ATAR Notes: Forum

Archived Discussion => 2009 => Mid-year exams => Exam Discussion => Victoria => Chemistry => Topic started by: jaques on September 26, 2009, 09:12:15 am

Title: can someone help me with this chem question please
Post by: jaques on September 26, 2009, 09:12:15 am

can anyone assist me with question 1 in the heinemann chemistry 2 textbook on page 448.
I get the concept but I'm having trouble understanding how two solids & both strong reductants are able to react together. I've checked the solutions but i still can't put  it together. It would be appreciated if someone could explain this in context of the electrochemical series please  :-[

thanks       

Title: Re: can someone help me with this chem question please
Post by: rajah21 on September 26, 2009, 09:39:29 am

Electroplating a cell requires setting up an electrolytic cell with the object to be plated (in this case, the iron locker key) as the cathode (negatively charged) and the metal you wish to electroplate with (in this case, copper) as the anode (positively charged).

a) Reaction at the anode (+): Cu (s) --> Cu²⁺ (aq) + 2e^-

Reaction at the cathode (-): Cu²⁺ (aq) + 2e^- --> Cu(s)

The electrolyte would be something that contains the ions of the metal that is to form the plating, e.g. CuSO₄ (aq).

b) If the locker key was connected to the positive terminal of the power supply, the key would become the anode and corrode via the reaction Fe (s) --> Fe²⁺ (aq) + 2e^-

Title: Re: can someone help me with this chem question please
Post by: jaques on September 26, 2009, 10:04:41 am

thanks

but may i ask if you were circling the reactants in the electrochemical series to explain this, then you couldn't be circling the two solids. 
for example you know how in spontaneous it's like;

strongest oxidant 



                            strongest reductant           



and non spontaneous its like;
                                     stronger reductant
 




weaker oxidant

then how would you explain          stronger reductant




                                               weaker reduactant 

Title: Re: can someone help me with this chem question please
Post by: chem-nerd on September 26, 2009, 01:48:50 pm

It's not the solid Fe and the solid Cu that are reacting together.

In this case, you want to copper-plate the iron key so you would need to have Cu²⁺ ions in the cell and a solid copper anode (to replenish the Cu²⁺ ions in solution via oxidation os the solid Cu).
Even though the solid Fe is a stronger reductant, it has been set as the cathode and in effect been rendered inert (reduction at cathode, solid Fe can't gain electrons). The next strongest reductant is then Cu solid.

For the cathode reaction you are looking for the strongest oxidant, of which Cu²⁺ is stronger than water.