Transcript Acids & Bases

Acids & Bases
pH Balance?
Video: Elements of Chemistry Acids, Bases & Salts
Household Acids & Bases Lab
Solution
Blue litmus
Red litmus
Universal
Indicator
pH
Ammonia
Put drop onto
plate.
Unplug pH
probe
Lemon juice
Add drop of
indicator.
When done.
Soft drink
Record.
Drain cleaner
Rinse out
plate at end
Detergent
of period
please
Vinegar
Baking soda
Antacid (MoM)
Mentos & Pop
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http://www.stevespanglerscience.com/exp
eriment/00000109
Properties of Acids vs Bases
Acids:
Taste Sour – vinegar!
Feel like water but sting
cuts.
Turn litmus red.
React with active metals to
form explosive H2 gas.
Act as electrolytes to
conduct electricity.
Neutralize bases!
Bases:
Taste bitter – soap!
Feel slippery.
Turn litmus blue.
Don’t react with most
metals.
Act as electrolytes to
conduct electricity.
Neutralize acids!
Arrhenius Acids & Bases
Acids:
 Release H+ ions by
dissociation.
 Example: HCl
 Combine H+ with any
negative ion on your
ion chart to form an
acid.
 Examples: ???
Bases:
 Release OH- ions by
dissociation.
 Example: NaOH
 Combine OH- with any
metal on the periodic
table to form a base.
 Examples: ???
Arrhenius Explanations
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H+ provides the sour taste & stings.
OH- the bitter taste & is slippery.
Dissociation of both acids & bases
produces dissolved ions which act as
electrolytes.
Neutralization occurs when H+ & OHcombine to form H2O. The left overs
produce a salt like NaCl.
Bronsted-Lowry Acids & Bases
Acids:
 Donate H+ ions.
 Example: Acetic acid
& amino acids.
 H+ ions are protons.
 Acids may be
monoprotic, diprotic
or triprotic.
 Examples:
Bases:
 Accept H+ ions.
 Example: Ammonia,
NH3
 All inclusive including
bases ignored by
Arrhenius.
Conjugate Acids & Bases
Acids release H+ & bases accept H+.
Once an acid releases its H+ it becomes a
base that can accept H+ & vice versa.
Examples:
H2CO3 vs HCO3-1
NH3 vs NH4+1
H2O vs H3O+1
Hydronium Ion
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Water is amphoteric – it can act as both an acid
& a base.
When water acts as a base, it forms the
hydronium ion.
H2O + H+  H3O+
H+ ions always bind to something.
When water acts as an acid it forms OH-.
H20  OH- + H+
The fraction of water that normally dissociates is
10-7 M. A very small fraction! 1/10million!
pH Measures the H+ Concentration
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pH uses logs which are just powers of 10.
pH measures the electric “potential” of H+
ions in a solution.
pH is calculated as the negative “power”
of 10 of the H+ ion concentration.
The equation for pH is pH = -log[H+]
[brackets] mean concentration in Molarity.
pH 7 is neutral, above 7 is basic & below 7
is acidic.
Simple pH Calculations
H+ Molarity
pH
.001
Power of
10
10-3
3
Acid or
Base?
Acid
.00001
10-5
5
Acid
.0000001
10-7
7
neutral
.000000001
10-9
9
Base
.000000000001
10-12
12
Base
.00047
10-3.3
3.3
Acid
pH Quiz – Determine the pH of:
1.
2.
3.
4.
A 4.63 x 10-8M solution of HNO3.
A 250L solution containing 4.3mol of HCl.
A 750.0ml solution containing 0.0046g of
HBr.
A 8.9L solution of 0.65mol of H2SO4.
Titrations 5/13/08
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Simulations
http://www.sciencegeek.net/Shockwave/Titratio
n.htm
Lesson:
Simulation Demo
Notes
Practice Problems
Work Problems
Asmt: Simulation Problems A-E find [H+] in M
Titrations
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Titrations measure the concentration of solutions
by finding out the amount of a known solution
needed to neutralize an unknown solution.
Neutralization occurs when Mol H+ = Mol of OHM = mol/L
mol = L x M
mol = M x V
MaVa = MbVb (a is for acid, b is for base)
Some acids are diprotic or triprotic, some bases
are multi-hydroxy.
AMaVa = BMbVb
(A is for # of H+, B is for # of OH-)
Friday 6-11-04
Prep:
1.
Litmus papers, droppers fill up bottles.
2.
Graduation Rehearsal
Class
1.
End of Year Schedule
2.
Vocabulary Assignment
3.
Lab – pH of Household Substances
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Predictions
Handling the pH probe & storage bottle
Litmus tests & universal indicator
Acid – Base Vocabulary
Acid
Base
Indicator
Neutralization
Hydronium ion
Amphoteric
Conjugate acid
Conjugate base
Dissociation
pH
Buffer
Titration
Equivalence point
pH of Household Substances
Sample Predict Red
Blue
Univ.
pH
Litmus Litmus Indicator
pH
Actual
pH of Household Substances
Make the following data table in your notebook.
Rank & predict pH of samples to be used: soda pop, drain
cleaner, vinegar, ammonia, lemon juice, detergent, baking
soda
½ fill a well in the plate for each sample.
Test with red litmus, blue litmus & then add 1 drop of
universal indicator to observe the color. Dispose down sink.
pH Probe:
1.
2.
3.
4.
5.
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Cap stays on probe. Place storage bottle by faucet.
Rinse probe with distilled water before each test.
Place probe in each sample bottle.
Swirl sample around probe for 30 seconds.
Record pH from top right corner of calculator.
Recap all bottles when not in use.
Monday 6/14/04
Prep:
1. Get copies of tracking hurricanes for 14 juniors.
2. Update Chemistry Aces
3. Prepare for Rainbow Titrations Lab
Class:
Recollect Final Answers from 5th Period
1.
Schedule of Week
2.
Due: Acids & Bases Vocabulary
3.
Review Household Acids & Bases
4.
Notes: Acids & Bases (10 points)
1.
2.
3.
Properties
Definitions
pH
Tuesday 6/15/04
Prep:
1. Print 40 copies of the Final Keys
2. Distribute supplies for Rainbow Titration
Lab (test burets & stopcocks)
Class:
1. Pass out Final Exams – check keys &
addition of scores. RECOLLECT!
2. Rainbow Titration Lab
Rainbow Titration Lab
Goal: Determine all the distinct colors and their
corresponding pH ranges for Universal Indicator.
Procedures for Each Trial:
1.
Add 25 ml of 0.1M HCl to a 100ml beaker. Add 6
drops of Universal. (Person A)
2.
Close the stopcock on the buret. Add 50 ml of 0.1M
NaOH to the buret. (Person B)
3.
Place the magnetic stir bar in the beaker of liquid &
turn it on a medium spin. (Person C)
4.
Set up the pH probe to monitor the liquid in the
beaker. (Person D)
5.
Open the stopcock to SLOWLY drip base from the
buret to the acid in the beaker. (Person B)
6.
Record your observations of colors & pH. (Everyone)
7.
Check your results with the instructor. (Everyone)
Monday 6/20/05
DMA: Copy 3 titration problems
1. Finish pH notes
2. Titration Notes
3. Demo: Titrate ?M H2SO4 w/ 2M NaOH
Asmt: 3 titration problems
Titration Problems
1.
2.
3.
If 20.00ml of acidic drain cleaner is
titrated completely by 18.02ml of 0.100M
NaOH, what is the acid’s concentration?
A 25.1ml volume of KOH is titrated with
43.2ml of 0.150M H2SO4. What is the
molarity of the KOH?
A volume of 34.0ml of 0.100M H3PO4
neutralizes 25.0ml of Ba(OH)2. What is
the concentration of the barium
hydroxide?
Tuesday 6/21/05
Prep:
Get copies of Acid-Base Mini-Exam
2.
Make fine cards!
Class:
1.
Pass out AP Bio stuff.
2.
Review a titration problem.
3.
Acid-Base Mini-Exam
4.
Pass back finals / fine cards / check basmati/ sign annuals.
Plan:
1.
Fill out fine cards!
2.
Call Mary Anne about visiting Bob.
After School:
1.
Help students.
2.
Clean up lab.
1.
Vinegar Titration Lab
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Add 10.0 ml of vinegar to the beaker. Add 4
drops of indicator B, phenolpthalein.
Fill the buret with 1.00M NaOH. Record the
starting volume.
Titrate until the mixture turns pink & stays pink.
Use the minimum of drops.
Measure the final volume and determine the
change in volume of the base.
Use AMaVa = BMbVb to determine the molarity
of the vinegar, HC2H3O2.
Antacid Titration Lab
Goal: Determine which Antacid will neutralize the greatest
amount of stomach acid – Rolaids, Tums, or Maalox
1.
2.
3.
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6.
7.
Pulverize a sample tablet with the mortar & pestle.
Dissolve sample with 25ml of distilled water & transfer
the solution to a 100ml beaker.
Add 4 drops of bromothymol blue? and the stir bar.
Add 0.1M HCl to the buret. Record precisely the
starting volume in the buret.
Use the minimum amount of 1.0M HCl needed to turn
the solution yellow? and stay clear.
Record the final volume of the buret. Find the change
in volume.
Repeat for each sample.
Friday 6/18/04
Prep:
1.
Set up titration demo.
2.
Get extra fine cards.
Class:
1.
Return book or receive fine card tied to grade
report.
2.
Check Basmati – bring personal issues to me
after mini-exam.
3.
Begin titration demo (5ml vs 50ml)
4.
Review for mini-exam, no 3x5 card
5.
Acids & Bases Mini-Exam – Check notes???
XC Asmt: 5 points if you bring treats for everyone
for Monday’s Annual Signing Party
Conjugate Acids & Bases
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Any acid that can release H+ can re-accept and
bind it to varying degrees.
Strong acids like HCl release essentially all H+
ions. HCl  H+ + ClWeak acids like in vinegar release a small
percentage of H+ ions. Most remain bound.
HC2H3O2  H+ + C2H3O2Salts contain positive & negative ions.
Any negative ion has some capacity to bind with
H+ ions to act like a base. Examples: ???
Conjugates represent examples with or without
H+ attached. Examples: ???
Equilibrium of Reversible Reactions
Carbonated Water:
CO2(g) + H2O (l)  H2CO3(aq)
H2CO3(aq)  H+(aq) + HCO3-(aq)
Le Chatelier’s Principal – When disturbed a
reaction will adjust to minimize the
disturbance. (Teeter totter analogy)
Carbonate pop by adding CO2(g) pressure.
CO2(g) + H2O (l)  H2CO3(aq)
Pop goes flat when container is opened!
CO2(g) + H2O (l)  H2CO3(aq)
Equilibrium Ratios
xA(aq) +
yB(aq)

zC(aq)
Equilibrium Ratio (K) = products/reactants
Keq = [C]z / [A]x[B]y
Coefficients = exponents!
Carbonated Water Equilibrium Ratio?
Each reaction has a different equilibrium ratio
value.
Large ratios favor the _________, while small
ratios favor the _________.