Ukuncibilika ne-Ksp: kuncibilika okungakanani, nokuthi kwakheka nini i-precipitate

Ukubhala isisho se-solubility product

Lapho into eqinile ye-ionic encibilika kancane ithintana nesixazululo sayo esigcwele, ukuncibilika nokwakheka kwe-precipitate kwenzeka ngamazinga alinganayo. Nge-calcium fluoride, CaF₂(s) ⇌ Ca²⁺(aq) + 2 F⁻(aq), futhi okungaguquki kokulingana ngu-Ksp = [Ca²⁺][F⁻]². Into eqinile iyashiywa ngoba iyisigaba esihlanzekile.

Ukugxila kwe-ayoni ngayinye kuphakanyiswa emandleni e-coefficient yayo esibalweni sokuncibilika. Nge-silver chromate, Ag₂CrO₄(s) ⇌ 2 Ag⁺(aq) + CrO₄²⁻(aq), Ksp = [Ag⁺]²[CrO₄²⁻]. Nge-lead(II) iodide, Ksp = [Pb²⁺][I⁻]².

Ukuncibilika kwe-molar, s, yinani lama-mole ento eqinile ancibilikayo ngelitha ngalinye lesixazululo esigcwele. Kuhlobene no-Ksp nge-stoichiometry yokuncibilika, ngakho u-Ksp nokuncibilika akuyona inombolo efanayo futhi akukwazi ukuqhathaniswa ngqo phakathi kosawoti bezinhlobo zamafomula ezihlukene.

Kusuka ku-Ksp kuya ekuncibilikeni kwe-molar

Isibonelo esisebenzile 1. I-silver chloride ino-Ksp = 1.6 × 10⁻¹⁰ kuSithasiselo J. Uma u-s mol/L encibilika, [Ag⁺] = [Cl⁻] = s, ngakho Ksp = s². Bese s = √(1.6 × 10⁻¹⁰) = 1.3 × 10⁻⁵ M. Ngo-M(AgCl) = 143.32 g/mol, lokho kungu-1.8 × 10⁻³ g ngelitha ngalinye, ama-milligram ambalwa.

Isibonelo esisebenzile 2. I-calcium fluoride ino-Ksp = 4.0 × 10⁻¹¹. Uma u-s mol/L encibilika, [Ca²⁺] = s no-[F⁻] = 2s, ngakho Ksp = s(2s)² = 4s³. Bese s = (4.0 × 10⁻¹¹ / 4) ephakanyiswe emandleni angu-1/3 = 2.2 × 10⁻⁴ M.

Qhathanisa kokubili. I-AgCl ino-Ksp omkhulu, kodwa i-CaF₂ incibilika cishe ngokuphindwe izikhathi ezingu-17 ngama-mole ngelitha. I-exponent ishintsha indlela u-Ksp ahambisana ngayo nokuncibilika, ngakho ungahlela ukuncibilika ngo-Ksp kuphela kosawoti abanesilinganiso sama-ayoni esifanayo.

• Usawoti we-1:1 njenge-AgCl noma i-CaCO₃: Ksp = s².
• Usawoti we-1:2 noma we-2:1 njenge-CaF₂, PbI₂ noma i-Ag₂CrO₄: Ksp = 4s³.
• Usawoti we-1:3 njenge-Al(OH)₃: Ksp = 27s⁴.

Kusuka ekuncibilikeni okulinganisiwe ubuyele ku-Ksp

Ukubala kuphinde kuhambe ngenye indlela. Ake sithi isixazululo esigcwele se-lead(II) iodide ku-25 °C sitholakala siqukethe u-0.70 g we-PbI₂ encibilikisiwe ngelitha ngalinye. Ngo-M(PbI₂) = 461.0 g/mol, s = 0.70 / 461.0 = 1.52 × 10⁻³ M.

I-PbI₂ ngayinye encibilikayo inikeza i-Pb²⁺ eyodwa ne-I⁻ ezimbili, ngakho [Pb²⁺] = 1.52 × 10⁻³ M no-[I⁻] = 3.04 × 10⁻³ M. Bese Ksp = (1.52 × 10⁻³)(3.04 × 10⁻³)² = 1.4 × 10⁻⁸, okuvumelana nenani likaSithasiselo J. Amaphutha amabili avamile lapha. Ukukhohlwa isici esingu-2 ku-[I⁻] kwenza u-Ksp abe mncane ngokuphindwe kane. Ukukhohlwa ukwenza isikwele sika-[I⁻] kunikeza amandla angalungile ka-s ngokuphelele.

Ukwengeza i-ayoni evamile kucindezela ukuncibilika

Uma isixazululo sesivele siqukethe enye yama-ayoni kasawoti, isimiso sika-Le Chatelier siphushela ukulingana kokuncibilika emuva entweni eqinile. Lona umphumela we-ayoni evamile.

Isibonelo esisebenzile. Thola ukuncibilika kwe-AgCl ku-NaCl engu-0.10 M. Manje [Cl⁻] = 0.10 + s, futhi u-s mncane kakhulu uma eqhathaniswa no-0.10, ngakho [Cl⁻] ≈ 0.10 M. Bese s = Ksp / [Cl⁻] = 1.6 × 10⁻¹⁰ / 0.10 = 1.6 × 10⁻⁹ M. Lokho kuphansi cishe ngokuphindwe izikhathi ezingu-8,000 kunasemanzini ahlanzekile, futhi u-s ngokusobala akabalulekile uma eqhathaniswa no-0.10, ngakho ukulinganisela kuyasebenza.

Nge-CaF₂ ku-NaF engu-0.010 M, [F⁻] ≈ 0.010 M no-s = 4.0 × 10⁻¹¹ / (0.010)² = 4.0 × 10⁻⁷ M, okuphansi cishe ngokuphindwe izikhathi ezingu-540 kunasemanzini ahlanzekile. Khumbula ukwenza isikwele sokugxila kwe-fluoride lapha, njengasesishweni sika-Ksp.

Ingabe izokwakha i-precipitate? Ukuqhathanisa u-Q no-Ksp

Ukubikezela ukuthi ukuxuba izixazululo ezimbili kukhiqiza into eqinile yini, bala i-ion product Q kusuka ekugxileni ngemva kokuxuba bese uyiqhathanisa no-Ksp. Uma u-Q emkhulu kuno-Ksp, isixazululo si-supersaturated futhi kwakheka i-precipitate. Uma u-Q emncane noma elingana no-Ksp, akwakheki into eqinile.

Isibonelo esisebenzile. Xuba u-50.0 mL we-Pb(NO₃)₂ engu-0.0010 M no-50.0 mL we-KI engu-0.0020 M. Ukuxuba kuphinda kabili ivolumu, ngakho ukugxila ngakunye kuba yingxenye: [Pb²⁺] = 5.0 × 10⁻⁴ M no-[I⁻] = 1.0 × 10⁻³ M. Q = (5.0 × 10⁻⁴)(1.0 × 10⁻³)² = 5.0 × 10⁻¹⁰. Lokho kungaphansi kuka-Ksp = 1.4 × 10⁻⁸, ngakho ayikho i-PbI₂ eyakha i-precipitate.

Phinda nge-KI engu-0.020 M. Manje [I⁻] = 1.0 × 10⁻² M ngemva kokuxuba no-Q = (5.0 × 10⁻⁴)(1.0 × 10⁻²)² = 5.0 × 10⁻⁸. Lokho kudlula u-Ksp, ngakho kwakheka i-PbI₂ ephuzi. Ukukhohlwa ukuhlanjululwa lapho kuxutshwa yiphutha elivame kakhulu kulezi zinkinga.

I-selective precipitation: ukuhlukanisa ama-ayoni ngo-Ksp

Lapho ama-ayoni amabili ngamunye engakha i-precipitate ne-reagent efanayo, leyo usawoti wayo odinga ukugxila okuphansi kwe-reagent yakha i-precipitate kuqala. Ukwengeza kancane kungabe kusuwahlukanisa.

Isibonelo esisebenzile. Isixazululo singu-0.010 M kokubili ku-Cl⁻ naku-CrO₄²⁻, futhi i-Ag⁺ yengezwa kancane. I-AgCl iqala ukwakheka lapho [Ag⁺] = 1.6 × 10⁻¹⁰ / 0.010 = 1.6 × 10⁻⁸ M. I-Ag₂CrO₄, eno-Ksp = 9.0 × 10⁻¹² evela kuSithasiselo J, iqala ukwakheka lapho [Ag⁺]² × 0.010 = 9.0 × 10⁻¹², ngakho [Ag⁺] = 3.0 × 10⁻⁵ M. I-AgCl yakha i-precipitate kuqala.

Ngesikhathi i-Ag₂CrO₄ ebomvu ivela, u-[Cl⁻] usehlele ku-1.6 × 10⁻¹⁰ / 3.0 × 10⁻⁵ = 5.3 × 10⁻⁶ M, ngakho kusala cishe amaphesenti angu-0.05 kuphela e-chloride esixazululweni. Lolo shintsho olucacile lombala luyisisekelo se-titration ye-Mohr ye-chloride.

Kungani abanye osawoti bencibilika kakhulu ku-asidi

Uma i-anion kasawoti iyisisekelo, njenge-OH⁻, CO₃²⁻ noma i-F⁻, ukwengeza i-asidi kususa leyo anion esixazululweni futhi kudonsela ukuncibilika phambili. Ama-hydroxide nama-carbonate ancibilika kangcono kakhulu ku-pH ephansi. Usawoti wama-anion ama-asidi aqinile, njenge-AgCl, awuthinteki ngale ndlela.

Isibonelo esisebenzile. I-magnesium hydroxide ino-Ksp = 8.9 × 10⁻¹². Emanzini ahlanzekile, Ksp = 4s³ unikeza s = 1.3 × 10⁻⁴ M no-[OH⁻] = 2.6 × 10⁻⁴ M, ngakho isixazululo esigcwele sine-pH 10.42. Uma kunalokho i-buffer igcina i-pH ku-9.00, bese [OH⁻] = 1.0 × 10⁻⁵ M no-s = 8.9 × 10⁻¹² / (1.0 × 10⁻⁵)² = 0.089 M, cishe ngokuphindwe izikhathi ezingu-700 ngaphezulu. Lokhu kuthatha ukuthi i-buffer inomthamo owanele wokumunca i-hydroxide ekhululwayo.

Amaphutha e-Ksp okufanele uwahlole ngaphambi kokuthumela

Amaphutha amaningi avela ku-stoichiometry yokuncibilika, hhayi emqondweni wokulingana ngokwawo. Ukubhala isibalo sokuncibilika nezingxenye zika-s ngaphansi kwaso kubamba amaningi awo.

• Ukubeka u-Ksp alingane no-s² kusawoti okhulula ama-ayoni amathathu noma ngaphezulu.
• Ukuphinda kabili ukugxila kwe-ayoni kodwa ungakwenzi isikwele esishweni, noma okuphambene.
• Ukuhlela ukuncibilika ngo-Ksp kosawoti abanezilinganiso zama-ayoni ezihlukene.
• Ukukhohlwa ukuhlanjulula zombili izixazululo lapho ubala u-Q ngemva kokuxuba.
• Ukunganaki i-ayoni evamile esivele ikhona.
• Ukufaka into eqinile esishweni sika-Ksp.