South Pasadena • AP Chemistry
Name ___________________________________
Period ___ Date ___/___/___
Complex Ions
1.
2.
HANDS ON PRACTICE
Observe the peacock blue solution of cupric sulfate. The pretty blue color is due to the complex ion,
tetraaquacopper(II) ion. Write the formula: ______________ This is also be called tetraaquacopper(II)
sulfate because there is a sulfate ion present. Sulfate ion is not part of the complex ion, however.
Place about a “finger’s worth” of the blue solution in the bottom of a test tube. Add a few drops of 1 M
NaOH. Mix and observe. Now think of this as a predicting reaction problem.
Solutions of sodium hydroxide and copper(II) sulfate are mixed.
3.
Add some concentrated ammonia solution to the copper(II) hydroxide suspension in the tube. Keep your
nose away from the fumes. The deep blue (indigo) color comes from the tetraamminecopper(II) ion.
Write the formula for the complex ion: ____________ Keep adding and mixing the ammonia solution
until all of the pale blue precipitate has become deep blue. Is the deep blue substance a precipitate? ___
[Note: if it is a precipitate, it will be opaque. If it is a complex ion, you will be able to see through it.]
Concentrated ammonia solution is added to a suspension of freshly precipitated copper(II) hydroxide.
4.
Remove some of the deep blue solution (into another test tube) until you have about a finger’s worth.
Add a few drops of 1 M hydrochloric acid solution now to the mixture. Observe the color where the acid
mixes with the deep blue solution. Mix and add acid until the entire solution is pale blue.
Ammonia is a proton acceptor (base). Write what happens to the ammonia: NH3 + H+ → ______
Will this new ion be attracted to Cu2+ ions? _____ The pale blue color is due to ____________
A solution of dilute hydrochloric acid is added to a solution of tetraamminecopper(II) sulfate.
5.
Finally, add enough HCl solution until the blue solid disappears.
A solution of hydrochloric acid is added to a suspension of copper(II) hydroxide.