <<, the st term in the denomintor cn lso be neglected: For diprotic wek cid For - nd - - α α α Isoionic Point: The p of pure, neutrl polyprotic cid (the nturl zwitterion) wter:, -,, nd O - Most nd - Isoelectric Point: p when verge chrge of thepolyprotic cid is zero (mino cids) Most nd -