Question

5. Why do different atoms/ions emit different colors of light?

2. An unknown solution tested in this experiment gave a yellow green flame test. Do you expect to observe a precipitate with the reagents used in Part C of this experiment?

Answer 1

5. Why do different atoms/ions emit different colors of light?

The Bohr model says that electrons exist only at certain allowed energy levels.

When you heat an atom, some of its electrons are "excited* to higher energy levels.

When an electron drops from one level to a lower energy level, it emits a quantum of energy.

The wavelength (colour) of the light depends on the difference in the two energy levels.

We can see only those transitions that correspond to a visible wavelength.

In a hydrogen atom, for example, we can see only the transitions from higher levels to n = 2 (the Balmer series).

           

Every element has its own characteristic set of energy levels.

Thus, an atom of Na has different energy levels and transitions than an atom of Li.

     

The different mix of energy differences for each atom produces different colours.

2. An unknown solution tested in this experiment gave a yellow green flame test. Do you expect to observe a precipitate with the reagents used in Part C of this experiment?

By observing flame colour Yellow-Green sample identified as a Barium, manganese(II), molybdenum.

If a reaction is known to produce a precipitate if ion A is present and a precipitate is formed when the reaction is run, then ion A may be present in solution (there may be, and usually are, other ions that will also precipitate with a particular reagent). If no precipitate is formed when the reaction is run, then ion A is clearly not present in the unknown solution and a different reaction will have to be run to determine what ions are present.