Ama-asidi, izisekelo ne-pH: ukudluliswa kwama-proton nesikali se-logarithm

Kusuka kuma-asidi ka-Arrhenius kuya ekudluliseni ama-proton kuka-Brønsted–Lowry

U-Arrhenius wachaza i-asidi njengenhlanganisela ekhiqiza ama-ayoni e-hydrogen emanzini nesisekelo njengekhiqiza ama-ayoni e-hydroxide. Incazelo isebenza ku-hydrochloric acid ne-sodium hydroxide, kodwa ayikwazi ukuchaza ukuthi kungani i-ammonia, NH₃, engenayo i-hydroxide, yenza amanzi abe yisisekelo.

Incazelo ka-Brønsted–Lowry ilungisa lokhu ngokugxila ku-proton. I-asidi ingumnikeli we-proton nesisekelo singumamukeli we-proton, ngakho ukusabela kwe-asidi nesisekelo ngakunye kungukudluliswa kwe-proton kusuka kuhlobo oluyodwa kuya kolunye. I-ammonia iyisisekelo ngoba yamukela i-proton evela emanzini: NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq).

I-proton ehlobile ayikho yodwa emanzini. Iyabopha nemolekyuli yamanzi ukwakha i-ayoni ye-hydronium, H₃O⁺. Osokhemisi kaningi babhala u-H⁺(aq) njengendlela emfushane, futhi izimpawu ezimbili zisho into efanayo ezibalweni ze-pH.

Ukuthola amabhangqa e-asidi nesisekelo e-conjugate

Lapho i-asidi inikela nge-proton, okusalayo kuyisisekelo sayo se-conjugate; lapho isisekelo samukela i-proton, siba yi-asidi yaso ye-conjugate. Amalungu amabili ebhangqa le-conjugate ahluka nge-H⁺ eyodwa ncamashi. Ku-HF(aq) + H₂O(l) ⇌ F⁻(aq) + H₃O⁺(aq), amabhangqa angu-HF/F⁻ no-H₃O⁺/H₂O.

Amanzi avela njengesisekelo ekusabeleni kwe-HF futhi njenge-asidi ekusabeleni kwe-ammonia. Uhlobo olungakwazi ukunikela noma ukwamukela i-proton lubizwa ngokuthi i-amphiprotic. I-hydrogen carbonate, HCO₃⁻, esinye isibonelo: ingalahlekelwa i-proton ibe ngu-CO₃²⁻ noma izuze eyodwa ibe ngu-H₂CO₃.

• Bhala isibalo bese uthola uhlobo olulahlekelwa u-H⁺ lapho luhamba lusuka kwesobunxele luya kwesokudla. Lokho yi-asidi.
• Thola uhlobo olutholwa u-H⁺. Lokho yisisekelo.
• Bhangqa isisabelo ngasinye nomkhiqizo ohluka kuso nge-H⁺ eyodwa, futhi uhlole ukuthi amashaji ahluka ngeyodwa.

Aqinile nabuthaka kuchaza izinga, hhayi ukugxila

I-asidi eqinile iyahlukana cishe ngokuphelele emanzini, ngakho imolekyuli ngayinye ye-asidi encibilikisiwe inikeza u-H₃O⁺ nesisekelo saso se-conjugate. Ama-asidi aqinile avamile yi-HCl, HBr, HI, HNO₃, HClO₄ ne-H₂SO₄ (ku-proton yayo yokuqala). Izisekelo eziqinile ezivamile yi-hydroxide zezinsimbi zeqembu 1 ne-calcium, strontium ne-barium. I-asidi ebuthakathaka iyahlukana ngokwengxenye kuphela, futhi kumiswa ukulingana phakathi kwemolekyuli nama-ayoni ayo.

Amandla nokugxila yimicabango ehlukene. Isixazululo esihlanjululiwe se-asidi eqinile singaba nama-ayoni e-hydronium ambalwa kunesixazululo esigxilile se-asidi ebuthaka. Ekugxileni okulinganayo, nokho, umehluko mkhulu. Isixazululo se-HCl esingu-0.10 mol/L sinoku-[H₃O⁺] = 0.10 mol/L ne-pH 1.00. I-acetic acid, enokuhlukana okungaguquki Ka = 1.8 × 10⁻⁵ (OpenStax Appendix H), iyahlukana cishe ngo-1 peresenti kuphela ku-0.10 mol/L, futhi i-pH yayo icishe ibe ngu-2.9. Izibalo zokulingana kwe-asidi ebuthaka ziyisihloko esihlukile; lesi sihlahlandlela sisebenzisa nje ukuqhathanisa.

Amandla e-asidi nesisekelo saso se-conjugate ayaxhumana. Izisekelo ze-conjugate zama-asidi aqinile, njenge-Cl⁻ ne-NO₃⁻, azinakho ukuthambekela kokwamukela i-proton emanzini.

Umkhiqizo we-ayoni wamanzi, i-pH ne-pOH

Ngisho namanzi acwebile aqukethe ama-ayoni ambalwa, ngoba amamolekyuli amanzi adlulisa ama-proton omunye komunye: 2 H₂O(l) ⇌ H₃O⁺(aq) + OH⁻(aq). Okungaguquki kokulingana kwalokhu kuzihlukanisa kungu-Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ ku-25 °C. Emanzini acwebile ukugxila okubili kuyalingana, 1.0 × 10⁻⁷ mol/L ngalinye. Esixazululweni samanzi sinoma isiphi ku-25 °C, uma wazi ukugxila okukodwa ungathola okunye ngokuhlukanisa u-Kw ngakho.

Ngoba lokhu kugxila kuhlanganisa amandla amaningi eshumi, osokhemisi basebenzisa ama-logarithm: pH = −log[H₃O⁺] ne-pOH = −log[OH⁻]. Ukuthatha i-logarithm engelihle yesisho sika-Kw kunikeza pH + pOH = 14.00 ku-25 °C. Ushintsho lweyunithi eyodwa ye-pH luyushintsho lokuphindwe ngeshumi kokugxila kwe-hydronium, ngakho isixazululo ku-pH 3 sinoku-[H₃O⁺] okuphindwe izikhathi ezingu-100 kunokwesinye ku-pH 5.

Okungathathi hlangothi kusho [H₃O⁺] = [OH⁻], okuyi-pH 7.00 kuphela ku-25 °C. U-Kw ukhula ngezinga lokushisa; i-OpenStax inikeza cishe 5.6 × 10⁻¹³ ku-100 °C, lapho amanzi angathathi hlangothi enepH eseduze no-6.1. Kuma-logarithm, inani lezindawo zamadesimali ku-pH lilingana nenani lezinombolo ezibalulekile ekugxileni.

Ukubala i-pH yama-asidi nezisekelo eziqinile

Isibonelo esisebenzile 1. Thola i-pH ye-nitric acid engu-4.6 × 10⁻³ mol/L. I-HNO₃ iqinile, ngakho [H₃O⁺] = 4.6 × 10⁻³ mol/L. pH = −log(4.6 × 10⁻³) = 2.34. Ukugxila kunezinombolo ezibalulekile ezimbili, ngakho i-pH inezindawo ezimbili zamadesimali. Bese [OH⁻] = (1.0 × 10⁻¹⁴)/(4.6 × 10⁻³) = 2.2 × 10⁻¹² mol/L, okuncane njengoba kulindelekile esixazululweni se-asidi.

Isibonelo esisebenzile 2. U-0.350 g we-potassium hydroxide uncibilikiswa ukwenza u-750.0 mL wesixazululo. Usebenzisa izisindo ze-athomu ezijwayelekile ze-IUPAC eziyiswe emadesimalini amabili (K 39.10, O 16.00, H 1.01), M(KOH) = 56.11 g/mol. n = 0.350 g / 56.11 g/mol = 6.24 × 10⁻³ mol, futhi [OH⁻] = 6.24 × 10⁻³ mol / 0.7500 L = 8.32 × 10⁻³ mol/L. pOH = 2.080, futhi pH = 14.00 − 2.080 = 11.92, ikhawulelwe ezindaweni ezimbili zamadesimali ngu-14.00.

Isibonelo esisebenzile 3. Thola i-pH ye-strontium hydroxide engu-3.60 × 10⁻³ mol/L. I-Sr(OH)₂ ikhulula ama-ayoni amabili e-hydroxide ngeyunithi yefomula ngayinye, ngakho [OH⁻] = 2 × 3.60 × 10⁻³ = 7.20 × 10⁻³ mol/L. pOH = 2.143 futhi pH = 14.00 − 2.143 = 11.86. Ukukhohlwa isici esingu-2 bekuzonikeza i-pH engaphansi ngo-0.30.

Isibonelo esisebenzile 4. Isixazululo sine-pH 4.62. Phendula i-logarithm: [H₃O⁺] = 10 ephakanyiswe emandleni −4.62 = 2.4 × 10⁻⁵ mol/L. Izindawo ezimbili zamadesimali ku-pH zivumela izinombolo ezibalulekile ezimbili ekugxileni. I-pOH ingu-14.00 − 4.62 = 9.38, ngakho [OH⁻] = 4.2 × 10⁻¹⁰ mol/L.

Amaphutha e-logarithm ne-stoichiometry emsebenzini we-pH

Amaphutha amaningi e-pH avela ku-logarithm noma efomulini ye-asidi noma yesisekelo. Ukuhlola okusheshayo kwengqondo kubamba amaningi: izixazululo ze-asidi ku-25 °C zine-pH engaphansi kuka-7, ezesisekelo ngaphezulu kuka-7, futhi isici ngasinye seshumi ekugxileni sihambisa i-pH ngeyunithi eyodwa.

Qaphela nge-asidi eqinile ehlanjululwe kakhulu. Isixazululo se-HCl esingu-1.0 × 10⁻⁸ mol/L asinayo i-pH 8, ebizoba yisisekelo. Ekugxileni okuphansi kangaka, ama-ayoni e-hydronium avela ekuzihlukaniseni kwamanzi awanganganyelwa, futhi ukwelashwa okugcwele kunikeza i-pH engaba ngu-6.98, ngaphansi kancane kokungathathi hlangothi.

• Ukulahla uphawu lokususa: −log yenombolo engaphansi kuka-1 iyinhle. I-pH engelihle esixazululweni esijwayelekile esihlanjululiwe ikhomba iphutha lophawu.
• Ukukhohlwa i-stoichiometry: i-Ca(OH)₂, Sr(OH)₂ ne-Ba(OH)₂ ngayinye ikhulula ama-OH⁻ amabili ngeyunithi yefomula.
• Ukusebenzisa i-pH lapho isisekelo sinikeza i-pOH: thola i-pOH ku-[OH⁻] kuqala, bese uguqula.
• Ukuthatha i-asidi ebuthaka njengeqinile: u-[H₃O⁺] ulingana nokugxila kwe-asidi kuphela kuma-asidi aqinile.
• Ukusebenzisa i-pH + pOH = 14.00 emazingeni okushisa akude no-25 °C.