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
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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.Slide10Slide11Slide12
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.Slide17Slide18
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.