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Cu does not dissolve in HCl but dissolves in nitric acid. Explain why?

Cu does not dissolve in HCl but dissolves in nitric acid. Explain why?

Grade:upto college level

2 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
7 years ago
Dissolution of a metal in HCl actually means that the metal has displaced H+ ions and form its own salt. However, copper is unable to displace H sine copper lies below H in electropositive character series.HNO3 is a strong oxidising agent also. Hence it rather oxidises copper to Cu2+ ions and hence copper dissolves in HNO3.
vector
13 Points
4 years ago
Use cell potential to explain why copper metal does not dissolve in a typical strong acid, such as hydrochloric acid,Cu( s ) + 2 H+ (aq)but will dissolve in 1 M nitric acid.3 Cu( s ) + 2 HNO3 (aq ) + 6 H +(aq ) 3 Cu 2+ (aq ) + 2 NO( g ) + 4 H 2 O( l)AnswerCopper does not dissolve in a typical strong acid because the overall cell potential for the oxidation of copper metal to Cu 2+ ions coupled with the reduction of H+ ions to H 2 is negative.Cu Cu 2+ + 2 e - Eo ox = -(0.34 V)+ 2 H + + 2 e - H2 Eo red =0.001Cu + 2 H + Cu 2+ + H 2 E o = E oox + E ored = -0.34 VCopper dissolves in nitric acid because the reaction at the cathode now involves the reduction of nitric acid to NO gas, and the potential for this half-reaction is strong enough to overcome the half-cell potential for oxidation of copper metal to Cu 2+ ions.3 (Cu Cu 2+ + 2 e - ) E oox = -(0.34 V)+ 2(HNO 3 + 3 H+ + 2e - NO + 2 H 2 O) E ored = 0.96 V3 Cu + 2 HNO3 + 6 H+ 3 Cu 2+ + 2 NO + 4 H 2 O E o = E oox + E ored = 0.62 V

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