Is food coloring polar or nonpolar? – (Polarity of food coloring)

The question is –

Is food coloring polar or nonpolar?

Answer:

⇒ Food coloring is most likely to be polar.

Explanation:

Food coloring is most likely to be polar as it is composed of dyes or pigments containing highly polar O-H, S=O, C-O, etc, bonds whose dipole moments stay uncancelled. 

Organic dyes containing conjugated systems and one or more chromophores or auxochromes form the primary component of food colorings.

Conjugation refers to the interlinking of pi-bonded systems. If C-C single and C=C double covalent bonds are present at alternating positions, the pi-bonded electrons can move from one place to another.

Chromophores are functional groups that give a chemical compound its characteristic color by absorbing visible light (400-800) nm.

Auxochromes are functional groups that do not absorb visible light themselves, but when attached to a chromophore, it helps them in absorbing visible light of even a lower frequency (higher wavelength).

Conjugated phenyl rings are an example of chromophores, while functional groups such as O-H, COOH, C=O, -NH₂, -SCH₃, -SO₃^2-, etc., are some prominent examples of auxochromes.

As per the above information, there are the following main types of covalent bonds present in food coloring:

• C-C or C=C
• C-H
• O-H
• C-O or C=O
• N-H
• S-O or S=O

A C-C or C=C is purely non-polar as zero, or no electronegativity difference exists between two identical carbon atoms.

A C-H bond is very weakly polar, having an electronegativity difference of 0.35 units between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom.

An O-H bond is strongly polar as it consists of an electronegativity difference of 1.24 units between oxygen (E.N = 3.44) and hydrogen. So it possesses a high dipole moment value.

Similarly, C-O and N-H bonds are polar with electronegativity differences of 0.89 units and 0.84 units, respectively. An electronegativity difference of 0.86 units is present between bonded atoms in S-O or S=O bonds.

The strong dipole moments of all the above bonds stay uncancelled in the conjugated molecule i.e., an organic dye. Therefore, food colorings are overall polar (net µ > 0).

Also, check –

⇒ How to identify polar or nonpolar compounds?