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Acids and Bases

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insel veraque

on 5 October 2012

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Transcript of Acids and Bases

Acids & Bases sour
corrosive to metals and skin
pH of <7 and a POH of >7
turns blue litmus paper red
contains hydrogen (H+ ions)
reacts with bases to form water and a salt bitter
slippery or soapy
pH of >7 and a POH of <7
turns red litmus paper blue, turns phenolphthalein pink/purple
contains hydroxide (OH- ions)
reacts with acids to form water and a salt Acid-Base Theories Svante Arrhenius The Arrhenius Definition of Acids and
Bases Strong electrolytes are completely dissociated into ions in water. The acid or base molecule does not exist in aqueous solution, only ions. Weak electrolytes are incompletely dissociated. Strengths of Acids and Bases Ways of Measuring pH The pH Scale When acids and bases react with each other, they can form a salt and (usually) water. This is called a neutralization reaction and takes the following form:

HA + BOH --> BA + H2O Neutralization Phenolphthalein as Indicator Acid-Base Titration Arrhenius proposed definitions for acids and bases, in 1884. He believed that acids were substances that produce hydrogen ions in solution and that bases were substances that produce hydroxide ions in solution. The Lewis Theory The Bronsted-Lowry Theory The universal aqueous acid–base definition of the Arrhenius concept is described as the formation of water from a proton and hydroxide ions, or hydrogen ions and hydroxide ions from the dissociation of an acid and base in aqueous solution.

H+ (aq) + OH− (aq) <--> H2O a salt and water are formed from the reaction between an acid and a base

acid + base --> salt + water 2 NaOH + H2SO4 --> Na2SO4 + 2 H2O Johannes Nicolaus Brønsted and Thomas Martin Lowry definitions of acidity and alkalinity are restricted to aqueous solutions, and refer to the concentration of the solvent ions According to Brønsted–Lowry definition, an acid is a compound that can donate a proton, and a base is a compound that can receive a proton. the general formula for acid–base reactions according to the Brønsted–Lowry definition is:

AH + B --> BH+ + A−- formation of conjugate acids and conjugate bases, produced by the transfer of a proton from the acid to the base The reaction of ammonia, a base, with acetic acid in absence of water can be described to give ammonium cation, an acid, and acetate anion, a base:

CH3COOH + NH3 --> NH+4 + CH3COO- also explains the dissociation of water into low concentrations of hydronium and hydroxide ions:

H2O + H2O <--> H3O+ + OH- Amphoteric HCl (acid) + H2O (base) --> H3O+ (acid) + Cl−- (base)

CH3COO- (base) + H2O (acid) --> CH3COOH (acid) + OH- (base) Although Brønsted–Lowry calls hydrogen-containing substances like HCl acids, KOH and KNH2 are not bases but salts containing the bases OH and NH2.

Also, some substances, which many chemists considered to be acids, such as SO3 or BCl3, are excluded from this classification due to lack of hydrogen. Gilbert Newton Lewis 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. HCl (aq) + NaOH (aq) H2O (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. A silver cation behaves as an acid with respect to ammonia, which behaves as a base, in the following reaction:

Ag+ + 2 :NH3 [H3N:Ag:NH3]+

The result of this reaction is the formation of an ammonia–silver adduct. Adducts involving metal ions are referred to as co-ordination compounds. What makes an acid or a base strong? state general properties of acids & bases identify common household acids & bases define an acid and a base 3 classes of reaction acid + metal --> salt + H2(g) acid + base --> salt + H2O acid + carbonate --> salt + H2O + CO2 Strong Acids Weak Acids Strong Bases Weak Bases •HCl - hydrochloric acid
•HNO3 - nitric acid
•H2SO4 - sulfuric acid
•HBr - hydrobromic acid
•HI - hydroiodic acid
•HClO4 - perchloric acid Include hydrofluoric acid, HF, and acetic acid, CH3COOH. Weak acids include:
Molecules that contain an ionizable proton. A molecule with a formula starting with H usually is an acid.
Organic acids containing one or more carboxyl group, -COOH. The H is ionizable.
Anions with an ionizable proton. (e.g., HSO4- --> →H+ + SO4 2-)
Cations
transition metal cations
heavy metal cations with high charge
NH4+ dissociates into NH3 + H+ Hydroxides of the Group I and Group II metals usually are considered to be strong bases.
LiOH - lithium hydroxide
NaOH - sodium hydroxide
KOH - potassium hydroxide
RbOH - rubidium hydroxide
CsOH - cesium hydroxide
*Ca(OH)2 - calcium hydroxide
*Sr(OH)2 - strontium hydroxide
*Ba(OH)2 - barium hydroxide Include ammonia, NH3, and diethylamine, (CH3CH2)2NH.
Most weak bases are anions of weak acids.
Weak bases do not furnish OH- ions by dissociation. Instead, they react with water to generate OH- ions. Monoprotic acids HCl --> H+ + Cl-

HNO --> H+ + NO3-

CH3COOH <--> H+ + CH3CO2- Polyprotic acids Diprotic acids

H2SO4 --> H+ + HSO4-

HSO4- <--> H+ + SO4 2- Triprotic acids

H3PO4 <--> H+ + HPO4-

HPO4- <--> H+ + HPO4 2-

HPO4 2- <--> H+ + PO4 3- The pH of a solution is a measure of the Hydrogen ion concentration ([H+]), which is a measure of acidity. A) Indicator methods
(B) Metal-electrode methods (including the hydrogen-electrode method, quinhydron-electrode method and antimony-electrode method)
(C) Glass-electrode methods Søren Peder Lauritz Sørensen A pH indicator (or pH paper) is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. strong acid + strong base, e.g., HCl + NaOH --> NaCl + H2O

strong acid + weak base, e.g., HCl + NH3 --> NH4Cl

HCl (aq) + NH3 (aq) --> NH4+ (aq) + Cl- while
NH4- (aq) + H2O --> NH3 (aq) + H3O+ (aq)

weak acid + strong base, e.g., HClO + NaOH --> NaClO + H2O

weak acid + weak base, e.g., HClO + NH3 --> NH4ClO Four combinations of strong and weak acids and bases: Now we're ready to titrate!
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