acids and bases pgcc chm 101 sinex. general properties acids taste sour turn litmus react with...
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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
Bronsted-Lowry
Lewis
only in water
any solvent
used in organic chemistry,wider range of substances
Examples
Arrhenius
Bronsted-Lowry
Lewis
HCl NaOH
HCl NH3
:NH3BF3
HCN
The hydrogen ion in aqueous solution
H+ + H2O H3O+ (hydronium ion)
The Bronsted-Lowry Concept
Conjugate pairs
HCl Cl- CH3COOH CH3COO-
NH4+ NH3 HNO3 NO3
-
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
H2SO4 + NaHCO3
H2O H+ + OH-
Does pure water conduct electrical current?
(H+)(OH-) = 10-14
For pure water: (H+) = (OH-) = 10-7M
This is neutrality and at 25oC 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+
A-
Strong Acid
100% dissociation of HA
Would the solution be conductive?
HA
H+
A-
Weak Acid
Partial dissociation of HA
Would the solution be conductive?
HA
H+
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
HCl NaOHHNO3 KOHH2SO4
Weak acids/bases – partial dissociation, both ions and molecules
CH3COOH NH3
pH
2 3 4 5 6 7 8 9 10 11 12
neutral @ 25oC(H+) = (OH-)
distilled water
acidic(H+) > (OH-)
basic or alkaline(H+) < (OH-)
natural waters pH = 6.5 - 8.5
normal rain (CO2)pH = 5.3 – 5.7
acid rain (NOx, SOx)pH of 4.2 - 4.4 in Washington DC area
0-14 scale for the chemists
fish populationsdrop off pH < 6 and to zero pH < 5
You are
here!
http://nadp.sws.uiuc.edu/isopleths
pH of Rainwateracross United States in 2001
Incre
asin
g a
cidity
Why is the eastern US more acidic?
air masses
What is acid rain?
CO2 (g) + H2O H2CO3 H+ + HCO3-
Dissolved carbon dioxide lowers the pH
Atmospheric pollutants from combustion
NO, NO2 + H2O … HNO3
SO2, SO3 + H2O … H2SO4
bothstrong acids
pH < 5.3
105
Db107
Bh
Behavior of oxides in water– Group Abasic amphoteric acidic
3A 4A 5A 6A 7A
1A
2A
8A
Group B
basic: Na2O + H2O 2NaOH(O-2 + H2O 2OH-)
acidic: CO2 + H2O H2CO3
When life goes either wayamphoteric (amphiprotic) substances
HCO3-
H2CO3 CO3-2
+ H+ - H+
Acting like a base
Acting like an acid
accepts H+ donates H+
pH
1 2 3 4 5 6 8 9 10 11
The biological view in the human body
gastric juice
vaginal fluid
urinesalivacerebrospinal fluid
bloodpancreatic juice
bileacidic basic/alkaline
7
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 - amphotericIt’s an acid and a base!
Loss of H+Gain of H+
H2N-CH2-COOH
H3N+-CH2-COOH H2N-CH2-COO-
Chime structure
The amino acid glycine - Zwitterion formation
Transfer of H+ from carboxylic acid group to amine group.
H2N-CH2-COOHH3N+-CH2-COO-
+ -
A dipolar ion forms.
intramolecular acid-base reaction
Chime structure
Show how water can be amphoteric.
H2O
+ H+ - H+
Dilution
water (solvent) solute
concentrated, Minitial
diluted, Mfinal
adding water lowers the solute concentration
moles of solute remain constant
Vinitial
Vfinal
molesinitial = molesfinal
Mfinal x Vfinal = Minitial x Vinitial
Titration Calculation
HCl + NaOH NaCl + HOH
at equivalence point: moleHCl = moleNaOH
moles = M x VL
Macid x Vinitial acid = Mbase x Vburet
A way to analyze solutions!
indicator