Which element is reduced in this reaction?

Question

2Cr(OH)₃+3OCl⁻+4OH⁻→2CrO₄⁻²+3Cl⁻+5H₂O
Enter the chemical symbol of the element.

Answer 1

You can tell already that the answer is going to be Cr or Cl (the O's and H's are always there).

 

On the left side, the Cr is in the +3 state since it is attached to three OH's, which are each -1, and the whole molecule is neutral. The Cl is in the +1 state: normally, Cl will go negative, but O is more electronegative (has a stronger hold on electrons). Since O is always -2 and the whole molecule is -1, we have -2(1) + x(1) = -1 --> x = +1.

 

On the right side, the Cr is in the +6 state (each O takes two electrons, and the whole molecule is -2, so we have (-2)(4) + x = -2 --> x = +6). The Cl is in the -1 state. Thus

 

Cr : +3 to +6 : was oxidized

Cl : +1 to -1 : was reduced