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ACIDS, BASES & SALTS. The Arrhenius Theory of Acids and Bases. Arrhenius Theory of Acids and Bases:. an acid contains hydrogen and ionizes in solutions to produce H + ions: HCl H + (aq) + Cl - (aq). Arrhenius Theory of Acids and Bases:.
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Arrhenius Theory of Acids and Bases: an acid contains hydrogen and ionizes in solutions to produce H+ ions: HCl H+(aq) + Cl-(aq)
Arrhenius Theory of Acids and Bases: a base contains an OH- group and ionizes in solutions to produce OH- ions: NaOH Na+(aq) + OH-(aq)
Neutralization • Neutralization: the combination of H+ with OH- to form water. • H+(aq) + OH-(aq) H2O (l) • Hydrogen ions (H+)in solution form hydronium ions (H3O+)
In Reality… H+ + H2O H3O+ Hydronium Ion (Can be used interchangeably with H+)
Commentary on Arrhenius Theory… One problem with the Arrhenius theory is that it’s not comprehensive enough. Some compounds act like acids and bases that don’t fit the standard definition.
Bronsted-Lowry Theory of Acids & Bases: • An acid is a proton (H+) donor • A base is a proton (H+) acceptor
for example… Proton transfer HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) Base Acid
Water is a proton donor, and thus an acid. another example… CONJUGATE BASE ACID NH3(aq) + H2O(l) NH4+ (aq) + OH- (aq) BASE CONJUGATE ACID Ammonia is a proton acceptor, and thus a base
Conjugate acid-base pairs • Conjugate acid-base pairs differ by one proton (H+) A conjugate acid is the particle formed when a base gains a proton. A conjugate base is the particle that remains when an acid gives off a proton.
Examples: In the following reactions, label the conjugate acid-base pairs: • H3PO4 + NO2- HNO2 + H2PO4- • CN- + HCO3- HCN + CO32- • HCN + SO32- HSO3- + CN- • H2O + HF F- + H3O+ acid base c. acid c. base base acid c. acid c. base acid base c. base c. acid c. base c. acid base acid
Amphoteric Substances A substance that can act as both an acid and a base (depending on what it is reacting with) is termed amphoteric. Water is a prime example.
ACIDS Have a sour taste Change the color of many indicators Are corrosive (react with metals) Neutralize bases Conduct an electric current BASES Have a bitter taste Change the color of many indicators Have a slippery feeling Neutralize acids Conduct an electric current Properties of Acids and Bases
Other Household Acids and Bases • Antacid: a weak base that neutralizes excess stomach acid. • The pH of shampoo is generally kept between 5 and 8. • Lemon juice is an acid that is sometimes used to help keep fruit looking fresh. What will happen to left apple?
Indicators- “Way Cool” Cyber-lab: http://www.miamisci.org/ph/phlemon.html
Strength of Acids and Bases • A strong acid dissociates completely in sol’n: • HCl H+(aq) + Cl-(aq) • A weak acid dissociates only partly in sol’n: • HNO2 H+(aq) + NO2-(aq) • A strong base dissociates completely in sol’n: • NaOH Na+(aq) + OH-(aq) • A weak base dissociates only partly in sol’n: • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
The Lewis Theory of Acids & Bases • Lewis acid: a substance that can accept an electron pair to form a covalent bond (electron pair acceptor). • Lewis base: a substance that can donate an electron pair to form a covalent bond (electron pair donor).
Neutralization • Neutralization: the formation of a coordinate covalent bond in which both electrons originated on the same (donor) atom.
Example 1: • Ionization of NH3: • NH3 + H2O NH4+ + OH- base + acid .. .. H H - .. .. .. + H O H H N H O H H N H + H
Example 2: • Auto-ionization of water: • H2O + H2O H3O+ + OH- + acid .. .. base .. .. - .. .. .. + H O H H O H O H H O H + H
Example 3: • Reaction of NH3 with HBr (a Lewis AND a Bronsted-Lowry acid-base reaction): • NH3 + HBr NH4+ + Br- base + acid .. .. H H - .. .. .. + H Br H N H Br H N H + H
Acid Base Theories Lewis Bronsted-Lowry Arrhenius
Acid-Base Reactions • Neutralization reactions: reactions between acids and metal hydroxide bases which produce a salt and water. • H+ ions and OH- ions combine to form water molecules: • H+(aq) + OH-(aq) H2O(l)
Example 1: the reaction of HCl and NaOH (there are 3 ways to write the chemical equation): • Balanced formula unit equation: • HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) • Total ionic equation: • H+(aq)+Cl-(aq)+Na+(aq)+OH-(aq)H2O(l)+Na+(aq)+Cl-(aq) • Net ionic equation: • H+(aq) + OH-(aq) H2O(l)
Example 2: Write the 3 types of equations for the reaction of hydrobromic acid, HBr, with potassium hydroxide, KOH. • Balanced formula unit equation: • HBr(aq) + KOH(aq) H2O(l) + KBr(aq) • Total ionic equation: • H+(aq)+Br-(aq)+K+(aq)+OH-(aq)H2O(l)+K+(aq)+Br-(aq) • Net ionic equation: • H+(aq) + OH-(aq) H2O(l)
Example 3: Write the 3 types of equations for the reaction of nitric acid, HNO3, with calcium hydroxide, Ca(OH)2. • Balanced formula unit equation: • 2HNO3(aq) + Ca(OH)2(aq) 2H2O(l) + Ca(NO3)2(aq) • Total ionic equation: • 2H+(aq)+2NO3-(aq)+Ca2+(aq)+2OH-(aq)2H2O(l)+Ca2++2NO3-(aq) • Net ionic equation: • H+(aq) + OH-(aq) H2O(l)