Buffer-yada iyo isleegga Henderson–Hasselbalch

Laba lammaane oo mid kastaa dhexdhexaadiyo hal khatar

Qaado isku-dhaf acetic acid ah, CH₃COOH, iyo sodium acetate, oo bixiya CH₃COO⁻. Haddii aashito xooggan lagu daro, ayoonka acetate ayaa qaata borotoonnada dheeraadka ah: CH₃COO⁻ + H₃O⁺ → CH₃COOH + H₂O. Haddii saldhig xooggan lagu daro, acetic acid ayaa dhexdhexaadisa: CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O.

Labada falgalba ku dhawaad way dhammaystirmaan, sidaa darteed aashitada ama saldhigga xooggan ee lagu daray waxaa loo beddelaa lammaanaha daciifka ah oo dheeraad ah. pH-gu weli wuu dhaqaaqaa, sababtoo ah saamiga aashitada iyo saldhiggu wuu isbeddelaa, laakiin wax yar oo keliya. Xal aashito daciif ah oo keligeed ahi ma samayn karo tan, sababtoo ah ku dhawaad ma laha saldhig isku-xidhan oo nuuga aashitada lagu daray.

Lammaanayaasha buffer-ka caadiga ah waxaa ka mid ah acetic acid iyo acetate, ammonium iyo ammonia, dihydrogen phosphate iyo hydrogen phosphate, iyo carbonic acid iyo hydrogen carbonate. Lammaanaha ugu dambeeya wuxuu ka caawiyaa in dhiigga aadanaha lagu hayo meel u dhow pH 7.4, sida OpenStax qaybta 14.6 sharxdo.

Ka soo saarista Henderson–Hasselbalch tibxaha Ka

Ka bilow Ka = [H₃O⁺][A⁻]/[HA] oo u xalli hydronium: [H₃O⁺] = Ka × [HA]/[A⁻]. Qaado −log labada dhinac si aad u hesho pH = pKa + log([A⁻]/[HA]). Kani waa isleegga Henderson–Hasselbalch.

Buffer gudihiisa, HA iyo A⁻ labaduba waxay ku jiraan qadarro badan, mid kastaana wuxuu xakameeyaa falgalka kan kale ee biyaha. Sidaa darteed uruurintooda isu-dheellitirku waxay ku dhawaad le'eg yihiin qadarrada aad isku dartay. Taasi waa sababta aad uruurinta la diyaariyey si toos ah ugu dhigi karto isleegga adigoon shax ICE isticmaalin.

Sababtoo ah labada lammaane waxay ku jiraan isla mug, saamiga uruurintu wuxuu le'eg yahay saamiga moolasha. Waxaad si toos ah u isticmaali kartaa moolasha, taasoo kaa badbaadinaysa tallaabo kadib marka aashito ama saldhig lagu daro.

Marka [A⁻] = [HA], erayga log waa eber iyo pH = pKa.
Koror kasta oo toban jibaar ah oo saamiga saldhigga iyo aashitada ah wuxuu pH kor ugu qaadaa hal cutub.
Saldhig isku-xidhan oo ka badan aashitada wuxuu bixiyaa pH ka sarreeya pKa; aashito ka badan waxay bixisaa pH ka hooseeya.

Tusaale la xaliyey: pH-ka buffer acetate ah

Buffer ayaa ka kooban 0.300 M CH₃COOH iyo 0.250 M CH₃COONa. Lifaaqa H wuxuu bixiyaa Ka = 1.8 × 10⁻⁵, sidaa darteed pKa = 4.745. Markaa pH = 4.745 + log(0.250/0.300) = 4.745 − 0.079 = 4.67.

Sii wad pKa-ga aan la dhoweyn ilaa dhammaadka. Haddii marka hore loo dhoweeyo 4.74 waxay bixisaa 4.66. Farqigu wuxuu ku jiraa hubanti la'aanta Ka laba tiro oo muhiim ah leh, laakiin dhoweynta mar keliya dhammaadka waxay jawaabahaaga ka dhigaysaa kuwo la jaanqaada furaha jawaabaha. pH-gu wax yar ayuu ka hooseeyaa pKa, sidii la filayey, sababtoo ah aashitadu wax yar ayay ka badan tahay saldhigga.

Tusaale la xaliyey: ku darista aashito xooggan, kadibna saldhig xooggan

Ku dar 0.0200 mol HCl 1.00 L oo buffer-ka kore ah. Marka hore samee dhexdhexaadinta, sida tallaabo istoikiyomitari: H₃O⁺ wuxuu 0.0200 mol acetate u beddelaa acetic acid. Acetic acid wuxuu ka kacaa 0.300 ilaa 0.320 mol acetate-kuna wuxuu ka dhacaa 0.250 ilaa 0.230 mol. Markaa pH = 4.745 + log(0.230/0.320) = 4.60. pH-gu wuxuu ka dhacay 4.67 ilaa 4.60, wax ka yar toban meelood meel cutub.

Ku darista isla 0.0200 mol HCl 1.00 L oo biyo saafi ah waxay bixin lahayd [H₃O⁺] = 0.0200 M iyo pH 1.70, hoos u dhac ka badan shan cutub oo laga bilaabo dhexdhexaad.

Hadda ku dar 0.0500 mol NaOH 1.00 L cusub oo buffer-kii asalka ahaa ah. Hydroxide-ku wuxuu 0.0500 mol acetic acid u beddelaa acetate, isagoo ka tagaya 0.250 mol aashito iyo 0.300 mol saldhig. pH = 4.745 + log(0.300/0.250) = 4.82, kor u kac 4.67 ka yimid oo ka yar 0.2. Biyo saafi ah isla NaOH-du waxay bixin lahayd pH 12.70.

Isla caqligaasi wuxuu kuu oggolaanayaa inaad buffer ku samayso dhexdhexaadin qayb ah. Isku darka 0.0400 mol acetic acid iyo 0.0150 mol NaOH wuxuu ka tagaa 0.0250 mol aashito iyo 0.0150 mol acetate, sidaa darteed pH = 4.745 + log(0.0150/0.0250) = 4.52, si kasta oo mugga ugu dambeeyaa ahaado.

Naqshadaynta buffer pH bartilmaameed ah

Marka hore dooro lammaane isku-xidhan oo pKa-giisu ku jiro hal cutub gudihiis pH-ga aad rabto. Kadib Henderson–Hasselbalch u isticmaal si rogan si aad u hesho saamiga, istoikiyomitari-na si aad saamiga ugu beddesho qadarro.

Tusaale la xaliyey. Ka diyaari buffer pH 9.50 ah 500.0 mL oo ammonia 0.200 M ah adigoo ku daraya ammonium chloride adag. Lammaanaha aashitadu waa NH₄⁺. Lifaaqa I, Kb(NH₃) = 1.8 × 10⁻⁵, sidaa darteed pKb = 4.745 iyo pKa(NH₄⁺) = 14.00 − 4.745 = 9.255. Saamiga loo baahan yahay waa [NH₃]/[NH₄⁺] = 10 oo kor loogu qaaday (9.50 − 9.255) = 1.76.

Fleesku wuxuu hayaa 0.5000 L × 0.200 mol/L = 0.100 mol NH₃, sidaa darteed wuxuu u baahan yahay 0.100 / 1.76 = 0.0569 mol NH₄⁺. Iyadoo M(NH₄Cl) = 53.49 g/mol, taasi waa qiyaastii 3.0 g oo ammonium chloride ah, oo lagu sheegay laba tiro oo muhiim ah sababtoo ah Kb wuxuu leeyahay laba. Ficil ahaan kadib waxaad pH-ga ku hubin lahayd mitir la habeeyey (calibrated) oo aad hagaajin lahayd.

Awoodda buffer-ka iyo xadka pH ee waxtarka leh

Xadka buffer-ku waa baaxadda pH ee buffer si wanaagsan u shaqeeyo. Saami 10:1 ama 1:10 ah wuxuu u dhigmaa pH = pKa ± 1, baaxaddaas dibaddeedana hal lammaane aad buu u yar yahay si uu u nuugo aashito ama saldhig badan oo dheeraad ah. Buffer-yada acetate waxay faa'iido leeyihiin qiyaastii pH 3.7 ilaa 5.7, buffer-yada ammonia-na qiyaastii 8.3 ilaa 10.3.

Awoodda buffer-ku waa qadarka aashito ama saldhig ee buffer nuugi karo kahor inta pH-giisu aad isu beddelin. Waxay ku xiran tahay inta lammaane kasta uu jiro, ma aha saamigooda oo keliya. Barbar dhig laba buffer acetate ah, mid kastaa 1.00 L oo leh aashito iyo saldhig siman. Labaduba waxay ka bilaabmaan pH = pKa = 4.74. Iyadoo 0.100 M mid kasta, ku darista 0.00500 mol HCl waxay pH hoos ugu dhigtaa 0.04, ilaa 4.70. Iyadoo 0.0100 M mid kasta, isla ku-daristu waxay hoos ugu dhigtaa ku dhawaad badh cutub, ilaa 4.27. Saamigu waa isku mid ahaa, laakiin buffer-ka khafiifka ahi wuxuu lahaa toban meelood meel awoodda.

Buffer wuu dhammaadaa marka aashitada ama saldhigga lagu daray ay isticmaasho dhammaan hal lammaane. Intaas kadib, pH-ga waxaa go'aamiya xad-dhaafka aashitada ama saldhigga xooggan, si degdeg ahna wuu isu beddelaa.

Khaladaadka jawaabta buffer-ka khaldan ka dhiga

Mushkiladaha buffer-ku waxay isku daraan laba nooc oo sababayn ah: istoikiyomitari dhexdhexaadinta iyo isu-dheellitir pH-ga. Ku hay nidaamkaas.

Qorista saamiga oo rogan. Waa saldhigga loo qaybiyey aashitada: log([A⁻]/[HA]).
Ku dhigidda HCl ama NaOH-da lagu daray isleegga Henderson–Hasselbalch kahor samaynta tallaabada dhexdhexaadinta.
Isticmaalidda pKb meesha pKa buffer ammonia ah. Ku beddel pKa + pKb = 14.00 25 °C.
Isku qasidda moolasha hal lammaane iyo uruurinta kan kale marka ay ku jiraan mugag kala duwan.
Malaynta in buffer weli shaqeeyo kadib marka aashitada ama saldhigga lagu daray ay dhaafaan qadarka hal lammaane.
U qaadashada aashito daciif ah oo keligeed ah, ama aashito daciif ah oo leh aashito xooggan, buffer.

Xadaynta iyo isticmaalka habboon

Henderson–Hasselbalch waa qiyaas. Waxay noqotaa mid aan la isku halleyn karin marka buffer-ku aad u khafiifsan yahay, marka saamigu aad uga baxsan yahay 10:1 ilaa 1:10, ama marka Ka uu ku filan yahay weynaan si aashitadu si la dareemi karo u ionaysato.
Dhammaan joogtooyinka iyo xidhiidhka pKa + pKb = 14.00 waxay khuseeyaan 25 °C. pH-ga buffer-ku wuxuu la wareegaa heerkulka.
Xisaabuhu waxay isticmaalaan uruurino halkii activities. Buffer-yada dhabta ah ee xoogga ayoonka sare leh, oo ay ku jiraan buffer-yada bayoolojiga, waxay ku kala duwanaan karaan toban meelood meel cutub pH ah ama ka badan.
Qaloocyada cabbiraadda buuxa iyo nidaamyada buffer-ka polyprotic-ga halkan lagama hadlin.