Su'aalo Tusaale ah oo Ka Hadlaya Xalalka Kaydka
Xalka kaydka, oo badanaa loo yaqaan buffer, waa xal ilaaliya pH-giisa xitaa marka lagu daro xaddi yar oo aashito ama saldhig xooggan ah. Awooddani waxay ka dhigaysaa xalalka kaydka mid muhiim u ah codsiyada kiimikada, bayoolojiga, iyo xitaa warshadaha kala duwan. Maqaalkan, waxaan ku sahamin doonnaa tusaalooyin qaar waxaanan ka wada hadli doonnaa xalalka kaydka.
Fahmidda Xalalka Kaydka
Xalalka kaydka guud ahaan waxay ka kooban yihiin isku darka aashito daciif ah iyo saldhiggeeda isku dhafan ama saldhig daciif ah iyo aashitada isku dhafan. Marka aashito ama saldhig lagu daro xalalkan, falcelinta ka dhalata waxay gacan ka geysataa ilaalinta pH-ga xalka gudaha xad gaar ah. Xaaladdan, pH waa cabbiraadda aashitada ama alkalinity-ga xalka.
Shaqada iyo Muhiimadda Xalalka Kaydka
Xalalka kaydka (buffers) waxay leeyihiin door muhiim ah oo ku saabsan dhinacyo kala duwan:
1. Bayoolajiga: Falcelin badan oo ensaymatik iyo fiisiyoolaji ah ayaa ka dhacda pH gaar ah, sidaa darteed xalalka kaydka ah waxay gacan ka geystaan ilaalinta xaaladaha ugu wanaagsan.
2. Warshadaha: Warshadaha cuntada iyo daawooyinka, xakamaynta pH-ga saxda ah ayaa muhiim u ah tayada iyo badbaadada badeecadaha.
3. Tijaabooyinka Kiimikada: Shaybaarka dhexdiisa, xalalka kaydka ah waxaa loo isticmaalaa in lagu xakameeyo pH inta lagu jiro falcelinta kiimikada.
Sida Xalalka Kaydka u Shaqeeyaan
Xalalka kaydka waxay ku shaqeeyaan mabda'a dheelitirka. Xal ka kooban aashito daciif ah \( HA \) iyo cusbada saldhigga isku dhafan \( A^- \), ku darista xaddi yar oo aashito ah ama saldhig ayaa kicin doonta falcelin barokac ah iyada oo aan isbeddel weyn ku imaanayn isku-darka aayadaha \( H^+ \).
Su'aalo iyo Doodo Tusaale ah
Si aan u sii fahanno, aan falanqeyno su'aalo iyo doodo la xiriira xalalka kaydka.
Su'aal 1aad: Xisaabinta pH-ga Xalka Kaydka Aashitada
Su'aal:
Xalka kaydka ah waxaa lagu sameeyaa iyadoo lagu qaso 0,1 mol oo acetic acid ah (CH₃COOH) iyo 0,1 mol oo sodium acetate ah (CH₃COONa) 1 litir oo xal ah. Joogtada kala-goynta acetic acid (\( K_a \)) waa \( 1,8 \jeer 10^{-5} \). Xisaabi pH-ga xalka.
Dood:
Xalkan kaydka ah wuxuu ka kooban yahay aashito daciif ah (CH₃COOH) iyo saldhiggeeda isku xiran (CH₃COO⁻). Waxaan isticmaali karnaa isla'egta Henderson-Hasselbalch si aan u xisaabinno pH-ga xalka kaydka:
\[ \text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right) \]
Halkee:
\[ \text{p}K_a = -\log (K_a) \]
\[ \text{p}K_a = -\log (1,8 \times 10^{-5}) \]
\[ \text{p}K_a \qiyaastii 4,74 \]
Maadaama fiirsashada \( [A^-] \) iyo \( [HA] \) ay isku mid yihiin (0,1 M):
\[ \text{pH} = 4,74 + \log \left( \frac{[0,1]}{[0,1]} \right) \]
\[ \text{pH} = 4,74 + \log(1) \]
\[ \qoraal{pH} = 4,74 \]
Markaa, pH-ga xalka kaydka ah waa 4,74.
Su'aal 2: Ku darista Aashitada Xalka Kaydka
Su'aal:
Waa maxay isbeddelka pH haddii 0,01 mol oo HCl ah lagu daro 1 litir oo xal kayd ah oo ka yimid Su'aasha 1aad?
Dood:
Ku darista HCl waxay kordhin doontaa xoogga \( H^+ \ ) ee xalka. Falcelinta dhacda waa:
\[ \qoraal{H}^+ + \qoraal{CH}_3\qoraal{COO}^- \rightarrow \qoraal{CH}_3\qoraal{COOH} \]
Waxaan u baahanahay inaan xisaabino inta moles ee \( H^+ \) iyo sida ay u saamayso isku-darka \( \text{CH}_3\text{COOH} \) iyo \( \text{CH}_3\text{COO}^- \).
Bilowgii:
\[ [\text{CH}_3\text{COO}^-] = 0,1 \, \text{mol} \]
\[ [\text{CH}_3\text{COOH}] = 0,1 \, \text{mol} \]
Ka dib marka lagu daro 0,01 mol oo HCl ah:
\[ [\text{CH}_3\text{COO}^-] = 0,1 – 0,01 = 0,09 \, \text{mol} \]
\[ [\text{CH}_3\text{COOH}] = 0,1 + 0,01 = 0,11 \, \text{mol} \]
Isticmaal isla'egta Henderson-Hasselbalch si aad u xisaabiso pH-ga cusub:
\[ \text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right) \]
\[ \text{pH} = 4,74 + \log \left( \frac{0,09}{0,11} \right) \]
\[ \text{pH} = 4,74 + \log(0,818) \]
\[ \text{pH} = 4,74 + (-0,088) \]
\[ \qoraal{pH} = 4,65 \]
Markaa, pH-ka xalka kaydka ka dib marka lagu daro HCl wuxuu isbeddelaa 4,74 ilaa 4,65.
Su'aal 3: Ku darista Saldhigga Xalka Kaydka
Su'aal:
Waa maxay isbeddelka pH haddii 0,01 mol oo NaOH ah lagu daro 1 litir oo xal kayd ah oo ka yimid Su'aasha 1aad?
Dood:
Ku darista NaOH waxay yarayn doontaa fiirsashada H⁺ ee xalka iyadoo la adeegsanayo OH⁻ oo ka timaadda NaOH. Falcelinta dhacda:
\[ \text{OH}^- + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COO}^- + \text{H}_2\text{O} \]
Bilowgii:
\[ [\text{CH}_3\text{COOH}] = 0,1 \, \text{mol} \]
\[ [\text{CH}_3\text{COO}^-] = 0,1 \, \text{mol} \]
Ka dib marka lagu daro 0,01 mol oo NaOH ah:
\[ [\text{CH}_3\text{COOH}] = 0,1 – 0,01 = 0,09 \, \text{mol} \]
\[ [\text{CH}_3\text{COO}^-] = 0,1 + 0,01 = 0,11 \, \text{mol} \]
Isticmaal isla'egta Henderson-Hasselbalch si aad u xisaabiso pH-ga cusub:
\[ \text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right) \]
\[ \text{pH} = 4,74 + \log \left( \frac{0,11}{0,09} \right) \]
\[ \text{pH} = 4,74 + \log(1,222) \]
\[ \text{pH} = 4,74 + 0,087 \]
\[ \qoraal{pH} = 4,83 \]
Markaa, pH-ka xalka kaydka ka dib marka lagu daro NaOH wuxuu isbeddelaa 4,74 ilaa 4,83.
Su'aal 4: Go'aaminta Halabuurka Kaydka oo leh pH gaar ah
Su'aal:
Si loo sameeyo 1 litir oo xal buffer ah oo leh pH 5,0 adoo isticmaalaya acetic acid (CH₃COOH) iyo sodium acetate (CH₃COONa), imisa moles oo qayb kasta ah ayaa loo baahan yahay? \(K_a \) oo acetic acid ah ayaa ah \( 1,8 \jeer 10^{-5} \).
Dood:
Isticmaal isla'egta Henderson-Hasselbalch si aad u hesho:
\[ \text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right) \]
Marka hore, xisaabi pKₐ:
\[ \text{p}K_a = -\log (1,8 \times 10^{-5}) \]
\[ \text{p}K_a \qiyaastii 4,74 \]
Kadib, geli qiimaha pH ee la rabo:
\[ 5,0 = 4,74 + \log \left( \frac{[A^-]}{[HA]} \right) \]
\[ 0,26 = \log \left( \frac{[A^-]}{[HA]} \right) \]
Isticmaalka sifooyinka logarithms-ka:
\[ \frac{[A^-]}{[HA]} = 10^{0,26} \]
\[ \frac{[A^-]}{[HA]} \qiyaastii 1,82 \]
Taas macnaheedu waa in 1 mole kasta oo CH₃COOH ah, 1,82 mole oo CH₃COONa ah ayaa loo baahan yahay. Saamigan 1 litir:
Tusaale ahaan, aan dhahno CH₃COOH = x mol, markaa CH₃COONa = 1,82x mol. Wadarta mugga waa (x + 1.82x) = 2,82x mol, maadaama aan sameyneyno 1 litir oo kayd ah, markaa:
\[ x + 1.82x = 1 \]
\[ 2.82x = 1 \]
\[ x = \frac{1}{2.82} \qiyaastii 0.355 \]
Sidaas, halabuurka loo baahan yahay:
– CH₃COOH: 0,355 mol
- CH₃COONa: 1,82 0,355 ≈ 0,646 mol
Sidaa darteed waxaan u baahanahay 0,355 mol oo acetic acid ah iyo 0,646 mol oo sodium acetate ah si aan u sameyno 1 litir oo xal kayd ah oo leh pH 5,0.
Maqaalkani wuxuu soo bandhigayaa dhibaatooyin kala duwan oo la xiriira xalalka kaydka iyo doodahooda si loo helo faham qoto dheer oo ku saabsan fikraddan. Waxaan rajeyneynaa in macluumaadkani uu waxtar u leeyahay fahamka sida xalalka kaydka u shaqeeyaan iyo codsiyadooda xaalado kala duwan.
