Methyl Orange PDF

Preview

Summary

Methyl Orange Lab Report...

Description

Synthesis and UV/Vis Spectral Analysis of Methyl Orange as Acid-Base Indicator

Results In this experiment, a diazonium coupling reaction was conducted to synthesize methyl roange with sulfanilic acid and N,N-dimethylaniline. The methyl orange product obtained through the coupling reaction was tested for its characteristic as a acid/base indicator through physical color change observations with the addition of acid and base as well as UV/Vis spectroscopy. As shown in Table 1, the theoretical yield of methyl orange based on calculations was 0.945 g. However, the actual yield of the mass came out to be 0.105 g. Therefore, the percent yield of the product was calculated as 11.11 %. Table 1: Percent Yield of Methyl Orange Theoretical Yield (g)

0.945

Actual Yield (g)

0.105

Percent Yield (%)

11.11

As shown in Table 2, when acid-base indicator test was conducted on the methyl orange product, in an acidic solution consisting of water and 5% HCl, the methyl orange made the solution turn pink/magenta. On the other hand, when 5% NaOH was added to the water and methyl orange solution, the solution in the test tube turned into light yellow solution. The acidic and basic methyl orange solutions were then transferred into a cuvette for UV/Vis spectral analysis. Also as shown in Table 2, through the spectrum, it was shown that the acidic methyl orange solution absorbed most of the light with 506.9 nm in wavelength while the basic methyl orange solution absorbed the light in the wavelength of 459.0.

Table 2: Acid/Base Indicator Test Observations and UV/Vis Spectroscopy Results Test Tube

Contents

Color Observations

λmax (UV/Vis Results; nm)

1

Methyl orange and water

Light yellow

N/A

2

Methyl orange, water, and 5% HCl

Pink

506.9 (green)

3

Methyl orange, water, and 5% NaOH

Light yellow

459.0 (blue)

Discussion In this experiment, the synthesis of methyl orange was accomplished by an azo coupling between a diazonium ion and an aromatic substrate. Specifically in this experiment, the diazonium ion was formed through the reaction between sulfanilic acid and sodium nitrate, with the addition of hydrochloric acid. Sulfanilic acid in nature is not soluble in an acidic solvent, and therefore it had to be dissolved in a basic solution, such as sodium nitrate, first. The addition of hydrochloric acid ultimately formed a nitrous acid and induced the precipitation of the diazonium salt intermediate. Then, the aromatic substrate, N,N-dimethylaniline was added to the diazonium ion, which led to the formation of methyl orange as shown in Figure 1. The good electrophilic characteristic of the diazonium salt intermediate allowed it to go through an electrophilic aromatic substitution reaction with the N-N-dimethylaniline, the nucleophile, as shown in Figure 1.

Figure 1: Reaction Scheme of Methyl Orange

The mass of the methyl orange product collected was significantly lower than the calculated theoretical yield. The mass of the actual yield could have been lost through the process of transferring and purifying the methyl orange product. However, the low turn out of product mass did not affect its ability to act as an acid-base indicator. The methyl orange product obtained through the coupling reaction was utilized to conduct an acid-base indicator test because methyl orange is often used as a acid or base indicator by displaying different colors upon the addition of acid or base. The acid-base indicator test displayed a general trend in the color change. When acid, HCl, was added to a solution of methyl orange dissolved in distilled water, the solution turned red/pink. When base, NaOH, was added to the methyl orange and distilled water solution, the solution turned yellow/light orange. The more acid was added, the redder in color the methyl orange solution became, and the more base was added, the lighter yellow in color the methyl orange solution became. The acidic and basic methyl orange solutions were placed in a cuvette for a UV/Vis spectroscopy. UV/Vis spectroscopy is used to measure the reflection or absorbance characteristics of a sample. The spectra, in this experiment, was used to determine the color of the sample. When UV light passes through a compound, the energy from the light promotes an electron from a bonding or nonbonding orbital into one of the empty antibonding orbitals. The jumping of electrons from one orbital to another requires certain amount of energy. This energy required for the jump is ultimately associated with the wavelength of light. Since energy is directly proportional to the frequency of light, a higher jump requires a higher frequency. However, since UV/Vis spectroscopy is based on the wavelength of the light instead of its frequency. When a frequency is high, the wavelength is low because the relationship between the frequency and wavelength is indirectly proportional. Therefore, the bigger the jump, higher the

frequency, and the lower the wavelength of the light absorbed. In an absorption spectrum, the absorbance, the measure of amount of light absorbed, is on the x-axis, while the wavelength is on the y-axis. Higher the value of absorbance, the greater the amount of a particular wavelength absorbed. The absorption peak of the spectra for the acidic methyl orange solution was at 506.9 nm (green), while the absorption peak for the basic methyl orange solution was at 459.0 nm (blue). Since the wavelength of light absorbed by the acidic methyl orange solution was green, the color of the solution displayed in the preparation test tube and the cuvette was pink/magenta, which is the color complementary to the color green. Similarly, since the color absorbed by the basic methyl orange solution was blue, the color displayed in the test tube and cuvette was light orange/yellow, which is the color complementary to the color blue. The color observed in the test tubes with the addition of acid (pink) and base (yellow) was as expected. As shown below in Figure 2, methyl orange, the azo dye, at a pH greater than 4.4 was expected to show a color change to yellow, while helianthin, the protonated dye, at a pH less than 3.2 was expected to display a red color. The red color was ultimately diluted with water to a light pink in order to run the UV/Vis spectroscopy.

Figure 2: Acid-Base Indicator Properties of Methyl Orange...