Chemistry

posted by .

In a lab, we added NH3(aq) to CuSO4(aq), and the solution turned dark blue with a precipitate.
The problem is that the products ( Cu(NH3)4 and SO4) should be soluble, no? The question is then, what is the percipitate?

The ppt is Cu(OH)2. The dark blue solution is Cu(NH3)42+ but if the (OH)- is high enough the hydroxide can (and does) form. USUALLY, adding an excess of NH3(aq) will dissolve the hydroxide and leave just the complex copper ion.

Sorry, I'm a bit confused. Can you explain how the ppt is formed? I don't really understand where the oh- comes from. is the NH3(aq) actually NH4+ and OH-?

As I understand it, doesn't CuSO4 + NH3 turn to Cu(NH3)4SO4 and then turns to Cu(NH3)4 and SO4?

An aqueous solution of NH3 is a weak base, forming ammonium ion and hydroxide ion.
NH3 + HOH <===> NH4^+ + OH^-

Copper sulfate is an ionic solid and dissociates in water as follows:
CuSO4(s) + HOH(l) ==> Cu^+2(aq) + SO4^-2(aq)

Then some of the copper(II) in solution reacts with the OH^- to form Cu(OH)2. Since that is sparingly soluble in water, it forms a precipitate.


Also the copper(II) reacts with ammonia to form the complex ion.
Cu^+2 + 4NH3 ==> Cu(NH3)4^+2

At the end, we have the ppt of Cu(OH)2, the dark blue copper ammine complex ion [Cu(NH3)4^+2], the sulfate ion [SO4^-2], unionized aqueous NH3, plus very small amounts of copper(II) ion, ammonium ion, hydroxide ion, and hydrogen ion (from the water). I hope I didn't misplace something. Check my thinking.

Usually, the copper hydroxide will dissolve and turn completely into the ammine complex if an excess (sometimes it takes a LARGE excess) of NH3 is added.

Thanks alot. Understood it perfectly.

[Cu(NH3)4]SO4 + (NH4)2S

  • Chemistry -

    Hi, I don´t understand it very well but I was taught that if NH3 is concentrated, the solution is a complex which is soluble. But if NH3 is dilluted (dillute solution), a sediment (coagulation) will create. It is because a dilluted NH3 behaves as a hydroxide:))

  • Chemistry -

    HOW DO YOU EVEN CHEMISRTY

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    How do I make NH3 to NH4? How would write an ionic equation?
  2. Chem

    A concentrated solution of ammonia is added to a solution of zinc oxide?
  3. Chemistry

    I'm trying to work out the equation for when ammonia solution is added to zinc hydroxide solution. I think a precipitate forms. [Zn(OH)4]2- + NH3(aq) + H2O(l) --> ?
  4. chem

    Equal volume of a 0.02 M Zn+ solution and a 2.0M NH3 solution are mixed. Kf for [Zn(NH3)4] is 4.1*10^8. If enough sodium oxalate is added to make the solution 0.1 M in oxalate, will ZnC2O4 precipitate. Ksp ZnC2O4= 2.7*10^-8. I set …
  5. percipitate and colour

    a few drops of NaOH are added to a sample of the unknown. A blue precipitate appears. Next, approximately 1mL of ammonia, NH3, is added. The precipitate dissolves, but the solution remains blue. Which ion is present. Explain
  6. Chemistry

    a few drops of NaOH are added to a sample of the unknown. A blue precipitate appears. Next, approximately 1mL of ammonia, NH3, is added. The precipitate dissolves, but the solution remains blue. Which ion is present. Explain
  7. Chemistry

    CuSO4(aq) + 4NH3(aq) → [Cu(NH3)4]SO4(aq) I know that adding nitric acid will reverse the reaction. But what is the actual chemical equation?
  8. college chem

    The cation M2+ reacts with NH3 to form a series of complex ions as follows: M2+ + NH3 M(NH3)2+ K1 = 102 M(NH3)2+ + NH3 M(NH3)2 2+ K2 = 103 M(NH3)2 2+ + NH3 M(NH3)3 2+ K3 = 102 A 1.0 × 10–3 mol sample of M(NO3)2 is added to 1.0 L …
  9. chemistry

    50.0 mL of a 0.00200 M Cd^2+ solution is titrated with 0.00400 M EDTA in the presence of 0.0750 M NH3 buffered at pH = 9.00. Determine pCd^2+ when 28.5 mL of EDTA solution have been added. Cd^2+ + Y^4- ?
  10. chem

    Calculate the equilibrium concentration of NH3,Cu^2+,[ Cu(NH3)]^2+ ,[Cu(NH3)2]^2+,[Cu(NH3)3]^2+,and[Cu(NH3)4]^2+ in a solution made by mixing 500.0 ml of 3.00 M NH3 with 500.0 ml of 2.00*10^-3 M Cu(NO3)2. The sequential equilibria …

More Similar Questions