네른스트 식. Cr | Cr^3+ (0.1 M) || Fe^2+ (0.01 M) | Fe

네른스트 식. Cr | Cr^3+ (0.1 M) || Fe^2+ (0.01 M) | Fe

 

 

Calculate the emf of the cell

Cr | Cr^3+ (0.1 M) || Fe^2+ (0.01 M) | Fe

E°(Cr^3+/Cr) = –0.75 V

E°(Fe^2+/Fe) = –0.45 V

 

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> 산화: Cr → Cr^3+ + 3e^-

> 환원: Fe^2+ + 2e^- → Fe

 

 

> 산화: 2Cr → 2Cr^3+ + 6e^-

> 환원: 3Fe^2+ + 6e^- → 3Fe

---> n = 6

 

 

> 전체: 2Cr(s) + 3Fe^2+(aq) → 2Cr^3+(aq) + 3Fe(s)

Q = [Cr^3+]^2 / [Fe^2+]^3

= (0.1)^2 / (0.01)^3

 

 

 

> E°(Cr^3+/Cr) = –0.75 V

> E°(Fe^2+/Fe) = –0.45 V

 

 

E°_cell = E°_red – E°_red

= (환원된 물질의 표준환원전위) – (산화된 물질의 표준환원전위)

( 참고 https://ywpop.tistory.com/4558 )

 

= (–0.45) – (–0.75) = +0.30 V

 

 

 

Nernst 식

E = E° – (0.0592 V / n) × logQ

( 참고 https://ywpop.tistory.com/2900 )

 

= (+0.30) – (0.0592 / 6) × log( (0.1)^2 / (0.01)^3 )

= +0.26 V

 

 

 

답: 0.26 V

 

 

 

 

[ 관련 예제 https://ywpop.tistory.com/19946 ] 네른스트 식. Fe | Fe^2+ (1.500 M) || Au^3+ (0.00400 M) | Au

 

 

 

[키워드] redox 2Cr + 3Fe^2+ → 2Cr^3+ + 3Fe, redox Cr + Fe^2+, redox Fe^2+ + Cr