Nickel and Copper joined then immersed in HCl

[AnonymousLover]

A block of Nickel and a block of Copper are joined together and then the combined block is placed in a solution of 1.0 M HCL (aq) at 25 degrees. It was observed that bubbles of gas are only evolved from the surface of the copper. Explain...

I don't get it, the solution (2009 STAV) says that 'a galvanic cell is set up between Ni and Cu in the presense of the electrolyte'... But Im thinking how can Ni (s) form a galvanic cell with Cu(s).

ANYBODY KNOW?

[peterle1]

This is just a guess but

you have
Cu2+(aq) + 2e <-> Cu(s) at 0.34 e volts

and then because you have it in a HCL solution you have to account for:

2H+ +2e- <-> H2(g) at 0.00 e volts

and then you have a

Ni2+ +2e- <-> Ni(s) at -0.23 e volts

because Cu cant react with H+ because it is a weaker redundant
i.e. the reaction is more preferable between H and nickel

But yeah if someone can better interpret this it would be much appreciated

[Mao]

Initially posted here: Re: Unit 4 Questions MEGATHREAD!

A block of nickel and a block of copper are joined together and then the combined block is placed in a solution of 1 M HCl solution at 25C. It was observered that ubbles of gas are only evolved from the surface of the copper. However if the two blocks are separated and placed in the same acid at 25C, the bubbles only appear on the nickel surface. Explain these observations and including half equations to support your explanations.

When Cu/Ni are joined: Ni --> Ni2+ + 2e, 2H+ + 2e --> H2.
So, near the nickel block, ample amounts of Ni2+ are formed. This repels H+ away from the Ni.
Since Cu/Ni are electrically connected, any part of Cu/Ni can act as the cathode. In this case, since the reactants (H+) finds it difficult to approach the Ni electrode due to repulsion, it makes sense that reduction would occur at the Cu surface (where Ni2+ is absent, thus no repulsion). :. Gas bubbles evolve at Cu surface.

When they are separated: Not in electrical contact. Cu does not react with H+, thus no bubble formation at Cu. Only Ni is reacting.
As Ni is no longer in electrical contact with Cu, H+ will have no choice but to approach the Ni electrode (despite the charge-charge repulsion). Bubbles evolve at Ni.
Note that due to this charge-charge repulsion, we will observe a smaller rate of reaction. (i.e. activation energy increases, which captures the repulsive barrier which H+ must overcome to reach the surface of Ni)

Moderator Action: Changed topic title to something more specific