Acid and base

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Acid and base

  1. 1. ACID AND BASE Submitted by : Macallan, Leewhere G. Rizano, Gerald III-Avogadro Submitted to : Mrs. Mary Grace Bumanlag
  2. 2. AN ACID–BASE REACTION IS A CHEMICAL REACTION THAT OCCURS BETWEEN AN ACID AND A BASE. SEVERAL CONCEPTS EXIST THAT PROVIDE ALTERNATIVE DEFINITIONS FOR THE REACTION MECHANISMS INVOLVED AND THEIR APPLICATION IN SOLVING RELATED PROBLEMS. DESPITE SEVERAL DIFFERENCES IN DEFINITIONS, THEIR IMPORTANCE BECOMES APPARENT AS DIFFERENT METHODS OF ANALYSIS WHEN APPLIED TO ACID–BASE REACTIONS FOR GASEOUS OR LIQUID SPECIES, OR WHEN ACID OR BASE CHARACTER MAY BE SOMEWHAT LESS APPARENT. THE FIRST OF THESE SCIENTIFIC CONCEPTS OF ACIDS AND BASES WAS PROVIDED BY THE FRENCH CHEMIST ANTOINE LAVOISIER, CIRCA 1776 Acid–base reaction
  3. 3. THE FIRST SCIENTIFIC CONCEPT OF ACIDS AND BASES WAS PROVIDED BY LAVOISIER CIRCA 1776. SINCE LAVOISIER'S KNOWLEDGE OF STRONG ACIDS WAS MAINLY RESTRICTED TO OXOACIDS, SUCH AS HNO 3 (NITRIC ACID) AND H 2SO 4 (SULPHURIC ACID), WHICH TEND TO CONTAIN CENTRAL ATOMS IN HIGH OXIDATION STATES SURROUNDED BY OXYGEN, AND SINCE HE WAS NOT AWARE OF THE TRUE COMPOSITION OF THEHYDROHALIC ACIDS (HF, HCL, HBR, AND HI), HE DEFINED ACIDS IN TERMS OF THEIR CONTAINING OXYGEN, WHICH IN FACT HE NAMED FROM GREEK WORDS MEANING "ACID-FORMER" (FROM THE GREEK ΟΞΥΣ (OXYS) MEANING "ACID" OR "SHARP" AND ΓΕΙΝΟΜΑΙ (GEINOMAI) MEANING "ENGENDER"). THE LAVOISIER DEFINITION WAS HELD AS ABSOLUTE TRUTH FOR OVER 30 YEARS, UNTIL THE 1810 ARTICLE AND SUBSEQUENT LECTURES BY SIR HUMPHRY DAVY IN WHICH HE PROVED THE LACK OF OXYGEN IN H2S, H2TE, AND THE HYDROHALIC ACIDS. HOWEVER, DAVY FAILED TO DEVELOP A NEW THEORY, CONCLUDING THAT "ACIDITY DOES NOT DEPEND UPON ANY PARTICULAR ELEMENTARY SUBSTANCE, BUT UPON PECULIAR ARRANGEMENT OF VARIOUS SUBSTANCES".[2] ONE NOTABLE MODIFICATION OF OXYGEN THEORY WAS PROVIDED BY BERZELIUS, WHO STATED THAT ACIDS ARE OXIDES OF NONMETALS WHILE BASES ARE OXIDES OF METALS. Lavoisier's oxygen theory of acids
  4. 4. CIRCA 1838 JUSTUS VON LIEBIG PROPOSED[3] THAT AN ACID IS A HYDROGEN-CONTAINING SUBSTANCE IN WHICH THE HYDROGEN COULD BE REPLACED BY A METAL.[4] THIS REDEFINITION WAS BASED ON HIS EXTENSIVE WORK ON THE CHEMICAL COMPOSITION OF ORGANIC ACIDS, FINISHING THE DOCTRINAL SHIFT FROM OXYGEN-BASED ACIDS TO HYDROGEN- BASED ACIDS STARTED BY DAVY. LIEBIG'S DEFINITION, WHILE COMPLETELY EMPIRICAL, REMAINED IN USE FOR ALMOST 50 YEARS UNTIL THE ADOPTION OF THE ARRHENIUS DEFINITION Liebig's hydrogen theory of acids
  5. 5. THE FIRST MODERN DEFINITION OF ACIDS AND BASES WAS DEVISED BY SVANTE ARRHENIUS. A HYDROGEN THEORY OF ACIDS, IT FOLLOWED FROM HIS 1884 WORK WITH FRIEDRICH WILHELM OSTWALD IN ESTABLISHING THE PRESENCE OF IONS IN AQUEOUS SOLUTION AND LED TO ARRHENIUS RECEIVING THE NOBEL PRIZE IN CHEMISTRY IN 1903. AS DEFINED BY ARRHENIUS: AN ARRHENIUS ACID IS A SUBSTANCE THAT DISSOCIATES IN WATER TO FORM HYDROGEN IONS (H+);[6]THAT IS, AN ACID INCREASES THE CONCENTRATION OF H+ IONS IN AN AQUEOUS SOLUTION. THIS CAUSES THE PROTONATION OF WATER, OR THE CREATION OF THE HYDRONIUM (H3O+) ION.[9] THUS, IN MODERN TIMES, THE USE OF H+ IS REGARDED AS A SHORTHAND FOR H3O+, BECAUSE IT IS NOW KNOWN THAT A BARE PROTON DOES NOT EXIST AS A FREE SPECIES IN AQUEOUS SOLUTION.[10] AN ARRHENIUS BASE IS A SUBSTANCE THAT DISSOCIATES IN WATER TO FORM HYDROXIDE (OH−) IONS; THAT IS, A BASE INCREASES THE CONCENTRATION OF OH− IONS IN AN AQUEOUS SOLUTION. Arrhenius definition Common acid–base theories
  6. 6. The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions, and refer to the concentration of the solvent ions. Under this definition, pure H2SO4 and HCl dissolved in toluene are not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. The universal aqueous acid–base definition of the Arrhenius concept is described as the formation of a water molecule from a proton and hydroxide ion. This leads to the definition that in Arrhenius acid–base reactions, a salt and water are formed from the reaction between an acid and a base.[6] This is a neutralization reaction - the acid and base properties of H+ and OH− are neutralized, for they combine to form H2O, the water molecule. The acid-base neutralization reaction can be put into a word equation: acid + base → salt + water The positive ion from a base and the negative ion from an acid form a salt together - in other words, an acid-base neutralization reaction is a double-replacement reaction. For example, when a neutralization reaction takes place between hydrochloric acid (HCl) and sodium hydroxide (NaOH), the products are sodium chloride (common table salt) and water. HCl(aq) + NaOH(aq) → NaCl + H2O Notice how the cations and the anions merely switched places: the Na+ from the NaOH combined with the Cl- from the HCl to form NaCl, while the OH− from the NaOH combined with the H+ from the HCl to form H2O.
  7. 7. The hydrogen requirement of Arrhenius and Brønsted–Lowry was removed by the Lewis definition of acid–base reactions, devised byGilbert N. Lewis in 1923,[16] in the same year as Brønsted–Lowry, but it was not elaborated by him until 1938.[2] Instead of defining acid–base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a Lewis base) to be a compound that can donate an electron pair, and an acid (a Lewis acid) to be a compound that can receive this electron pair.[17] In this system, an acid does not exchange atoms with a base, but combines with it. For example, consider this classical aqueous acid–base reaction: Lewis definition
  8. 8. HCL (AQ) + NAOH (AQ) → H 2O (L) + NACL (AQ)THE LEWIS DEFINITION DOES NOT REGARD THIS REACTION AS THE FORMATION OF SALT AND WATER OR THE TRANSFER OF H+ FROM HCL TO OH− . INSTEAD, IT REGARDS THE ACID TO BE THE H+ ION ITSELF, AND THE BASE TO BE THE OH− ION, WHICH HAS AN UNSHARED ELECTRON PAIR. THEREFORE, THE ACID–BASE REACTION HERE, ACCORDING TO THE LEWIS DEFINITION, IS THE DONATION OF THE ELECTRON PAIR FROM OH− TO THE H+ ION. THIS FORMS A COVALENT BOND BETWEEN H+ AND OH− , THUS PRODUCING WATER (H 2O). BY TREATING ACID–BASE REACTIONS IN TERMS OF ELECTRON PAIRS INSTEAD OF SPECIFIC SUBSTANCES, THE LEWIS DEFINITION CAN BE APPLIED TO REACTIONS THAT DO NOT FALL UNDER OTHER DEFINITIONS OF ACID–BASE REACTIONS. FOR EXAMPLE, A SILVER CATION BEHAVES AS AN ACID WITH RESPECT TO AMMONIA, WHICH BEHAVES AS A BASE, IN THE FOLLOWING REACTION: AG+ + 2 :NH 3 → [H 3N:AG:NH 3]+
  9. 9. THE RESULT OF THIS REACTION IS THE FORMATION OF AN AMMONIA–SILVER ADDUCT. IN REACTIONS BETWEEN LEWIS ACIDS AND BASES, THERE IS THE FORMATION OF AN ADDUCT[17] WHEN THE HIGHEST OCCUPIED MOLECULAR ORBITAL (HOMO) OF A MOLECULE, SUCH AS NH 3 WITH AVAILABLE LONE ELECTRON PAIR(S) DONATES LONE PAIRS OF ELECTRONS TO THE ELECTRON-DEFICIENT MOLECULE'S LOWEST UNOCCUPIED MOLECULAR ORBITAL (LUMO) THROUGH A CO-ORDINATE COVALENT BOND; IN SUCH A REACTION, THE HOMO-INTERACTING MOLECULE ACTS AS A BASE, AND THE LUMO-INTERACTING MOLECULE ACTS AS AN ACID.[17] IN HIGHLY-POLAR MOLECULES, SUCH AS BORON TRIFLUORIDE(BF 3),[17] THE MOST ELECTRONEGATIVE ELEMENT PULLS ELECTRONS TOWARDS ITS OWN ORBITALS, PROVIDING A MORE POSITIVE CHARGE ON THE LESS-ELECTRONEGATIVE ELEMENT AND A DIFFERENCE IN ITS ELECTRONIC STRUCTURE DUE TO THE AXIAL OR EQUATORIAL ORBITING POSITIONS OF ITS ELECTRONS, CAUSING REPULSIVE EFFECTS FROM LONE PAIR – BONDING PAIR (LP–BP) INTERACTIONS BETWEEN BONDED ATOMS IN EXCESS OF THOSE ALREADY PROVIDED BY BONDING PAIR – BONDING PAIR (BP– BP) INTERACTIONS.[17] ADDUCTS INVOLVING METAL IONS ARE REFERRED TO AS CO- ORDINATION COMPOUNDS
  10. 10. THIS ACID–BASE THEORY WAS A REVIVAL OF OXYGEN THEORY OF ACIDS AND BASES, PROPOSED BY GERMAN CHEMIST HERMANN LUX[18][19] IN 1939, FURTHER IMPROVED BY HÅKON FLOOD CIRCA 1947[20] AND IS STILL USED IN MODERN GEOCHEMISTRY AND ELECTROCHEMISTRY OF MOLTEN SALTS. THIS DEFINITION DESCRIBES AN ACID AS AN OXIDE ION (O2− ) ACCEPTOR AND A BASE AS AN OXIDE ION DONOR. FOR EXAMPLE:[21] MGO (BASE) + CO 2 (ACID) → MGCO 3CAO (BASE) + SIO 2 (ACID) → CASIO 3NO− 3 (BASE) + S 2O2− 7 (ACID) → NO+ 2 + 2 SO2− 4 Lux–Flood definition Other acid–base theories
  11. 11. IN 1963,[22] RALPH PEARSON PROPOSED AN ADVANCED QUALITATIVE CONCEPT KNOWN AS HARD SOFT ACID BASE PRINCIPLE, LATER MADE QUANTITATIVE WITH HELP OF ROBERT PARR IN 1984. 'HARD' APPLIES TO SPECIES THAT ARE SMALL, HAVE HIGH CHARGE STATES, AND ARE WEAKLY POLARIZABLE. 'SOFT' APPLIES TO SPECIES THAT ARE LARGE, HAVE LOW CHARGE STATES AND ARE STRONGLY POLARIZABLE. ACIDS AND BASES INTERACT, AND THE MOST STABLE INTERACTIONS ARE HARD–HARD AND SOFT–SOFT. THIS THEORY HAS FOUND USE IN ORGANIC AND INORGANIC CHEMISTRY. Pearson definition
  12. 12. MIKHAIL USANOVICH DEVELOPED A GENERAL THEORY THAT DOES NOT RESTRICT ACIDITY TO HYDROGEN-CONTAINING COMPOUNDS, BUT HIS APPROACH, PUBLISHED IN 1938, WAS EVEN MORE GENERAL THAN LEWIS THEORY.[2] USANOVICH'S THEORY CAN BE SUMMARIZED AS DEFINING AN ACID AS ANYTHING THAT ACCEPTS NEGATIVE SPECIES OR DONATES POSITIVE ONES, AND A BASE AS THE REVERSE. THIS DEFINED THE CONCEPT OF REDOX (OXIDATION- REDUCTION) AS A SPECIAL CASE OF ACID-BASE REACTIONS SOME EXAMPLES OF USANOVICH ACID-BASE REACTIONS INCLUDE: NA 2O (BASE) + SO 3 (ACID) → 2 NA+ + SO2− 4 (SPECIES EXCHANGED: ANION O2− )3 (NH 4) 2S (BASE) + SB 2S 3 (ACID) → 6 NH+ 4 + 2 SBS3− 4 (SPECIES EXCHANGED: ANION S2− )NA (BASE) + CL (ACID) → NA+ + CL− (SPECIES EXCHANGED: ELECTRON) Usanovich definition
  13. 13.  An acid–alkali reaction is a special case of an acid–base reaction, where the base used is also an alkali. When an acid reacts with an alkali it forms a metal salt and water. Acid– alkali reactionsAcid–alkali reaction  are also a type of neutralization reaction.  In general, acid–alkali reactions can be simplified to  OH− (aq) + H+ (aq) → H 2Oby omitting spectator ions.  Acids are in general pure substances that contain hydrogen ions (H+ ) or cause them to be produced in solutions. Hydrochloric acid (HCl) and sulfuric acid (H 2SO 4) are common examples. In water, these break apart into ions:  HCl → H+ (aq) + Cl− (aq)H 2SO 4 → H+ (aq) + HSO− 4(aq)To produce hydroxide ions in water, the alkali breaks apart into ions as below:  NaOH → Na+ (aq) + OH− Acid–alkali reaction

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