ACIDS AND BASES

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ACIDS AND BASES
Acids found around the house
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Citric - all citrus fruit
Acetic acid – vinegar
Carbonic – soda
Tannic – tea
Lactic- milk, yogurt
Sulfuric – car battery
Hydrochloric – metal and masonry cleaning
• Organic acids are those made by an organism
• Mineral acids or inorganic are those that can be
made directly at the lab bench, also referred to
as industrial acids.
3 Common Industrial Acid
1. Sulfuric ( H2SO4 ) used in most manufacturing
Conc 98 % , specific gravity 1.84g/ml
dilute = 1 part acid to 5 parts water
2. Hydrochloric (HCl ) masonry and metal
cleaning .
Conc 36 % , specific gravity 1.19 g/ml
dilute = 1 part acid to 4 parts water.
3 Nitric acid ( HNO3 ) Tanning leather, making
fertilizer and explosives
Conc 70 % Specific gravity 1.42 g/ml
dilute = 1 part acid to 3 parts water
Demo the three.
Acids
• Have a sour taste
• Affect indicators
blue litmus turns red
• Acids neutralize bases
to make a salt + water
• Are electrolytes
• Many React with metals
to release hydrogen
Bases
• Have a bitter taste
• Affect indicators
red litmus turns blue
B-B base = blue
• Bases neutralize acids
to make a salt + water
• Are electrolytes
• Feel slippery
Common bases around the house
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Milk of magnesa Mg(OH)2
Draino NaOH
House hold Ammonia NH4OH
Rolaids Mg(OH)2 / CaCO3
Tums Al(OH)3 ?
Milanta , peptobismo
Lime CaO for the lawn. Plus H2O makes
Ca(OH)2
Arrhenius’s Theory of ionization
H+
•
H2O + H2O → H3O+
+
OH• Water + water yields Hydronium ion
+
hydroxide ion
• If H2O loses an H+ what do you have left?
an OH- ion
• You get 1.0 x 10-7 H3O+ and 1.0 X 10-7
OH- for every liter of pure water.
• Notice that the hydronium and hydroxide ion
concentrations are equal, that’s a neutral
solution.
• When H3O+ > OH- its an acid
• When OH- > H3O+ it’s a base
• The pH scale is a system to express the
“ power of hydronium” .
The pH of a neutral solution is 7
The H3O+ concentration is 1.0 X 10 -7
When pH is 3,
[H3O+ ] = 1.0 x 10 -3
When pH is 9
[H3O+ ] is 1.0 x 10 -9
[ ] means concentration in moles/liter is
• This true so long as the conc is 1.0 times the
exponent.
• If its not, its math time.
• pH = -log( H3O+ )
• What is the pH when[ H3O+ ] is 3.4 x 10-5 ?
• - log 3.4 2nd ee – 5 ) enter
• You get 4.468521 or 4.47 as the pH
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Other direction
pH = 4.47 what is the [H3O+] ?
Antilog ( -ph ) = [ H3O+ ]
2nd log - 4.47 ) enter
You get 3.4 x 10-5
Back to Arrhenius
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In a neutral solution [ H3O+ ] = [ OH- ]
Because both equal 1.0 x 10-7
[ H3O+ ] X [ OH- ] = 1.0 x 10-14
Which is a constant, so given either the [H3O+]
or the [OH- ] you can solve for the other.
• [ H3O+ ] = 1.0 x 10-14
[ OH- ]
[ OH- ] =
1.0 x 10-14
[ H3O+ ]
pOH = -Log[OH]
pH + pOH = 14
if you know either the pH or the pOH, just
subtract the one you have from 14 and you have
the other one.
• Bronsted and Lowery
Defined an acid as a proton donor and a base as a
proton accepter.
There for any substance that contains ionizable
hydrogen is an acid.
And any negative ion can be a base.
HCl
+ H2O → H3O+ + Cl-
in the forward reaction the HCl is the acid and
the water is the base.
Short form
HCl → H+ + Clit is assumed you know
the water is required.
Conjugate acid base pairs
A conjugate base is a base that is produced when
an acid gives up a proton.
H2SO4 → HSO4- + H+
In this case the HSO4- is the base produced when
the H2SO4 gave up the H+ because the bisulfate
ion has a negative charge it is a base according
to Bronsted/Lowery
The only difference between a conjugate acid/base
pair is one stinking hydrogen.
The acid has it and the base does not.
So to determine the conjugate base all you do is
subtract one H from the acid and make the
resulting ion (-)
Do some practice problems
Monoprotic acids only have one ionizable
Hydrogen , ionizable means that the H can be
seperated from the rest of the formula. HCl,
HNO3, H C2H3O2
Diprotic acids have two ionizable hydrogens
H2SO4 and H2CO3
Triprotic acids have three.
Write some ionization equations
H3PO4
Amphprotic substances are those that can act as
either an acid or a base.
The HSO4- ion has an ionizable Hydrogen and a
negative charge. So it can give up the H to act
as an acid or since its negative it can accept an H
to act as a base.
These substances are commonly called Buffers.
Why?
Titration
• Acid buret
Base buret
The Process of reacting a solution of known concentration with one of unknown concentration
to determine The concentration of the unknown solution.
Titration uses knowledge of balanced equations
and mass/mass problems to determine the
concentration of an unknown solution.
If you know the moles of one reactant, it is
possible to calculate the moles of the other
from the balanced equation. Then if volume of
liquid is also known, molarity can be
determined.
This sounds hard, but there is an easy way to do it
if we convert molarity to normality.
Normality / + charge = molarity
So
Molarity x ( + charge ) = normality
.4M H2SO4
.4M x +2 (from the two H’s)=.8N
Titration equation
Normaliy of acid x volume of acid = Normality
of base x volume of base.
NaVa = NbVb
easy math plug in the three knowns and solve for
the missing one.
If necessary convert back to molarity
Titration curve and equivalence
point
The equivalence point is the point where you have
added an equivalent amount of base to the acid
which will just neutralize the acid. The indicator
will change color and your done. ( the end point)
Strong and weak acids
HCl → H+ + Cl-
100 molecules → 100 ions + 100 ions
Every molecule of acid ionizes, that a strong acid.
HC2H3O2 → H+ + C2H3O2100 molecules → 10 ions + 10 ions + 90
HC2H3O2 that did nothing , that’s a weak acid.
Only 10 % of the acid did any thing.
Strong and weak bases do the same thing.
Acid Anhydrides
Non metallic oxides that react with water to form
and acid. That’s what causes acid rain.
SO2 + H2O → H2SO3 sulfurous acid
CO2 + H2O → H2CO3 carbonic acid
Basic anhydride
Is a metallic oxide that reacts with water to form a
base.
CaO + H2O → Ca(OH)2
Any of the group I or II elements do the same
thing.
Naming acids
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Binary acids , contain only two elements
HCl Hydro-chloric acid
HF
Hydro-floric acid
HBr Hydro-bromic acid
HI
Hydro-iodic acid
Ternary or Oxy acids
• Contain Hydrogen , oxygen and a third element.
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per = 1 more (O) HClO4
Root acid
HCLO3
1 less (O)
HClO2
2 Less (O)
HClO
perchloric acid
chloric acid
chlorous acid
hypochlorous
Other Root acids
• If you understand the previous system, and Know the
names and formulas of the following root acids,
(memorize them) naming oxy-acids is easy.
• H2SO4 - sulfuric acid
• HNO3 - nitric acid
• H2CO3 - carbonic acid
• H3PO4 - phosphoric acid
• HCLO3 - chloric acid
Making acid solutions from the
concentrated liquid
• Question : How much concentrated sulfuric acid
is needed to make 400ml of .3M H2SO4 ?
• Using molarity x fw x Liters = grams
• .3 M x 98 x .400 L = 11.7 grams H2SO4
so how many ml of the conc liquid do we need?
Concentrated H2SO4 is 98 % acid and has a
specific gravity of 1.84g/ml
• That means each ml of the acid has a mass of 1.84 grams.
1.84 gram
x .98
1.80 grams dry weight per ml
From above we needed 11.7 grams dry weight
11.7 grams x 1 ml
=
1.80 grams
6.6 ml of conc H2SO4
Place 6.6 ml of conc acid in a graduated cylinder and add enough
water to bring the total volume to 400ml and you are done.
I forgot about Lewis acids
Work in progress
not done yet
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