Acid and Base Equilibrium CHM1025C

Acid and Base Equilibrium CHM1025C

Arrhenius Acid: A substance that make H (H3O ) when dissolved in water. Base: A substance that makes OH- when dissolved in water. An acid/base reaction occurs when and H from an acid reacts with an OH- from a base.

Acids Strong acids: Dissociate completely when dissolved in water. – HCl, HNO3 Weak acids only dissociate a little bit. – CH3CO2H

Base Strong base: dissociates completely when dissolved in water. – NaOH, KOH Weak base: Makes only a little bit of OH – NH3

Electrolyte Electrolyte: A substance that produces ions when dissolved in water. NaCl, HCl and NaOH are all strong electrolytes because they dissociate essentially completely into ions. Strong acids and strong bases are strong electrolytes. CH3CO2H, HF and NH3 are examples of weak electrolytes because they produce only a few ions.

1.00 M Acetic acid, a weak acid CH3COOH (aq) H2O(l) H3O (aq) CH3COO-(aq) H O CH CO K 3 3 2 CH 3CO 2 H The Ka for this reaction is 1.8 x 10-5. Since little of the CH3CO2H dissociates, we can call it 1 M. For every H3O there will be one CH3COO-. Let these concentrations x x [H ] [CH3COO-] .00042

Brønsted-Lowry Definition Acid: A proton donor. Base: A proton acceptor. An acid base reaction is one where there is a proton transfer. A broader definition than the Arrhenius definition. conjugate base: The acid without an H . conjugate acid: The base with an H .

TABLE: Relative Strengths of Acids and Their Conjugate Bases Strong Acids Weak Acids Acid HI H2SO4 HC1 HNO3 H3O HSO4H3PO4 HF CH3CO2H H2CO3 H2S H2PO4NH4 C6H5 OH HCO3 HPO42H2O C2H5 OH Hydroiodic acid Sulfuric acid Hydrochloric acid Nitric acid Hydronium ion Hydrogen sulfate ion Phosphoric acid Hydrofluoric acid Acetic acid Carbonic acid Hydrogen sulfide Dihydrogen phosphate ion Ammonium ion Phenol Bicarbonate ion Hydrogen phosphate ion Water Ethanol Conjugate Base IHSO4 Cl NO3H2 O SO42H2PO4 F CH3CO2HCO3HS HPO4 2NH3 C 6 H5 O2CO3 PO43OHC 2 H5 O- Iodide ion Hydrogen sulfate ion Chloride ion Nitrate ion Water Sulfate ion Dihydrogen phosphate ion Fluoride Ion Acetate ion Bicarbonate ion Hydrogen sulfide ion Hydrogen phosphate ion Ammonia Phenoxide ion Carbonate ion Phosphate ion Hydroxide ion Ethoxide ion Given on test Weak Bases Strong Bases

A standard acid/base reaction Acid Base c. base c. acid ex: CH3COOH H2O CH3COO- H3O NH3 H2O NH4 OH-

More on Acid Base reactions Water is amphoteric or amphiprotic, it can act as both an acid and a base. All acid base reactions are equilibrium reactions The equilibrium lies to the side of the weaker acid. When the equilibrium lies to the right, a lot of reaction occurs and there is often heat released or there is a color change . When the equilibrium lies to the left very little reaction occurs. (no heat )

Water Water auto-ionizes H2O H2O H3O OHacid base [10-7M] [10-7M] éëH 3O ùûéëOH - ùû é 3O ùéOH - ù 1 10 - 14 K H ë ûë û 2 [ H 2O]

Acids and pH [H ] or [H3O ] [OH-] 0.1 M HCl pure water 0.1 M NaOH 0.100 or 1.00 x10-1 1.00 x10-13 1x10-7 1.00 x10-13 1x10-7 0.100 or 1.00 x10-1 13 pH 1 7 pOH 13 7 acid or basic 1 neutral Acid Basic [H3O ] [OH-] [H3O ] [OH-] [H3O ] [OH-]

pH scale Lemon juice Soda vinegar ammonia Comet cleanser drano

The big six 1. [H3O ] [OH-] 1 x 10-14 2. pH -log[H3O ] 3. pOH -log[OH-] 4. [H3O ] 10-pH 5. [OH-] 10-pOH 6. pH pOH 14

The [H ] or [H3O ] of 0.1 M NH3 The pH is 11.13. What is the [H3O ] ? pH -log [H3O ] [H3O ] 10-pH [H3O ] 10-11.13 7.41 x 10-12

Filling out a table - [H3O ] [OH ] .0800 M HCl .0800 M CH3CO2H pH .0800 2.92 pOH

Buffer solution A buffer solution keeps the pH approximately the same even upon the addition of a strong acid or strong base. Need a weak acid. Its conjugate base. Present in a large enough quantity to resist the pH changes.

CH3CO2H/CH3CO2 - If you add an acid, H , The base of the buffer reacts. – H CH3CO2- CH3CO2H – H3O CH3CO2- H2O CH3CO2H Of you add a base, OH-, the acid of the buffer system reacts. – CH3CO2H OH- H2O CH3CO2-

Titrations How many mL of 0.660M H2SO4 are required to react completely with 72.5 mL of 0.137M NaOH?