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Benzoic Acid is a colourless crystalline solid and a simple carboxylic acid. The name is derived from gum benzoin, which was for a long time its only known source. Benzoic Acid occurs naturally in many plants and it serves as an intermediate in the biosynthesis of many secondary metabolites. Salts of Benzoic Acid are used as food preservatives and benzoic acid is an important precursor for the industrial synthesis of many other organic substances. The salts and esters of benzoic acid are known as benzoates.
calibration of bomb calorimeters
The calibration of an oxygen bomb calorimeter system( also called standardization) is done using a tablet of benzoic acid. DDS Calorimeters manufacture our own benzoic acid tablets, which are suitable for use in all our oxygen bomb calorimeter systems. During this calibration process, a known amount of heat i introduced into the calorimeter by the combustion of a benzoic acid tablet. This produces the energy equivalent of the calorimeter for a specific temperature rise.
Before an unknown sample can be tested, the heat capacity or energy equivalent( EE or E) of the bomb calorimeter must be known. The value resulting from the burning of the calibration standard Benzoic Acid represents the heat capacity of the calorimeter( including the bomb vessel, insulating polystyrene or ATC and all other parts of the calorimeter system). Energy equivalents are determined at regular intervals by burning a sample of the standardization material with a known heat of combustion( Benzoic Acid at 26.454KJ) under controlled and reproducible operating conditions.
• 0.5g Benzoic Acid Tablets are white with a " DDS " marking
• 1.0g Benzoic Acid Tablets are white with a " BA " marking
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Although benzoic acid has many uses outside of bomb calorimetry, we will touch on the subject of its use in calorimetry. Benzoic acid is relatively non-toxic and occurs naturally in plants. Appreciable amounts of it has been found in most berries( around 0.05 %) and is formed in apples after infection with a specific fungus.
LABORATORY USE
Due to its constant value it is the ideal substance for calibration in bomb calorimeters. For this purpose we press the powdery substance into tablets of approximately 0.5 grams and 1.0 grams, with a calorific value of approximately 26.454KJ / g.
DESIRABLE PROPERTIES
Benzoic Acid tablets used for combustion calorimetry should adhere to the following requirements:
• It must be readily available in pure form
• It must be stable
• It must not be hydroscopic
• It must not be volatile
• It must be easily brought into a form suitable for combustion
• It should offer no unusual difficulties during combustion in the bomb
• The value of the heat of combustion is characterized with suitable accuracy
Benzoic Acid manufactured and supplied by DDS Calorimeters is supplied in a colourless to white solid tablet / pellet with aromatic-like odour.
DDS Calorimeters manufactures our own Benzoic Acid Tablets for use with the DDS Calorimeters range or any other calorimeter system. Contact us for more information.
DDS Calorimeters | Feb / March 2017 Issue www. ddscalorimeters. com