Xisaabaha cabbiraadda: laga bilaabo mugga buret-ka ilaa qadarka walaxda la cabbirayo

Saddexda tiro ee xisaab kasta oo cabbiraad ah u baahan tahay

Cabbiraadda, xal uruurintiisu la yaqaan (cabbiraha) ayaa buret looga daraa walaxda la cabbirayo (analyte-ka) ilaa falgalka u dhexeeya uu dhammaado. Xisaab kastaa waxay isticmaashaa saddex macluumaad: uruurinta cabbiraha, mugga cabbiraha ee la shubay, iyo saamiga moolka ee isleegga isu-dheellitiran.

Waddadu had iyo jeer waa isku mid. Mugga cabbiraha u beddel litir oo ku dhufo uruurintiisa si aad u hesho moolasha cabbiraha, n = c × V. Isticmaal saamiga moolka si aad ugu beddesho moolasha walaxda la cabbirayo. Kadib u beddel wax kasta oo su'aashu weydiiso: uruurin, culeys, ama boqolkiiba muunad.

Barta sinnaantu waa barta cabbiraha lagu daray uu si sax ah ula mid noqdo walaxda la cabbirayo saamiga istoikiyomitari. Barta dhammaadku waa waxa aad dhab ahaan aragto, sida tilmaame midab beddelaya. Hab wanaagsan wuxuu labadaba ka dhigaa kuwo ku dhawaad is-waafaqa, farqiga yar ee u dhexeeyana waxaa loo yaqaan khaladka cabbiraadda.

Halbeegidda sodium hydroxide iyadoo la isticmaalayo potassium hydrogen phthalate

Ma samayn kartid xal sodium hydroxide ah oo sax ah adigoo miisaamaya walaxda adag. Kuuskuusyada NaOH waxay hawada ka nuugaan biyo iyo kaarboon laba-ogsaydh, sidaa darteed culeyskoodu dhammaantiis ma aha NaOH. Halkii, xal si qiyaas ah loo diyaariyey ayaa la halbeegaa: waxaa lagu cabbiraa halbeeg koowaad, walax saafi ah oo deggan ku filan in si toos ah loo miisaamo.

Potassium hydrogen phthalate, KHC₈H₄O₄ (oo badanaa loo yaqaan KHP), waa doorasho caadi ah. Waa walax adag oo deggan oo aan biyo nuugin (non-hygroscopic) oo leh hal hydrogen aashito ah, NIST-na waxay u caddaysay heer ka mid ah halbeeg koowaad oo acidimetric ah (SRM 84L). Culeyskeeda molar ee weyn wuxuu sidoo kale macnaheedu yahay in muunad caadi ahi miisaanto qiyaastii badh garaam, sidaa darteed khaladka miisaanka ee qaraabada ahi waa yar yahay.

Tusaale la xaliyey 1. Muunad KHP ah oo 0.5106 g ah waxay u baahan tahay 24.68 mL oo xal NaOH ah si ay u gaarto barta dhammaadka phenolphthalein. Falgalku waa 1:1: KHC₈H₄O₄(aq) + NaOH(aq) → KNaC₈H₄O₄(aq) + H₂O(l). Adigoo isticmaalaya culeysyada atamka caadiga ah ee IUPAC (K 39.098, C 12.011, H 1.008, O 15.999), M(KHP) = 204.22 g/mol. n(KHP) = 0.5106 g ÷ 204.22 g/mol = 2.500 × 10⁻³ mol, taasoo le'eg n(NaOH). c(NaOH) = 2.500 × 10⁻³ mol ÷ 0.02468 L = 0.1013 mol/L, oo lagu sheegay afar tiro oo muhiim ah sababtoo ah culeyska iyo mugga mid kastaa wuxuu leeyahay afar.

Aashitooyinka diprotic-ga ah waxay beddelaan saamiga moolka

Sulfuric acid wuxuu molekiyuul kasta hydroxide-ka siiyaa laba borotoon: H₂SO₄(aq) + 2 NaOH(aq) → Na₂SO₄(aq) + 2 H₂O(l). Sidaa darteed mool kasta oo aashito ah wuxuu isticmaalaa laba mool oo saldhig ah, saamiga moolkuna waa inuu ka yimaadaa isleeggan, ma aha caado ah in cabbiraadaha loo qaato 1:1.

Tusaale la xaliyey 2. Muunad sulfuric acid ah oo 25.00 mL ah ayaa lagu cabbiraa NaOH-da 0.1013 mol/L ee tusaalaha 1, barta dhammaadkuna waxay timaadaa 18.45 mL. n(NaOH) = 0.1013 mol/L × 0.01845 L = 1.869 × 10⁻³ mol. n(H₂SO₄) = 1.869 × 10⁻³ mol ÷ 2 = 9.345 × 10⁻⁴ mol. c(H₂SO₄) = 9.345 × 10⁻⁴ mol ÷ 0.02500 L = 0.03738 mol/L. Isticmaalidda saami 1:1 ah si khalad ah waxay bixin lahayd 0.07476 mol/L, si sax ah laba jibaarka qiimaha dhabta ah.

Aashitooyinka polyprotic-ga ah ee ka daciifsan waxay u baahan yihiin taxaddar dheeraad ah. Phosphoric acid, borotoonnadu waxay ku baxaan tallaabooyin si cad u kala gooni ah, sidaa darteed saamigu wuxuu ku xiran yahay barta sinnaanta ee tilmaamahaagu ogaado. Sheeg barta dhammaadkaas kahor intaadan dooran saamiga moolka.

Cabbiraadaha redoks: permanganate iyo iron(II)

Cabbiraaduhu kuma koobna aashitooyinka iyo saldhigyada. Xalka aashitada ah, permanganate wuxuu oksaydheeyaa iron(II): MnO₄⁻(aq) + 5 Fe²⁺(aq) + 8 H⁺(aq) → Mn²⁺(aq) + 5 Fe³⁺(aq) + 4 H₂O(l). Manganese wuxuu ka gudbaa +7 ilaa +2, isagoo helaya shan elektaroon, halka iron kastaa lumiyo mid, sidaa darteed hal ayoon permanganate ah wuxuu la falgalaa shan ayoon oo iron(II) ah.

Permanganate wuxuu u shaqeeyaa tilmaame isaga u gaar ah. Ayoonka MnO₄⁻ waa guduud aad u qoto dheer, Mn²⁺-na ku dhawaad midab ma leh, sidaa darteed dhibicda ugu horreysa ee xad-dhaafka ahi waxay fleeska ka dhigtaa casaan-khafiif ah oo sii jira. Potassium permanganate ma aha halbeeg koowaad, xalalkiisuna si tartiib ah ayay u burburaan, sidaa darteed waa la halbeegaa kahor isticmaalka, badanaa iyadoo laga eegayo sodium oxalate.

Tusaale la xaliyey 3. Muunad macdanta iron ah oo 1.2084 g ah ayaa la milaa, dhammaan iron-keeduna waxaa hoos loogu dhigaa Fe²⁺. Cabbiraaddu waxay u baahan tahay 26.34 mL oo KMnO₄ 0.02150 mol/L ah. n(MnO₄⁻) = 0.02150 mol/L × 0.02634 L = 5.663 × 10⁻⁴ mol. n(Fe²⁺) = 5 × 5.663 × 10⁻⁴ mol = 2.832 × 10⁻³ mol. Adigoo isticmaalaya Fe 55.845 g/mol, culeyska iron-ku waa 0.1581 g, macdantuna waa 0.1581 g ÷ 1.2084 g × 100 = 13.09 boqolkiiba iron culeys ahaan.

Dib-u-cabbiraadaha walxaha adag ee si tartiib ah u falgala

Muunadaha qaarkood si degdeg ah uma milmaan ama uma falgalaan si loogu sameeyo cabbiraad toos ah. Calcium carbonate ee kiniinka antacid-ka waa tusaale: wuxuu la falgalaa aashito, laakiin waa walax adag falgalkuna wuxuu sii daayaa kaarboon laba-ogsaydh, taasoo adkeysa in la arko barta dhammaadka oo fiiqan. Dib-u-cabbiraadda waxaad ku dartaa xad-dhaaf la cabbiray oo hal reagent ah, u oggolow falgalka inuu dhammaado, kadibna cabbir wixii ka haray.

Tusaale la xaliyey 4. Qayb 0.5000 g ah oo kiniin antacid ah oo la burburiyey ayaa lagu daaweeyaa 50.00 mL oo HCl 0.2000 mol/L ah, oo aad uga badan inta loo baahan yahay in lala falgalo dhammaan CaCO₃-giisa: CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). Kadib marka xalka la karkariyo si CO₂ looga saaro, aashitada ka hartay waxay u baahan tahay 21.38 mL oo NaOH 0.1000 mol/L ah. HCl la daray: 0.2000 × 0.05000 = 1.000 × 10⁻² mol. HCl ka haray, oo le'eg NaOH-da la isticmaalay: 0.1000 × 0.02138 = 2.138 × 10⁻³ mol. HCl uu kiniinku isticmaalay: 1.000 × 10⁻² − 2.138 × 10⁻³ = 7.862 × 10⁻³ mol.

Carbonate-ku wuxuu aashitada la falgalaa 1:2, sidaa darteed n(CaCO₃) = 7.862 × 10⁻³ ÷ 2 = 3.931 × 10⁻³ mol. Iyadoo M(CaCO₃) = 100.09 g/mol, culeysku waa 0.3935 g (0.39345 g kahor dhoweynta), taasoo ah 78.69 boqolkiiba qaybta 0.5000 g ah. Ka-jarku waa tallaabada inta badan laga booddo. La'aanteed, waxaad xisaabin lahayd aashitada fleeska ku hartay, ma aha aashitada kiniinku isticmaalay.

Doorashada tilmaamaha iyo farsamada buret-ka

Tilmaamuhu wuxuu midabka ku beddelaa xad qiyaastii ah pKa ± 1-kiisa, sidaa darteed dooro mid xadkiisu ku dhaco qaybta qotada dheer ee qalooca cabbiraadda. Aashito xooggan iyo saldhig xooggan oo qiyaastii ah 0.1 mol/L, barta sinnaantu waxay ku taal pH 7.00, pH-guna wuxuu ku boodaa dhawr cutub hal ama laba dhibcood gudahood, sidaa darteed dhawr tilmaame oo caadi ah ayaa bixiya barta dhammaadka oo fiiqan, oo ay ka mid tahay phenolphthalein. Aashito daciif ah iyo saldhig xooggan, barta sinnaantu waa saldhig: OpenStax waxay xisaabisaa pH 8.72 ee acetic acid 0.100 mol/L ah oo lagu cabbiray NaOH 0.100 mol/L ah. Phenolphthalein, oo noqda casaan-khafiif ka sarreeya qiyaastii pH 8.3, ayaa ku habboon xaaladdaas. Methyl orange (Ka = 4.0 × 10⁻⁴ OpenStax, sidaa darteed pKa ≈ 3.4) wuxuu midabka beddeli lahaa goor aad u hore.

Buret 50 mL ah waxaa lagu akhriyaa 0.01 mL, mug kasta oo la shubayna waa farqiga laba akhrin. Hubanti la'aan qiyaastii ah ±0.02 mL waa 0.08 boqolkiiba shubid 25 mL ah laakiin 0.4 boqolkiiba mid 5 mL ah. Taasi waa sababta hababka loo naqshadeeyo si mugga cabbiruhu ugu dhaco bartamaha xadka buret-ka.

• Buret-ka ku biyo-raaci dhawr milliliter oo cabbiraha ah kahor intaadan buuxin, si biyaha ka hadhay aysan u khafiifin.
• Ka saar xumbada hawada ee caarada kahor akhrinta koowaad.
• Akhri salka meniscus-ka adigoo indhahaagu isla heerkiisa joogaan, oo diiwaan geli labada akhrin, ma aha farqiga oo keliya.
• Marka hore samee cabbiraad qiyaas ah, kadibna ku celi ilaa laba cabbiraad oo taxaddar leh ay si dhow isu waafaqaan.

Khaladaadka xisaabta cabbiraadda iyo hubintooda

Jawaabaha khaldan badankoodu waxay ka yimaadaan saamiga moolka ama cutubyada, ma aha kimistariga. Kahor intaadan xisaabin, qor isleegga isu-dheellitiran oo goobaabi isku-dhuftayaasha cabbiraha iyo walaxda la cabbirayo.

• U isticmaalidda C₁V₁ = C₂V₂ cabbiraad. Jid-gaabkaasi wuxuu u yaal khafiifinta wuxuuna u qaataa saami 1:1, taasoo ku fashilanta H₂SO₄, Ba(OH)₂ iyo MnO₄⁻/Fe²⁺.
• Ku haynta mugagga milliliter halka uruurintu tahay mol/L. U beddel litir, ama si joogto ah u isticmaal millimool.
• Illaawidda ka-jarka dib-u-cabbiraadda.
• Isticmaalidda culeyska qaacidada ee nooc khaldan, sida NaOH halkii KHP laga isticmaali lahaa halbeegidda.
• Sheegidda tirooyin muhiim ah oo ka badan inta buret-ka iyo miisaanku taageeraan. Afar ayaa caadi u ah shaqada mugga ee taxaddarka leh.
• Malaynta in xalku dhexdhexaad yahay barta sinnaanta kasta. Taasi waxay khusaysaa aashito xooggan iyo saldhig xooggan oo keliya.