How to Test for Methyl Yellow

Yellow Color

• 1

  Pour the yellow liquid into a clear glass beaker.

• 2

  Analyze the color of the liquid. At a neutral pH methyl yellow should be a butter yellow color. Methyl yellow was once used as a color enhancer before its toxicity was detected, so a liquid containing methyl yellow should be an extremely vibrant yellow.

• 3

  Prepare a strong solution of hydrochloric acid. Add the hydrochloric acid to the yellow mixture slowly using a pipette dropper. Observe the color of the liquid. If it begins to change after several drops this is an indication methyl yellow is present in the mixture or solution.

• 4

  Continue adding the hydrochloric acid to the yellow liquid until you have added enough to drastically alter the pH of the yellow liquid, reducing it to below 2.9. If the yellow liquid in the mixture has turned bright red, this confirms the presence of methyl yellow in the beaker.

Red Color

• 5

  Transfer the red liquid into a clear glass beaker.

• 6

  Observe the color of the liquid in the beaker. At certain, very low, pHs, methyl yellow appears bright red. If there are areas of bright red within the liquid in the glass beaker, this is an indication of the presence of methyl yellow.

• 7

  Prepare a strong solution of sodium hydroxide. Draw some of the sodium hydroxide into a pipette dropper and begin to drop it into the mixture in the glass beaker. As this strong alkali raises the pH of the solution in the beaker, you should begin to notice a change in its color.

• 8

  Continue to add the sodium hydroxide to the beaker until you have added enough to raise the pH above a level of 4.0. At this point the solution should have transformed from red to a bright yellow color, confirming that methyl yellow is present within the mixture.