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
If the color of the original sample was NOT blue, then the ppt with NaOH probably is Cu(OH)2 and the addition of ammonia produces a dark blue solution of Cu(NH3)4^+2. (I don't see a DARK BLUE solution mentioned so I may be taking something for granted here.)
To determine the ion present in the solution, we need to understand the reactions that occurred when the NaOH and ammonia were added. Let's break down the steps:
1. Addition of NaOH: When a few drops of NaOH (sodium hydroxide) are added to a solution, it reacts with certain metal ions to form precipitates. In this case, a blue precipitate was formed, indicating the presence of a metal ion that can react with NaOH to form an insoluble compound.
2. Addition of NH3: Ammonia (NH3) is a weak base. When it is added to a solution containing a metal hydroxide precipitate, it can react to form soluble complexes. If the blue precipitate dissolves upon the addition of ammonia, it suggests the formation of a complex ion with the metal.
Now, let's review some possible metal ions that can form a blue precipitate with NaOH and continue to stay in solution when ammonia is added:
1. Copper (Cu2+): When NaOH is added to a copper-containing solution, a blue precipitate of copper(II) hydroxide (Cu(OH)2) is formed. Upon addition of ammonia, copper(II) hydroxide will dissolve to form a deep blue complex known as tetraamminecopper(II) complex, [Cu(NH3)4]2+. The solution will remain blue in the presence of excess ammonia.
Therefore, the most likely ion present in the solution is the copper(II) ion (Cu2+).
It's important to note that confirming the presence of a specific ion requires additional tests or analyses. The explanation provided is based on the given information and the common behavior of certain metal ions with NaOH and ammonia.