Which two substances react spontaneously?

(A) $\ce{Ag}$ and $\ce{Cu}$

(B) $\ce{Ag+}$ and $\ce{Cu}$

(C) $\ce{Ag}$ and $\ce{Cu^2+}$

(D) $\ce{Ag+}$ and $\ce{Cu^2+}$

$\tiny{\text{Taken from 2012 Chem Olympiad}}$

The given answer is B, yet I am unclear as to why. I believe it has something to do with reduction potentials/redox or the gibbs free energy. Can someone please explain?

  • $\begingroup$ Do you have data regarding the reduction potentials of these species and elementary idea about what these values suggest? This can only be solved with known reduction potential data. $\endgroup$ – Satwik Pasani Mar 12 '14 at 4:55
  • $\begingroup$ This was from the 2012 chem olympiad and they do not provide a table of reduction potentials (and you obviously can't bring your own :P). So in the absence of that info how would you solve it? $\endgroup$ – 1110101001 Mar 12 '14 at 6:01
  • $\begingroup$ You then need an idea about their reduction potentials, or equivalently, their relative position in the electrochemical/activity series. $\endgroup$ – Satwik Pasani Mar 12 '14 at 9:48

From the faint outline of electrochemical series I remember $Cu$ is above $Ag$. The substance which is above is able to displace the substance below from its aqueous solution(obviously lower substance is in ionic form).

Hence $(B)$ is true.

We were made to learn this outline in lower class :

K Na Ca Mg Al Zn Fe Pb H Cu Hg Ag Au Pt

  • $\begingroup$ By displace you mean act as a reducing agent? $\endgroup$ – 1110101001 Mar 12 '14 at 18:16
  • $\begingroup$ Yep...btw kids are taught in the way of simple displacement reaction. In higher classes, they introduce the electrode potentials and other stuff. Like : $Cu + AgNO_3$ ... $\endgroup$ – evil999man Mar 13 '14 at 4:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.