Gwajin kwalbar shuɗi: sinadarai, hanya, da abubuwan lura

Wata kwalba mai tsabta tana kan teburin gwaji. Tana kama da ruwa. Wani ya girgiza ta, sai ruwan ya koma shuɗi mai ƙarfi. Idan aka ajiye ta, shuɗin yana ɓacewa cikin minti ɗaya ko biyu. A sake girgiza ta, shuɗin ya dawo. Cika kwalba sau ɗaya na iya ba da damar maimaita wannan sau ashirin ko fiye.

Yawancin ɗalibai suna zaton akwai wani abu da aka ɓoye a cikin kwalbar, ko kuma girgizawar tana gauraya yadudduka biyu. Duk waɗannan hasashe biyun suna zama darasi mai amfani domin ba daidai ba ne. Launin yana fitowa ne daga sinadarin rini guda ɗaya, methylene blue, wanda yake ko'ina cikin ruwan. Abin da ke canzawa shi ne yawan electrons da rinin yake ɗauke da su. Gwajin yana bayyana zagayen redox da ido, kuma kowane abin da ajin zai iya gani—lokacin girgizawa, zafin jiki, da concentration—yana da alaƙa da wani ɓangare na sinadaran aikin.

Siffofi biyu na rini guda ɗaya

Methylene blue da aka oxidise tsarin zobe ne mai lebur kuma mai cajin tabbatacce. Yana tsotse haske sosai a kusan 600 zuwa 700 nanometres, wanda ido yake gani a matsayin shuɗi mai duhu. An yi bayani kan siffofin biyu da spectra ɗinsu a jagorar tsari da halayen methylene blue.

Reduction yana ƙara electrons biyu da proton guda ɗaya, yana samar da leucomethylene blue: marar caji, ba lebur ba, kuma a aikace marar launi. A cikin alkaline solution, half-reaction ɗin shi ne MB+ + H2O + 2 e- ⇌ LMB + OH-. Matakin yana iya komawa baya gaba ɗaya. Shuɗi yana nufin oxidised, rashin launi yana nufin reduced, kuma babu wani yanayi na uku da za a bi diddiginsa; wannan ne ya sa gwajin ya dace sosai a matsayin farkon gabatarwa ga sinadaran redox.

Zagayen: glucose yana reduce, oxygen yana sake oxidise

Kwalbar tana ɗauke da sinadarai uku masu aiki: methylene blue, glucose, da alkali mai ƙarfi, wato potassium ko sodium hydroxide. Alkali yana sa glucose ya koma siffofi masu reactive da aka deprotonate waɗanda ke bayar da electrons ga rinin:

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

Wannan mataki mai jinkiri yana kawar da launin yayin da kwalbar take tsaye. Glucose shi ne sacrificial donor kuma ana cinye shi. Rinin kuwa kawai yana jigilar electrons, saboda haka ɗigon kaɗan na iya aiki a cikin kwalba gaba ɗaya. Tsofaffin bayanan koyarwa a aji suna cewa glucose yana zama gluconic acid. Wannan taƙaitaccen bayani yana iya hasashen abin da za a gani, amma ya kamata malamai su sani cewa bai cika ba: wani binciken tsarin aikin da aka wallafa a Royal Society Open Science ya bibiyi oxidation ɗin daga reactive enediolate zuwa dicarbonyl wanda ke rarrabuwa zuwa ƙananan acids.

Girgizawa yana juya abin da ake gani. Motsi yana narkar da oxygen daga iskar da ke makale a sararin saman ruwan, sannan oxygen yana sake oxidise rinin da aka reduce:

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

Idan aka bar kwalbar a tsaye, dissolved oxygen yana ƙarewa, glucose yana sake reduce rinin, kuma launin yana dusashewa. Bayan zagaye da yawa, sakamakon sinadaran gaba ɗaya shi ne oxidation na sugar ta iska, yayin da rinin yake zagayawa ba tare da canzawa ba a matsayin redox mediator. Mediator ne maimakon strict catalyst, domin oxidation na sugar yana iya faruwa ba tare da shi ba, kuma dusashewar ba decomposition ba ce: da an lalata rinin, girgizawa ba za ta iya dawo da shi ba. Don kiyaye dye stocks su kasance stable tsakanin gwaje-gwaje, duba bayanan kula kan sarrafawa da adana methylene blue solutions.

Hanyar gudanar da gwaji ƙarƙashin kulawa

Wannan gwaji ne da ake gudanarwa ƙarƙashin kulawa, ba aikin gida ba. Alkali yana buƙatar kariyar ido, safar hannu, da malami wanda ke da alhakin shirye-shirye da tsaftacewa. Tsare-tsaren gwaji biyu da aka rubuta suna da tsari iri ɗaya amma sun bambanta a ma'auni.

Takardar umarni ta gwajin da sashen chemistry na Indiana University ya wallafa tana amfani da kusan 5 percent potassium hydroxide, 4 percent glucose, da 1 percent aqueous methylene blue. Zuba adadi iri ɗaya na alkali da glucose solutions a cikin kwalba mai haske mai nauyin 250 ko 500 millilitre har sai ta cika rabi, a bar sauran a matsayin sararin iska. Ƙara ɗigon rini kaɗan, rufe kwalbar, hatimce wurin haɗuwar murfin, sannan a bar ta har sai shuɗin ya ɓace. Hanyar Royal Society of Chemistry tana faɗaɗa wannan ra'ayi zuwa 1 litre stoppered flask: 300 millilitres na ruwa, 10 grams na glucose, 8 grams na potassium hydroxide (ko 6 grams na sodium hydroxide), tare da 'yan millilitres na dilute dye stock.

Don gudanarwa, a girgiza da ƙarfi. Cikakken shuɗi yana bayyana cikin seconds. A ajiye flask ɗin sannan a auna lokacin dusashewar. Royal Society of Chemistry ta ruwaito fiye da zagaye ashirin a kowane cika. Kada a taɓa cika kwalbar har bakin ta: idan babu iskar da ta makale a ciki, babu ajiyar oxygen da za ta narke.

Abin da za a lura da shi, da abin da ke canza lokacin

Auna abubuwa uku: lokacin girgizawa har ya zama cikakken shuɗi (seconds), lokacin tsayawa har ya zama marar launi (har zuwa 'yan minutes), da yawan zagaye kafin shuɗin ya fara rauni. Kusa da ƙarshen kowace dusashewa, lura da saman ruwan. Wani siririn yadudduka na shuɗi yakan daɗe a wurin haɗuwar iska da ruwa, inda oxygen yake ci gaba da shiga ta diffusion. Wannan layin diffusion ne da aka sa ya zama abin gani.

Blue bottle reaction yana bin empirical rate law da aka bayar tare da hanyar Royal Society of Chemistry: rate = k[MB oxidised][glucose]OH-. Kowane term gwaji ne da za a iya yi a aji. Ƙarin glucose, alkali, ko rini yana rage tsawon lokacin shuɗin. Ƙarin zafi yana hanzarta dusashewa; flask mai sanyi yana yin aiki a hankali. Girgizawa da ƙarfi yana narkar da ƙarin oxygen, saboda haka shuɗin yana daɗewa. Babban sararin iska yana tsawaita lokacin gudanar da gwajin. Idan zagayen suka fara rauni daga ƙarshe kuma ruwan ya fara zama rawaya, sugar ya ƙare kuma side products sun taru. Wannan endpoint ɗin ma sakamako ne da ya dace a rubuta.

Takardar rubuta abubuwan lura

Kwafi wannan teburin cikin littattafan rubutu, row ɗaya ga kowane trial. Wannan takardar tare da reaction diagram da ke sama su ne kadarorin da za a iya bugawa na wannan labarin.

Tambayoyin hasashe, a amsa kafin kowane trial:

• Kwalbar tana shuɗi nan da nan bayan girgizawa. Wace sifar rini ce ta fi yawa, kuma me ya sa ta zama haka?
• Kwalbar tana tsaye kuma launin yana dusashewa. Wace reaction ce ke rinjaye, kuma wane ingredient ne ake cinye?
• Bayan zagaye da yawa, shuɗin yana zama raunana kuma ya ɗan koma rawaya. Za a farfaɗo da shi da rini, alkali, ko glucose, kuma me ya sa?
• Zana yadda launi yake canzawa da lokaci a zagaye guda. Nuna inda oxygen yake shiga solution. Amsoshin malami: (1) oxidised methylene blue, wanda dissolved oxygen daga sararin iska ya sake oxidise; (2) reduction ta glucose, ana cinye glucose; (3) glucose, limiting donor, domin rinin yana zagayawa ba tare da canzawa ba; (4) saurin tashi yayin girgizawa, sauka a hankali yayin tsayawa, oxygen yana shiga ne kawai yayin tashin.

Makusantan gwaje-gwajen da ya dace a ambata

Traffic light demonstration yana amfani da indigo carmine maimakon methylene blue, yana wucewa ta rawaya, ja, da kore yayin oxygenation. Ana amfani da sunan green bottle a fannoni daban-daban: wani lokaci ga wannan variant, wani lokaci kuma ga formulations masu fi karkata zuwa kore kamar tsarin ascorbic acid ko wani enzymatic cycling system da American Chemical Society ta bayyana. A faɗi sunan variant ɗin da yake kan tebur domin ɗalibai kada su haɗa abubuwan lura daga chemistry daban-daban.

Tsaro da sarrafawa

Kulawa a duk lokacin gwajin. A yi amfani da kariyar ido daga fesawar sinadarai da safar hannu yayin sarrafa alkaline solution ko girgiza stoppered vessel. Alkali yana ƙone fata, rinin yana barin tabo a fata da zane, kuma dye stocks da aka shirya da ethanol suna ƙara flammable solvent a teburin gwaji. A riƙe vessel ɗin a rufe yayin girgizawa. Bayan an gama, a ajiye spent solutions domin sarrafa su bisa ƙa'idodin laboratory na cibiyarku. Ka'idojin alkaline waste mai ɗauke da rini sun bambanta tsakanin cibiyoyi da jurisdictions, saboda haka a bi hanyar da laboratory ɗinku ya amince da ita maimakon ɗauko wata daga wani tushe.

Idan ana son lambobi maimakon canjin launi, quantitative assays na methylene blue suna ci gaba daga inda wannan gwajin ya tsaya.

Dalilin da ya sa malamai ke ci gaba da amfani da wannan kwalba

Flask guda ɗaya yana tattara ra'ayoyi huɗu. Redox yana zama launi maimakon ma'ana kawai. Mediator yana nuna yadda ɗan ƙaramin adadin wani abu zai iya nuna abin da ke faruwa a babban adadin wani. Kinetics yana bayyana dabam da thermodynamics a ido: oxygen yana rinjaye yayin da girgizawa ke samar da shi, glucose kuma yana rinjaye idan samarwar ta tsaya. Kuma diffusion, ɗaya daga cikin matakai mafi shiru a chemistry, shi ne tushen dukkan wasan, domin kowane walƙiyar shuɗi tana farawa ne lokacin da oxygen ya ketare daga iska zuwa ruwa. Gwajin da ke ba ɗalibai damar yin hasashe, auna lokaci, da bayyana duk wannan da stopwatch da tebur ya cancanci wurinsa a kan teburin gwaji.