Explanation of a chemical reaction

[smithy1992]

Good afternoon,

The following experiment+observation is given. I look for the explanation of the observations (means: why 1. a white residuum appears and 2. why a blue fluorescence is detected).


Brass consists of zinc, tin and copper, the following reaction shall analyse these properties:
1. Solubilize in in half concentrated HNO3
2. Evaporation until dry
3. Add diluted HCl
-> a white residuum appears
4. Add zinc-granules
5. Heating in a test tube (half fulled with water)

-> observation: blue fluorescence


I assumed that the white residdum is zinc!?

Thank you very much for your aid.

Franziska

 

[Nino MMP]

The white residue that appeared is likely zinc oxide, which forms when zinc reacts with the diluted HCl. The blue fluorescence is likely due to the formation of zinc chloride when zinc reacts with the heat. Zinc chloride is known to emit a blue light when exposed to ultraviolet light.

 

[Blueshift5]

Good afternoon Franziska,

From the given experiment and observations, it appears that the white residuum is indeed zinc. This is because when brass is dissolved in half concentrated HNO3, it reacts with the zinc present in the brass, forming zinc nitrate and releasing hydrogen gas. When the solution is evaporated until dry, the zinc nitrate is left behind as a white residuum.

The addition of diluted HCl in step 3 serves to neutralize any excess HNO3 and also dissolves any remaining zinc nitrate. This results in the formation of zinc chloride, which is a white solid.

When zinc granules are added in step 4 and the mixture is heated in a test tube, the zinc reacts with the water present in the test tube, forming zinc oxide and releasing hydrogen gas. The heating also helps to break down any remaining zinc nitrate and zinc chloride.

The blue fluorescence observed in step 5 is due to the presence of zinc oxide. When heated, zinc oxide releases energy in the form of light, resulting in the blue fluorescence.

Overall, the chemical reaction that is occurring in this experiment is the dissolution of brass in nitric acid, followed by the formation of zinc nitrate and zinc chloride. The addition of zinc granules and heating leads to the formation of zinc oxide, which produces the blue fluorescence. I hope this helps to explain the observations you have made. Please let me know if you have any further questions or need clarification.