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Aluminum Hydroxide Formation

Could you please help me better understand the formation of aluminum hydroxide --- for instance:

Again, lets assume we have a generally weak acid solution to which we add aluminum sulfate. The objective is to precipitate aluminum hydroxide per the following reaction which I believe to be correct.

Al2(SO4)3 + HCO3- = 2Al(OH)3 + SO4--

I do not want Al2(SO4)3 + H2O = 2Al(OH)3 + H2SO4

I want to ensure that the reaction prefers or goes in the direction of the first equation.

However, pH has something to do as to which reaction is favored ---- if pH is too low I believe the second equation is favored. If pH is closer to neutral then I believe the first equation is favored.

But why specifically does aluminum hydroxide formation seem to be maximum at a pH between 4.5 and 5.5 per literature?? Why not pH 6 or even 7? What is so special about pH 5 when it comes to Al(OH)3 formation?

Solution Preview

Let me explain first of all what is so special about pH 5 in case of aluminum hydroxide.

It is connected with the soil acidity or basicity apart from many other biological processes going on in human body. pH value of the soil is one of the environmental factors affecting the plant growth. This value is responsible for the availability of various nutrients by plants. There are different pH values for the growth of different plants.Plants like blueberries and conifers grow best in acid soil ( pH 5.0 ...

Solution Summary

The solution discusses aluminum hydroxide formation.