Question

Most transition metals can exist in more than one oxidation state, and as such, can form oxides with different formulas. If a basic solution containing 1.89 g of dissolved copper(II)chloride dihydrate (molar mass = 170.48 g/mol) is reacted with excess hydrazine, N2H4, a red form of copper oxide is created. If that solid is isolated, it has a mass of 0.79 g after drying. 

What is the formula of this copper oxide?
Did the oxidation state of copper change during this reaction?

Answer 1

- The formula of the formed copper oxide is Cu₂O

- The oxidation state of copper does change from (II) to (I), because copper is reduced.

Step-by-step explanation:

Hydrazine (N₂H₄) is a well known reducing agent, so it reduces copper(II)chloride (CuCl₂). The oxidation state of Cu in CuCl₂ is +2:

CuCl₂ → Cu²⁺ + 2 Cl⁻

Thus, when Cu²⁺ is reduced to an oxide, it is formed copper(I) oxide (Cu₂O), which is a red solid. According to this, we can conclude:

- The formula of the formed copper oxide is Cu₂O.

- The oxidation state of copper does change from (II) to (I), because copper is reduced.