Ama-asidi nezisekelo ezibuthaka: kusuka ku-Ka no-Kb kuya ku-pH

Ukufunda u-Ka, u-Kb nezikali zawo ze-p

Ku-asidi ebuthaka u-HA, i-ionization HA(aq) + H₂O(l) ⇌ H₃O⁺(aq) + A⁻(aq) ino-constant Ka = [H₃O⁺][A⁻]/[HA]. Amanzi ayisincibilikisi futhi ayashiywa. U-Ka omkhulu usho i-asidi eqinile kakhulu. Esisekelweni esibuthaka B, ukusabela B(aq) + H₂O(l) ⇌ BH⁺(aq) + OH⁻(aq) kuno-Kb = [BH⁺][OH⁻]/[B].

Ngoba lokhu okungaguquki kuhlanganisa amandla amaningi eshumi, kuvame ukubikwa njengo-pKa = −log Ka no-pKb = −log Kb. Isikali sihamba ngokuhlehla: u-pKa omncane usho i-asidi eqinile kakhulu. USithasiselo H unikeza u-Ka = 1.8 × 10⁻⁵ we-acetic acid (pKa 4.74), 6.4 × 10⁻⁴ we-hydrofluoric acid (pKa 3.19) no-4.9 × 10⁻¹⁰ we-hydrocyanic acid (pKa 9.31). U-Ka we-HF mkhulu cishe ngokuphindwe isigidi kunowe-HCN, nakuba zombili zibizwa ngokuthi ezibuthaka.

Isibonelo esisebenzile: i-pH ye-asidi ebuthaka ngendlela emfushane ka-x omncane

Thola i-pH ye-acetic acid engu-0.200 M, CH₃COOH. Vumela u-x abe yinani elenza i-ionization. Ekulinganeni [H₃O⁺] = [CH₃COO⁻] = x no-[CH₃COOH] = 0.200 − x. Umnikelo wamanzi uqobo ku-H₃O⁺ (10⁻⁷ M) awubalulekile uma uqhathaniswa nowe-asidi.

Bhala 1.8 × 10⁻⁵ = x² / (0.200 − x). Ngoba u-Ka mncane, thatha ukuthi u-x mncane kakhulu kuno-0.200 bese umsusa ku-denominator. Bese x² = 1.8 × 10⁻⁵ × 0.200 = 3.6 × 10⁻⁶ no-x = 1.9 × 10⁻³ M. Hlola: 1.9 × 10⁻³ / 0.200 ingaphansi nje kwephesenti elingu-1, ngaphansi kakhulu komkhawulo wamaphesenti angu-5, ngakho indlela emfushane iyasebenza. pH = −log(1.9 × 10⁻³) = 2.72, kubikwe ezindaweni ezimbili zedesimali ngoba u-Ka unezinombolo ezibalulekile ezimbili.

Qhathanisa lokho ne-asidi eqinile ekugxileni okufanayo, ebizonikeza i-pH 0.70. I-asidi ebuthaka inokugxila kwe-hydronium okucishe kube yingxenye eyodwa kweyikhulu.

Isibonelo esisebenzile: lapho indlela emfushane yehluleka futhi udinga i-quadratic

Thola i-pH ye-nitrous acid engu-0.0500 M, HNO₂, eno-Ka = 4.6 × 10⁻⁴ evela kuSithasiselo H. Indlela emfushane inikeza x = √(4.6 × 10⁻⁴ × 0.0500) = 4.8 × 10⁻³ M, okungamaphesenti angu-9.6 ka-0.0500. Lokho kwehluleka ukuhlola kwamaphesenti angu-5, ngakho xazulula isibalo esiphelele.

Hlela kabusha u-4.6 × 10⁻⁴ = x² / (0.0500 − x) ube x² + (4.6 × 10⁻⁴)x − 2.3 × 10⁻⁵ = 0. I-root enhle ingu-x = 4.57 × 10⁻³ M, ngakho pH = 2.34 futhi i-asidi inamaphesenti angu-9.1 e-ionization. Indlela emfushane ibizonikeza i-pH 2.32. Umehluko ka-0.02 ubukeka umncane, kodwa mkhulu kunokunemba kuka-0.01 okusekelwa yidatha, ngakho impendulo ye-quadratic yiyona okufanele ibikwe.

Umthetho wesithupha osheshayo: indlela emfushane ngokuvamile iphephile lapho ukugxila kokuqala okuhlukaniswe ngo-Ka kungaphezu kwamakhulu ambalwa. Lapha u-0.0500 / 4.6 × 10⁻⁴ ucishe abe ngu-110 kuphela, yingakho yehlulekile. Noma kunjalo yenza ukuhlola kwamaphesenti angu-5 njalo.

Iphesenti le-ionization liyakhuphuka njengoba i-asidi ihlanjululwa

Iphesenti le-ionization ngu-[H₃O⁺] ekulinganeni ohlukaniswe ngokugxila kokuqala kwe-asidi, uphindaphindwe ngo-100. Ku-asidi ebuthaka aliguquki. Ukuxazulula isibalo esiphelele se-acetic acid kunikeza amaphesenti angu-0.94 ku-0.200 M, angu-3.0 ku-0.0200 M nangu-9.0 ku-0.00200 M.

Isizathu yisimiso sika-Le Chatelier esisetshenziswe ekuhlanjululweni. Ukuhlanjulula kwehlisa konke ukugxila, okwehlisa u-Q ngaphansi kuka-Ka, futhi ukulingana kushintshela ema-ayonini amaningi. I-pH isakhuphuka ngokuhlanjululwa, isuka ku-2.72 iye ku-3.23 iye ku-3.74 kulolu chungechunge, kodwa cishe ngengxenye yeyunithi kuphela ngokuhlanjululwa ngakunye okuphindwe kayishumi, hhayi iyunithi ephelele obungayibona ku-asidi eqinile.

Isibonelo esisebenzile: isisekelo esibuthaka ne-pOH yaso

Thola i-pH ye-ammonia engu-0.120 M, eno-Kb = 1.8 × 10⁻⁵ evela kuSithasiselo I. Itafula linesimo esifanayo nese-asidi, kodwa umkhiqizo yi-hydroxide: [NH₄⁺] = [OH⁻] = x no-[NH₃] = 0.120 − x.

Bese x² = 1.8 × 10⁻⁵ × 0.120, ngakho x = [OH⁻] = 1.5 × 10⁻³ M. Ukuhlola kunikeza iphesenti elingu-1.2, ngakho indlela emfushane iyasebenza. pOH = −log(1.47 × 10⁻³) = 2.83, futhi pH = 14.00 − 2.83 = 11.17. Iphutha elivame kakhulu lapha ukubika u-2.83 njenge-pH. Isisekelo kufanele sinikeze i-pH engaphezu kuka-7.

Usawoti ama-ayoni awo asabela namanzi

Kunoma yiliphi ibhangqa le-asidi nesisekelo le-conjugate emanzini, Ka × Kb = Kw = 1.0 × 10⁻¹⁴ ku-25 °C. Uma i-asidi iqinile kakhulu, isisekelo sayo se-conjugate sibuthaka kakhulu. Lokhu kukuvumela ukuthi uthole okungaguquki amatafula angakubhali.

Isibonelo esisebenzile 1. Thola i-pH ye-sodium acetate engu-0.100 M. I-Na⁺ ayisabeli namanzi, kodwa i-acetate iyisisekelo esibuthaka. U-Kb wayo ungu-1.0 × 10⁻¹⁴ / 1.8 × 10⁻⁵ = 5.6 × 10⁻¹⁰. Bese [OH⁻] = √(5.6 × 10⁻¹⁰ × 0.100) = 7.5 × 10⁻⁶ M, pOH = 5.13 no-pH = 8.87. Isixazululo siyisisekelo kancane.

Isibonelo esisebenzile 2. Thola i-pH ye-ammonium chloride engu-0.200 M. I-Cl⁻ iyisisekelo se-conjugate se-asidi eqinile futhi ayinamthelela olinganisekayo, kodwa i-NH₄⁺ iyi-asidi ebuthaka eno-Ka = 1.0 × 10⁻¹⁴ / 1.8 × 10⁻⁵ = 5.6 × 10⁻¹⁰. Bese [H₃O⁺] = √(5.6 × 10⁻¹⁰ × 0.200) = 1.1 × 10⁻⁵ M, futhi pH = 4.98.

• I-cation evela esisekelweni esiqinile (Na⁺, K⁺) ne-anion evela ku-asidi eqinile (Cl⁻, NO₃⁻): akuthathi hlangothi.
• I-cation evela esisekelweni esiqinile ne-anion ye-asidi ebuthaka (CH₃COO⁻, F⁻, CN⁻): kuyisisekelo.
• I-cation eyi-asidi ye-conjugate yesisekelo esibuthaka (NH₄⁺) ne-anion ye-asidi eqinile: kune-asidi.
• Womabili ama-ayoni ayasabela: qhathanisa u-Ka we-cation no-Kb we-anion. Noma iyiphi i-constant enkulu iyanqoba.

Ama-asidi e-polyprotic alahlekelwa ama-proton awo ngamunye ngamunye

Ama-asidi afana ne-carbonic acid, H₂CO₃, ne-phosphoric acid, H₃PO₄, ano-Ka owodwa nge-proton ngayinye, futhi ngamunye mncane kakhulu kunalowo owandulelayo. Nge-carbonic acid, uSithasiselo H ubhala u-Ka1 = 4.3 × 10⁻⁷ no-Ka2 = 4.7 × 10⁻¹¹. Ngoba u-Ka1 mkhulu ngokuphindwe izinkulungwane kuno-Ka2, cishe yonke i-hydronium ivela esinyathelweni sokuqala.

Isibonelo esisebenzile. Nge-carbonic acid engu-0.0330 M, thatha isinyathelo sokuqala njenge-asidi ebuthaka eyodwa: [H₃O⁺] = √(4.3 × 10⁻⁷ × 0.0330) = 1.2 × 10⁻⁴ M, ngakho pH = 3.92. Isinyathelo sesibili asikushintshi kakhulu lokhu. Ngoba u-[H₃O⁺] no-[HCO₃⁻] acishe alingane, ayakhansela esishweni sika-Ka2, futhi u-[CO₃²⁻] uphuma ecishe alingane no-Ka2, 4.7 × 10⁻¹¹ M.

Amaphutha e-asidi nesisekelo esibuthaka okufanele uwaqaphele

Ngaphambi kokuqeda, buza ukuthi impendulo inengqondo yini. Isixazululo se-asidi ebuthaka kufanele sibe ne-pH ephakeme kune-asidi eqinile yokugxila okufanayo, kanti isisekelo esibuthaka sibe ne-pH ephansi kunesisekelo esiqinile.

• Ukuthatha i-asidi ebuthaka njengeqinile futhi ubeke u-[H₃O⁺] alingane nokugxila kokuqala.
• Ukweqa ukuhlola kwamaphesenti angu-5 ngemva kokususa u-x.
• Ukubika i-pOH njenge-pH yesisekelo, noma ukukhohlwa ukuguqula ekugcineni.
• Ukusebenzisa u-Ka lapho kudingeka u-Kb we-anion kasawoti. Guqula ngo-Kw kuqala.
• Ukuthatha i-Cl⁻, NO₃⁻ noma i-Na⁺ sengathi ziyayishintsha i-pH.
• Ukwengeza i-hydronium ye-ionization yesibili kweyokuqala ku-asidi ye-polyprotic lapho u-Ka2 emncane kakhulu kuno-Ka1.
• Ukubika izindawo zedesimali eziningi ku-pH kunezinombolo ezibalulekile ezikhona ku-Ka.