Acids n Bases_2
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Transcript of Acids n Bases_2
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2Acids
Have a sour taste. Vinegar is a solution of acetic acid. Citrus
fruits contain citric acid.
React with certain metals to produce hydrogen gas.
React with carbonates and bicarbonates to produce carbon
dioxide gas
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Bases
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Acid and Bases
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Acid and Bases
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Acid and Bases
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Some Properties of Acids
Produce H+ (as H3O+) ions in water (the hydronium ion is a
hydrogen ion attached to a water molecule)
Taste sour
Corrode metals
Electrolytes
React with bases to form a salt and water
pH is less than 7
Turns blue litmus paper to red Blue to Red A-CID
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Some Properties of Bases
Produce OH- ions in water
Taste bitter, chalky
Are electrolytes
Feel soapy, slippery
React with acids to form salts and water
pH greater than 7
Turns red litmus paper to blue Basic Blue
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Acid/Base definitions
Definition #1: Arrhenius (traditional)
Acids produce H+ ions (or hydronium ionsH3O
+)
Bases produce OH- ions
(problem: some bases dont have hydroxideions!)
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9Arrhenius acid is a substance that produces H+ (H3O
+) in water
Arrhenius base is a substance that produces OH- in water
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Acid/Base Definitions
Definition #2: Brnsted Lowry
Acids proton donor
Bases proton acceptor
A proton is really just a hydrogenatom that has lost its electron!
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A Brnsted-Lowryacidis a proton donor
A Brnsted-Lowrybaseis a proton acceptor
acid conjugatebase
base conjugateacid
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ACID-BASE THEORIES
The Brnsted definition means NH3 isaBASEin water and water isitself anACID
BaseAcidAcidBase
NH4+ + OH-NH3 + H2O
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Conjugate Pairs
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Learning Check!
Label the acid, base, conjugate acid, andconjugate base in each reaction:
HCl + OH- Cl- + H2O
H2O + H
2SO
4 HSO
4- + H
3O+
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15Acids & Base Definitions
Lewis acid - asubstance that
accepts an electronpair
Lewis base - asubstance thatdonates an electronpair
Definition #3 Lewis
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Formation ofhydronium ion is also anexcellent example.
Lewis Acids & Bases
Electron pair of the new O-H bondoriginates on the Lewis base.
HH
H
BASE
OHOH
H+
CID
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Lewis Acid/Base Reaction
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The pH scale is a way ofexpressing the strength ofacids and bases. Instead ofusing very small numbers, wejust use the NEGATIVE powerof 10 on the Molarity of the H+(or OH-) ion.
Under 7 = acid7 = neutral
Over 7 = base
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pH of Common
Substances
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More About Water
H2O can function as both an ACID and a BASE.
In pure water there can beAUTOIONIZATION
Equilibrium constant for water = Kw
Kw = [H3O+
] [OH-
] = 1.00 x 10-14
at 25o
C
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pH [H
+
] [OH
-
] pOH
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22pH testing
There are several ways to test pH
Blue litmus paper (red = acid)
Red litmus paper (blue = basic)
pH paper (multi-colored)
pH meter (7 is neutral, 7base)
Universal indicator (multi-colored)
Indicators like phenolphthaleinNatural indicators like red cabbage,
radishes
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23Paper testing
Paper tests like litmus paper and pH
paper Put a stirring rod into the solution
and stir.
Take the stirring rod out, and
place a drop of the solution fromthe end of the stirring rod onto apiece of the paper
Read and record the colorchange. Note what the colorindicates.
You should only use a smallportion of the paper. You can useone piece of paper for several
tests.
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pH meter
Tests the voltage of theelectrolyte
Converts the voltage topH
Very cheap, accurate
Must be calibrated witha buffer solution
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pH indicators Indicators are dyes that can be
added that will change color inthe presence of an acid or base.
Some indicators only work in aspecific range of pH
Once the drops are added, the
sample is ruined
Some dyes are natural, like radishskin or red cabbage
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26Setup for titrating an acid with a base
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Titration
1. Add solution from the buret.
2. Reagent (base) reacts withcompound (acid) in solution
in the flask.3. Indicator shows when exact
stoichiometric reaction hasoccurred. (Acid = Base)
This is calledNEUTRALIZATION.
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PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH.
What do you do?
Add water to the 3.0 M solution to lowerits concentration to 0.50 M
Dilute the solution!
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PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What doyou do?
But how much water
do we add?
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PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What do
you do?
How much water is added?
The important point is that --->
moles of NaOH in ORIGINAL solution =
moles of NaOH in FINAL solution
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PROBLEM: You have 50.0 mL of 3.0 M NaOH andyou want 0.50 M NaOH. What do you do?
Amount of NaOH in original solution =
M V =
(3.0 mol/L)(0.050 L) = 0.15 mol NaOH
Amount of NaOH in final solution must also =
0.15 mol NaOH
Volume of final solution =
(0.15 mol NaOH) / (0.50 M) = 0.30 L
or 300 mL
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PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What doyou do?
Conclusion:
add 250 mL
of waterto50.0 mL of
3.0 M NaOH
to make 300mL of 0.50 M
NaOH.
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A shortcut
M1 V1 = M2 V2
Preparing Solutions by
Dilution