Cov Lus Nug Piv Txwv Sib Tham Txog Lub Zog thiab pH ntawm Cov Acids thiab Bases
Lub zog acid-base thiab pH yog cov ncauj lus tseem ceeb hauv chemistry, tshwj xeeb tshaj yog hauv thaj chaw ntawm acids thiab bases. Hauv tsab xov xwm no, peb yuav tham txog yuav ua li cas txiav txim siab lub zog acid thiab base thiab xam pH ntawm cov tshuaj siv ntau qhov piv txwv teeb meem.
Kev Taw Qhia Txog Cov Acids thiab Bases
Assam
Cov kua qaub yog ib qho tshuaj uas muaj peev xwm tso tawm cov hydrogen ions (H⁺) thaum yaj hauv dej. Raws li lawv lub peev xwm tso tawm H⁺ ions, cov kua qaub raug muab faib ua ob hom:
1. Cov kua qaub muaj zog: Ib cov kua qaub uas yaj 100% hauv cov kua, thiab tso cov H⁺ ions tawm tag nrho. Piv txwv li: Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃).
2. Cov kua qaub tsis muaj zog: Cov kua qaub uas tsuas yog ib feem ntawm cov kua tawg, tsuas yog qee cov molecule tso tawm H⁺ ions. Piv txwv li: Acetic acid (CH₃COOH), carbonic acid (H₂CO₃), hydrocyanic acid (HCN).
puag
Lub hauv paus yog ib qho tshuaj uas tuaj yeem tso tawm cov hydroxide ions (OH⁻) thaum yaj hauv dej. Raws li lawv lub peev xwm los tso tawm OH⁻ ions, cov hauv paus kuj raug faib ua ob hom:
1. Lub hauv paus muaj zog: Lub hauv paus uas rhuav tshem 100% hauv cov kua, tso tawm OH⁻ ions tag nrho. Piv txwv li: Sodium hydroxide (NaOH), potassium hydroxide (KOH).
2. Lub hauv paus tsis muaj zog: Lub hauv paus uas tsuas yog ib feem ntawm kev sib cais hauv cov kua, tsuas yog qee cov molecules tso tawm OH⁻ ions. Piv txwv li: Ammonia (NH₃), magnesium hydroxide (Mg(OH)₂).
Lub tswv yim pH
pH yog qhov ntsuas ntawm qhov acidity lossis alkalinity ntawm cov tshuaj. Nws yog txhais tias yog cov logarithm tsis zoo ntawm qhov concentration ntawm hydrogen ion (H⁺):
\[ \text{pH} = – \log [H⁺] \]
Rau cov kev daws teeb meem yooj yim, pOH kuj tseem siv, uas yog txhais tias yog logarithm tsis zoo ntawm hydroxide ion (OH⁻) concentration:
\[ \text{pOH} = – \log [OH⁻] \]
Kev sib raug zoo ntawm pH thiab pOH yog:
\[ \text{pH} + \text{pOH} = 14 \]
pH 7 hu ua nruab nrab, pH tsawg dua 7 yog acidic, thiab pH ntau dua 7 yog alkaline.
Cov Lus Nug Piv Txwv thiab Kev Sib Tham
Piv txwv lus nug 1: Xam pH ntawm cov kua qaub muaj zog
Lus Nug: Txheeb xyuas pH ntawm 0,01 M HCl kua.
Kev Sib Tham: HCl yog ib qho kua qaub muaj zog uas yuav tawg ua H⁺ thiab Cl⁻ ions tag nrho. Vim tias nws muaj 1:1 molarity ntawm HCl thiab H⁺, qhov concentration ntawm H⁺ yog 0,01 M.
\[ \text{pH} = – \log [H⁺] \]
\[ \text{pH} = – \log (0,01) \]
\[ \text{pH} = 2 \]
Yog li, pH ntawm 0,01 M HCl kua yog 2.
Piv txwv lus nug 2: Xam tus pH ntawm cov kua qaub tsis muaj zog
Lo lus nug: Txheeb xyuas pH ntawm 0,1 M CH₃COOH (acetic acid) kua yog tias \(K_a\) ntawm CH₃COOH yog \(1,8 \times 10^{-5} \).
Kev Sib Tham: Cov kua qaub tsis muaj zog tsis sib cais tag nrho, yog li peb siv qhov kev sib cais ntawm cov kua qaub (K_a) los txiav txim siab qhov concentration ntawm H⁺. Rau CH₃COOH, qhov kev sib cais yog:
\[ \text{CH₃ COOH} \rightleftharpoons \text{H⁺} + \text{CH₃ COO⁻} \]
Los ntawm txoj cai ntawm cov tshuaj buffer, peb xav tias \( x \) yog qhov concentration ntawm H⁺ ions tsim:
\[ K_a = \frac{ [H⁺][CH₃ COO⁻] }{ [CH₃ COOH] } \]
\[ 1,8 \times 10^{-5} = \frac{ (x)(x) }{ 0,1 – x} \]
Vim tias \(x \) me heev piv rau 0,1 M, peb tuaj yeem tsis quav ntsej x hauv tus lej faib:
\[ 1,8 \times 10^{-5} \approx \frac{ x^2 }{ 0,1 } \]
\[ x^2 \kwv yees li 1,8 \times 10^{-6} \]
\[ x \approx \sqrt{ 1,8 \times 10^{-6} } \]
\[ x \kwv yees li 1,34 \times 10^{-3} \]
Yog li, qhov concentration ntawm H⁺ yog \( 1,34 \times 10^{-3} \):
\[ \text{pH} = – \log [H⁺] \]
\[ \text{pH} = – \log (1,34 \times 10^{-3}) \]
\[ \text{pH} \kwv yees li 2,87 \]
Yog li, pH ntawm 0,1 M CH₃COOH kua yog li 2,87.
Piv txwv lus nug 3: Xam pH ntawm lub hauv paus muaj zog
Lus Nug: Txheeb xyuas pH ntawm 0,01 M NaOH kua.
Kev Sib Tham: NaOH yog lub hauv paus muaj zog uas yuav tawg ua Na⁺ thiab OH⁻ ions. Vim tias nws muaj 1:1 molarity ntawm NaOH thiab OH⁻, qhov concentration ntawm OH⁻ yog 0,01 M.
\[ \text{pOH} = – \log [OH⁻] \]
\[ \text{pOH} = – \log (0,01) \]
\[ \text{pOH} = 2 \]
Siv txoj kev sib raug zoo \( \text{pH} + \text{pOH} = 14 \):
\[ \text{pH} = 14 – \text{pOH} \]
\[ \text{pH} = 14 – 2 \]
\[ \text{pH} = 12 \]
Yog li, pH ntawm 0,01 M NaOH kua yog 12.
Piv txwv lus nug 4: Xam tus pH ntawm lub hauv paus tsis muaj zog
Lo lus nug: Txheeb xyuas pH ntawm 0,1 M NH₃ kua yog tias \(K_b\) ntawm NH₃ yog \(1,8 \times 10^{-5} \).
Kev Sib Tham: Cov hauv paus tsis muaj zog tsis sib cais tag nrho, yog li peb siv qhov kev sib cais tsis tu ncua (K_b) los txiav txim siab qhov concentration ntawm OH⁻. Rau NH₃, qhov kev sib cais yog:
\[ \text{NH₃ + H₂O} \rightleftharpoons \text{NH₄⁺ + OH⁻} \]
Siv tib txoj kev rau cov kua qaub tsis muaj zog, peb xav tias \( y \) yog qhov concentration ntawm OH⁻ ions tsim:
\[ K_b = \frac{ [NH₄⁺][OH⁻] }{ [NH₃] } \]
\[ 1,8 \times 10^{-5} = \frac{(y)(y)}{0,1 – y } \]
Yog tias \( y \) me me, qhov equation yuav ua:
\[ 1,8 \times 10^{-5} \approx \frac{ y^2 }{ 0,1 } \]
\[ y^2 \kwv yees li 1,8 \times 10^{-6} \]
\[ y \approx \sqrt{ 1,8 \times 10^{-6} } \]
\[ y \kwv yees li 1,34 \times 10^{-3} \]
Qhov concentration ntawm OH⁻ yog \( 1,34 \times 10^{-3} \):
\[ \text{pOH} = – \log [OH⁻] \]
\[ \text{pOH} = – \log (1,34 \times 10^{-3}) \]
\[ \text{pOH} \kwv yees li 2,87 \]
Siv txoj kev sib raug zoo \( \text{pH} + \text{pOH} = 14 \):
\[ \text{pH} = 14 – 2,87 \]
\[ \text{pH} \kwv yees li 11,13 \]
Yog li, pH ntawm 0,1 M NH₃ kua yog li 11,13.
Xaus
Kev txiav txim siab qhov pH ntawm cov tshuaj thiab kev nkag siab txog lub zog ntawm cov kua qaub thiab cov hauv paus yog cov hauv paus tseem ceeb hauv kev kawm txog tshuaj lom neeg. Cov kua qaub muaj zog thiab cov hauv paus sib cais tag nrho hauv cov tshuaj, thaum cov kua qaub tsis muaj zog thiab cov hauv paus tsuas yog sib cais ib nrab xwb. Siv \(K_a \) thiab \(K_b \) ua rau nws yooj yim los xam pH ntawm cov kua qaub tsis muaj zog thiab cov hauv paus. Cov txuj ci no yog qhov tseem ceeb rau kev siv hauv ntau qhov chaw, suav nrog kev lag luam, tshuaj, thiab kev tshuaj lom neeg ib puag ncig. Los ntawm kev nkag siab txog cov ntsiab lus thiab kev kawm piv txwv, peb tuaj yeem daws cov teeb meem ntsig txog pH thiab lub zog acid-base hauv lub neej txhua hnub.
