Transcript Acids and Bases - Bishop Montgomery High School


Dissociation: when Ionic compounds dissolve
in water, the ions _____________
E.g.

NaCl(s) 

FeCl3(s) 

Al2N3(s) 

Ca(OH)2(s) 
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Precipitation Reactions (aka Double Rep. rns)
When 2 aqueous (aq) solutions combine to
form a
. (insoluble compound)
What are compounds are insoluble?
See Table B-9 (p.R54) & Table 18-1 (p.561)
E.g.
Will the following dissolve or not?
◦ KCl
CaCO3
Double Replacement Rns:
KCl(aq) + AgNO3(aq)  ?
Na2SO4(aq) + BaCl2(aq)  ?
BaSO4
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Includes only those compounds & ions that
undergo a
change in an aqueous solution.
E.g. (Using the previous Double Rep. rns)
(1) KCl(aq) + AgNO3(aq)  ?
Separate all aqueous compounds
K+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)  K+(aq) + NO3-(aq) + AgCl(s)
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Now cross out like terms  Net Ionic Eqn:
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(2) Na2SO4(aq) + BaCl2(aq) 
Acids are composed of
(HF, HCl,
HI, HBr or H2S) or
(HNO3, H2SO4,
H3PO4, H2CO3…) that are dissolved in water.
i.e. all acids are aqueous solutions.
e.g. Hydrochloric Acid
HCl(aq) 

just a proton (+) : does not want to exist by
itself, so it attaches itself to a water molecule.
i.e. HCl(aq) + H2O(l) 

Hydronium Ion
Strong electrolytes are any soluble
substance/compound that (almost) completely
dissolves and separates into its ions.
e.g. all soluble salts like:
and most acids like:
Weak electrolytes are where only a small amount
dissolves and separates into its ions (and may
reverse back.)
e.g. weak acids: CH3COOH acid (Acetic Acid – Vinegar)
CH3COOH(aq) 
e.g. very strong acid: HF (why?)
HF(aq) 
How to recognize an acid…
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_________ (but don’t taste 
them)
Change colors of an
______________________
Some react with metals to
produce ___ gas (a useful
test in the lab)
React with ________ to
produce ________ in soln.
Conducts ___________
How to name an acid
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______ acids: contain
only __ different
elements; hydrogen
and an
electronegative atom
(non-metal)
_________: acids that
have oxygen as well
as hydrogen and a
non-metal
Common acids
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Industrial
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__________ acid: used in fertilizer, dehydrating
agent (that is what makes it dangerous to you)
________ acid: volatile acid used ion explosives
_________ acid: non-toxic when diluted used in
beverages (Coke) and cleaning solution
___________ acid: Organically produced by the
stomach. AKA muriatic acid is used in pools. Can
be used to remove metal impurities
_______ acid: vinegar: (good for egg dying) In
a pure form it can freeze in a cold room (17ºC)
How to recognize a
base

____________ (but again don’t
taste them)
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Change colors of an _________
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Dilute bases are _______ (more
so than plain water)
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React with ____ to produce ___
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Conducts ____________
How we define acids and
bases
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Acids and bases have many characteristics,
thus we define them based on which
characteristic is helpful or important for
the situation
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For today we will look at the __________
definition
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__________ acids and bases are defined
looking at their conductivity and so,
necessary production of ions. (Svante
Arrhenius 1859-1927)
Arrhenius Acids
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Arrhenius acid: Produces ___ ions in an
aqueous solution (these ___ ions are taken
up by water immediately)
Strong acid ionizes completely… giving up all
available ___
Weak acids give up some ___ ions but hold
on to others
Arrhenius Base
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+
+
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Arrhenius base makes
_____ ions in solution
Strong base makes lots
of _____ ions… ionizes
completely
Weak base makes
some _____ ions but
some do not ionize
Show how each of these would react with
water based on Arrhenius definitions…
HBr(g) + H2O(l)

NaOH(s) + H2O(l) 
Water is an extremely weak electrolyte.
A few of the water molecules
H2O(l)  H+(aq) + OH-(aq)
i.e. 2 water molecules (via a proton transfer)
become a
ion & a
ion.
H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
Out of 5.5x108 molecules of water, only ONE will
do this – very WEAK! And therefore too weak
to conduct electricity.
This equates to a concentration of:
M = 1x10-7 mol/L  (M = 1x10-7M)
A new way to represent concentration (instead of
M ) is
i.e.
&

And
is always constant.
So, the Ionisation constant of water (KW) is:
KW =
= (1x10-7M)(1x10-7M)
KW =
@ 25oC
(KW will increase slightly with increasing Temp.)
If a solution is neutral, then [H+] must = [OH-]
e.g.
Acids produce a higher concentration of H+ ions.

Bases produce a higher concentration of OH- ions.

[H+]
> 1x10-7M
= 1x10-7M
< 1x10-7M
[OH-]
E.g. What is the concentration of [H+] & [OH-] in a
1x10-3M HCl(aq) solution?
HCl has 1 H+ (
) in its formula and
 [H+] = 1x10-3M
[H+][OH-] = KW
[OH-] =
KW .
[H+]
[OH-] =
E.g. What is the concentration of [H+] & [OH-] in a
3x10-4M H2SO4(aq) solution?
H2SO4 has 2 H+‘s (
) in its formula and
 [H+] =
[H+] =
[H+][OH-] = KW
[OH-] =
KW .
[H+]
[OH-] =
E.g. What is the concentration of [H+] & [OH-] in a
1.4x10-5M H3PO4(aq) solution?
H3PO4 has 3 H+ ‘s(
) in its formula and
 [H+] =
[H+] =
[H+][OH-] = KW
[OH-] =
KW .
[H+]
[OH-] =
E.g. What is the concentration of [H+] & [OH-] in a
5x10-6M KOH(aq) solution?
KOH has 1 OH- in its formula and
 [OH-] =
[OH-] =
[H+][OH-] = KW
[H+] =
KW .
[OH-]
[H+] =
E.g. What is the concentration of [H+] & [OH-] in a
4x10-3M Ca(OH)2(aq) solution?
Ca(OH)2 has 2 OH- ‘s in its formula and
 [OH-] =
[OH-] =
[H+][OH-] = KW
[H+] =
KW .
[OH-]
[H+] =
The pH scale
Using concentrations is not a convenient way to
express the acidity or basicity of a solution.
A better way is to represent the concentration
using a pH scale.
pH means “
” which is French
for “
”.
Defn: “The pH of a solution is defined as the
negative log of the hydronium concentration.”
pH =
For example, water – considered a neutral
solution, has the following pH level.
pH = -log[H+]
=
=
pH =
An acid has a higher concentration of H+ ions
and so the concentration will have a lower
negative 10 power.
Therefore, for an acid, the pH level will be
So, for a base, the pH level will be
See Table 19-5 (p.598)
Examples:
What is the pH of a 1x10-4M HNO3 solution?
HNO3 is monoprotic acid,
 [H+] =
What is the pH of a 4x10-6M H3PO4 solution?
What about Bases?
What is the pH of a 2x10-3M KOH solution?
First: [OH-] = 2x10-3M
[OH-] = 2x10-3M
(because it’s a base)
[H+][OH-] = KW
=
pH = -log[H+]
=
pH =
Titration
Analytical method in which a
___________ solution
(acid/base) is used to
determine the
concentration of an
unknown solution
(base/acid).
_________ solution
unknown solution
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Setup for titrating an acid with a base
• Equivalence point (endpoint)
Point at which equal amounts of ___ and ____ have been
added.
Determined by…
-________ color change (due to:)
-dramatic change in ____
Measuring pH with wide-range paper
Narrow-Range pH Paper
Some Acid-Base Indicators
Indicator
Crystal violet
Thymol blue
Orange IV
Methyl orange
Bromcresol green
Methyl red
Chlorophenol red
Bromthymol blue
Phenol red
Neutral red
Thymol blue
Phenolphthalein
Thymolphthalein
Alizarin yellow
Indigo carmine
pH Range in which
Color Change Occurs
0.0 - 1.6
1.2 - 2.8
1.4 - 2.8
3.2 - 4.4
3.8 - 5.4
4.8 - 6.2
5.2 - 6.8
6.0 - 7.6
6.6 - 8.0
6.8 - 8.0
8.0 - 9.6
8.2 - 10.0
9.4 - 10.6
10.1 - 12.0
11.4 - 13.0
Color Change
as pH Increases
yellow to blue
red to yellow
red to yellow
red to yellow
yellow to blue
red to yellow
yellow to red
yellow to blue
yellow to red
red to amber
yellow to blue
colorless to pink
colorless to blue
yellow to blue
blue to yellow
The concentration (M) of a standard is known (usually a
base, like NaOH). It is used to determine the unknown
concentration of an acid (like HCl).
The equivalence point is when the number of moles of H+
ions is equal to the number of moles of OH- ions.
moles H+ = moles OH-
Where:
= # H+’s in the acid’s formula, and
= # OH-’s in the base’s formula.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Example:
A titration shows that 42.5 mL of 1.3M KOH are
required to neutralize 50.0 mL of H2SO4. Find the
concentration of H2SO4.
Example:
35.62 mL of NaOH is neutralized with 25.2 mL of
0.0998 M H3PO4 by titration to an equivalence
point. What is the concentration of the NaOH?