Are there any ions or substances that are colorless in acidic aqueous solutions but yellow-green in alkaline aqueous solutions?
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The water sample was alkaline and green in color; after adjusting its pH to acidic using hydrochloric acid, the color faded. When the pH was then adjusted back to alkaline using sodium hydroxide, a yellow-green color reappeared.
It’s best to conduct a qualitative test; asking in this way makes it difficult to give an accurate judgment.
Yes, the components of various types of wastewater are complex; it is not possible to draw conclusions based solely on color changes under acidic or alkaline conditions – it could be organic substances. I have also encountered a type of waste whose rinsing water is dark yellow and weakly acidic; after neutralizing it to a weakly alkaline condition, no precipitate was observed, but the yellow color almost completely faded. The source of the waste refuses to provide information on the actual origin of the materials, so it’s not possible to determine what is causing the problem; P