IONIZATION OF CARBOXYLIC ACIDS CARBOXYLIC ACIDS An acid

IONIZATION OF CARBOXYLIC ACIDS

CARBOXYLIC ACIDS An acid is a molecule or ion capable of donating a proton, or, alternatively, capable of forming a covalent bond with an electron pair. The first category of acids are the proton donors, or Brønsted–Lowry acids.

Brønsted–Lowry theory, also called proton theory of acids and bases, a theory, introduced independently in 1923 by the Danish chemist Johannes Nicolaus Brønsted and the English chemist Thomas Martin Lowry, stating that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.

What is IONIZATION Strictly defined, ionization is the complete loss of an electron from an atomic or molecular species. The resulting species is called an ion. In chemical equations, the charge on ions is shown as a superscript, such as in this simple ionization reaction: M → M+ + e Ions may ionize further: M+ → M 2+ + e. M 2+ → M 3+ + e. M 3+ →. . . etc

Cations Positively charged ions are often referred to as cations. Negative Ions / Anions Although in strict terms ionization refers to the formation of a positive ion, in normal usage, the word also includes the formation of a negative ion: M + e - → MNegatively charged ions are often referred to as anions.

Ionization Examples Direct Ionization of Elements Metals typically form cations and non-metals typically form anions. Some elements, such as carbon, gold, and the noble gases, do not readily form ions. The alkali metals in Group 1 of the periodic table and the halides in Group 17 ionize very readily. Alkali metals need only lose one electron to obtain a full electron shell: likewise, halides need only gain one electron to achieve this. For example, sodium and chlorine react spontaneously by ionizing to form the ionic compound sodium chloride: 2 Na(s) + Cl 2(g) → 2 Na. Cl(s)

Define ionization of carboxilyic acid : Water-soluble carboxylic acids ionize slightly in water to form moderately acidic solutions. Their aqueous solutions exhibit the typical properties of acids, such as changing litmus from blue to red. The anion formed when a carboxylic acid dissociates is called the carboxylate anion (RCOO−).

Acid Strength and the Acid Dissociation Constant (Ka) 1. The magnitude of the equilibrium constant for an ionization reaction can be used to determine the relative strengths of acids and bases. For example, the general equation for the ionization of a weak acid in water, where HA is the parent acid and A− is its conjugate base, is as follows:

HA(aq)+H 2 O(l)⇌H 3 O+(aq)+A−(aq) The equilibrium constant for this dissociation is as follows: K=[H 3 O+][A−][H 2 O][HA]

As we noted earlier, the concentration of water is essentially constant for all reactions in aqueous solution, so [H 2 O] in Equation 16. 4. 2 can be incorporated into a new quantity, the acid ionization constant (Ka. Ka), also called the acid dissociation constant: Ka=K[H 2 O]=[H 3 O+][A−][HA](16. 4. 3) Ka=K[H 2 O]=[H 3 O+][A−][HA]

Thus the numerical values of K and Ka. Ka differ by the concentration of water (55. 3 M). Again, for simplicity, H 3 O+ can be written as H+H+ in Equation 16. 4. 3. Keep in mind, though, that free H+H+ does not exist in aqueous solutions and that a proton is transferred to H 2 O in all acid ionization reactions to form hydronium ions, H 3 O+. The larger the Ka. Ka, the stronger the acid and the higher the H+H+ concentration at equilibrium. Like all equilibrium constants, acid–base ionization constants are actually measured in terms of the activities of H+H+ or OH−OH−, thus making them unitless. The values of Ka. Ka for a number of common acids are given in Table

Table 16. 4. 1: Values of Ka. Ka, p. Ka, Kb. Kb, and p. Kb for Selected Acids (HAHA and Their Conjugate Bases (A−A−) HAHA Ka. Ka p. Ka A−A− Kb. Kb p. Kb Acid *The number in parentheses indicates the ionization step referred to for a polyprotic acid. 5. 5× 10− 2 2× 1092× 1 hydroiodic acid HIHI − 9. 3 I−I− 45. 5× 10− 2 23. 26 09 4 H 2 SO 4 H 2 1× 1021× 1 HSO− 4 HS 1× 10− 161 sulfuric acid (1)* − 2. 0 16. 0 SO 4 02 O 4− × 10− 16 4. 3× 10− 1 HNO 3 HN 2. 3× 1012. NO− 3 NO 3 nitric acid − 1. 37 64. 3× 10− 1 15. 37 O 3 3× 101 − 6 1. 0× 10− 1 H 3 O+H 3 O hydronium ion 1. 0 0. 00 H 2 O 41. 0× 10− 1 14. 00 + 4 9. 8× 10− 1 HSO− 4 HS 1. 0× 10− 2 SO 2− 4 SO sulfuric acid (2)* 1. 99 39. 8× 10− 1 12. 01 O 4− 1. 0× 10− 2 42− 3 1. 6× 10− 1 6. 3× 10− 4 hydrofluoric acid HFHF 3. 20 F−F− 11. 6× 10− 1 10. 80 6. 3× 10− 4 1