Dab tsi yog pH meter txoj kab nqes
Txoj kab nqes ntawm PH meter yog siv los ntawm PH meter los hloov cov teeb liab millivolt ntawm cov electrode mus rau pH tus nqi. Nws yog hais txog qhov sib txawv voltage ntsuas nrog sib txawv buffers, muab faib los ntawm qhov tsis sib txawv pl. Txoj kab nqes hauv pH ntsuas yog xam raws li Nernst kab zauv. Feem ntau, qhov sib npaug tsis tshwm sim kom txog thaum txoj kab nqes yog calibrated. Txoj kev nqes hav yog qhov taw qhia tseem ceeb los txiav txim siab seb lub neej ntawm cov electrode puas lawm. Feem ntau, muaj peb theem ntawm electrode lub neej. Txoj kab nqes ntawm lub electrode tshiab tom qab calibration yog nyob nruab nrab ntawm 95 feem pua thiab 105 feem pua. Yog tias txoj kab nqes qis dua 90, nws raug nquahu kom hloov cov electrode, txwv tsis pub nws yuav cuam tshuam nws qhov ntsuas qhov tseeb. pH calibration tov rau pH meter calibration. Kev suav ntawm txoj kab nqes yog cuam tshuam nrog cov electrode ntsuas lub peev xwm ntawm cov tshuaj koj npaj. Rau peb txoj kev daws teeb meem tsis zoo, ob feem ntau yog xaiv rau calibration. Yog tias tag nrho peb qhov kev daws teeb meem tsis muaj feem cuam tshuam rau hauv qhov ntsuas, txoj kab nqes yuav txawv raws li.
Lub pH meter yog ib qho cuab yeej siv los ntsuas pH tus nqi ntawm cov tshuaj. Lub pH meter ua haujlwm ntawm lub hauv paus ntsiab lus ntawm lub roj teeb galvanic. Lub zog electromotive nruab nrab ntawm ob lub electrodes ntawm galvanic roj teeb yog raws li Nernst txoj cai, uas tsis yog tsuas yog rau cov khoom ntawm electrodes lawv tus kheej, tab sis kuj rau cov concentration ntawm hydrogen ions nyob rau hauv cov tshuaj. Muaj kev sib raug zoo ntawm electromotive quab yuam ntawm thawj lub roj teeb thiab cov concentration ntawm hydrogen ions, thiab qhov tsis zoo logarithm ntawm cov concentration ntawm hydrogen ions yog pH tus nqi. Lub pH meter yog ib qho cuab yeej tshuaj ntsuam xyuas dav siv hauv kev ua liaj ua teb, kev tiv thaiv ib puag ncig thiab kev lag luam. Av pH yog ib qho tseem ceeb ntawm cov khoom tseem ceeb ntawm cov av. Nyob rau hauv tus txheej txheem ntawm kev txiav txim siab pH, yam xws li qhov kub thiab txias thiab ionic lub zog ntawm cov tshuaj yuav tsum tau kuaj.
pH yog dab tsi? pH yog ib lo lus luv luv ntawm lo lus Latin "Pondus hydrogenii" (Pondus=siab, siab hydrogenium=}hydrogen), uas yog siv los ntsuas qhov kev ua ntawm hydrogen ions hauv ib yam khoom. Cov dej num no ncaj qha ntsig txog acidity, nruab nrab thiab alkalinity ntawm cov kua dej aqueous. Cov dej yog tshuaj nruab nrab, tab sis nws tsis yog tsis muaj ions. Txawm hais tias cov dej ntshiab huv yog me ntsis dissociated: Hais lus nruj me ntsis, hydrogen nuclei tsis muaj nyob hauv lub xeev dawb ua ntej hydration nrog dej molecules.
H2O ntxiv rau H2O=H3O ntxiv rau OHˉ, txij li qhov concentration ntawm hydronium ion (H3O ntxiv) raug kho raws li qhov concentration ntawm hydrogen ion (H ntxiv), cov qauv saum toj no tuaj yeem ua kom yooj yim rau hauv cov qauv hauv qab no: H2O{ {6}}H plus plus OHˉ
Qhov zoo hydrogen ion ntawm no yog hais tias "H ntxiv ion" lossis "hydrogen nucleus" hauv chemistry. Hydronium nuclei yog txhais tau tias "hydronium ions". Tsis zoo hydroxide ions hu ua "hydroxide ions".
Siv txoj cai lij choj ntawm kev txiav txim loj, qhov sib npaug tas li tuaj yeem pom rau kev sib cais ntawm cov dej ntshiab:
K=H3O plus ×OH-————H2O
Txij li thaum tsuas yog ib qho me me ntawm cov dej sib cais, qhov loj molar concentration ntawm dej yog qhov ua tau tas li, thiab muaj qhov sib npaug ntawm K kom tau txais cov khoom ion KW ntawm cov dej.
KW=K × H2O KW= H3O plus ·OH－=10－7·10－7=10－14mol/l (25 degree)
Hais tias yog, muaj 10-7 moles ntawm H3O ntxiv ions thiab 10-7 moles ntawm OHˉ ions nyob rau hauv ib liter ntawm dej ntshiab ntawm 25 degree .
Hauv cov tshuaj nruab nrab, qhov concentration ntawm hydrogen ions H ntxiv thiab hydroxide ions OHˉ yog ob qho tib si 10-7mol/l. zoo li:
Yog tias muaj ntau tshaj ntawm hydrogen ions H ntxiv, cov tshuaj yog acidic. Cov kua qaub yog ib yam khoom uas muaj peev xwm dissociate hydrogen ions H ntxiv rau hauv cov kua dej. Ib yam li ntawd, yog tias OHˉions tau tso tawm, ces cov tshuaj yog alkaline. Yog li, muab tus nqi H ntxiv yog txaus los qhia cov yam ntxwv ntawm cov tshuaj, txawm tias nws yog acidic lossis alkaline. Txhawm rau zam qhov kev suav ntawm lub zog tsis zoo ntawm cov molecular concentration, tus kws tshawb fawb biologist Soernsen tau hais hauv xyoo 1909 tias qhov tsis yooj yim no tau hloov los ntawm logarithms thiab txhais tias "pH qhov tseem ceeb". Kev txhais lej ntawm pH yog qhov tsis zoo logarithm ntawm hydrogen ion concentration. Ntawd yog, pH=-log[H ntxiv].
