Izibalo ze-titration: kusuka kuvolumu ye-buret kuya enanini le-analyte

Izinombolo ezintathu ezidingwa yizo zonke izibalo ze-titration

Ku-titration, isixazululo sokugxila okwaziwayo (i-titrant) sengezwa sisuka ku-buret siya entweni elinganiswayo (i-analyte) kuze kube yilapho ukusabela phakathi kwazo kuphelele. Zonke izibalo zisebenzisa izingcezu ezintathu zolwazi: ukugxila kwe-titrant, ivolumu ye-titrant ethululiwe, nesilinganiso sama-mole esivela esibalweni esilinganisiwe.

Umzila uhlala ufana. Guqula ivolumu ye-titrant ibe ngamalitha bese uyiphindaphinda ngokugxila kwayo ukuze uthole ama-mole e-titrant, n = c × V. Sebenzisa isilinganiso sama-mole ukuguqula kube ama-mole e-analyte. Bese uguqulela kunoma yini umbuzo oyibuzayo: ukugxila, isisindo, noma iphesenti lesampula.

I-equivalence point yiphuzu lapho i-titrant engeziwe ilingana ncamashi ne-analyte ngesilinganiso se-stoichiometric. I-endpoint yilokho okubonayo ngempela, njenge-indicator eshintsha umbala. Indlela enhle yenza kokubili kucishe kuqondane, futhi umehluko omncane phakathi kwakho ubizwa ngokuthi iphutha le-titration.

Ukumisa i-sodium hydroxide nge-potassium hydrogen phthalate

Awukwazi ukwenza isixazululo se-sodium hydroxide esinembile ngokukala into eqinile. Amaphilisi e-NaOH amunca amanzi ne-carbon dioxide emoyeni, ngakho isisindo sawo akusona sonke i-NaOH. Kunalokho, isixazululo esilungiswe cishe siyamiswa: senziwa i-titration ngokuqhathaniswa ne-primary standard, into ehlanzekile futhi ezinzile ngokwanele ukuthi ikalwe ngqo.

I-potassium hydrogen phthalate, KHC₈H₄O₄ (evame ukubizwa ngokuthi i-KHP), iyinto ekhethwa kakhulu. Iyinto eqinile ezinzile, engeyona i-hygroscopic ene-hydrogen eyodwa ene-asidi, futhi i-NIST iqinisekisa ibanga layo njenge-primary standard ye-acidimetric (SRM 84L). Isisindo sayo se-molar esikhulu sisho nokuthi isampula evamile isinda cishe uhhafu wegremu, ngakho iphutha lokukala elihlobene lincane.

Isibonelo esisebenzile 1. Isampula ye-KHP engu-0.5106 g idinga u-24.68 mL wesixazululo se-NaOH ukuze ifike ku-endpoint ye-phenolphthalein. Ukusabela kungu-1:1: KHC₈H₄O₄(aq) + NaOH(aq) → KNaC₈H₄O₄(aq) + H₂O(l). Usebenzisa izisindo ze-athomu ezijwayelekile ze-IUPAC (K 39.098, C 12.011, H 1.008, O 15.999), M(KHP) = 204.22 g/mol. n(KHP) = 0.5106 g ÷ 204.22 g/mol = 2.500 × 10⁻³ mol, okulingana no-n(NaOH). c(NaOH) = 2.500 × 10⁻³ mol ÷ 0.02468 L = 0.1013 mol/L, kubikwe ngezinombolo ezibalulekile ezine ngoba isisindo nevolumu ngakunye kunezine.

Ama-asidi e-diprotic ashintsha isilinganiso sama-mole

I-sulfuric acid inikela ngama-proton amabili ngemolekyuli ngayinye ku-hydroxide: H₂SO₄(aq) + 2 NaOH(aq) → Na₂SO₄(aq) + 2 H₂O(l). Ngakho i-mole ngayinye ye-asidi idla ama-mole amabili esisekelo, futhi isilinganiso sama-mole kufanele sivele kulesi sibalo, hhayi emkhubeni wokuthatha ama-titration njengo-1:1.

Isibonelo esisebenzile 2. Isampula ye-sulfuric acid engu-25.00 mL yenziwa i-titration nge-NaOH engu-0.1013 mol/L evela esibonelweni 1, futhi i-endpoint ifika ku-18.45 mL. n(NaOH) = 0.1013 mol/L × 0.01845 L = 1.869 × 10⁻³ mol. n(H₂SO₄) = 1.869 × 10⁻³ mol ÷ 2 = 9.345 × 10⁻⁴ mol. c(H₂SO₄) = 9.345 × 10⁻⁴ mol ÷ 0.02500 L = 0.03738 mol/L. Ukusebenzisa isilinganiso esingu-1:1 ngephutha bekuzonikeza u-0.07476 mol/L, okuphindwe kabili ncamashi inani langempela.

Ama-asidi e-polyprotic abuthaka adinga ukuqapha okwengeziwe. Nge-phosphoric acid, ama-proton aphuma ngezinyathelo ezihlukene ngokucacile, ngakho isilinganiso sincike ekutheni iyiphi i-equivalence point i-indicator yakho eyibonayo. Sho leyo endpoint ngaphambi kokuthi ukhethe isilinganiso sama-mole.

Ama-titration e-redox: i-permanganate ne-iron(II)

Ama-titration awakhawulelwe kuma-asidi nezisekelo. Esixazululweni se-asidi, i-permanganate yenza i-oxidation ye-iron(II): MnO₄⁻(aq) + 5 Fe²⁺(aq) + 8 H⁺(aq) → Mn²⁺(aq) + 5 Fe³⁺(aq) + 4 H₂O(l). I-manganese isuka ku-+7 iye ku-+2, izuza ama-electron amahlanu, kanti i-iron ngayinye ilahlekelwa eyodwa, ngakho i-ayoni eyodwa ye-permanganate isabela nama-ayoni amahlanu e-iron(II).

I-permanganate isebenza njenge-indicator yayo. I-ayoni ye-MnO₄⁻ ibubende kakhulu kanti i-Mn²⁺ icishe ingabi nambala, ngakho iconsi lokuqala elingaphezulu lenza ifulaski libe nombala opinki ophaphathekile ohlala njalo. I-potassium permanganate ayiyona i-primary standard, futhi izixazululo zayo ziyabola kancane kancane, ngakho ziyamiswa ngaphambi kokusetshenziswa, ngokuvamile ngokuqhathaniswa ne-sodium oxalate.

Isibonelo esisebenzile 3. Isampula yensimbi engcolile ye-iron engu-1.2084 g iyancibilikiswa futhi yonke i-iron yayo yenziwa i-reduction ibe yi-Fe²⁺. I-titration idinga u-26.34 mL we-KMnO₄ engu-0.02150 mol/L. n(MnO₄⁻) = 0.02150 mol/L × 0.02634 L = 5.663 × 10⁻⁴ mol. n(Fe²⁺) = 5 × 5.663 × 10⁻⁴ mol = 2.832 × 10⁻³ mol. Usebenzisa u-Fe 55.845 g/mol, isisindo se-iron singu-0.1581 g, futhi insimbi engcolile ingu-0.1581 g ÷ 1.2084 g × 100 = 13.09 amaphesenti e-iron ngesisindo.

Ama-back titration ezintweni eziqinile ezisabela kancane

Amanye amasampula awancibiliki noma awasabeli ngokushesha ngokwanele ukuze kwenziwe i-titration eqondile. I-calcium carbonate ephilisini le-antacid iyisibonelo: isabela ne-asidi, kodwa iyinto eqinile futhi ukusabela kukhulula i-carbon dioxide, okwenza i-endpoint ecacile kube nzima ukuyibona. Ku-back titration wengeza inani elikalwe elingaphezulu le-reagent eyodwa, uvumele ukusabela kuphele, bese wenza i-titration yanoma yini esele.

Isibonelo esisebenzile 4. Ingxenye engu-0.5000 g yephilisi le-antacid eligayiwe iphathwa ngo-50.00 mL we-HCl engu-0.2000 mol/L, okungaphezu kokwanele ukusabela nayo yonke i-CaCO₃ yalo: CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). Ngemva kokuba isixazululo sibiliswe ukuxosha i-CO₂, i-asidi esele idinga u-21.38 mL we-NaOH engu-0.1000 mol/L. I-HCl engeziwe: 0.2000 × 0.05000 = 1.000 × 10⁻² mol. I-HCl esele, elingana ne-NaOH esetshenzisiwe: 0.1000 × 0.02138 = 2.138 × 10⁻³ mol. I-HCl edliwe yiphilisi: 1.000 × 10⁻² − 2.138 × 10⁻³ = 7.862 × 10⁻³ mol.

I-carbonate isabela ngo-1:2 ne-asidi, ngakho n(CaCO₃) = 7.862 × 10⁻³ ÷ 2 = 3.931 × 10⁻³ mol. Ngo-M(CaCO₃) = 100.09 g/mol, isisindo singu-0.3935 g (0.39345 g ngaphambi kokuyisa), okungamaphesenti angu-78.69 engxenye engu-0.5000 g. Ukususa yisinyathelo esivame kakhulu ukweqiwa. Ngaphandle kwaso, ubuzobe ubala i-asidi esele efulaskini, hhayi i-asidi esetshenziswe yiphilisi.

Ukukhetha i-indicator nobuchwepheshe be-buret

I-indicator ishintsha umbala ebangeni elicishe libe yi-pKa yayo ± 1, ngakho khetha eyodwa ebanga layo liwela engxenyeni ewumqansa yejika le-titration. Ku-asidi eqinile nesisekelo esiqinile cishe ku-0.1 mol/L, i-equivalence point iku-pH 7.00 futhi i-pH yeqa amayunithi amaningana ngaphakathi kwamaconsi amabili noma kamunye, ngakho ama-indicator amaningana avamile anikeza i-endpoint ecacile, kuhlanganise ne-phenolphthalein. Ku-asidi ebuthaka nesisekelo esiqinile, i-equivalence point iyisisekelo: i-OpenStax ibala i-pH 8.72 ye-acetic acid engu-0.100 mol/L eyenziwe i-titration nge-NaOH engu-0.100 mol/L. I-phenolphthalein, eba pinki ngaphezu kwe-pH 8.3 cishe, ifanele leso simo. I-methyl orange (Ka = 4.0 × 10⁻⁴ ku-OpenStax, ngakho pKa ≈ 3.4) ibizoshintsha umbala kusenesikhathi kakhulu.

I-buret engu-50 mL ifundwa ku-0.01 mL, futhi ivolumu ngayinye ethululiwe ingumehluko wokufundwa okubili. Ukungaqiniseki okucishe kube ngu-±0.02 mL kungamaphesenti angu-0.08 okuthululwe okungu-25 mL kodwa kungamaphesenti angu-0.4 okungu-5 mL. Yingakho izindlela ziklanywa ukuze ivolumu ye-titrant iwele maphakathi nebanga le-buret.

• Hlambulula i-buret ngama-milliliter ambalwa e-titrant ngaphambi kokuyigcwalisa, ukuze amanzi asele angayihlanjululi.
• Susa ibhamuza lomoya esihlokweni ngaphambi kokufunda kokuqala.
• Funda ingezansi le-meniscus ezingeni lamehlo, futhi urekhode kokubili ukufunda, hhayi umehluko kuphela.
• Yenza i-titration yokulinganisela kuqala, bese uphinda kuze kube yilapho ama-titration amabili enziwe ngokucophelela evumelana kakhulu.

Amaphutha ezibalo ze-titration nokuhlola kwawo

Izimpendulo eziningi ezingalungile zivela esilinganisweni sama-mole noma kumayunithi, hhayi kukhemistri. Ngaphambi kokubala, bhala isibalo esilinganisiwe bese uzungeza ama-coefficient e-titrant ne-analyte.

• Ukusebenzisa u-C₁V₁ = C₂V₂ ku-titration. Leyo ndlela emfushane ingeyokuhlanjulula futhi ithatha isilinganiso esingu-1:1, esehluleka ku-H₂SO₄, Ba(OH)₂ no-MnO₄⁻/Fe²⁺.
• Ukushiya amavolumu engama-milliliter kanti ukugxila kungu-mol/L. Guqula ube amalitha, noma usebenzise ama-millimole ngokungaguquki.
• Ukukhohlwa ukususa ku-back titration.
• Ukusebenzisa isisindo sefomula sohlobo olungalungile, njenge-NaOH esikhundleni se-KHP ekumiseni.
• Ukubika izinombolo ezibalulekile eziningi kunalezo i-buret nesikali ezizisekelayo. Ezine zijwayelekile emsebenzini we-volumetric owenziwe ngokucophelela.
• Ukucabanga ukuthi isixazululo asithathi hlangothi kuyo yonke i-equivalence point. Lokho kuyiqiniso kuphela ku-asidi eqinile nesisekelo esiqinile.