Isivivinyo sebhodlela eliluhlaza okwesibhakabhaka: ikhemistri, inqubo, nokubonwayo

Ibhodlela elicacile lihlezi ebhentshini. Libukeka njengamanzi. Othile uyalinyakazisa, bese uketshezi luba luhlaza okwesibhakabhaka olugqamile. Uma libekwa phansi, umbala oluhlaza okwesibhakabhaka uyanyamalala phakathi komzuzu owodwa noma emibili. Linyakazise futhi, umbala ubuye. Ukugcwaliswa okukodwa kungaphinda lokhu izikhathi ezingamashumi amabili noma ngaphezulu.

Abafundi ngokuvamile bacabanga ukuthi kukhona obekufihlwe ebhodleleni, noma ukuthi ukunyakazisa kuhlanganise izingqimba ezimbili. Kokubili lokhu kuqagela kuyaphutha ngendlela efundisayo. Umbala uvela kudayi owodwa, i-methylene blue, okhona kulo lonke uketshezi. Okushintshayo inani lama-electron athwalwa udayi. Lo mbukiso ungumjikelezo we-redox obonakalayo, futhi konke okuguquguqukayo ikilasi elingakubona, isikhathi sokunyakazisa, izinga lokushisa, nokugxila, kuhambisana nengxenye ethile yekhemistri.

Izinhlobo ezimbili zodayi ofanayo

I-methylene blue ene-oxidation iyisakhiwo sezindandatho esiyisicaba, esinokushajwa okuhle. Imunca kakhulu cishe ku-600 kuya ku-700 nanometres, iso elikubona njengokuluhlaza okwesibhakabhaka okujulile. Lezi zinhlobo ezimbili nama-spectra azo kuchazwe kumhlahlandlela wesakhiwo nezakhiwo ze-methylene blue.

I-reduction yengeza ama-electron amabili ne-proton, kwakheke i-leucomethylene blue: ayinashaji, ayisicaba ngokuphelele, futhi empeleni ayinambala. Kusixazululo se-alkaline i-half-reaction ibhalwa MB+ + H2O + 2 e- ⇌ LMB + OH-. Lesi sinyathelo sibuyiseleka ngokuphelele. Okuluhlaza okwesibhakabhaka kusho ukuthi kune-oxidation, okungenambala kusho ukuthi kune-reduction, futhi asikho isimo sesithathu okufanele silandelwe, okuyikho okwenza lokhu kube isingeniso esicacile sokuqala sekhemistri ye-redox.

Umjikelezo: i-glucose iyanciphisa, i-oxygen iphinde yenze i-oxidation

Ibhodlela liqukethe izithako ezintathu ezisebenzayo: i-methylene blue, i-glucose, ne-alkali enamandla, i-potassium noma i-sodium hydroxide. I-alkali ikhuthaza i-glucose ukuba yakhe izinhlobo ezisebenzayo ezilahlekelwe yi-proton, ezinikeza udayi ama-electron:

reducing sugar + MB (blue, oxidised) -> oxidised sugar products + LMB (colourless)

Lesi sinyathelo esihamba kancane sisusa umbala lapho ibhodlela limile. I-glucose ingumnikeli osetshenziswayo futhi iyaphela. Udayi uthwala ama-electron kuphela, ngakho amaconsi ambalwa anele ebhodleleni lonke. Izincazelo ezindala zasekilasini zithi i-glucose iba yi-gluconic acid. Lokho kufingqa kuyakwazi ukubikezela okubonwayo, kodwa abafundisi kufanele bazi ukuthi akuphelele: ukuhlaziywa kwendlela yokusabela okushicilelwe ku-Royal Society Open Science kulandela i-oxidation idlule ku-enediolate esebenzayo iye ku-dicarbonyl ehlukana ibe ama-acid amancane.

Ukunyakazisa kubuyisela umphumela obonakalayo. Ukunyakaziswa kufaka i-oxygen evela emoyeni ovaleleke esikhaleni esingenhla ukuthi incibilike, bese i-oxygen iphinde yenze i-oxidation kudayi ose-reduced:

LMB (colourless) + O2 -> MB (blue) + reduced oxygen products

Uma kushiywe kumile, i-oxygen encibilikile iyaphela, i-glucose iphinde inciphise udayi, bese umbala uyafiphala. Ngemva kwemijikelezo eminingi, ikhemistri iyonke iwukwenziwa kwe-oxidation kushukela ngomoya, kuyilapho udayi uzungeza ungashintshi njengomlamuli we-redox. Ungumlamuli kunokuba ube yi-catalyst eqinile, ngoba i-oxidation kashukela iyaqhubeka noma ungekho, futhi ukufiphala akukhona ukubola: udayi owonakalisiwe ubungeke uvuselelwe ngokunyakazisa. Ukuze ugcine izitoko zodayi zizinzile phakathi kwemibukiso, bheka amanothi ngokuphathwa nokugcinwa kwezixazululo ze-methylene blue.

Inqubo yombukiso ogadiwe

Lona ngumbukiso ogadiwe, hhayi umsebenzi wasekhaya. I-alkali idinga ukuvikelwa kwamehlo, amagilavu, nomfundisi ophethe ukulungiselela nokuhlanza. Amafomula amabili abhalwe phansi ayavumelana ngesakhiwo kodwa ahlukene ngesikali.

Ishidi lemiyalelo elisekela umbukiso njengoba ushicilelwe umnyango wekhemistri wase-Indiana University lisebenzisa cishe 5 percent potassium hydroxide, 4 percent glucose, kanye 1 percent aqueous methylene blue. Thela amanani alinganayo ezixazululo ze-alkali ne-glucose ebhodleleni elicacile elingu-250 noma 500 millilitre lize ligcwale uhhafu, ushiye okunye kube yisikhala somoya. Faka amaconsi ambalwa odayi, vala, uqinise indawo yokuvala, bese uyeka lime kuze kuphele okuluhlaza okwesibhakabhaka. Inqubo ye-Royal Society of Chemistry ikhulisa umqondo ofanayo uye ku-1 litre stoppered flask: 300 millilitres of water, 10 grams of glucose, 8 grams of potassium hydroxide (or 6 grams of sodium hydroxide), plus a few millilitres of dilute dye stock.

Ukuze wenze umbukiso, nyakazisa ngamandla. Umbala oluhlaza okwesibhakabhaka ogcwele uvela ngemizuzwana. Beka iflaski phansi bese ulinganisa isikhathi sokufiphala. I-Royal Society of Chemistry ibika imijikelezo engaphezu kwamashumi amabili ngokugcwaliswa okukodwa. Ungalokothi ugcwalise ibhodlela lize lichichime: ngaphandle komoya ovalelekile akukho kugcinwa kwe-oxygen engancibilika.

Okufanele ukubhekwe, nokuthi yini eshintsha isikhathi

Linganisa izinto ezintathu: ukunyakazisa kuze kube luhlaza okwesibhakabhaka ngokuphelele (seconds), isikhathi sokuma kuze kungabi nambala (up to a few minutes), kanye nenani lemijikelezo ngaphambi kokuba okuluhlaza okwesibhakabhaka kube buthaka. Lapho ukufiphala ngakunye kusondela ekupheleni, bheka indawo engaphezulu. Ungqimba oluncane oluluhlaza okwesibhakabhaka luvame ukuhlala isikhathi eside emngceleni womoya, lapho i-oxygen iqhubeka nokudiffuseka ingena. Lowo mugqa uwukubonakala kwe-diffusion.

Ukusabela kwebhodlela eliluhlaza okwesibhakabhaka kulandela i-empirical rate law ebikwe kanye nenqubo ye-Royal Society of Chemistry: rate = k[MB oxidised][glucose]OH-. Ingxenye ngayinye ingaba yisivivinyo sasekilasini. I-glucose, i-alkali, noma udayi omningi kunciphisa isikhathi sokuhlala kuluhlaza okwesibhakabhaka. Ukufudumala kusheshisa ukufiphala; iflaski ebandayo iba nesivinini esiphansi. Ukunyakazisa ngamandla kakhulu kuncibilikisa i-oxygen eningi, ngakho okuluhlaza okwesibhakabhaka kuhlala isikhathi eside. Isikhala somoya esikhulu sandisa isikhathi sokusebenza. Lapho imijikelezo ekugcineni iba buthaka futhi uketshezi luba phuzi, ushukela usuphelile futhi imikhiqizo eseceleni isinqwabelene. Lelo phuzu lokugcina nalo liwumphumela okufanele urekhodwe.

Iphepha lokurekhoda okuphawuliwe

Kopisha leli thebula ezincwadini zamanothi, umugqa owodwa ngesivivinyo ngasinye. Leli phepha lomsebenzi kanye nomdwebo wokusabela ongenhla kuyizinto eziphrintekayo zalesi sihloko.

Imibuzo yokubikezela, ephendulwa ngaphambi kwesivivinyo ngasinye:

• Ibhodlela liluhlaza okwesibhakabhaka ngokushesha ngemva kokunyakaziswa. Iyiphi indlela yodayi egqamile, futhi yini eyenze yaba njalo?
• Ibhodlela limile bese umbala uyafiphala. Yikuphi ukusabela okunqobayo, futhi yisiphi isithako esisetshenziswayo size siphele?
• Ngemva kwemijikelezo eminingi okuluhlaza okwesibhakabhaka kuba buthaka futhi kuphuze. Kuvuselele ngodayi, i-alkali, noma i-glucose, futhi kungani?
• Dweba umbala uma kuqhathaniswa nesikhathi somjikelezo owodwa. Maka lapho i-oxygen ingena khona esixazululweni.

Izimpendulo zomfundisi: (1) oxidised methylene blue, ephinde yenziwa i-oxidation yi-oxygen encibilikile evela esikhaleni somoya; (2) reduction by glucose, glucose consumed; (3) glucose, umnikeli onqumayo, ngoba udayi uzungeza ungashintshi; (4) ukukhuphuka ngokushesha lapho kuny akaziswa, ukwehla kancane lapho kumile, ukungena kwe-oxygen ngesikhathi sokukhuphuka kuphela.

Izinhlobo ezisondelene okufanele ziqanjwe

Umbukiso we-traffic light usebenzisa i-indigo carmine esikhundleni salokhu futhi udlula kokuphuzi, okubomvu, nokuluhlaza ngokufakwa kwe-oxygen. Igama elithi green bottle lisetshenziswa ngokukhululekile: kwesinye isikhathi kulowo mhlobo, kwesinye isikhathi kumafomula aluhlaza kakhulu njengezinhlelo ze-ascorbic acid noma uhlelo lomjikelezo lwe-enzyme oluchazwe yi-American Chemical Society. Qamba ngokucacile ukuthi yimuphi umhlobo osebhentshini ukuze abafundi bangahlanganisi okuphawuliwe okuvela kumakhemistri ahlukene.

Ukuphepha nokuphathwa

Ukugadwa ngaso sonke isikhathi. Ukuvikelwa kwamehlo ekuchaphazekeni kwamakhemikhali kanye namagilavu lapho kuphathwa isixazululo se-alkaline noma kuny akaziswa isitsha esivaliwe. I-alkali iyasha, udayi ungcolisa isikhumba nendwangu, futhi izitoko zodayi ezenziwe nge-ethanol zengeza i-solvent evuthayo ebhentshini. Gcina isitsha sivaliwe lapho usinyakazisa. Ngemva kwalokho, gcina izixazululo ezisetshenzisiwe ukuze ziphathwe ngokwemithetho yelabhorethri yesikhungo sakho. Izidingo zemfucuza ene-alkaline nedayi ziyahluka phakathi kwezikhungo nezindawo zomthetho, ngakho landela inqubo yelabhorethri yakho kunokuba uthathe eyomunye umthombo.

Uma ufuna izinombolo esikhundleni sokushintsha kombala, ama-assay anobuningi e-methylene blue aqhubeka lapho lo mbukiso uphela khona.

Kungani othisha beqhubeka nokusebenzisa leli bhodlela

Iflaski eyodwa ihlanganisa imiqondo emine. I-redox iba umbala kunokuba ibe incazelo kuphela. Umlamuli ukhombisa ukuthi inani elincane lenye into lingabika ngesamba esikhulu senye. I-kinetics ihlukaniswa ne-thermodynamics ngendlela ebonakalayo: i-oxygen iba namandla lapho ukunyakazisa kuyiletha, i-glucose iba namandla lapho ukunikezwa kwayo kumiswa. Futhi i-diffusion, inqubo ethule kunazo zonke ekhemistrini, iyona eyenza wonke lo mbukiso usebenze, ngoba konke ukubaneka okuluhlaza okwesibhakabhaka kuqala lapho i-oxygen iwela isuka emoyeni ingena emanzini. Umbukiso ovumela abafundi ukuthi babikezele, balinganise isikhathi, futhi bachaze konke lokho nge-stopwatch nethebula ufanelwe indawo yawo ebhentshini.