Balance the redox reaction H+ (aq) + Cr (s) --> H2 (g) + Cr2+ ?

I do not know why they multiplied the reaction by two at the very end.
I keep getting 2H+ + Cr ---> H2 + Cr2+ (Might be wrong)

Thank you.

1 Answer
anor277
Apr 17, 2018

Well, you have it. Use the method of half-equations....#Cr(s)+ 2H^+ rarr Cr^(2+) + H_2(g)#

Explanation:

Hydrogen ion is REDUCED to dihydrogen gas..

#H^+ +e^(-) rarr 1/2H_2(g)# #(i)#

#"Chromium metal"# is oxidized to #"chromous ion"#:

#Cr(s) rarr Cr^(2+) +2e^(-)# #(ii)#

And so we add TWO of the former to one of the latter: #2xx(i)+(ii)#

We do the multiplication to eliminate the electrons, which are particles of CONVENIENCE...

#Cr(s)+ 2H^+ rarr Cr^(2+) + H_2(g)#

It would be hard to find an acid that would perform the oxidation selectively.... Chromous acetate is obtained by reduction of #Cr^(3+)# with zinc metal....

Claro?

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