Respuesta :
Cr(OH)₃ undergo a oxidation reaction (increase in oxidation number) from +3 to +6, so Cr(OH)₃ is the reducing agent
Further explanation
Reduction oxidation reaction or abbreviated Redox is a chemical reaction in which there are changes in oxidation numbers
The general formula for determining oxidation numbers:
- 1. Single element atomic oxidation = 0. For example Ar, Mg, Cu, Fe, N₂, O₂, etc. = 0, Group IA (Li, Na, K, Rb, Cs, and Fr)= +1 ,Group IIA (Be, Mg, Ca, Sr and Ba)= +2
- H atoms in compounds = +1, except metal hydride compounds (Hydrogens that bind to groups IA or IIA) oxidation numbers H = -1, for example LiH, MgH₂, etc.
- 2. O atoms in compounds = -2, except OF2 = + 2 and at peroxide (Na₂O₂, BaO₂) = -1 and superoxide, for example KO₂ = -1/2.
- 3. The oxidation number in the uncharged compound = 0,
On reaction :
2Cr(OH)₃+3OCl⁻+4OH⁻→2CrO₄²⁻+3Cl⁻+5H₂O
Oxidation number at Cr(OH)₃
Cr + 3. H + 3.O = 0
Cr + 3.1. + 3.-2 = 0
Cr + 3 -6 = 0
Cr = +3
Oxidation number at CrO₄²⁻
Cr + 4.O = -2
C + 4.-2 = -2
C = +6
The oxidation number Cr in Cr(OH)₃ is +3 and the oxidation number Cr in CrO₄²⁻ is +6, the change in oxidation number C from +3 to +6 is 3, so the Cr atom experiences an oxidation reaction (increase in oxidation number)
Oxidation number at OCl⁻
O + Cl = -1
-2 + Cl = -1
Cl = +1
Oxidation number at Cl⁻
Cl⁻ = =-1
The oxidation number Cl in OCl⁻ is +1 and the oxidation number Cl in Cl⁻ is -1, the change in Cl oxidation number from +1 to -1 is -2, so that the Cl atom experiences a reduction reaction (decreasing the oxidation number)
While O and H atoms do not experience changes in oxidation numbers (O = -2 and H = +1)
So the reducing agent which is experienced with an oxidation reaction (increase in oxidation number) is Cr(OH)₃
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Keywords: reduction, oxidation
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The substance that is a reducing agent is Cr(OH)3.
The term "reducing agent" implies a specie whose oxidation number increases from left to right in the reaction equation. So an the reducing agent must have a lower oxidation number on the left hand side of the reaction equation, but a higher oxidation number on the right hand side of the reaction equation.
We must look out for this as we study the equation;
2Cr(OH)3 + 3OCl^− + 4OH^− ------> 2CrO4^2- + 3Cl^− + 5H2O
It is easy to see from the equation that the oxidation number of chromium increased from +3 on the left hand side of the reaction equation to +6 on the right hand side of the reaction equation.
This means that Cr(OH)3 must be the reducing agent in this reaction.
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