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 red red to blue

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

Examples The hydrogen ion in aqueous solution H+ + H2O  H3O+ (hydronium ion) Examples Arrhenius HCl NaOH Bronsted-Lowry HCl HCN NH3 Lewis BF3 :NH3

The Bronsted-Lowry Concept Conjugate pairs HCl Cl- CH3COOH CH3COO- NH4+ NH3 HNO3 NO3- How does a conjugate pair differ? H+ transfer

Neutralization HCl + NaOH  NaCl + HOH HCl + Mg(OH)2  In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH)2  H2SO4 + NaHCO3 

How are (H+) and (OH-) related? Does pure water conduct electrical current? Water is a very, very, very weak electrolyte. H2O  H+ + OH- How are (H+) and (OH-) related? (H+)(OH-) = 10-14 For pure water: (H+) = (OH-) = 10-7M This is neutrality and at 25oC is a pH = 7. water

Let’s examine the behavior of an acid, HA, in aqueous solution. CHM 101 Let’s examine the behavior of an acid, HA, in aqueous solution. Sinex HA What happens to the HA molecules in solution?

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

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

At any one time, only a fraction of the molecules are dissociated. HA  H+ + A- HA H+ Weak Acid 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 HCl NaOH HNO3 KOH H2SO4 Weak acids/bases – partial dissociation, both ions and molecules CH3COOH NH3

pH acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area 0-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12 acidic (H+) > (OH-) neutral @ 25oC (H+) = (OH-) distilled water basic or alkaline (H+) < (OH-) normal rain (CO2) pH = 5.3 – 5.7 fish populations drop off pH < 6 and to zero pH < 5 natural waters pH = 6.5 - 8.5

When life goes either way amphoteric (amphiprotic) substances Acting like a base Acting like an acid HCO3- + H+ - H+ H2CO3 CO3-2 accepts H+ donates H+

pH The biological view in the human body acidic basic/alkaline saliva 1 2 3 4 5 6 7 8 9 10 11 saliva blood urine gastric juice vaginal fluid pancreatic juice bile cerebrospinal fluid Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003)

Show how water can be amphoteric.

Dilution Mfinal x Vfinal = Minitial x Vinitial water (solvent) solute moles of solute remain constant diluted, Mfinal Vfinal molesinitial = molesfinal Vinitial concentrated, Minitial adding water lowers the solute concentration Mfinal x Vfinal = Minitial x Vinitial

Titration Calculation indicator HCl + NaOH  NaCl + HOH A way to analyze solutions! at equivalence point: moleHCl = moleNaOH moles = M x VL Macid x Vinitial acid = Mbase x Vburet