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strength of Acids and Bases strength of Acids and Bases

strength of Acids and Bases - PowerPoint Presentation

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strength of Acids and Bases - PPT Presentation

amp Salts and Buffers Chapter 193 and 195 Notes 21 Part 1 Strengths of Acids and Bases How is there is a difference Citrus fruits contain citric acid that we can eat Industrial companies use sulfuric acid that can cause severe burns to the skin ID: 269225

buffer acid weak base acid buffer base weak buffers acids bases salt solution dissociation blood added constant strong strength

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Slide1

strength of Acids and Bases&Salts and Buffers

Chapter 19.3 and 19.5

Notes #21Slide2

Part 1: Strengths of Acids and BasesSlide3

How is there is a difference?Citrus fruits contain citric acid that we can eat.Industrial companies use sulfuric acid that can cause severe burns to the skin.Why are some acids weak and some acids strong?Slide4

Determining the Strength of an AcidUse the acid dissociation constant (Ka) is a ratio:

Weak acids have small

Ka

values.

=Less dissociation/ Slightly ionize

The stronger an acid is, the larger is its

Ka

value

.

=More dissociation/ Completely Ionize

Dissociated

Non-DissociatedSlide5

Larger Ka = Stronger AcidSlide6

Strength of BasesSimilar to acids, bases have the base dissociation constant (Kb).

Strong bases

: dissociate completely into the hydroxide ion and metal ion.

Weak Bases

: dissociate slightly into hydroxide ion and conjugate acid.Slide7

Table of Relative StrengthsSlide8

Explain

In the graph for the strong acid, why are the heights of H

3

O

+

and A

-

bars the same as the height of the HA bar?

Inferring

In the graph of the weak acid, why is the height of the H

3O+ the same as the distance from the top of the second HA bar to the dotted line?Slide9

Calculate the Ka of a weak acid.Slide10
Slide11
Slide12

Part 2: Buffers and SaltsSlide13

What is a salt?It is a compound that contains an anion from an acid and a cation from a base. They form as a result of an acid-base neutralization reaction.

Not just table salt! Although, this is also considered a salt.

HCl

+

NaOH

 NaCl + H

2

O

KOH + HNO

3

 KNO3

+ H2OSlide14

Solutions made from these salts can be neutral, acidic, or basic.Slide15

Universal indicator solution has been added to each of these 0.10

M

aqueous salt solutions.

NH

4

Cl

pH 5.3

NaCl

pH 7

CH

3

COONa

pH 5.3

Universal Indicator

: Like a liquid pH strip. Changes the solution to a color to tell you the

pH.Slide16

BuffersA Buffer is made by making a solution that contains a mixture of:a

weak acid and its salt or

a weak base and its salt.

Characteristics of a Buffer Solution:

The pH of a

buffer remains relatively constant when small amounts of acid or base are added. The buffer capacity

is the amount of acid or base that can be added to a buffer solution before a significant change in pH occurs.Slide17
Slide18

Buffers Contd…Buffers have neutralizing “powers”. In a sense, it eats up the acid or base you have to remain at a constant

pH.

Eventually, the buffer will be used up, and the pH can then change dramatically. Slide19

How to choose a BufferThe pH of the acid or base being added to the buffer should be within the pH range of the buffer.

Buffer System

pH Range

Monohydrogen

phosphate/

dihydrogen

phosphate

6.1-7.4

Ethanoate

/

ethanoic

acid3.7-5.6Carbonate/ hydrogen carbonate

9.2-11.0Phosphate/ monohydrogen phosphate11.0-12.0

Question: Which of these buffers would be effective at pH 5.0?Slide20

Importance of Buffers

The chemical processes inside a living cell are very sensitive to

pH.

Human

blood is normally maintained at a pH very close to 7.4.

You have learned

about chemical processes that ensure that the pH of blood is kept near 7.4.

Buffer: Carbonic Acid/bicarbonateSlide21

The Buffer in Our BloodAn abnormal pH level of the blood can be due to several factors: overexerting your body through exercise, improper diet, drug consumption, and other biological factors such as kidney failure (since the kidneys are responsible for removing excess H+ ions and other components of the pH

buffer).

Below 6.8 (acidosis) or above 7.8 (alkalosis) will result in death.