Halogen Reactions

Written by Sean

Purpose – Exploring Halogen Reactions

Through this experiment the electronegativity of several Halogens will be determined through attempted chemical reactions. Electronegativity is the power of an atom to pull electrons toward itself, which usually forms a bond with another atom and thus creates a molecule. If this molecule is polar, that is, that one of the atoms attracts electrons more than the others; it will be soluble in polar liquids and the same with nonpolar molecules and liquids. In this experiment two molecules will be mixed and the more electronegative one will form a halogen and the lesser electronegative will become a halide.

Procedure

Dillon, Stephanie. “Halogen Reactions.” CHM1045L Online Manual. Spring 2010. 13 April 2010 <http://www.chem.fsu.edu/chemlab/chm1045lmanual/halogens/procedure.html>. Experimenter tested solubility of K salts, Na salt solubility data was received from Alex Macdonell.

Data

Solubility Test*

Element Involved

Solubility results

Observations

KBr

Dissolves easily in water, doesn’t dissolve at all in hexane

Crystals disappear upon shaking water. Salt in hexane remains solid

KCl

Dissolves in water, doesn’t dissolve at all in hexane

Crystals disappear upon shaking water. Salt in hexane remains solid

KI

Dissolves in water after mixing, doesn’t dissolve at all in hexane

Crystals disappear upon shaking water. Salt in hexane remains solid

*Results were the same for Na Salts

Electronegativity Test

Elements Involved

Reaction?

Observations

I2 + hexane

yes

Top hexane layer is a deep fuchsia and bottom layer is the gold/yellow color of I2.
Br2 + hexane

yes

Top layer is slightly lighter gold than Br2 and the bottom is a deeper yellow.
Cl2 + hexane

no

The top layer is clear and the bottom layer is also mostly clear with a slight hint of green/yellow.
Cl2  + I

yes

Top layer is deep fuchsia, there is a middle layer of yellow and the bottom is clear.
Cl2  + Br

yes

Top is light yellow which fades to line of deeper yellow and bottom is clear.
Br2 + I

yes

Top is fuchsia, bottom is transparent gold color.
Br2 + Cl

no

Looks the same as Br2 + hexane
I2+ Cl

no

Top layer is fuchsia and bottom is transparent gold/yellow.
I2+ Br

no

Top layer is again fuchsia and bottom layer is slightly deeper yellow.

 

Calculations

Cl2  + 2I à I2+ 2Cl

Cl2  + 2Br à Br2 + 2Cl

Br2 + 2I à  I2+ Br

Br2 + 2Cl à No RXN

I2+ 2Cl à No RXN

I2+ 2Br  àNo RXN

Conclusion

In this experiment combinations of Br, Cl, and I were mixed together in hexane as either a halogen or a halide. Because the halogen is the more stable and thus the more desired form, the element that came out of the reaction as a halogen was more electronegative. According to that I is the most electronegative as no matter what it was mixed with and in what form, I2 was left in the test tube. When I was mixed with both Cl2 and Br2 the halogens were oxidized and became halides while the I became I2. And nothing added to I2 changed the contents of the test tube at all. The results of the lab do not agree with prediction because the periodic property of electronegativity is that it decreases in a group as atomic number increases.

If the visible contents of the test tube remain unchanged then no reaction had occurred. The solubility tests indicated that the halides would not dissolve or react with the hexane. If this were not the case determining if reactions had occurred would have been near impossible. Possible errors of the experiment were that the reagents were not uniform throughout when mixed.

This experiment uses a qualitative colorimetric process, which means that the colors of the solutions were recorded and used to determine the contents of a test tube. No calculations needed to be made. Hydrofluoric acid is weak because the fluorine is so electronegative that it will bond not only to the water molecules but also to loose hydrogen. These leaves less free hydrogen and reduces the strength of the acid.