The Boron Group - Group 13: Case studies

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Chapter: Essentials of Inorganic Chemistry : The Boron Group - Group 13

1. Boric acid – API analysis 2. Aluminium hydroxide tablets

Case studies


1. Boric acid – API analysis

Boric acid is known to have antifungal and antimicrobial properties and therefore has a clinical use. Typical pharmaceutical analysis of boric acid as an API includes its reaction with a known amount of mannitol and subsequent titration of unreacted mannitol.

(a)    Research the chemical structure of mannitol including its stereochemistry.

(b)   Describe the reaction of boric acid and mannitol, including relevant chemical equations.

(c)    For the analysis of boric acid as an API, 1.0 g of the acid is typically dissolved in 100 ml of water, and 15.0 g of mannitol is added. The solution is then titrated with 1 M sodium hydroxide (NaOH) solution using phenolphthalein as indicator.

Calculate the volume of NaOH needed in this titration if the API has a purity of 99%.

(d)   Research the typically accepted error margins for the purity of boric acid as an API.



2. Aluminium hydroxide tablets

Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch of aluminium hydroxide tablets. The description of your brief states that you are supposed to analyse the API in these tablets following standard quality assurance guidelines.

Typical analysis methods used for quality purposes are often based on titration reactions, but also a variety of other quantitative analysis methods such as gravimetric analysis can be used. Typically, a certain amount of the tablet powder is dissolved in water, and hydrochloride acid (HCl) is added. An excess of the precipitation reagent is added, and the solution is stirred until precipitation is completed. The precipitate is then filtered, dried to constant weight and weighed.

(a)    Draw the chemical formula of aluminium hydroxide.

(b)   Research the type of analysis used. Within your studies, you should look at a variety of precipitation reagents and understand how different factors can influence this method.

(c)    Formulate the relevant chemical equations.

(d)   The package states that each tablet contains 475 mg aluminium hydroxide. For the experiment, 20 tablets are weighed (total weight 12.5 g) and powdered. An amount of powder containing 0.4 g aluminium hydroxide is dissolved in water and HCl, and reacted with excess 8-hydroxy quinolone. After stirring this solution for 2 h near the boiling point, the precipitate is filtered and dried overnight in the oven at 100 C.

The precipitate weighs 2.0 g.

Calculate the amount of aluminium hydroxide present in your sample. Express your answer in grams and moles.

(e)    Critically discuss your result in context with the stated value for the API.

(f)     Research the typically accepted error margins.


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