Thekey difference between citric acid and acetic酸是柠檬酸有三个carboxylic acidgroups, whereas acetic acid has one carboxylic acid group.
Both citric acid and acetic acid are organic carboxylic acid compounds having the carboxylic acid functional group (-COOH). However, they differ from each other according to the number of carboxylic acid groups in these molecules.
What is Citric Acid?
Citric acid is an organic compound having the chemical formula HOC(COOH). It is a colorless weak organic acid and naturally occurs in citrus fruits. In biochemical terms, citric acid is an intermediate in the citric acid cycle during the metabolism of all aerobic organisms. Typically, about 2 million tons of citric acid are manufactured annually. This substance is widely important as an acidifier and as a flavoring agent. It is also important as achelating agent.
The molar mass of this compound is 192 g/mol in its anhydrous state. When isolated, citric acid appears as a white solid that is odorless. The density of the anhydrous form is about 1.66 g/cm3. Its melting point is 156 degrees Celsius, and its boiling point is 310 degrees Celsius. However, it starts to decompose at about 175 degrees Celsius. Moreover, citric acid is soluble in acetone, alcohol, ether, ethyl acetate, but it’s insoluble in toluene. The crystal structure of the solid citric acid is monoclinic.
Typically, this acid can be found in many different fruits and vegetables but mainly in citrus fruits. For example, lemon and lime have a very high content of citric acid. When industrially preparing this substance, it was first done by treating the juice with hydrated lime (calcium hydroxide) to get the precipitate of calcium citrate, which is then isolated and converted back to citric acid using sulfuric acid. However, in modern industries, citric acid is prepared by fungal fermentation methods.
What is Acetic Acid?
乙酸是具有化学式CH的有机化合物3COOH. It is also known asethanoic acidand occurs as an acidic, colorless liquid having a heavily vinegar-like odor. The molar mass of this compound is 60 g/mol. The density can be given as 1.05 g/cm3. The melting point ranges from 61 to 62 degrees Celsius, and the boiling point can range from 118 to 119 degrees Celsius. It is miscible with water.
我们可以说乙酸是第二个最简单的羧酸，因为它具有连接到碳原子的一个羧酸功能基。（最简单的羧酸是甲酸 - hcooh，羧酸基团没有附着在任何碳原子上）。乙酸在许多不同的行业中很重要，例如乙酸纤维素，乙酸聚氯乙烯，合成纤维等在食品工业中，这种化学物质可作为食品添加剂，具有E数字E260。
The carboxylic acid functional group in an acetic acid molecule can undergo partial ionization to form acetate ion and hydrogen cation (proton). Releasing this proton causes the acidic nature of acetic acid. Therefore, we can name this chemical as a weakmonoprotic acid（这意味着它部分解离并每个分子给出一个质子）。通常，固体乙酸具有分子的链，这些分子通过氢键互连。在其蒸气相中，我们可以检测乙酸分子的二聚体。在其液态下，它是一种亲水性极性溶剂。
摘要 - 柠檬酸与乙酸
The carboxylic acid functional group has the chemical formula –COOH. Citric acid and acetic acid contain this type of functional group in their molecules. The key difference between citric acid and acetic acid is that citric acid has three carboxylic acid groups, whereas acetic acid has one carboxylic acid group.
1.“”Citrus fruits” By Scott Bauer, USDA – The research agency of the United States Department of Agriculture, with the ID K7226-29 (Public Domain) via Commons Wikimedia
2. “Acetic Acid Hydrogenbridge V.1”Jü-通过Commons Wikimedia自己的工作（公共领域）