Chemistry 1105 background An extremely large class of reactions Found in Biochemistry Cleaning products Industrial fabrication foods Theory Historically known but not understood GayLussac defined them in 1814 ID: 569576
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Slide1
Acids-Bases and Indicators
Chemistry 1105Slide2
background
An extremely large class of reactions
Found in
Biochemistry –
Cleaning products
Industrial fabrication
foodsSlide3
Theory
Historically known but not understood
Gay-Lussac defined them in 1814
But in terms of each other
Svante Arrhenius won the Nobel Prize for his definition the Acids and Base work
This is still the one most often used for acids and bases Slide4
Definitions
Arrhenius Acid
Releases hydrogen ion
Produces
H
3
O
+
HNO
3
+ H
2
O
→ H
3
O
+
+ NO
3
-
Arrhenius BASE
Releases OH ion in water
NaOH + H
2
O
Na
+
+ OH
-
+
H
2
OSlide5
Strong vs. Weak
Strong Acid/Base
Completely Dissociates
No Equilibrium
No Reactants Are Observed After Reaction
HNO
3
+ H
2
O
→ H
3
O
+
+ NO
3
-
NaOH + H
2
O
→ Na
+
+ OH
-
+ H
2
O
Only Few Strong Acids And BasesSlide6
Strong vs. Weak
Weak Acid/Base
Partially Dissociates
Reaction Is In Equilibrium
Products And Reactants Observed
HF + H
2
O ↔ H
3
O
+
+ F
-Slide7
pH
Reference is Water
Water is amphoteric- Characteristics of both acid and base
H
2
O + H
2
O ↔ H
3
O+ + OH
-
In Pure Water,
[H
3
O+] = 1.0 x 10^(-7)
[OH
-
] = 1.0 x 10^(-7)
pH = -log [H
3
O+] = -log(1.0 x 10^(-7)) = 7
Most water is not 7
Our is between 4-5Slide8
history
Brønsted and Lowery in 1923
Showed that an acid or a base could be donors and acceptors with a H present
HF + H2O ↔ H3O+ + F-
And as in water
H
2
O ↔ H+ + OH
-
Where HO- a
Lewis base
and H+ the
Lewis acid
. Slide9
Indicators
Complex molecules that absorb light at different wavelengths
Acid or a base and it reacts with the compound
Changes the wavelength and thus the colorSlide10
Indicators
Iitmus paper- made from lichens
Red, acid,
Blue, base
Lots of possible indicators and more daily
Thymolblue
Methyl orange
Yamada is a universal indicator
Red to orange in acid, green at neutral, and blue to indigo in acidSlide11
Acid Content
The number of hydrogen ions available in the acid
Sulfuric acid H
2
SO
4
ACID CONCENT =2
HCl = 1
Measured by TitrationsSlide12
Titrations
Titration
is a procedure used to determine the concentration of an acid or base.
Neutralization HCl+NaOH
NaCl+H
2
O
Need to know
The initial concentration of the base
The initial volume of acid
The amount of base that is used to neutralize the acid Slide13
Titration
Moles of acid = moles of the base
Changes pH starts acidic goes basic
At neutralization of strong acid and strong base =7 Neutral.
Not always 7, Depends on the acid and the baseSlide14
Experimental Procedure
Acid and Base
In 5 wells 3 drops of X and 3 drops of Y
Using litmus paper blue and red record reaction
One drop yamada, thymolblue, methy orange
pH scale
10 wells add one drop of each of the std solutions1-10
Then add I drop yamada, record colorSlide15
pH scale
Determine the pH of the X and Y
Now test pH using Yamada
Nitric acid (0.1 M)
Acetic acid (0.1 M)
Ammonia hydroxide (0.1 M)Slide16
Titration
Use unknown acid from above
Add one drop in each of 10 wells
Add one drop Yamada to each
well number 1 add 1 drop NaOH
Well number 2 add 2 drops etc. to ten with 10 drops
Now repeat with the other unknown base and titrate with acid Slide17
1) Place 3 drops of solution X
Place 3 drops of solution Y
2) Test pH with red and blue litmus paper,
Yamada, bromocresol, and thymol blue
Indicators.
3)Place 5 drops of each pH solution 1-10 in
Separate wells.
Add one drop of YAMADA indicator
4)Using the scale determine pH of solutions
X and Y.
5) Take 5 drops of 0.1M nitric acid and 5 drops
of 0.1M acetic acid and test with Yamada indicator
Creating a pH scale
1
2
3
4
5
6
7
8
9
10
NOTE: THE COLORS ARE JUST AN EXAMPLE DO NOT REPRESENT REAL
COLORS IN THE EXPERIMENT
1
X
Y
Slide18
How should it look?Slide19
Titration
In 12 different clean wells place:
1 drop of BASE (unknown X or Y) to each wells
1 drop of indicator
Titrate with base HCl 0.005M adding
1 drop to well 1
2 drops to well 2
3 drops to well 3
Continue until you find the green neutral colorSlide20
Titration
Add 0.005M NaOH
In 12 different clean wells place:
1 drop of ACID (unknown X or Y) to each wells
1 drop of indicator
Titrate with base NaOH 0.005M adding
1 drop to well 1
2 drops to well 2
3 drops to well 3
Continue until you find the green neutral colorSlide21
Titration
In 12 different clean wells place:
1 drop of ACID (unknown X or Y) to each wells
1 drop of indicator
Titrate with base NaOH 0.005M adding
1 drop to well 1
2 drops to well 2
3 drops to well 3
Continue until you find the green neutral colorSlide22
Acid and Base
Which well is neutralization
How many drops
Do report
(Note: Each drop is 0.05 mls)