Acids and Bases Essential Question: How do you compare the properties of acids and bases?

What are the properties of acids? Taste sour pH less than 7 Turns blue litmus paper to red (BRA) Form H+ ions (Hydrogen) in solution Corrosive React with most metals to form Hydrogen gas * Good conductors of electricity React with bases

What are the properties of bases or alkaline? Taste bitter pH greater than 7 Turns red litmus paper to blue (RBB) Form OH- (hydroxide ions) in a solution Feels soapy or slippery React with fats to make soap Dissolves fats and oils Reacts with acids and neutralizes it

What is a pH? pH measures how acidic or basic is the substance

What is a pH scale? pH 1-6 – ACID pH 1 – strong acid pH 6 – weak acid pH 7 – neutral pH 8-14 – bases pH 8 – weak base pH 14 – strong base

What is a salt A salt is a neutral substance produced from reaction of an acid and a base

Concept map

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

across United States in 2001 pH of Rainwater across United States in 2001 You are here! air masses Increasing acidity Why is the eastern US more acidic? http://nadp.sws.uiuc.edu/isopleths

What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O  H2CO3  H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O …  HNO3 both strong acids SO2, SO3 + H2O …  H2SO4 pH < 5.3

Behavior of oxides in water– Group A 105 Db 107 Bh basic amphoteric acidic 8A 1A 3A 4A 5A 6A 7A 2A Group B basic: Na2O + H2O  2NaOH (O-2 + H2O  2OH-) acidic: CO2 + H2O  H2CO3

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)

Does the pH influence the activity of an enzyme? Trypsin is a digestive enzyme. Where? Intestinal pH range 7.0-8.5

The amino acid glycine - amphoteric It’s an acid and a base! Gain of H+ Loss of H+ H3N+-CH2-COOH H2N-CH2-COO- H2N-CH2-COOH Chime structure

- + The amino acid glycine - Zwitterion formation Transfer of H+ from carboxylic acid group to amine group. - + A dipolar ion forms. H2N-CH2-COOH Chime structure H3N+-CH2-COO- intramolecular acid-base reaction

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