Respuesta :
a) Balanced equation;
[tex]Au +3 NO^{-} _{3} +4Cl^{- }+6H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + 3NO_{2} + 3H_{2} O[/tex]
b) oxidizing agent: N
  reducing agent: Au
a) The unbalanced redox equation is as follows:
[tex]Au + NO^{-} _{3} +Cl^{- }+H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + NO_{2} + H_{2} O[/tex]
Balance all atoms other than H and O.
[tex]Au + NO^{-} _{3} +4Cl^{- }+H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + NO_{2} + H_{2} O[/tex]
The oxidation number of gold changes from 0 to +3. The change in the oxidation number of gold is 3.The oxidation number of nitrogen changes from +5 to +4. The change in the oxidation number of nitrogen is 1.
So,
[tex]Au +3 NO^{-} _{3} +4Cl^{- }+H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + 3NO_{2} + H_{2} O[/tex]
Now balance O atoms on RHS,
[tex]Au +3 NO^{-} _{3} +4Cl^{- }+H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + 3NO_{2} + 3H_{2} O[/tex]
Now, balance hydrogen atoms on RHS,
[tex]Au +3 NO^{-} _{3} +4Cl^{- }+6H^{+}[/tex] ⇒ [tex]AuCl^{-}_{4} + 3NO_{2} + 3H_{2} O[/tex]
This is the balanced chemical equation.
b) oxidizing agent: N
  reducing agent: Au
Learn more about oxidation number here;
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