This is a complex question! I will try to explain simply. Hydrolysis is a chemical process by which a chemical compound reacts with water to produce what are called precipitates. This is a pretty complex process, but very simply, aluminium sulfate is one of the special compounds that can react with water to do this. Basically what happens is that the aluminium and sulfate molecules that make up the aluminium sulfate compound break apart and rearrange themselves with the molecules that comprise the water (hydrogen and oxygen molecules) to form a couple of different end products, notably, a diluted form of sulfiric acid. pH is a measure of acidity/alkalinity (or acids and bases). Alkaline solutions have a high pH and acidic solutions have low pH numbers. This is also sort of complicated, but basically, if something is too alkaline (basic), you have to add acid to neutralize the solution. Since the hydrolysis of aluminium sulfate produces an acid, some gardeners may use it in gardening to bring the pH of an alkaline soil to a more neutral level. On the other hand, lime (which has a large percentage of a chemical compound called calcium carbonate) reacts with water, too. Instead of producing acid, though, it produces an alkaline compound (calcium hydroxide). Because of this, the pH of the final product is higher (more alkaline/basic). Ultimately, this has an effect on your gardening because some plants prefer more acidic soil and some prefer more alkaline conditions to grow properly (my mom told me that). Ultimately, acids and bases are used all the time to neutralize solutions and mixtures in the lab. I think soil is no exception! :) I really hope this helps. If you're still at a loss, let me know and I'll try my best to clarify. It's kind of complex and difficult to get without a few years of chemistry under your belt. :) Best of luck with your gardening!!
