Chpter 14
1 ACIDS/BASES Acids hve tste, rect with most metls to produce, rect with most crbontes to produce, turn litmus nd phenolphthlein. Bses hve tste rect very well well with most metls or crbontes, turn litmus, nd phenolphthlein. Hydronium ion: An cid produces when mixed with wter; bse produces in wter. This is the Arrhenius definition. The hydroxide ions could be present in the originl compound: + - Soluble ionic compound: NOH (q) N (q) + OH (q) Hydronium or hydroxide ions cn lso be produced by rection of certin substnces with wter: HNO 3 (q) + H2 O(l) K = NH 3(q) + H2 O (l) K = The equilibrium constnts K nd K b lwys refer to the rection of some compound with to produce hydronium nd hydroxide ions respectively. The lrger the vlue of K the the cid. In similr wy the lrger the vlue of K b the stronger the bse. Strong cids hve K vlues tht re. All other cids re clssified s nd would hve K vlues tht re or. Exmple: Write the chemicl eqution tht represents the K for formic cid. How mny rrows should it hve?
2 1- Exmple: Write the chemicl eqution tht represents the K b for HCO 3. How mny rrows should it hve? BRONSTEAD-LOWRY DEFINITION OF ACID AND BASE + - HCHO 2 3 2(q) + HO 2 HO 3 (q) + CHO 2 3 2 (q) HC2H3O 2 would be clssified s n cid becuse. During the rection is trnsferred from HC2H3O 2 to H2O. Another wy of defining cids nd bses is in + + + terms of trnsfer of H. An cid is H nd bse would be H. In the reverse rection, hydronium ion would be clssified s /n nd cette ion s /n. HCHO + HO HO + CHO + - 2 3 2 2 3 2 3 2 - HC2H3O 2 nd C2H3O 2 re clled (CABP). Wht is the other CABP in the eqution: Exmple 1: Identify the conjugte cid-bse pirs in the following eqution. HSO + SO HSO + SO - 2- - 2-4 3 3 4 The cid in the CABP differs from the bse by conjugte cid conjugte bse mount of + chrge mount of - chrge number of H toms
3 Exmple 1: conjugte cid HCO - 3 2- HPO 4 conjugte bse HCO - 3 2- HPO 4 STRENGTH OF CONJUGATE ACIDS AND BASES In the chrt, the cid strength increses from to. Strong cids re nd bove. The bse strength increses from to. The strong bses re nd below. The stronger the cid the the bse its conjugte bse is. Any cid bove ** is n Arrhenius nd will usully produce when mixed with wter. Any bse ** tht is wter is n Arrhenius bse nd will usully produce when mixed with wter. ** If chemicl ppers in both columns you need to determine if it is better cid or better bse. Exmple: Which is the stronger cid: HCN or HNO 2 Exmple: Which is the stronger bse: HCO or CO - 2-3 3 ACID BASE REACTIONS When n cid rects with bse, the products re the. If the stronger cid nd bse re on the rectnt side, the vlue of K will be. If the stronger cid nd bse re on the product side, the vlue of K will be. In n queous solution the strongest bse thn cn exist is becuse sulfide nd oxide would rect with.
4 K For Acids t 25 C - Acid HA A K - 11 Hydriodic HI I 10-9 Hydrobromic HBr Br 10-7 Perchloric HClO4 ClO 4 10-7 Hydrochloric HCl Cl 10-3 Chloric HClO3 ClO 3 10-2 Sulfuric (1) H2SO4 HSO4 10 - Nitric HNO3 NO3 20 + Hydronium ion H3O H2O - -1 Iodic HIO3 IO3 1.6 x 10 - -2 Oxlic (1) H2C2O4 HC2O4 5.9 x 10 - -2 Sulfurous (1) H2SO3 HSO3 1.54 x 10-2- -2 Sulfuric (2) HSO4 SO4 1.2 x 10 - -2 Chlorous HClO2 ClO2 1.1 x 10 - -3 Phosphoric H3PO4 H2PO4 7.52 x 10 - -4 Hydrofluoric HF F 6.6 x 10 - -4 Nitrous HNO2 NO2 4.6 x 10 - -4 Formic HCOOH HCOO 1.77 x 10 - -5 Benzoic C6H5COOH C6H5COO 6.46 x 10-2- -5 Oxlic (2) HC2O4 C2O4 6.4 x 10 - -5 Acetic CH3COOH CH3COO 1.76 x 10 - -7 Crbonic (1) H2CO3 HCO3 4.3 x 10-2- -7 Sulfurous (2) HSO3 SO3 1.02 x 10 - -8 Hydrosulfuric H2S HS 9.1 x 10-2- -8 Phosphoric (2) H2PO4 HPO4 6.23 x 10 - -8 Hypochlorous HClO ClO 3.0 x 10 + -10 Ammonium ion NH4 NH3 5.6 x 10 - -10 Hydrocynic HCN CN 4.93 x 10-2- -11 Crbonic (2) HCO3 CO3 4.8 x 10 2-3- -13 Phosphoric (3) HPO4 PO4 2.2 x 10 Wter H2O OH - - 2- hydroxide OH O - 2- hydrogen sulfide HS S
5 px px = where X is WARNING: This log is log bse. pk pk = EXAMPLE 1: Is formic cid strong or wek cid? Clculte pk for formic cid. EXAMPLE 2: The pk for benzoic cid is 4.20. Clculte the vlue of K for benzoic cid. Is benzoic cid wek or strong cid?. Is it weker or stronger thn formic? cid K pk formic benzoic IMPORTANT POINT: The stronger the cid the the K nd the the pk ph ph = WARNING: ph is the log of the concentrtion of not the log of the concentrtion of.
6-5 Exmple: Wht re ph of 0.2 M HCl nd 0.2 M HC2H3O 2 (K = 1.8 x 10 )? IMPORTANT POINT: For the sme initil concentrtion, the stronger the cid the the ph. + Exmple: Clculte the [H3O ] in solution whose ph = 4.85 poh poh = - - Exmple: Clculte the poh of solution contining 0.25 M OH nd the [OH ] in - solution whose poh is 4.5. Which is the stronger bse (contins concentrtion of OH )? IMPORTANT POINT: The stronger the bse the the poh.
7 Exmple 1: Clculte the poh of 0.1 M B(OH) solution. 2-5 Exmple 2: Clculte the poh in 0.5 M NH 3 solution. K b = 1.8 x 10 + - RELATIONSHIP BETWEEN [H3O ] AND [OH ] Whenever wter is present, this equilibrium is estblished very fst: + - + - 2 H2 O (l) H3 O (q) + OH (q) K = K = [H3O ][OH ] TEMPERATURE ( C) K w 0 0.114 x 10-14 10 0.292 x 10-14 20 0.681 x 10-14 25 1.01 x 10-14 30 1.47 x 10-14 40 2.92 x 10-14 50 5.47 x 10-14 60 9.61 x 10-14 Unless otherwise specified, the temperture should be ssumed to be nd K w is nd pk = w
8 - + In cid solutions there must be some OH nd in bse solutions there is some H3O. In n cidic solution the concentrtion of is greter thn. In bsic solution the concentrtion of is greter thn. - Exmple 1: Wht is the concentrtion of OH in 0.2 M cetic cid? Wht is the concentrtion + of H O in 0.1 M B(OH)? 3 2 solution + [H3O ] - [OH ] prents of H O + 0.2 M HC2H3O2 3 prents of OH - cidic or bsic? 0.1 M B(OH) 2 RELATIONSHIP BETWEEN ph AND poh ph + poh = Exmple 1: Wht is the ph of pure wter t 25 deg C? At 0 deg C?
9 Exmple 2: solution ph poh 0.2 M HC2H3O2 2.72 0.1 M B(OH) 2 0.70 POLYPROTIC ACIDS - + H2SO 3 (q) + H2 O (l) HSO 3 (q) + H3 O (q) K = - 2- + HSO 3 (q) + H2 O (l) SO 3 (q) + H3 O (q) K = Exmple 1: Clculte the ph of 0.1 M sulfurous cid solution.
IMPORTANT POINT Only the first rection in polyprotic cid needs to be used to find 3 the ph unless the second K is not smll nd t lest 10 times smller thn the first K. If you wnt to know the concentrtion of n ion not in the first rection you will need to solve the other equtions. 2- Exmple 2: Clculte the [SO 3 ] in 0.1 M sulfurous cid solution. 10 RELATIONSHIP BETWEEN K AND K FOR A CONJUGATE ACID/BASE PAIR b HA + + K (q) - A (q) + + K b K x K = b = pk w These formuls re vlid only for Exmple 1: Look up the vlue of K for HClO nd clculte K b. This is K b for. Write the chemicl eqution tht belongs to this K. b Exmple 2: Clculte the vlue of K b for HCO 1-3 1- Exmple 3: Is HCO 3 better s n cid or bse?
11 ** Go bck nd look t pge 4. Is solution of NHCO 3 cidic or bsic? ACID-BASE PROPERTIES OF SALTS compound color of phenolphthlein N3PO4 To simplify clcultions tht involve chemicl systems tht contin more thn one reversible rection, we will ttempt to find ONE equilibrium (the Principl Equilibrium) tht cn be used to determine concentrtions. When we hve series of cid/bse equilibri, we cn use the following rule: The principl rection will be rection tht rects the cid with the bse. The cid nd bse must be chosen from the chemicls dded. Write the principl rections occurring in ech of the following solutions: 1. NBr (q) Slts contining the ions tht re weker cids nd bses thn wter re. 2. NH4NO 3(q) Slts contining ions tht re stronger cids thn wter re 3. N2CO3(q) Slts tht contin ions tht re stronger bses thn wter re. Exmple: Would NHSO 3 (q) be cidic, bsic or neutrl?
12 METAL IONS slt (0.1 M) ph Cu(NO 3) 2 Slts tht contin highly chrged metl ions (especilly metls) re +. The higher the chrge/size rtio the cidic. Why would N not be expected to be very cidic? 2+ How cn Cu ct s n cid if it hs no H? In solution, most metl ions exist s complex ions with wter. The wters connected to the metl ion tend to be cidic thn wter not bonded to the metl ion. The rection is relly: HO + HO HO + OH where the * chemicls re bound to the metl ion. * + -* 2 2 3 STRENGTH OF BINARY ACIDS As you go down column in the periodic tble, the strength of binry cids. STRENGTH OF OXY-ACIDS Within ech group rnk the following ccording to incresing cid strength:. HNO 3 HNO2 b. HClO 3 HClO HClO4 c. H2SO 4 H2SO3
13 Assign oxidtion numbers to N, Cl, nd S in ech cid. The stronger oxycid is the one with the oxidtion number Exmple: Which is stronger cid: HClO or HClO 2 ACID/BASE CHARACTERISTICS OF OXIDES The binry oxides cn be cidic (produces or rects with ), bsic (produces or rects with, or mphoteric (rects with nd ). Look t the Periodic Tble. The oxides of the non metls re when mixed with wter. For multiple oxides with the sme non-metl, the more cidic will be the one with the higher. The oxides of the lkli metls nd lkline erth metls re when mixed with wter. The oxides of the trnsitionl metls. Exmple 1: Exmple 2: Is CO cidic, bsic, neither, both when mixed with wter? When sulfur is burned, SO 2 is produced. Is SO 2 cidic, bsic, neither, both when mixed with wter? Is SO more or less cidic thn SO? 2 3 ANOTHER DEFINITION OF ACID AND BASE - LEWIS A Lewis cid is n electron pir. A Lewis bse is n electron pir.