We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Benzoic acid occurs naturally in many plants and serves as an intermediate in the biosynthesis of many secondary metabolites. At a temperature of 0 degrees celsius, the solubility of benzoic acid in water corresponds to 1.7 grams per litre. Polyprotic acids are acids that can lose more than one proton. pKa values for strong acids can, however, be estimated by theoretical means. Acetic acid is a relatively weak acid, at least when compared to sulfuric acid (Ka = 109) or hydrochloric acid (Ka = 107), both of which undergo essentially complete dissociation in water. Table \(\PageIndex{1}\) at the end of the text lists exact or approximate pKa values for different types of protons that you are likely to encounter in your study of organic and biological chemistry.

Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications! As you continue your study of organic chemistry, it will be a very good idea to commit to memory the approximate pKa ranges of some important functional groups, including water, alcohols, phenols, ammonium, thiols, phosphates, carboxylic acids and carbons next to carbonyl groups (so-called a-carbons). The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Definitions of the acid dissociation constant and pKa are given below the figures, together with the definition of some classes of organic acids.
Write down an expression for the acidity constant of acetic acid, CH 3 COOH. Because dividing by 1 does not change the value of the constant, the "1" is usually not written, and Ka is written as: \[ K_{eq} = K_{a} = \dfrac{[CH_3COO^-][H_3O^+]}{[CH_3COOH]} = 1.75 \times 10^{-5}\]. Chemists often use pKa values as a more convenient term to express relative acidity. Looking at Table \(\PageIndex{1}\), you see that the pKa of carboxylic acids are in the 4-5 range, the pKa of sulfuric acid is –10, and the pKa of water is 14. Likewise, we can use Table \(\PageIndex{1}\) to predict that para-hydroxyphenyl acetaldehyde, an intermediate compound in the biosynthesis of morphine, has a pKa in the neighborhood of 10, close to that of our reference compound, phenol. One of the components of toothpaste, mouthwash, and face wash creams is C. This compound is also used in the manufacture of dyes and in insect repellants. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Benzoic acid has a colourless appearance in its solid state, which is of a crystalline nature. Only emails and answers are saved in our archive. We don't collect information from our users.

An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. In the table below, pKa1 and pKa2 for water solutions at 25°C are given together with boiling and melting point, density and molecular weight, as well as number of carbon, hydrogen and oxygen atoms in each molecule. The lower the pKa value, the stronger the acid. This compound exists as a crystalline, colorless solid under normal conditions. The definition can then be written more simply, HA = A- + H+        and           Ka = [A-]*[H+] / [HA], This is the definition in common usage.

The larger the value of pKa, the smaller the extent of dissociation at any given pH - that is, the weaker the acid. The crystal structure is monoclinic. The chemical species HA, A− and H3O+ are said to be in equilibrium when their concentrations do not change with the passing of time. The commercial production of benzoic acid is done via the partial oxidation of toluene with oxygen, catalyzed by manganese or cobalt naphthenates. Your email address will not be published. Below the table, figures showing the fractions of the different acid forms in aqueous solutions at varying pH are given for some common diprotic organic acids (values calculated from the tabulated pKas). Then we have more than one dissiciation constant; Ka1, Ka2, etc..  and similar pKa1, pKa2, etc. It can also be prepared by oxidizing benzyl chloride or benzyl alcohol, or any other derivative of the benzyl group. Salts of benzoic acid are used as food preservatives.

Some important uses of C6H5COOH are listed below. These are the groups that you are most likely to see acting as acids or bases in biological organic reactions. The term ‘benzoate’ refers to the esters and salts of C6H5COOH. These applications will - due to browser restrictions - send data between your browser and our server. Doing the math, we find that the pKa of acetic acid is 4.8. A weak acid has a pKa value in the approximate range −2 to 12 in water. where HA is an acid that dissociates into A, This is the definition in common usage. Alkane: An acyclic saturated hydrocarbon, with the general formula CnH2n+2. Benzoic acid /bɛnˈzoʊ.ɪk/ is a white (or colorless) solid with the formula C6H5CO2H. Aldehyde and aromatic protons are not at all acidic (pKa values are above 40 – not on our table). The name is derived from gum benzoin, which was for a long time its only source.


What, for example, is the pKa of cyclohexanol? We don't save this data. This compound can also be prepared via the hydrolysis of benzamide and benzonitrile. Your email address will not be published. A word of caution: when using the pKa table, be absolutely sure that you are considering the correct conjugate acid/base pair. The use of pKa values allows us to express the acidity of common compounds and functional groups on a numerical scale of about –10 (very strong acid) to 50 (not acidic at all).

Our table of pKa values will also allow us to compare the strengths of different bases by comparing the pKa values of their conjugate acids. Also called paraffin. Phenol: An alcohol where the hydroxyl group is bound to a phenyl group, with the formula C6H5OH.

The physical and chemical properties of C6H5COOH are discussed in this subsection.

Then, a solution with 50% dissociation has pH equal to the pKa of the acid. Google use cookies for serving our ads and handling visitor statistics. It is soluble in benzene, carbon tetrachloride.

This chemical reaction is illustrated below. Alcohol: An organic compound in which the hydroxyl functional group (–OH) is bound to a saturated carbon atom. You can see that hydroxide ion is a stronger base than ammonia (NH3), because ammonium (NH4+, pKa = 9.2) is a stronger acid than water (pKa = 14.0).