# Molar ratios not leading to complete reaction in Schweizer's reagent production

In my home lab, I've reacted $$\ce{Cu(OH)2}$$ with aqueous ammonia to produce Schweizer's reagent. However, I'm surprised by the amount of ammonia required to react with this amount of $$\ce{Cu(OH)2}$$. Have I mistaken some calculation or formula?

Background/procedures:

8.89 g of copper (II) hydroxide was prepared by combining 24.98 g of $$\ce{CuSO4 (aq)}$$ with excess aqueous ammonia, to which was added 8.01 g $$\ce{NaOH (aq)}$$, precipitating a blue-green solid, which was filtered and allowed to dry, producing a blue-green powder with no visible hint of black copper oxide. This is believed to be reasonably pure copper (II) hydroxide.

This 8.89 g of copper (II) hydroxide was combined with aqueous ammonia (assayed at "28% to 30%"), gradually, in amounts of 30 mL, 30 mL, 70 mL, and 70 mL, a total of 200 mL. Also, 80 mL of distilled water was added, but I assume this is merely diluting the reagent and not affecting the reaction.

At each addition of aqueous ammonia, more of the copper hydroxide reacted to form a clear, deep blue liquid, consistent with the expected appearance of Schweizer's reagent. However, a sizable amount of green-blue solid remains:

Assumptions and calculations:

• 8.89 g $$\ce{Cu(OH)2}$$, with a molar mass of 97.56 g/mol, equals 0.0911 mol $$\ce{Cu(OH)2}$$.
• 200 mL of "28-30%" aqueous ammonia, at roughly 14 mol/L, equals 2.8 mol $$\ce{NH3}$$.
• Balanced equation for this reaction is $$\ce{Cu(OH)2 + 4 NH3 -> [Cu(NH3)4](OH)2}$$ ; this indicates a ratio of 1:4 for copper hydroxide to ammonia.
• However, my ratio so far is closer to 1:28, and it's still not enough.

Question:

If my calculations are correct, I've added about 7 times the amount of ammonia needed to fully react with this amount of copper hydroxide, but it appears not all of it has reacted. Where have I miscalculated?

• I remember notes the proper procedure is precipitation Cu(OH)2 by NaOH, decanting and dissolving it in ammonia. There was warning the S. reagent prepared by other way does not dissolve cellulose. Oct 2 '19 at 13:45