The compound Al2S3, also known as aluminum sulfide, is considered insoluble in water.
When aluminum sulfide is introduced to water, it does not dissolve but rather reacts with water to produce hydrogen sulfide gas and aluminum hydroxide. The reaction can be summarized as follows:
2 Al2S3 + 6 H2O → 6 H2S + 2 Al(OH)3
This reaction indicates that while Al2S3 does not dissolve exclusively as a soluble substance in water, it undergoes a chemical change leading to other products. This characteristic behavior of forming insoluble aluminum hydroxide makes it clear why Al2S3 is predominantly considered insoluble in water.