Qhov nqes hav ntawm pH meter yog dab tsi?
Lub pH meter txoj kab nqes yog siv los ntawm pH meter los hloov lub millivolt teeb liab ntawm cov electrode mus rau pH tus nqi. Nws yog tau los ntawm kev faib qhov sib txawv voltage ntsuas nrog sib txawv buffers los ntawm tsis pl qhov sib txawv. Qhov nqes hav hauv pH meter yog xam raws li qhov sib npaug Nernst. Feem ntau, txoj kab nqes tsis tshwm kom txog thaum qhov sib npaug yog calibrated. Txoj kev nqes hav yog ib qho kev ntsuas rau kev txiav txim siab seb lub electrode lub neej puas lawm.
Xav tau cov ntsuas. Feem ntau, muaj peb theem ntawm electrode lub neej. Tom qab calibration, txoj kab nqes ntawm cov electrode tshiab yog nyob nruab nrab ntawm 95% thiab 105%. 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. Muaj peb tus qauv buffers. Thaum calibrating, feem ntau yog ob yog txaus. Yog tias tag nrho peb qhov kev koom tes hauv calibration, cov nqes hav yuav txawv raws li.
pH meter yog hais txog cov cuab yeej siv los ntsuas pH tus nqi ntawm cov tshuaj. Lub pH meter ua haujlwm raws li lub hauv paus ntsiab lus ntawm lub roj teeb tseem ceeb. Lub zog electromotive nruab nrab ntawm ob lub electrodes ntawm thawj lub roj teeb yog raws li Nernst txoj cai, uas muaj feem xyuam rau ob qho tib si cov khoom ntawm cov electrodes thiab cov concentration ntawm hydrogen ions hauv cov tshuaj. Muaj kev sib raug zoo ntawm electromotive quab yuam ntawm thawj lub roj teeb thiab hydrogen ion concentration. Qhov tsis zoo logarithm ntawm hydrogen ion concentration yog tus nqi pH. pH meter yog ib qho cuab yeej tshuaj ntsuam xyuas dav siv hauv kev ua liaj ua teb, kev tiv thaiv ib puag ncig, kev lag luam thiab lwm yam. Av pH yog ib qho tseem ceeb ntawm cov khoom tseem ceeb ntawm cov av. Cov yam ntxwv xws li qhov kub thiab txias thiab lub zog ionic ntawm cov tshuaj yuav tsum tau ntsuas yuav tsum tau txiav txim siab thaum lub sijhawm ntsuas pH.
pH yog dab tsi? pH yog cov ntawv luv ntawm lo lus Latin "Pondus hydrogenii" (Pondus=siab, siab hydrogenium=}hydrogen) thiab yog siv los ntsuas qhov kev ua ntawm hydrogen ions hauv ib yam khoom. Qhov kev ua no yog 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 sib cais hauv cov lej: hais lus nruj me ntsis, hydrogen nuclei tsis muaj nyob hauv lub xeev dawb ua ntej hydrating nrog dej molecules.
H2O+ H2O=H3O++ OHˉ. Txij li thaum cov concentration ntawm hydronium ions (H3O +) raug kho tib yam li cov concentration ntawm hydrogen ions (H+), cov qauv saum toj no tuaj yeem ua kom yooj yim rau hauv cov qauv hauv qab no: H2O=H++ OHˉ
Qhov zoo hydrogen ions ntawm no tau hais tias "H + ions" lossis "hydrogen nuclei" hauv chemistry. Hydronium nuclei yog sawv cev ua "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 los qhia txog kev sib cais ntawm cov dej ntshiab:
K=H3O+×OH-----H2O
Txij li tsuas yog ib qho me me ntawm cov dej sib cais, cov molar concentration ntawm cov dej yog qhov ua tau tas mus li, thiab muaj qhov sib npaug ntawm K uas tuaj yeem siv los suav cov khoom ion KW ntawm dej.
KW=K × H2O KW= H3O+ ·OH－=10－7·10－7=10－14mol/l (25 degree)
Hais tias yog, rau ib liter ntawm dej ntshiab ntawm 25 degree, muaj 10-7 moles ntawm H3O+ ions thiab 10-7 moles ntawm OHˉ ions.
Hauv cov tshuaj nruab nrab, qhov concentration ntawm hydrogen ions H + thiab hydroxide ions OHˉ yog ob qho tib si 10-7mol / l. zoo li:
Yog tias muaj ntau tshaj hydrogen ions H +, cov tshuaj yog acidic. Acid yog ib yam khoom uas muaj peev xwm dissociate hydrogen ions H + nyob rau hauv ib tug aqueous tov. Ib yam li ntawd, yog tias OHˉ ion tso tawm, cov tshuaj yog alkaline. Yog li, muab tus nqi H + txaus los qhia cov yam ntxwv ntawm cov tshuaj, txawm tias nws yog acidic lossis alkaline. Txhawm rau zam kom tsis txhob siv lub zog tsis zoo ntawm qhov ntsuas molecular no los laij, tus kws tshawb fawb biologist Soernsen tau hais hauv xyoo 1909 tias qhov tsis yooj yim no yuav tsum tau siv. Cov nqi raug hloov los ntawm logarithms thiab txhais tias "pH tus nqi". Ua lej, pH txhais tau tias yog qhov tsis zoo logarithm ntawm hydrogen ion concentration. Qhov ntawd yog pH=-log[H+].
