Acids and Bases: Properties, Theories, and pH Calculations, Slides of Chemistry

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Acids and Bases

Properties of Acids

•^

Sour taste

-^

Change color of vegetable dyes

-^

React with “active” metals– Like Al, Zn, Fe, but not Cu, Ag or Au

Zn + 2 HCl



ZnCl

2

• H

2

• Corrosive -^

React with carbonates, producing CO

2

• Marble, baking soda, chalk

CaCO

3

• 2 HCl



CaCl

2

• CO

2

• H

O 2

•^

React with bases to form ionic salts– And often water

Arrhenius Theory

•^

Acids ionize in water to H

ions and anions

•^

Bases ionize in water to OH

ions and cations

•^

Neutralization reaction involves H

combining

with OH

to make water

•^

H

+^

ions are

protons

•^

Definition only good in water solution

-^

Definition does not explain why ammoniasolutions turn litmus blue– Basic without OH

-^ ions

Brønsted-Lowery Theory

•^

H

transfer reaction

• Since H

is a proton, also known as proton transfer reactions

•^

Acid is H

+^

donor; Base is H

+^

acceptor

• Base must contain an unshared pair of electrons -^

In the reaction, a proton from the acid molecule istransferred to the base molecule– H forms a bond to lone pair electrons on the base molecule– We consider only 1 H transferred in each reaction

-^

Products are called the

Conjugate Acid and Conjugate

Base^ – After reaction, the original acid is the

conjugate base

and the

original base is changed to what is now called the

conjugate

acid

Example

• Determine what species you will get if you

remove 1 H

from the acid

• The Conjugate Base will have one more

negative charge than the original acid

H

PO 3

4

H

+ H

PO 2

-1 4

Write the conjugate base for the acid H

PO 3

Brønsted-Lowery Theory

•^

In this theory, instead of the acid, HA, dissociating intoH

(aq) and A

(aq); The acid donates its H to a water

molecule

HA + H

O 2

A

-

+ H

O 3

+

A

is the conjugate base, H

O 3

is the conjugate acid

•^

H

O 3

+

is called

hydronium ion

•^

In this theory, substances that do not have OH

ions

can act as a base if they can accept a H

from water

H

O + :B 2

OH

-

+ H-B

+

Figure 15.1: Graphicalrepresentation of thebehavior of acids inaqueous solution

Figure 15.2: Therelationship of acidstrength andconjugate basestrength

Water as an Acid and a Base

-^

Amphoteric substances

can act as either an

acid or a base

• Water as an acid, NH

3

+ H

O 2

NH

+1 4

+ OH

• • Water as a base, HCl + H

O 2

H

O 3

• Cl

• • Water can even react with itself

H

O + H 2

O 2

H

O 3

+ OH

Autoionization of Water

• Water is an extremely weak electrolyte
  • therefore there must be a few ions present

H

O + H 2

O 2

H

O 3

+ OH

• • all water solutions contain

both

H

O 3

and OH

• • the concentration of H

O^3

and OH

are equal

– [H

O 3

] = [OH

] = 10

M @ 25°C

• K

w

= [H

O 3

] x [OH

] = 1 x 10

@ 25°C

– K

w^

is called the

ion product constant

for water

• as [H

O 3

] increases, [OH

-^ ] decreases

Example

Determine the given information and theinformation you need to find

Given [H

] = 10.0 M

Find [OH

]

Solve the Equation for the UnknownAmount

]

[H

K

]

OH[

]

[OH x ]

[H

K

w^1

(^1) -

(^1) -

1

w









Determine the [H

] and [OH

] in a

10.0 M H

solution

Convert all the information to ScientificNotation and Plug the given informationinto the equation.

Given [H

] = 10.0 M

= 1.00 x 10

1

M

K

w^

= 1.0 x 10

M

10 x

10 x

10 x

]

OH[

] K [H

]

OH[

(^15) -

14 1

(^1) -

w^1

(^1) -









Example

Determine the [H

] and [OH

] in a

10.0 M H

solution

Figure 15.3: The pHscale and pH valuesof some commonsubstances

Figure 15.4: A pH meter