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Acids and Bases. PGCC CHM 101 Sinex. 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. General properties. blue to red. red to blue. Definitions.

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acids and bases

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

General properties

blue to red

red to blue

definitions
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
Examples

The hydrogen ion in aqueous solution

H+ + H2O  H3O+ (hydronium ion)

Arrhenius

HCl

NaOH

Bronsted-Lowry

HCl

HCN

NH3

:NH3

Lewis

BF3

the bronsted lowry concept
The Bronsted-Lowry Concept

Conjugate pairs

CH3COOHCH3COO-

HCl Cl-

NH4+NH3

HNO3NO3-

How does a conjugate pair differ?

H+transfer

neutralization
Neutralization

In general: Acid + Base  Salt + Water

All neutralization reactions are double displacement reactions.

HCl + NaOH  NaCl + HOH

HCl + Mg(OH)2

H2SO4 + NaHCO3

slide7

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

slide8

Let’s examine the behavior of an acid, HA, in aqueous solution.

HA

What happens to the HA molecules in solution?

slide9

100% dissociation of HA

HA

H+

Strong Acid

A-

Would the solution be conductive?

slide10

Partial dissociation of HA

HA

H+

Weak Acid

A-

Would the solution be conductive?

slide11

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 and Weak Acids/Bases

Strong acids/bases – 100% dissociation into ions

HClNaOH

HNO3KOH

H2SO4

Weak acids/bases – partial dissociation, both ions and molecules

CH3COOHNH3

slide13

acid rain (NOx, SOx)

pH of 4.2 - 4.4 in Washington DC area

pH

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

slide14

Increasing acidity

pH of Rainwater

across United States in 2001

You are here!

air masses

Why is the eastern US more acidic?

http://nadp.sws.uiuc.edu/isopleths

what is acid rain
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

slide16

105

Db

107

Bh

Behavior of oxides in water– Group A

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

slide17

- H+

+ H+

When life goes either way

amphoteric (amphiprotic) substances

Acting like

a base

Acting like an acid

HCO3-

H2CO3

CO3-2

accepts H+

donates H+

slide18

pH

The biological view in the human body

acidic

basic/alkaline

1

2

3

4

5

6

7

8

9

10

11

blood

saliva

urine

gastric juice

pancreatic juice

vaginal fluid

bile

cerebrospinal fluid

Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003)

slide19

Does the pH influence the activity of an enzyme?

Trypsin is a digestive enzyme. Where?

Intestinal pH range 7.0-8.5

slide20

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

slide21

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

slide22

- H+

+ H+

Show how water can be amphoteric.

H2O

slide23

Dilution

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

slide24

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