Piv txwv ntawm Cov Lus Nug Sib Tham Txog Kev Sib Thooj Hydrolysis
Kev sib xyaw ntsev yog ib qho xwm txheej tshuaj lom neeg uas muaj kev sib xyaw ntawm ntsev nrog dej, tsim cov kua qaub lossis cov hauv paus ua cov khoom seem. Cov txheej txheem no feem ntau yog ib qho tseem ceeb hauv cov lus qhia chemistry vim tias kev nkag siab txog kev sib xyaw ntsev tuaj yeem muab kev nkag siab tseem ceeb rau cov khoom ntawm cov tshuaj thiab pab txiav txim siab pH ntawm cov tshuaj. Hauv tsab xov xwm no, peb yuav tham txog ntau qhov piv txwv ntawm cov teeb meem thiab lawv cov tshuaj cuam tshuam nrog kev sib xyaw ntsev.
Cov Ntsiab Lus Tseem Ceeb ntawm Kev Ntshav Hydrolysis
Kev sib cais ntsev tshwm sim thaum cov ntsev lwj hauv dej thiab nws cov ions sib xyaw nrog cov dej molecules los tsim cov kua qaub lossis cov hauv paus. Tsis yog txhua cov ntsev yuav hydrolyze hauv dej; qee qhov yog nruab nrab, txhais tau tias lawv tsis hloov pH ntawm cov tshuaj. Txawm li cas los xij, qee cov ntsev tuaj yeem tsim cov kua qaub lossis cov hauv paus, nyob ntawm qhov chaw ntawm cov kua qaub thiab cov hauv paus uas tsim cov ntsev.
Yuav kom nkag siab txog lub mechanism no, nws yog ib qho tseem ceeb kom paub tias:
- Cov ntsev ntawm cov kua qaub muaj zog thiab cov hauv paus muaj zog (xws li NaCl) feem ntau tsis dhau hydrolysis thiab cov tshuaj tseem nyob nruab nrab.
– Cov ntsev ntawm cov kua qaub tsis muaj zog thiab cov hauv paus muaj zog (xws li CH3COONa) feem ntau tsim cov tshuaj yooj yim.
- Cov ntsev ntawm cov kua qaub muaj zog thiab cov hauv paus tsis muaj zog (xws li NH4Cl) feem ntau tsim cov kua qaub.
- Cov ntsev ntawm cov kua qaub tsis muaj zog thiab cov hauv paus tsis muaj zog tuaj yeem cuam tshuam nrog dej thiab txiav txim siab qhov pH kawg nyob ntawm qhov sib piv ntawm cov kua qaub thiab cov hauv paus.
Cov Lus Nug Piv Txwv thiab Kev Sib Tham
Lo lus nug 1: Hydrolysis ntawm Potassium Acetate (CH3COOK)
Lo lus nug:
Cov kua potassium acetate (CH3COOK) puas yog acidic, basic, lossis neutral? Sau qhov hydrolysis reaction uas tshwm sim thiab txiav txim siab pH ntawm cov kua.
Kev Sib Tham:
Potassium acetate (CH3COOK) yog ntsev ntawm cov kua qaub tsis muaj zog (acetic acid, CH3COOH) thiab cov hauv paus muaj zog (potassium hydroxide, KOH). Los ntawm qhov no, peb tuaj yeem xaus lus tias cov tshuaj CH3COOK yuav yog cov hauv paus vim tias cov acetate ion (CH3COO⁻) tuaj yeem hydrolyze hauv dej.
Cov tshuaj tiv thaiv yog raws li nram no:
\[ CH_3COO^- + H_2O \rightleftharpoons CH_3COOH + OH^- \]
Cov ions acetate (CH3COO⁻) txais cov protons (H⁺) los ntawm dej (H2O) los ua cov acetic acid (CH3COOH) thiab hydroxide ions (OH⁻). Qhov muaj cov hydroxide ions (OH⁻) hauv cov kua ua rau nws yooj yim.
Yuav kom paub txog pH, peb xav tau qhov concentration ntawm OH⁻ ions. Piv txwv li, peb muaj cov kua 0,1 M CH3COOK thiab qhov ionization constant ntawm acetic acid (Ka) yog 1,8 × 10⁻⁵.
Cov kauj ruam uas tau ua yog:
1. Siv tus nqi tsis hloov pauv (Kb) rau CH3COO⁻ ion:
\[ K_b = \frac{K_w}{K_a} = \frac{10^{-14}}{1,8 \times 10^{-5}} = 5,56 \times 10^{-10} \]
2. Tshem tawm cov CH3COO⁻ ions hauv cov kua:
\[ K_b = \frac{[CH_3COOH][OH^-]}{[CH_3COO^-]} \]
Cia qhov degree ntawm dissociation yog 'x':
\[ 5,56 \times 10^{-10} = \frac{x^2}{0,1-x} \]
Yog tsis quav ntsej tus lej me me \(x\) hauv tus lej denominator, peb tuaj yeem ua kom yooj yim dua:
\[ x^2 \kwv yees li 5,56 \times 10^{-11} \Rightarrow x = \sqrt{5,56 \times 10^{-11}} = 7,45 \times 10^{-6} \]
OH⁻ kev sib xyaw ua ke:
\[ [OH^-] = 7,45 \times 10^{-6} \]
pOH ntawm cov tshuaj:
\[ pOH = -\log [OH^-] = -\log (7,45 \times 10^{-6}) \approx 5,13 \]
Siv kev sib raug zoo ntawm pH thiab pOH:
pH = 14 – pOH = 14 – 5,13 = 8,87 \]
Yog li, CH3COOK kua yog qhov yooj yim nrog pH ntawm li 8,87.
Lo Lus Nug 2: Hydrolysis ntawm Ammonium Chloride (NH4Cl)
Lo lus nug:
Cov kua ammonium chloride (NH4Cl) puas yog acidic, basic, lossis neutral? Sau qhov hydrolysis reaction uas tshwm sim thiab txiav txim siab pH ntawm cov kua.
Kev Sib Tham:
Ammonium chloride (NH4Cl) yog ntsev ntawm cov kua qaub muaj zog (HCl) thiab cov hauv paus tsis muaj zog (NH3). Los ntawm qhov no, peb tuaj yeem xaus lus tias cov tshuaj yog acidic vim tias cov ammonium ion (NH4⁺) tuaj yeem hydrolyze hauv dej.
Cov tshuaj tiv thaiv yog raws li nram no:
\[ NH_4^+ + H_2O \rightleftharpoons NH_3 + H_3O^+ \]
Cov ion ammonium (NH4⁺) pub cov protons (H⁺) rau cov dej molecule (H2O) los ua cov ammonia (NH3) thiab hydronium ions (H3O⁺). Qhov muaj cov hydronium ions (H3O⁺) nyob rau hauv cov kua no ua rau cov kua muaj kua qaub.
Piv txwv li, peb muaj cov kua 0,1 M NH4Cl. Lub hauv paus ionization tas mus li (Kb) rau NH3 yog 1,8 × 10⁻⁵.
Cov kauj ruam uas tau ua yog:
1. Siv cov kua qaub tsis hloov pauv (Ka) rau NH4⁺ ion:
\[ K_a = \frac{K_w}{K_b} = \frac{10^{-14}}{1,8 \times 10^{-5}} = 5,56 \times 10^{-10} \]
2. Tshem tawm cov NH4⁺ ions hauv cov kua:
\[ K_a = \frac{[NH_3][H_3O^+]}{[NH_4^+]} \]
Cia qhov degree ntawm dissociation yog 'x':
\[ 5,56 \times 10^{-10} = \frac{x^2}{0,1-x} \]
Yog tsis quav ntsej tus lej me me \(x\) hauv tus lej denominator, peb tuaj yeem ua kom yooj yim dua:
\[ x^2 \kwv yees li 5,56 \times 10^{-11} \Rightarrow x = \sqrt{5,56 \times 10^{-11}} = 7,45 \times 10^{-6} \]
Kev sib xyaw ntawm H3O⁺:
\[ [H_3O^+] = 7,45 \times 10^{-6} \]
pH ntawm cov tshuaj:
pH = -log [H3O^+] = -log (7,45 x 10^{-6}) \approx 5,13 \]
Yog li, NH4Cl kua yog acidic nrog pH ntawm li 5,13.
Hauv ob qho piv txwv saum toj no, peb pom tias kev txheeb xyuas hom hydrolysis tuaj yeem pab txiav txim siab qhov xwm txheej ntawm cov tshuaj. Los ntawm kev siv qhov sib npaug ntawm ionization (Ka lossis Kb) thiab ob peb qhov kev xav yooj yim, peb tuaj yeem daws cov teeb meem no yooj yim heev.
Qhov kev sib tham txog cov teeb meem hydrolysis ntsev no tsis yog tsuas yog cob qhia cov txuj ci kev xam lej xwb tab sis kuj ua rau nkag siab tob txog cov ntsiab lus tseem ceeb ntawm cov tshuaj lom neeg. Kev nkag siab txog cov ions ntawm ntau lub hauv paus chiv keeb pab txhawb cov protons lossis cov neeg txais rau cov dej molecules, thiab qhov no cuam tshuam li cas rau pH ntawm cov tshuaj, yog qhov tseem ceeb rau kev paub ntau yam hauv chemistry.
