Aashitooyinka, saldhigyada iyo pH: wareejinta borotoonka iyo cabbirka logarithm-ka

Laga bilaabo aashitooyinka Arrhenius ilaa wareejinta borotoonka ee Brønsted–Lowry

Arrhenius wuxuu aashito ku qeexay isku-dhis soo saara ayoonnada hydrogen biyaha ku jira, saldhigna sida mid soo saara ayoonnada hydroxide. Qeexiddu waxay u shaqeysaa hydrochloric acid iyo sodium hydroxide, laakiin ma sharxi karto sababta ammonia, NH₃, oo aan lahayn hydroxide, biyaha uga dhigto saldhig.

Qeexidda Brønsted–Lowry waxay tan hagaajisaa iyadoo diiradda saarta borotoonka. Aashitadu waa bixiye borotoon, saldhiggu waa aqbale borotoon, sidaa darteed falgal aashito–saldhig kasta waa wareejin borotoon hal nooc ilaa mid kale. Ammonia waa saldhig sababtoo ah waxay ka aqbashaa borotoon biyaha: NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq).

Borotoon qaawan biyaha kuma jiro xor ahaan. Wuxuu ku xidhmaa molekiyuul biyo ah si uu u sameeyo ayoonka hydronium, H₃O⁺. Kimistariyaashu badanaa waxay qoraan H⁺(aq) sida soo koob, labada qoritaanna macnahooda isku mid ayuu yahay xisaabaha pH.

Helidda lammaanayaasha aashito–saldhig ee isku-xidhan

Marka aashito borotoon bixiso, waxa haraa waa saldhigeeda isku-xidhan; marka saldhig borotoon aqbalo, wuxuu noqdaa aashitadiisa isku-xidhan. Labada xubnood ee lammaane isku-xidhan waxay ku kala duwan yihiin si sax ah hal H⁺. HF(aq) + H₂O(l) ⇌ F⁻(aq) + H₃O⁺(aq), lammaanayaashu waa HF/F⁻ iyo H₃O⁺/H₂O.

Biyuhu waxay ka muuqdaan sida saldhig falgalka HF iyo sida aashito falgalka ammonia. Nooca bixin kara ama aqbali kara borotoon waxaa loo yaqaan amphiprotic. Hydrogen carbonate, HCO₃⁻, waa tusaale kale: wuxuu lumin karaa borotoon si uu u noqdo CO₃²⁻ ama helo mid si uu u noqdo H₂CO₃.

• Qor isleegga oo hel nooca lumiya H⁺ marka bidix ilaa midig loo socdo. Taasi waa aashitada.
• Hel nooca helaya H⁺. Taasi waa saldhigga.
• Lammaanee falgale kasta iyo wax-soo-saarka ka duwan hal H⁺, oo hubi in dallacaaduhu ku kala duwan yihiin hal.

Xooggan iyo daciif waxay qeexaan baaxad, ma aha uruurin

Aashito xooggani waxay ionaysanaysaa ku dhawaad gabi ahaan biyaha, sidaa darteed molekiyuul aashito ah kasta oo la milay wuxuu bixiyaa H₃O⁺ iyo saldhigeeda isku-xidhan. Aashitooyinka xooggan ee caadiga ahi waa HCl, HBr, HI, HNO₃, HClO₄ iyo H₂SO₄ (borotoonkiisa koowaad). Saldhigyada xooggan ee caadiga ahi waa hydroxide-yada biraha kooxda 1 iyo kuwa calcium, strontium iyo barium. Aashito daciif ahi waxay ionaysanaysaa qayb ahaan oo keliya, isu-dheellitirna waxaa lagu dhisaa u dhexeeya molekiyuulka iyo ayoonnadiisa.

Xoogga iyo uruurintu waa fikrado kala duwan. Xal khafiif ah oo aashito xooggan ah wuxuu yeelan karaa ayoonno hydronium oo ka yar xal uruuran oo aashito daciif ah. Uruurin isku mid ah, hase yeeshee, farqigu waa weyn yahay. Xal HCl ah oo 0.10 mol/L wuxuu leeyahay [H₃O⁺] = 0.10 mol/L iyo pH 1.00. Acetic acid, oo leh joogtada ionaysiga aashitada Ka = 1.8 × 10⁻⁵ (OpenStax Lifaaqa H), waa qiyaastii 1 boqolkiiba oo keliya ionaysan 0.10 mol/L, pH-keedana waa qiyaastii 2.9. Xisaabaha isu-dheellitirka aashitada daciifka ahi waa mawduuc gooni ah; hagahan wuxuu isticmaalaa barbar dhigga oo keliya.

Xoogga aashitada iyo saldhigeeda isku-xidhan waa isku xidhan yihiin. Saldhigyada isku-xidhan ee aashitooyinka xooggan, sida Cl⁻ iyo NO₃⁻, waxay leeyihiin u janjeera la tixgelin karin oo ah inay aqbalaan borotoon biyaha.

Wax-soo-saarka ayoonka ee biyaha, pH iyo pOH

Xataa biyo saafi ah waxay ka kooban yihiin dhawr ayoon, sababtoo ah molekiyuullada biyuhu waxay wareejiyaan borotoonno midba midka kale: 2 H₂O(l) ⇌ H₃O⁺(aq) + OH⁻(aq). Joogtada isu-dheellitirka ee is-ionaysigan waa Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ 25 °C. Biyaha saafiga ah labada uruurin way le'eg yihiin, 1.0 × 10⁻⁷ mol/L mid walba. Xal biyo ku jira kasta 25 °C, haddii aad ogtahay hal uruurin waxaad heli kartaa tan kale adigoo Kw ku qaybinaya.

Sababtoo ah uruurintan waxay ka kooban yihiin awoodo toban oo badan, kimistariyaashu waxay isticmaalaan logarithm: pH = −log[H₃O⁺] iyo pOH = −log[OH⁻]. Qaadashada logarithm-ka taban ee eraygii Kw waxay bixisaa pH + pOH = 14.00 25 °C. Isbeddel hal cutub pH ah waa isbeddel toban jibaar ah oo uruurinta hydronium ah, sidaa darteed xal pH 3 ah wuxuu leeyahay 100 jibaar [H₃O⁺] ee mid pH 5 ah.

Dhexdhexaad macnaheedu waa [H₃O⁺] = [OH⁻], taasoo ah pH 7.00 25 °C oo keliya. Kw wuu kordhaa heerkulka; OpenStax waxay bixisaa qiyaastii 5.6 × 10⁻¹³ 100 °C, halkaas oo biyaha dhexdhexaadka ahi ay leeyihiin pH u dhow 6.1. Logarithm-yada, tirada meelaha tobanlaha ee pH waxay le'eg tahay tirada tirooyinka muhiimka ah ee uruurinta.

Xisaabinta pH ee aashitooyinka iyo saldhigyada xooggan

Tusaalaha la xaliyey 1. Hel pH ee nitric acid 4.6 × 10⁻³ mol/L. HNO₃ waa xoog badan, sidaa darteed [H₃O⁺] = 4.6 × 10⁻³ mol/L. pH = −log(4.6 × 10⁻³) = 2.34. Uruurintu waxay leedahay laba tiro oo muhiim ah, sidaa darteed pH wuxuu leeyahay laba meelood oo tobanle. Kadibna [OH⁻] = (1.0 × 10⁻¹⁴)/(4.6 × 10⁻³) = 2.2 × 10⁻¹² mol/L, aad u yar sida laga filayo xal aashito ah.

Tusaalaha la xaliyey 2. 0.350 g potassium hydroxide ayaa la milay si loo sameeyo 750.0 mL xal. Adigoo isticmaalaya culeysyada atamka caadiga ah ee IUPAC oo loo dhoweeyey laba meelood oo tobanle (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, iyo [OH⁻] = 6.24 × 10⁻³ mol / 0.7500 L = 8.32 × 10⁻³ mol/L. pOH = 2.080, iyo pH = 14.00 − 2.080 = 11.92, oo ku xaddidan laba meelood oo tobanle 14.00.

Tusaalaha la xaliyey 3. Hel pH ee strontium hydroxide 3.60 × 10⁻³ mol/L. Sr(OH)₂ wuxuu sii daayaa laba ayoon hydroxide ah cutub qaacido kasta, sidaa darteed [OH⁻] = 2 × 3.60 × 10⁻³ = 7.20 × 10⁻³ mol/L. pOH = 2.143 iyo pH = 14.00 − 2.143 = 11.86. Ilaawidda arrinta 2 waxay bixin lahayd pH qiyaastii 0.30 oo aad u hooseeya.

Tusaalaha la xaliyey 4. Xal wuxuu leeyahay pH 4.62. Rog logarithm-ka: [H₃O⁺] = 10 oo loo qaaday awoodda −4.62 = 2.4 × 10⁻⁵ mol/L. Labada meel ee tobanlaha ee pH waxay oggolaadaan laba tiro oo muhiim ah uruurinta. pOH waa 14.00 − 4.62 = 9.38, sidaa darteed [OH⁻] = 4.2 × 10⁻¹⁰ mol/L.

Khaladaadka logarithm-ka iyo istoikiyomitari ee shaqada pH

Khaladaadka pH intooda badan waxay ka yimaadaan logarithm-ka ama qaacidada aashitada ama saldhigga. Hubin degdeg ah oo macquul ah ayaa qabata qaar badan: xalalka aashitada 25 °C waxay leeyihiin pH ka hooseeya 7, kuwa saldhigga ahna ka sarreeya 7, arrin toban jibaar ah oo uruurinta ahna wuxuu pH u dhaqaajiyaa hal cutub.

Ka taxadar aashitooyinka xooggan ee aad u khafiifka ah. Xal HCl ah oo 1.0 × 10⁻⁸ mol/L ma laha pH 8, taasoo noqon lahayd saldhig. Uruurinta hoose ee noocaas ah, ayoonnada hydronium ee ka yimaadda ionaysiga biyaha lafteeda lama dhimi karo, daaweyn buuxdana waxay bixisaa pH qiyaastii 6.98, wax yar ka hooseeya dhexdhexaad.

• Tuurista calaamadda taban: −log ee lambar ka yar 1 waa togan. pH taban oo xal khafiif ah oo caadi ahi wuxuu muujiyaa khalad calaamad.
• Ilaawidda istoikiyomitari: Ca(OH)₂, Sr(OH)₂ iyo Ba(OH)₂ mid kastaa wuxuu sii daayaa laba OH⁻ cutub qaacido kasta.
• Isticmaalka pH marka saldhiggu bixiyo pOH: marka hore ka hel pOH [OH⁻], kadibna u beddel.
• U aqoonsiga aashito daciif ah sida mid xooggan: [H₃O⁺] wuxuu le'eg yahay uruurinta aashitada aashitooyinka xooggan oo keliya.
• Ku dabaqidda pH + pOH = 14.00 heerkulka aad uga fog 25 °C.