Fa'ata'ita'iga o Fesili Talanoaga e uiga i le Eletise
O le electrochemistry o se lala o le kemisi e suʻesuʻeina le sootaga i le va o tali faʻakemikolo ma suiga i le malosi eletise. I le electrochemistry, e lua manatu autu: o le oxidation (le faʻasaʻolotoina o electrons) ma le reduction (le maua o electrons). O nei faiga e mafai ona matauina i ituaiga e lua o electrochemical cells: voltaic cells (galvanic cells) ma electrolytic cells. O loʻo i lalo nisi o faʻataʻitaʻiga o faʻafitauli ma a latou faʻamatalaga e fesoasoani ia te oe e malamalama ai i le electrochemistry.
Fa'ata'ita'iga Fesili 1: Sela Voltaic
Fesili:
Tuuina atu i se sela voltaic ma electrodes zinc (Zn) ma le copper (Cu) ua feso'ota'i e ala i se salt bridge. E fufui le Zn i totonu o se 1 M ZnSO4 solution ma e fufui le Cu i totonu o se 1 M CuSO4 solution. Tusi i lalo tali e tutupu i electrodes ta'itasi ma fuafua le potential difference (EMF) o le voltaic cell. Fa'amatalaga masani o le potential electrode:
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
\[ E^o_{\text{Cu}^{2+}/\text{Cu}} = +0.34 \, \text{V} \]
Talanoaga:
O le laasaga muamua o le fuafuaina lea o le tali redox e tupu. I totonu o se voltaic cell, e tupu se tali redox faafuaseʻi pe a tupu
– E fa'a'okesa'oina le zinc (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– E fa'aitiitia le kopa (Cu):
\[ \text{Cu}^{2+} (aq) + 2e^- \rightarrow \text{Cu (s)} \]
O le aofaʻi atoa o le redox reaction i totonu o se voltaic cell e:
\[ \text{Zn (s)} + \text{Cu}^{2+} (aq) \rightarrow \text{Zn}^{2+} (aq) + \text{Cu (s)} \]
O le isi mea, o le a matou fuafuaina le eseesega o le gafatia o le sela:
\[ E_{\text{cell}} = E^o_{\text{cathode}} – E^o_{\text{anode}} \]
O fea:
– O le cathode o le eletise lea e tupu ai le fa'aitiitia (Cu).
– O le anode o le electrode lea e tupu ai le oxidation (Zn).
O lena la,
\[ E_{\text{sel}} = 0.34 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E_{\text{sel}} = 0.34 \, \text{V} + 0.76 \, \text{V} = 1.10 \, \text{V} \]
I'uga:
– O le tali atu e tupu i le anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– O le tali atu e tupu i le cathode (Cu):
\[ \text{Cu}^{2+} (aq) + 2e^- \rightarrow \text{Cu (s)} \]
– Eseesega o le gafatia o le sela (EMF): 1.10 V
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Fa'ata'ita'iga Fesili 2: Sela Eletise
Fesili:
I le electrolysis o se vaifofo NaCl, ta'u mai tali e tutupu i le cathode ma le anode pe afai e fa'aaogaina se electrode inert, e pei o le platinum (Pt). Fa'atatau le aofa'i atoa o le mamafa e mana'omia e gaosia ai le 1 kalama o le Cl2. (Ar Cl = 35.5)
Talanoaga:
O le laasaga muamua o le tusi i lalo o tali e tutupu i eletise taitasi i le fofo masima NaCl.
– I le cathode (fa'aitiitiga):
I lenei faagasologa, o le a faʻaitiitia ai H+ ions mai le vai:
\[ 2H_2O(l) + 2e^- \au taumatau H_2(g) + 2OH^-(aq) \]
– I le anode (oxidation):
O le a fa'a'okeseneina le ion Cl- e avea ma kasa Cl2:
\[ 2Cl^-(aq) \taumatau Cl_2(g) + 2e^- \]
Tali Atoa:
O le tali atoa lea e tupu i le electrolysis o le fofo NaCl e faapea:
\[ 2NaCl(aq) + 2H_2O(l) \au taumatau 2NaOH(aq) + H_2(g) + Cl_2(g) \]
Ina ia fuafua le totogi e manaʻomia e gaosia ai le 1 kalama o le Cl2, e manaʻomia ona tatou fuafuaina le aofaʻi o moles o le Cl2:
\[ \text{Mamafa o le Cl}_2 = 1 \text{ kalama} \]
\[ \text{Ar Cl}_2 = 2 \times 35.5 = 71 \text{ gram/mol} \]
\[ \text{Numera o mole o le Cl}_2 = \frac{1}{71} \text{ mol} \]
E faʻavae i luga o le fua faʻatatau o le tali atu i le anode, e gaosia le 1 mol o le Cl2 mai le 2 mol o electrons:
\[ 2Cl^- \rightarrow Cl_2 + 2e^- \]
I se isi faaupuga, o le 1 mole o le Cl2 e manaʻomia ai le 2 mole o eletise.
Numera o mole o eletise:
\[ \text{Numera o mole o eletise} = 2 \times \frac{1}{71} = \frac{2}{71} \text{ mol} \]
E mafai ona fuafuaina le totogi manaʻomia e faʻaaoga ai le tau o Faraday (F = 96485 C/mol e^-):
\[ Q = n \times F \]
\[ Q = \left(\frac{2}{71} \text{ mol}\right) \times 96485 \text{ C/mol} \]
\[ Q = 2718 \text{ C} \]
I'uga:
– Tali atu i le cathode:
\[ 2H_2O(l) + 2e^- \au taumatau H_2(g) + 2OH^-(aq) \]
– Tali atu i le anode:
\[ 2Cl^-(aq) \taumatau Cl_2(g) + 2e^- \]
– O le aofaʻi atoa e manaʻomia e gaosia ai le 1 kalama o le Cl2 e 2718 C.
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Faataitaiga 3: Sootaga Nernst ma Tuutuuga e Lē Masani
Fesili:
Fuafua le gafatia o se sela voltaic e faia mai eletise Ag/Ag+ ma le maualuga o le ion siliva e 0.1 M ma eletise Zn/Zn2+ ma le maualuga o le 0.01 M. O le gafatia masani o le eletise e faapea:
\[ E^o_{\text{Ag}^{+}/\text{Ag}} = +0.80 \, \text{V} \]
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
Talanoaga:
O le laasaga muamua o le tusia lea o tali e tutupu:
– Oksida i le anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– Fa'aitiitiga i le cathode (Ag):
\[ \text{Ag}^{+} (aq) + e^- \rightarrow \text{Ag (s)} \]
Tali atoa:
\[ \text{Zn (s)} + 2\text{Ag}^{+} (aq) \rightarrow \text{Zn}^{2+} (aq) + 2\text{Ag (s)} \]
E faʻavae i luga o le fua faʻatatau a Nernst:
\[ E_{\text{Cell}} = E^o_{\text{Cell}} – \left( \frac{0.0592}{n} \right) \log \left( \frac{[\text{product}]}{[\text{reactant}]} \right) \]
O fea:
\[ n = 2 \]
Muamua, fuafua le E^o_{\text{Sel}}:
\[ E^o_{\text{Sel}} = E^o_{\text{Ag}^{+}/\text{Ag}} – E^o_{\text{Zn}^{2+}/\text{Zn}} \]
\[ E^o_{\text{Sel}} = 0.80 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E^o_{\text{Cell}} = 1.56 \, \text{V} \]
Sosoo ai, fuafua le gafatia moni o le sela i le maualuga ua tuʻuina atu:
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{[\text{Zn}^{2+}]}{[\text{Ag}^{+}]^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{0.01}{(0.1)^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – 0.0296 \log \left( \frac{0.01}{0.01} \right) \]
\[ E_{\text{Cell}} = 1.56 \, \text{V} \]
I'uga:
– E tumau pea le tutusa o tali e tutupu i le anode ma le cathode
– O le gafatia o le sela i se tulaga tuʻuina atu e 1.56 V
O lenei tusiga o loʻo faʻaalia ai le auala e foia ai ni ituaiga faʻafitauli i le electrochemistry, e aofia ai faʻafitauli e aofia ai voltaic cells, electrolytic cells, ma faʻatusatusaga e faʻaaoga ai le Nernst Equation. O se malamalamaga maeʻaeʻa i mataupu faavae i tua atu o redox reactions ma le mafai ona faʻaaoga faʻamatalaga electrochemical e taua tele mo le manuia i le foia o nei ituaiga faʻafitauli.
