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Titration of Sulfuric Acid and Aluminum in an Electroplating Bath

Aluminum and sulfuric acid contents in an acidic electroplating bath are determined by direct titration with sodium hydroxide. Three equivalence points are found.

Background

Titration with caustic soda to determine the sum of acid and aluminum. Both aluminium and sulphuric acid can be determined by titration using sodium hydroxide (NaOH). Neutralization happens when NaOH reacts with sulphuric acid. When the whole of sulphuric acid gets neutralized, NaOH starts reacting with aluminium and forms aluminium hyrdoxide (Al[OH]₃), an insoluble precipitate. This shows that both sulphuric acid and aluminium reacts separately with NaOH producing two distinct chemical endpoints. 

In the performance of the anodizing process, chemical analysis of of the anodizing bath plays a crucial role. Here sulphuric acid and aluminium are the important components of the anodizing bath. Anodizing efficiency goes down due to higher energy consumption when aluminum content is too low. An ideal range of the sulphuric acid needs to be maintained to properly balance the oxide formation rate.