Conjugate acids and bases

Different definitions of acids and bases Acids are proton donors (Brønsted Lowry definition)Acids are proton donors (Brønsted Lowry definition) –they generate H 3 O + in water (Arrhenius definition) Bases are proton acceptorsBases are proton acceptors –they generate OH - in water which is an acid/base?which is an acid/base? HF + H 2 0  H 3 O + + F -HF + H 2 0  H 3 O + + F - NaHCO 3 + H 2 0  Na + +H 2 O + CO 2 + OH -NaHCO 3 + H 2 0  Na + +H 2 O + CO 2 + OH - By Arrhenius, HF is an acid, is a NaHCO 3 base.By Arrhenius, HF is an acid, is a NaHCO 3 base.

Follow the proton HF + H 2 0  H 3 O + + F -HF + H 2 0  H 3 O + + F - NaHCO 3 + H 2 0  Na + + H 2 O+CO 2 +OH -NaHCO 3 + H 2 0  Na + + H 2 O+CO 2 +OH - What about the reverse reaction?What about the reverse reaction? H+H+ H+H+ H+H+ H+H+

Conjugate acids and bases When you run the reverse reaction you find the products are also acids and bases. The acids and bases that are formed are called conjugate acids or basesWhen you run the reverse reaction you find the products are also acids and bases. The acids and bases that are formed are called conjugate acids or bases H HF  H 3 O + + F -H HF  H 3 O + + F - base acid conjugate acid conjugate basebase acid conjugate acid conjugate base NaHCO 3 + H 2 0  Na + +H 2 O + CO 2 + OH -NaHCO 3 + H 2 0  Na + +H 2 O + CO 2 + OH - base acid CA CBbase acid CA CB

Label Acid, Base, Conjugate Acid, Conjugate Base HClO 3 + H 2 0  ClO 3 - +H 3 O +HClO 3 + H 2 0  ClO 3 - +H 3 O + A B CB CA A B CB CA ClO - + H 2 0  HClO + OH -ClO - + H 2 0  HClO + OH - B A CA CB B A CA CB HSO H 2 O  SO H 3 O +HSO H 2 O  SO H 3 O + A B CB CA A B CB CA LiOH + H 2 O  Li + + H 2 O + OH -LiOH + H 2 O  Li + + H 2 O + OH - B A CA CB B A CA CB

Conjugate acids and bases … Conjugate acids and bases determine if an acid or base is strong or weak.Conjugate acids and bases determine if an acid or base is strong or weak. If the conjugate acid/base readily reacts to run the reverse reaction it is a weak acid/base.If the conjugate acid/base readily reacts to run the reverse reaction it is a weak acid/base. If it does not react in the reverse reaction the acid or base is strong.If it does not react in the reverse reaction the acid or base is strong.

More with conjugate acids/bases H 2 SO 4 + H 2 O  H 3 O + + HSO 4 -H 2 SO 4 + H 2 O  H 3 O + + HSO 4 - Sulfuric acid is a strong acid so its conjugate base, HSO 4 -, will not run the reverse reaction.Sulfuric acid is a strong acid so its conjugate base, HSO 4 -, will not run the reverse reaction. HSO 4 - is actually an acid in water.HSO 4 - is actually an acid in water. HSO H 2 O  H 3 O + + SO 4 2-HSO H 2 O  H 3 O + + SO 4 2- SO 4 2- will run the reverse reaction, so it is a weak acidSO 4 2- will run the reverse reaction, so it is a weak acid

Strong acids and bases The strong acids and bases have no reverse reaction.The strong acids and bases have no reverse reaction. They are not an equilibrium reaction.They are not an equilibrium reaction. HCl + H 2 O  H 3 O + + Cl -HCl + H 2 O  H 3 O + + Cl - No amount of stress will force this reaction the other way.No amount of stress will force this reaction the other way. (no way to make it less acidic, without a different reaction)(no way to make it less acidic, without a different reaction)

Strong acids AcidformulaAcidFormula Hydrochloric acid HCl Sulfuric Acid H 2 SO 4 Hydrobromic acid HBr Nitric Acid HNO 3 Hydriodic acid HI Perchloric Acid HClO 4

Strong Bases NameFormulaNameFormula Sodium Hydroxide NaOH Calcium Hydroxide Ca(OH) 2 Potassium Hydroxide KOH Strontium Hydroxide Sr(OH) 2 Barium Hydroxide Ba(OH) 2 these make a lightning bolt on the periodic table!

Weak acids and bases can be forced the other waycan be forced the other way So ammonia…So ammonia… NH 3 + H 2 O NH 4 + +OH -NH 3 + H 2 O NH 4 + +OH - Ammonia is a gas with a distinct odorAmmonia is a gas with a distinct odor Ammonium and hydroxide are both odorless.Ammonium and hydroxide are both odorless. If base is added to the solution you will smell ammonia, if hydroxide is removed you won’t smell anything.If base is added to the solution you will smell ammonia, if hydroxide is removed you won’t smell anything.

Pet “Stain” Problem Urine has ammonia in it.Urine has ammonia in it. Most cleansers are basic.Most cleansers are basic. After cleaning, we still leaves small amounts behind.After cleaning, we still leaves small amounts behind. If it is small amount of ammonia and a basic cleanser the equilibrium will be shifted to the ammonia side so some thing with a great sense of smell (dog) could pick it up.If it is small amount of ammonia and a basic cleanser the equilibrium will be shifted to the ammonia side so some thing with a great sense of smell (dog) could pick it up. A slightly acidic cleanser shifts the equilibrium to the ammonium side to solve this problemA slightly acidic cleanser shifts the equilibrium to the ammonium side to solve this problem

Other weak acids and bases Weak AcidsWeak Acids –Acetic Acid (vinegar) –Citric Acid –Ascorbic Acid (vitamin C) –Boric Acid –Carbonic Acid Weak BasesWeak Bases –Sodium Bicarbonate –Ammonia –Sodium Hypochlorite (bleach)