Ntxhais vs Co-precipitation
Nyob rau hauv analytical chemistry, nag lossis daus yog cov txheej txheem tseem ceeb los cais tawm cov khoom sib xyaw / cov khoom tawm ntawm kev daws. Insolubility, purity, yooj yim rau lim, un-reactivity nrog atmospheric tshuaj yog ib co ntawm cov yam ntxwv tseem ceeb ntawm ib tug precipitate, uas tso cai rau lawv siv rau analytical lub hom phiaj.
nag xob nag cua
Precipitates yog cov khoom uas muaj cov khoom hauv cov tshuaj. Qee zaum cov khib nyiab yog tshwm sim los ntawm cov tshuaj tiv thaiv hauv cov tshuaj. Cov khoom no thaum kawg yuav nyob rau hauv vim lawv qhov ntom, thiab nws yog hu ua precipitate. Hauv centrifugation, lub resulting precipitated kuj hu ua pellet. Cov tshuaj saum toj no cov nag lossis daus yog hu ua supernatant. Lub particle loj nyob rau hauv precipitate hloov ntawm lub sij hawm mus rau lub sij hawm. Colloidal suspensions muaj cov khoom me me, uas tsis nyob hauv, thiab tsis tuaj yeem lim tau yooj yim. Crystals tuaj yeem lim tau yooj yim, thiab lawv loj dua.
Txawm hais tias ntau tus kws tshawb fawb tau tshawb fawb txog cov txheej txheem ntawm precipitate tsim, cov txheej txheem tseem tsis tau nkag siab tag nrho. Txawm li cas los xij, nws tau pom tias qhov loj me me ntawm cov nag lossis daus yog cuam tshuam los ntawm cov dej nag 'solubility, kub, reactant concentrations thiab tus nqi ntawm cov reactants sib xyaw. Precipitates tuaj yeem tsim nyob rau hauv ob txoj kev; los ntawm nucleation thiab particle loj hlob. Hauv nucleation, ob peb ions, atoms lossis molecules tuaj ua ke los tsim cov khoom ruaj khov. Cov khoom me me no hu ua nuclei. Feem ntau, cov nuclei tsim nyob rau saum npoo ntawm cov khoom raug tshem tawm. Thaum cov nucleus no nthuav tawm ntxiv rau cov ions, atoms lossis molecules, ntxiv nucleation lossis kev loj hlob ntxiv ntawm cov khoom tuaj yeem tshwm sim. Yog hais tias nucleation tseem tshwm sim, ib qho precipitate uas muaj ntau qhov me me tshwm sim. Piv txwv li, yog tias kev loj hlob predominates, ib qho me me ntawm cov khoom loj yog tsim. Nrog nce tus txheeb ze super-saturation, tus nqi ntawm nucleation nce. Feem ntau, nag lossis daus tshwm sim qeeb. Yog li ntawd, thaum lub precipitating reagent yog ntxiv maj mam mus rau ib qho kev daws teeb meem ntawm ib qho analyte, super-saturation tuaj yeem tshwm sim. (Supersaturated tov yog cov tshuaj tsis ruaj khov uas muaj cov kuab tshuaj ntau dua li cov tshuaj saturated.)
"Co- nag lossis daus yog txheej txheem uas ib txwm muaj cov dej sib xyaw ua ke los ntawm kev daws los ntawm nag lossis daus." Muaj plaub hom kev sib koom ua ke raws li qhov chaw adsorption, mix- crystal formation, occlusion thiab mechanical entrapment. Deg adsorption yuav siv qhov chaw rau precipitates nrog thaj chaw loj dua. Tshwj xeeb coagulated colloids paug los ntawm txoj kev no. Hauv kev sib xyaw ua ke- siv lead ua, ib qho ntawm cov ions hauv cov iav siv lead ua yog hloov los ntawm lwm cov ion. Deg adsorption thiab mix- crystal formation yog cov txheej txheem equilibrium, whereas lwm ob yog kinetic phenomena. Thaum cov khoom siv lead ua loj hlob sai, cov kab mob tuaj yeem nkag mus rau hauv cov siv lead ua loj hlob thiab qhov no hu ua occlusion. Mechanical entrapment yog lub tshuab uas muaj qee qhov kev daws teeb meem hauv cov muaju. Qhov no tshwm sim thaum ob lub pob zeb loj hlob nyob ze ua ke, kom lawv loj hlob ua ke.
Dab tsi yog qhov sib txawv ntawm nag lossis daus?
• nag lossis daus yog nyob ntawm cov khoom tsis sib haum los ntawm kev daws. Co-precipitation yog ib txheej txheem uas ib txwm soluble tebchaw yog nqa tawm ntawm kev daws los ntawm precipitate.
• Nyob rau hauv nag lossis daus, feem ntau insoluble compounds yog precipitated. Tab sis nyob rau hauv cov nag lossis daus ib txwm soluble tebchaw yog precipitated.
• Cov nag xob nag cua sib xyaw ua ke nrog cov kab mob sib kis rau hauv nag lossis daus, qhov nag lossis daus tuaj yeem ua rau ob qho tib si huv thiab tsis huv.
