Acids and Bases PGCC CHM 101 Sinex

General properties ACIDS Taste sour Turn litmus React with active metals – Fe, Zn React with bases BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids blue to redred to blue

Definitions Acids – produce H + Bases - produce OH - Acids – donate H + Bases – accept H + Acids – accept e - pair Bases – donate e - pair Arrehenius Bronsted-Lowry Lewis only in water any solvent used in organic chemistry, wider range of substances

Examples Arrhenius Bronsted-Lowry Lewis HCl NaOH HClNH 3 :NH 3 BF 3 HCN The hydrogen ion in aqueous solution H + + H 2 O  H 3 O + (hydronium ion)

The Bronsted-Lowry Concept Conjugate pairs HCl Cl - CH 3 COOH CH 3 COO - NH 4 + NH 3 HNO 3 NO 3 - How does a conjugate pair differ? H + transfer

Neutralization In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH) 2  H 2 SO 4 + NaHCO 3 

H 2 O  H + + OH - Does pure water conduct electrical current? (H + )(OH - ) = For pure water: (H + ) = (OH - ) = M This is neutrality and at 25 o C is a pH = 7. Water is a very, very, very weak electrolyte. How are (H + ) and (OH - ) related? water

HA Let’s examine the behavior of an acid, HA, in aqueous solution. What happens to the HA molecules in solution?

HA H+H+ A-A- Strong Acid 100% dissociation of HA Would the solution be conductive?

HA H+H+ A-A- Weak Acid Partial dissociation of HA Would the solution be conductive?

HA H+H+ A-A- Weak Acid HA  H + + A - At any one time, only a fraction of the molecules are dissociated.

Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HClNaOH HNO 3 KOH H 2 SO 4 Weak acids/bases – partial dissociation, both ions and molecules CH 3 COOHNH 3

pH o C (H + ) = (OH - ) distilled water acidic (H + ) > (OH - ) basic or alkaline (H + ) < (OH - ) natural waters pH = normal rain (CO 2 ) pH = 5.3 – 5.7 acid rain (NO x, SO x ) pH of in Washington DC area 0-14 scale for the chemists fish populations drop off pH < 6 and to zero pH < 5

You are here! pH of Rainwater across United States in 2001 Increasing acidity Why is the eastern US more acidic? air masses

What is acid rain? CO 2 (g) + H 2 O  H 2 CO 3  H + + HCO 3 - Dissolved carbon dioxide lowers the pH Atmospheric pollutants from combustion NO, NO 2 + H 2 O …  HNO 3 SO 2, SO 3 + H 2 O …  H 2 SO 4 both strong acids pH < 5.3

105 Db 107 Bh Behavior of oxides in water– Group A basicamphotericacidic 3A 4A 5A 6A 7A 1A 2A 8A Group B basic: Na 2 O + H 2 O  2NaOH (O -2 + H 2 O  2OH - ) acidic: CO 2 + H 2 O  H 2 CO 3

When life goes either way amphoteric (amphiprotic) substances HCO 3 - H 2 CO 3 CO H + - H + Acting like a base Acting like an acid accepts H + donates H +

pH The biological view in the human body gastric juice vaginal fluid urine saliva cerebrospinal fluid blood pancreatic juice bile acidicbasic/alkaline 7 Tortora & Grabowski, Prin. of Anatomy & Physiology, 10 th ed., Wiley (2003)

Does the pH influence the activity of an enzyme? Trypsin is a digestive enzyme. Where? Intestinal pH range

The amino acid glycine - amphoteric It’s an acid and a base! Loss of H + Gain of H + H 2 N-CH 2 -COOH H 3 N + -CH 2 -COOHH 2 N-CH 2 -COO - Chime structure

The amino acid glycine - Zwitterion formation Transfer of H + from carboxylic acid group to amine group. H 2 N-CH 2 -COOH H 3 N + -CH 2 -COO A dipolar ion forms. intramolecular acid-base reaction Chime structure

Show how water can be amphoteric. H2OH2O + H + - H +

Dilution water (solvent)solute concentrated, M initial diluted, M final adding water lowers the solute concentration moles of solute remain constant V initial V final moles initial = moles final M final x V final = M initial x V initial

Titration Calculation HCl + NaOH  NaCl + HOH at equivalence point: mole HCl = mole NaOH moles = M x V L M acid x V initial acid = M base x V buret A way to analyze solutions! indicator