Hauv chemistry, pH yog qhov ntsuas logarithmic siv los txiav txim siab acidity ntawm nruab nrab. Qhov no yog kwv yees li lub hauv paus tsis zoo 10 logarithm ntawm molar concentration, ntsuas nyob rau hauv units ntawm moles ib liter ntawm hydrogen ions. Nws tuaj yeem raug hu ua qhov ntsuas ntawm acidity ntawm ib puag ncig. Ntau qhov tseeb, nws yog lub hauv paus tsis zoo 10 logarithm ntawm hydrogen ion kev ua haujlwm. Ntawm 25 ° C, cov kev daws teeb meem nrog pH tsawg dua 7 yog acidic, thiab cov kev daws teeb meem nrog pH ntau dua 7 yog qhov yooj yim. Qhov nruab nrab pH tus nqi yog qhov ntsuas kub nyob ntawm thiab tsawg dua 7 thaum qhov kub nce. Cov dej ntshiab yog nruab nrab, pH=7 (ntawm 25 ° C), tsis yog acidic lossis alkaline. Raws li kev ntseeg nrov, tus nqi pH tuaj yeem tsawg dua 0 lossis siab dua 14 rau cov kua qaub thiab cov hauv paus muaj zog heev, feem.
Daim ntawv thov
Kev ntsuas pH yog qhov tseem ceeb hauv agronomy, tshuaj, chemistry, kho dej thiab ntau qhov chaw.
PH nplai yog cuam tshuam rau cov txheej txheem kev daws teeb meem, cov kua qaub uas tsim los ntawm thoob ntiaj tebkev pom zoo. Thawj cov qauv pH raug txiav txim siab los ntawm kev ntsuas qhov sib txawv ntawm qhov sib txawv ntawm hydrogen electrode thiab tus qauv electrode xws li nyiaj chloride. Cov pH ntawm aqueous daws tuaj yeem ntsuas nrog lub iav electrode thiab pH ntsuas los yog ntsuas.
Qhib
Lub tswv yim pH yog thawj zaug los ntawm Danish chemist Søren Peter Laurits Sørensen ntawm Carlsberg lub chaw kuaj mob hauv xyoo 1909 thiab tau hloov kho rau qib pH tam sim no hauv xyoo 1924 kom haum rau cov ntsiab lus thiab kev ntsuas ntawm cov hlwb electrochemical. Hauv kev ua haujlwm thaum ntxov, cov ntawv sau muaj tsab ntawv H hauv tus lej p, uas txhais tau tias: pH.
Nyob hauv lub npe
Lub ntsiab lus tseeb ntawm p yog qhov tsis txaus ntseeg, tab sis raws li Carlsberg Foundation, pH txhais tau tias "lub zog ntawm hydrogen." Nws kuj tau raug qhia tias p yog cov lus German potenz ("lub zog"), lwm tus hais txog Fabkis puisance (tseem lub ntsiab lus "lub zog", raws li qhov tseeb tias Carlsberg laboratory yog Fabkis). Lwm qhov kev tawm tswv yim yog tias p yog hais txog lub sij hawm Latin pondus hydroii (tus nqi ntawm hydrogen), potentio hydroii (muaj peev xwm ntawm hydrogen), los yog muaj peev xwm hydroli (hydrogen peev xwm). Nws kuj tau hais tias Sørensen siv cov tsiaj ntawv p thiab q (feem ntau conjugate cov ntawv hauv lej) yooj yim los qhia txog kev ntsuas ntsuas (p) thiab siv tshuaj (q). Tam sim no, nyob rau hauv chemistry, p stands rau cov zauv logarithm, thiab kuj yog siv nyob rau hauv lub sij hawm pKa, siv rau dissociation tas li ntawm acidity ntawm ib tug nruab nrab.
Asmeskas kev pab cuam
Bacteriologist Alice Evans, paub txog kev cuam tshuam ntawm nws txoj haujlwm ntawm cov khoom noj siv mis thiab zaub mov kev nyab xeeb, tau lees paub William Mansfield Clark thiab nws cov npoj yaig rau kev tsim cov txheej txheem ntsuas pH hauv xyoo 1910, uas tom qab ntawd muaj kev cuam tshuam dav rau hauv chav kuaj thiab kev lag luam. siv. Hauv nws cov ntawv sau cia, nws tsis hais ntau npaum li cas lossis tsawg npaum li cas Clarke thiab nws cov npoj yaig paub txog Sorensen txoj haujlwm xyoo dhau los. Twb tau nyob rau lub sijhawm ntawd, cov kws tshawb fawb tau nquag kawm txog qhov teeb meem ntawm acidity / alkalinity ntawm ib puag ncig.
Kev cuam tshuam ntawm acid
Dr. Clark qhov kev saib xyuas tau qhia txog cov txiaj ntsig ntawm cov kua qaub rau cov kab mob loj hlob. Thiab ua tsaug rau qhov no, nws ntxiv lub tswv yim ntawm kev tshawb fawb ntawm hydrogen index ntawm acidity ntawm ib puag ncig. Nws pom tias nws yog qhov kev siv ntawm cov kua qaub nyob rau hauv cov nqe lus ntawm cov concentration ntawm hydrogen ions uas cuam tshuam rau lawv txoj kev loj hlob. Tab sis cov txheej txheem uas twb muaj lawm rau kev ntsuas cov acidity ntawm nruab nrab txiav txim siab tus nqi, tsis yog qhov kev siv ntawm cov kua qaub. Tom qab ntawd, nrog nws cov npoj yaig, Dr. Clark tau tsim cov txheej txheem meej rau kev ntsuas qhov concentration ntawm hydrogen ions. Cov txheej txheem no tau hloov txoj kev titration imprecise rau kev txiav txim siab acid nyob rau hauv cov chaw soj ntsuam lom neeg thoob ntiaj teb. Nws kuj tau pom tias lawv tuaj yeem siv rau hauv ntau qhov kev lag luam thiab lwm yam txheej txheem uas lawv tau siv dav.
Kev ua tau zoo
thawj txoj kev ntsuas pH hluav taws xob tau tsim los ntawm Arnold Orville Beckman, tus xibfwb ntawm California Institute of Technology, xyoo 1934. Nws yog nyob rau ntawm no uas lub zos citrus growerSunkist xav tau txoj hauv kev zoo dua rau kev sim ceev pH ntawm cov txiv qaub uas lawv tau sau los ntawm cov vaj txiv hmab nyob ze. Kev cuam tshuam ntawm acidity ntawm nruab nrab yog ib txwm coj mus rau hauv tus account.
Piv txwv li, rau kev daws nrog hydrogen ion kev ua ntawm 5 × 10 –6 (ntawm qib no, qhov no yog, qhov tseeb, tus naj npawb ntawm moles ntawm hydrogen ions ib liter ntawm kev daws), peb tau txais 1 / (5 × 10-6)=2 × 105. Yog li, xws li cov tshuaj muaj pH ntawm 5.3. Nws ntseeg tau tias cov huab hwm coj ntawm ib mole ntawm dej, mole ntawm hydrogen ions thiab mole ntawm hydroxide ions yog feem ntau 18 g, 1 g thiab 17 g, tus nqi ntawm cov ntshiab 107 moles (pH 7) ntawm dej muaj txog 1 g ntawm dissociated hydrogen ions (los yog, Ntau qhov tseeb, 19 g ntawm H 3 O + hydronium ions) thiab 17 g hydroxide ions.
Lub luag haujlwm ntawm qhov kub thiab txias
Nco ntsoov tias pH yog qhov kub thiab txias. Piv txwv li, ntawm 0 ° C pH ntawm cov dej ntshiab yog 7.47. Ntawm 25 ° C nws yog 7, thiab ntawm 100 ° C nws yog 6.14.
Electrode peev xwm yog proportional rau pH thaum pH txhais raws li kev ua ub no. Kev ntsuas pH raug raug nthuav tawm hauv tus qauv thoob ntiaj teb ISO 31-8.
Ib lub xov tooj ntawm tes galvanic tau teeb tsa los ntsuas lub zog hluav taws xob hluav taws xob (EMF) nruab nrab ntawm cov khoom siv hluav taws xob thiab hydrogen ion kev ua kom pom cov electrode thaum ob qho tib si rau hauv tib lub aqueous tov. Cov khoom siv electrode yuav yog cov khoom siv nyiaj chloride lossis calomel electrode. Ib qho hydrogen ion xaiv electrode yog tus qauv rau cov ntawv thov no.
Txhawm rau muab cov txheej txheem no rau hauv kev xyaum, iav electrode yog siv los ntawm cov khoom siv hydrogen electrode loj heev. Nwsmuaj ib tug built-in siv electrode. Nws kuj tseem raug ntsuas los tiv thaiv cov kev daws teeb meem tsis zoo nrog kev paub txog kev ua haujlwm hydrogen ion. IUPAC tau pom zoo siv cov txheej txheem tsis muaj kev daws teeb meem nrog cov haujlwm H + paub. Ob lossis ntau qhov kev daws teeb meem tsis yog siv los suav rau qhov tseeb tias txoj kab nqes yuav tsawg dua qhov zoo tagnrho. Txhawm rau siv qhov kev ntsuas ntsuas no, cov electrode yog thawj zaug rau hauv cov qauv kev daws teeb meem thiab pH meter nyeem tau teeb tsa rau tus nqi ntawm tus qauv tsis.
Yuav ua li cas ntxiv?
Kev nyeem ntawv los ntawm cov txheej txheem thib ob tsis muaj kev daws teeb meem yog tom qab ntawd kho siv txoj kab nqes tswj kom sib npaug rau qib pH rau cov tshuaj ntawd. Thaum siv ntau tshaj ob qhov kev daws teeb meem, cov khoom siv hluav taws xob tau ntsuas los ntawm kev ua kom haum cov pH qhov tseem ceeb rau txoj kab ncaj nraim tiv thaiv tus qauv tsis muaj nuj nqis. Kev lag luam tus qauv kev daws teeb meem feem ntau yog muab nrog cov ntaub ntawv hais txog tus nqi ntawm 25 ° C thiab qhov kho kom haum rau lwm qhov kub.
Definition characteristic
pH nplai yog logarithmic thiab, yog li ntawd, pH yog qhov tsis muaj qhov loj me, feem ntau siv, ntawm lwm yam, los ntsuas cov kua qaub ntawm qhov chaw sab hauv ntawm tes. Qhov no yog Sorensen lub ntsiab lus qub, uas tau hloov pauv xyoo 1909.
Txawm li cas los xij, nws tuaj yeem ntsuas ncaj qha rau hydrogen ion concentration yog tias cov electrode raug ntsuas raws li cov ntsiab lus ntawm hydrogen ion concentrations. Ib txoj hauv kev los ua qhov no, uas tau siv dav, yog titrate ib qho kev daws teeb meem ntawm kev paub txog concentrationmuaj zog acid nrog rau kev daws ntawm ib tug paub concentration ntawm ib tug muaj zog alkali nyob rau hauv lub xub ntiag ntawm ib tug kuj siab concentration ntawm ib tug txhawb electrolyte. Txij li cov kua qaub thiab alkali concentrations paub, nws yog ib qho yooj yim los xam cov hydrogen ion concentration kom lub peev xwm muaj feem xyuam rau qhov ntsuas tus nqi.
Cov ntsuas tuaj yeem siv los ntsuas pH siv qhov tseeb tias lawv cov xim hloov. Kev pom kev sib piv ntawm cov xim ntawm cov tshuaj ntsuam xyuas nrog cov qauv xim teev tso cai rau pH ntsuas nrog cov lej raug. Kev ntsuas qhov tseeb yog ua tau yog tias cov xim ntsuas spectrophotometrically siv lub colorimeter lossis spectrophotometer. Qhov taw qhia universal yog tsim los ntawm kev sib xyaw ntawm cov ntsuas kom muaj cov xim hloov mus tas li los ntawm pH 2 mus rau pH 10. Daim ntawv qhia thoob ntiaj teb yog tsim los ntawm cov ntawv nqus dej uas tau impregnated nrog cov ntsuas universal. Lwm txoj hauv kev los ntsuas pH yog siv lub ntsuas pH hluav taws xob.
ntsuas qib
ntsuas pH hauv qab li 2.5 (kwv yees 0.003 moles ntawm acid) thiab siab dua li 10.5 (li 0.0003 moles ntawm alkali) yuav tsum muaj cov txheej txheem tshwj xeeb vim Nernst txoj cai raug ua txhaum ntawm cov txiaj ntsig zoo li no thaum siv iav electrode. Ntau yam ua rau qhov no. Nws tsis tuaj yeem xav tias cov dej hloov pauv muaj peev xwm yog ywj siab ntawm pH. Tsis tas li ntawd, huab cua pH txhais tau hais tias cov tshuaj yog concentrated, yog li cov electrode muaj peev xwm cuam tshuam los ntawm kev hloov hauv ionic zog. Thaum pH siab, iav electrode tej zaum yuavraug rau alkaline yuam kev raws li cov electrode ua rhiab heev rau cov concentration ntawm cations xws li Na + thiab K + hauv kev daws. Cov khoom siv hluav taws xob tshwj xeeb muaj nyob rau uas ib nrab kov yeej cov teeb meem no.
Runoff los ntawm mines lossis kuv pov tseg tuaj yeem ua rau pH qis heev.
dej ntshiab yog nruab nrab. Nws tsis yog acidic. Thaum cov kua qaub yaj hauv dej, pH yuav qis dua 7 (25 ° C). Thaum ib qho alkali yaj hauv dej, pH yuav ntau dua 7. A 1 mol tov ntawm cov kua qaub muaj zog xws li hydrochloric acid muaj pH ntawm xoom. Ib qho kev daws teeb meem ntawm alkali muaj zog xws li sodium hydroxide ntawm qhov concentration ntawm 1 mol muaj pH ntawm 14. Yog li, ntsuas pH qhov tseem ceeb feem ntau yuav nyob hauv thaj tsam ntawm 0 mus rau 14, txawm tias tsis zoo pH qhov tseem ceeb thiab qhov tseem ceeb. saum 14 no yeej ua tau.
Ntau yam nyob ntawm acidity ntawm cov tshuaj nruab nrab. Vim tias pH yog qhov ntsuas logarithmic, qhov sib txawv ntawm ib chav tsev pH yog sib npaug li kaum npaug ntawm qhov sib txawv ntawm hydrogen ion concentration. Neutrality PH tsis ncav cuag 7 (ntawm 25 ° C), txawm hais tias feem ntau qhov no yog qhov kwv yees zoo. Neutrality yog txhais raws li cov xwm txheej uas [H+]=[OH-]. Txij li thaum tus kheej-ionization ntawm dej khaws cov khoom ntawm cov concentrations [H +] × [OH-]=Kw, nws tuaj yeem pom tau tias ntawm nruab nrab [H+]=[OH-]=√Kw lossis pH=pKw / 2.
PKw yog kwv yees li 14, tab sis nyob ntawm ionic zog thiab kub, yog li pH tus nqi nruab nrab kuj tseem ceeb, uas yuav tsum nyob nruab nrab.qib. Cov dej ntshiab thiab kev daws ntawm NaCl hauv cov dej ntshiab yog qhov nruab nrab vim tias kev sib cais ntawm cov dej ua rau tib tus nqi ntawm ob qho tib si ions. Txawm li cas los xij, pH ntawm cov tshuaj nruab nrab NaCl yuav txawv me ntsis ntawm pH ntawm nruab nrab cov dej ntshiab, vim tias kev ua haujlwm ntawm hydrogen thiab hydroxide ions nyob ntawm lub zog ionic, yog li Kw txawv nrog lub zog ionic.
Cov xim cog qoob loo uas tuaj yeem siv los ua pH ntsuas pom muaj nyob hauv ntau cov nroj tsuag, suav nrog hibiscus, liab cabbage (anthocyanin), thiab liab cawu cub. Citrus kua txiv yog acidic vim nws muaj citric acid. Lwm cov carboxylic acids muaj nyob rau hauv ntau lub neej. Piv txwv li, lactic acid yog tsim los ntawm cov leeg nqaij. Lub xeev ntawm protonation ntawm phosphate derivatives, xws li ATP, nyob ntawm acidity ntawm pH nruab nrab. Kev ua haujlwm ntawm hemoglobin oxygen hloov enzyme cuam tshuam los ntawm pH hauv cov txheej txheem hu ua cov nyhuv hauv paus.
hiav txwv dej
Hauv dej hiav txwv, pH feem ntau txwv rau ntawm 7.5 thiab 8.4. Nws ua lub luag haujlwm tseem ceeb hauv cov pa roj carbon monoxide hauv dej hiav txwv, thiab muaj pov thawj ntawm cov dej hiav txwv txuas ntxiv acidification los ntawm carbon dioxide emissions. Txawm li cas los xij, kev ntsuas pH yog qhov nyuaj los ntawm cov khoom siv tshuaj lom neeg ntawm cov dej hiav txwv, thiab muaj ntau qhov sib txawv pH teev nyob rau hauv tshuaj oceanography.
Special Solutions
Raws li ib feem ntawm kev ua haujlwm txhais ntawm cov kua qaub (pH) nplai, IUPAC txhais cov kev daws teeb meem tsis nyob hauv pH ntau yam (feem ntau hu uaNBS lub NIST). Cov kev daws teeb meem no muaj lub zog ionic tsawg (≈0.1) piv rau cov dej hiav txwv (≈0.7) thiab vim li ntawd tsis pom zoo siv rau hauv seawater pH characterization vim qhov sib txawv ntawm lub zog ionic ua rau muaj kev hloov pauv hauv electrode. Txhawm rau daws qhov teeb meem no, ib qho kev hloov pauv ntawm cov buffers raws li cov dej hiav txwv dag tau tsim.
Cov koob tshiab no daws qhov teeb meem ntawm ionic lub zog sib txawv ntawm cov qauv thiab cov buffers, thiab cov pH tshiab rau nruab nrab acidity yog hu ua cov nplai, feem ntau hu ua pH. Qhov ntsuas tag nrho tau txiav txim siab siv qhov nruab nrab uas muaj sulfate ions. Cov ions no tau ntsib protonation, H + + SO2-4 ⇌ HSO-4, yog li tag nrho cov nplai suav nrog kev cuam tshuam ntawm ob qho tib si protons (dawb hydrogen ions) thiab hydrogen sulfide ions:
[H+] T=[H+] F + [HSO-4].
Lwm qhov ntsuas dawb, feem ntau hu ua pHF, tshem tawm qhov kev txiav txim siab no thiab tsom tshwj xeeb rau [H+]F, ua rau nws yooj yim sawv cev ntawm hydrogen ion concentration. Tsuas yog [H +] T tuaj yeem txiav txim siab, yog li [H +] F yuav tsum kwv yees siv [SO2-4] thiab qhov ruaj khov tsis tu ncua HSO-4, KS:
[H +] F=[H+] T - [HSO-4]=[H+] T (1 + [SO2-4] / K S) -1.
Txawm li cas los xij, nws nyuaj rau kwv yees KS hauv dej hiav txwv, txwv qhov kev siv tau yooj yim dua qhov ntsuas dawb.
Lwm qhov ntsuas, lub npe hu ua seawater scale, feem ntau hu ua pHSWS, coj mus rau hauv tus account ntxiv proton bonding ntawm hydrogen ions thiab fluoride ions, H + + F- ⇌HF. Qhov tshwm sim yog cov lus qhia hauv qab no rau [H+] SWS:
[H+] SWS=[H+] F + [HSO-4] + [HF]
Txawm li cas los xij, qhov txiaj ntsig ntawm kev txiav txim siab qhov nyuaj ntxiv no nyob ntawm cov ntsiab lus fluorine ntawm qhov nruab nrab. Piv txwv li, nyob rau hauv dej hiav txwv, sulfate ions pom nyob rau hauv ntau dua concentrations (> 400 zaug) dua li cov concentrations ntawm fluorine. Raws li qhov tshwm sim, rau qhov ua tau zoo tshaj plaws, qhov sib txawv ntawm cov nplai thiab cov dej hiav txwv me me heev.
Qhov peb qhov sib npaug hauv qab no qhia txog peb qhov pH ntsuas:
pHF=- log [H+] FpHT=- log ([H+] F + [HSO-4])=- log [H+] TpHSWS=- log ([H+] F + [HSO-4] + [HF])=- log [H+]
Los ntawm qhov kev pom zoo, peb qhov pH nplai ntawm ib puag ncig acidic (lossis dej hiav txwv) txawv ntawm lawv cov txiaj ntsig txog li 0.12 pH units, thiab qhov sib txawv ntau dua li qhov feem ntau xav tau rau qhov tseeb ntawm Kev ntsuas pH, tshwj xeeb tshaj yog nyob rau hauv kev sib raug zoo nrog carbonate system dej hiav txwv.
