ACIDS AND BASES

ACIDSTaste sourTurn litmusReact with active

metals – Fe, Zn

React with bases

BASESTaste bitterTurn litmusFeel soapy or

slippery (react with fats to make soap)React with acids

GENERAL PROPERTIES

blue to red red to blue

Acids – produce H+

Bases - produce OH-

Acids – donate proton (H+)

Bases – accept proton (H+)

Acids – accept e- pair Bases – donate e- pair

DEFINITIONS

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 solutionH+ + 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

A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor

acid conjugate basebase conjugate

acid

CONJUGATE PAIRS

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-) =

This is 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

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

KW: THE ION-PRODUCT CONSTANT OF WATER

If water conducts electricity, ions must exist Water exists as an equilibrium, which is referred to

as the of water:H2O + H2O

Simplified reaction:

Kc =[H3O+] [OH–]

[H2O]2Kw =or

Note: H+ is just shorthand for H3O+

Kc =[H+] [OH–]

[H2O]Kw =or

KW What is the value of Kw?

It has been measured at

To determine the pH of a substance we look for the following relationship between [H+] and [OH-]:

when the solution isacidicbasic

neutral

Pure water is neutral since [H+] and [OH–] must be

PH When there is a change in [H+] it is by

a change in [OH–], since Kw is constant, and must always equal

[H+] is commonly referred to because it is critical to chemical and biochemical reactions

A quick method of denoting [H+] is via pH By definition

The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of ‘6’ is as violent as a ‘5’

Thus, the pH scale condenses possible values of [H+] to a

CALCULATIONS WITH PH pH = – log [H+], what is pH if [H+] = 6.3 x

10–5?

• What is [H+] if pH = 7.4?• To solve this we must rearrange our equation

[H+] = 10–pH mol/L

EQUATIONS AND PRACTICE

pH =

• You will need to memorize the following:

pOH =

[H+] = [OH–] =

pH + pOH =

MEASURING PH pH can be measured in several ways Usually it is measured with a

Colored indicators are a crude measure of pH, but are useful in certain applications

MEASURING PH pH meters are more

accurate, but they must be calibrated prior to use

Calibration means setting to a

A pH meter is calibrated with a solution of known pH often called a

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+

Show how water can be amphoteric.

H2O

+ H+ - H+

Dilutionwater (solvent) solute

concentrated, Minitial

diluted, Mfinal

adding water lowers the solute concentration

moles of solute remain constant

Vinitial

Vfinal

molesinitial = molesfinal

Titration CalculationHCl + NaOH NaCl + HOH

at equivalence point: moleHCl = moleNaOH

A way to analyze solutions!

indicator