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4/29/2008

Electrolytes, Acids, Bases, and Salts

Steve Czerwinski Prep Chemistry 10

Lesson Objectives

· Define:

­ Electrolyte ­ Nonelectrolyte ­ Oxidation and Reduction ­ Anode ­ Cathode ­ Dissociation ­ Dynamic Equilibrium ­ Acid Strong and Weak ­ Base Strong and Weak ­ Salts

· List the names and formulas of seven common acids

Electrolytes

· Electrolytes are substances whose water solutions contain ions

­ CuCl 2

water +2 1 Cu (aq) + 2 Cl (aq)

· Solutions of electrolytes can conduct an electric current because they contain free ions · Conduction of electricity means that ions can transfer electrons at electrodes

­ Anode: Electrode where oxidation (loss of electrons) takes place ­ Cathode: Electrode where reduction (gain of electrons) takes place

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Electrolytes

· Nonelectrolytes: Substance whose water solution does not contain ions

­ C H OH 2 5

water

C H OH (solution) 2 5

· The intermolecular bonding of H O with 2 Ethyl Alcohol (EtOH) molecules produces a solution which will not conduct an electric current · There are no free ions from the EtOH in the solution

Dissociation/Ionization

· Dissociation: The pulling apart of existing ions

­ NaCl (s)

water + Na (aq) + Cl (aq) in solution

· Ionization: The formation of new ions

+ ­ HCl + H O H O + Cl 2 3

­ ­ HCl

water

+ (H O + H ) 2 + H (aq) + Cl (aq)

Acids

· Acids are compounds which, when put into H O, produce free hydrogen 2 + (H ) ions in solution · The ions react with H O to produce 2 + H O (Hydronium) ions 3 · Strength of Acids:

­ Strong Acid: Ionize almost completely in H O 2 ­ Weak Acid: Ionizes to a small degree only in H O 2

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Acids

· Weak Acid: Since this acid does not ionize readily, a dynamic equilibrium is established in solution

+ ­ HCN + H O H O + CN 2 3 + ­ (H O + H ) 2 ­ The double arrow indicates a system of dynamic equilibrium in which the rate of the forward reaction equals the rate of the reverse reaction

Acids

· Weak Acid:

+ + ­ In these reactions, the concentration of H O or H ions 3 and CN ions is small compared to the concentration on HCN molecules

· Therefore, this is a weak acid

· Common Acids:

­ Hydrochloric (HCl) STRONG Monoprotic ­ Nitric (HNO ) STRONG Monoprotic 3 ­ Sulfuric (H SO ) STRONG Diprotic 2 4 ­ Phosphoric (H PO ) MEDIUM Triprotic 3 4 ­ Acetic (CH COOH) WEAK Monoprotic 3 ­ Hydrocyanic (HCN) WEAK Monoprotic ­ Carbonic Acid (H CO ) WEAK Diprotic 2 3 ­ Water (HOH) WEAK

Bases

· Bases are compounds which, when put into H O, produce free OH 2 (Hydroxide) ions · All metal hydroxides are bases:

­ KOH, NaOH, LiOH

· Strength of Bases:

­ NH OH and H O are weak bases 4 2 ­ NaOH and KOH are strong bases

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Water as an Acid and Base

· Water can function as both a weak acid and a weak base. · Water molecules selfionize to a small extent according to:

­

+ H O H 2 + OH

+ ­ The concentration of H and OH is very small

Salts

· Salts are ionic compounds which contain the positive ion of a base and the negative ion of an acid · Types:

­ Normal Salts: Ionic compound which when put into water release positive + and negative ions OTHER THAN H AND OH

· NaCl, KNO , CaBr 3 2

Salts

· Types:

­ Hydroxysalts: Ionic compound which only a part of the hydroxide groups in a metal hydroxide have been replaced

· Ba(OH)Cl, Barium Hydroxychloride · Bi(OH) Cl, Bismuth Dihydroxychloride 2

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Salts

· Types:

­ Hydrogen Salts: Ionic compound which only a part of the acidic hydrogens in an acid have been replaced by a metal

· NaHCO , Sodium Bicarbonate 3 · NaH PO , Sodium Dihydrogen Phosphate 2 4 · Ca(HSO ) , Calcium Hydrogen Sulfate 4 2

· Hydrogen Salts and Hydroxysalts can + release H and OH ions in solution

­ ­

water NaH PO 2 4 H PO 1 water 2 4 + Na + H PO 1 2 4 + H + HPO 2 4

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