Acids, Bases and pH - WELCOME TO CHEMISTRY!...Acid-base Indicators • Acid-base indicator = a weak...
Transcript of Acids, Bases and pH - WELCOME TO CHEMISTRY!...Acid-base Indicators • Acid-base indicator = a weak...
-
Acids, Bases and pHChapter 19
-
Compounds That Become Acids When Dissolved in Water
General Formula: HX
H+ X-
monatomic
or
polyatomic
anion
-
Naming Acids (p. 250)
Binary acids
Hydro_______ic Acid
HCl: Hydrochloric acid
HBr: Hydrobromic acid
HS: Hydrosulfuric acid
Oxyacids
ite becomes ous
Acid from chlorite:
HClO2 = chlorous acid
Acid from phosphite:
H3PO3 = phosphorous acid
ate becomes ic
Acid from sulfate:
H2SO4 = sulfuric acid
-
Compounds That Become Acids When Dissolved in Water
Your turn:
HBr
HNO2
HNO3
-
Compounds That Become Acids When Dissolved in Water
Your turn:
HBr
hydrobromic acid
HNO2nitrous acid
HNO3nitric acid
-
Practice
Name or write formulas for the following acids:
1. Phosphoric Acid 5. HClO42. Hydrochloric Acid 6. HI
3. Chlorous Acid 7. H2S
4. Sulfurous Acid 8. HC2H3O29. Write the balanced formula, total ionic and net
ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide
-
Practice
Name or write formulas for the following acids:
1. phosphoric acid H3PO42. hydrochloric acid HCl
3. chlorous Acid HClO24. sulfurous Acid H2SO35. HClO4 perchloric acid
6. HI hydroiodic acid
7. H2S hydrosulfuric acid
8. HC2H3O2 acetic acid
-
Practice
9. Write the balanced formula, total ionic and net ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide
(put answer on front whiteboard)
-
Properties of Acids and Bases
Acids Bases
Taste sour Taste bitter
Feel wet Feel slippery
Turn litmus RED Turn litmus BLUE
Conduct electricity Conduct electricity
React with most metals Do NOT react with most metals
Contain more H+ than OH- Contain more OH- than H+
pH between 0 and 7 pH between 7 and 14
strong acid + strong base salt + H2O
-
Arrhenius acids and bases
Acid: compound containing H that ionizes to yield H+ in solution
HCl(g) H+
(aq) + Cl-(aq)
HCl(g) + H2O(l) H3O+
(aq) + Cl-(aq)
Base: compound containing OH that ionizes to yield OH- in solution
NaOH(s) Na+
(aq) + OH-(aq)
*Note: Every Arrhenius acid/base is also a Brønsted-Lowry acid/base.
H2O
H2O
-
Autoionization of Water
In pure water :
[H3O+] = 1.0 x 10-7 M AND [OH-] = 1.0 x 10-7 M
If we add acid [H3O+] increases and [OH-] decreases.
[H3O+] = 1.0 x 10-4 M [OH-] = 1.0 x 10-10 M
If we add base, the reverse is true:
[H3O+] = 1.0 x 10-10 M [OH-] = 1.0 x 10-4 M
What is the product of [H3O+] x [OH-] in each case?
H2O + H2O H3O
++ OH-
-
The pH Scale
pOH = - log [OH-]
= - log (1.0 x 10-7)
= -(-7)
= 7
pH = - log [H+]
= - log (1.0 x 10-7)
= -(-7)
= 7
Pure Water
basis of neutral pH 7:[H+] = [OH-]
-
Concentration, pH and pOH(for strong acids and bases)
Concentration is given in terms of molarity (M)
Concentration of H+ = [H+] = = 0.0100 M
In scientific notation: [H+] = 1.00 x 10-2 M
Find pH: pH = -log[1.00 x 10-2 M] pH = 2
Find pOH: pH + pOH = 14 pOH = 12
Find [OH-]: [OH-] = 10-pOH = 10-12 [OH-] = 1.00 x 10-12 M
0.0100 moles H+
L solution
-
Converting between Concentration and pH
pH pOH[H+] [OH-]10-pOH
-log[H+ ]
14-pH
pHpOH [H+][OH-] 10-pH
-log[OH- ]
14-pOH
1.00 x 10-4 M 4 10 1.00 x 10-10 M
1.00 x 10-11 M 11 3 1.00 x 10-3 M
-
Practice
pH + pOH = 14; pH = -log[H+]; pOH = -log[OH-]
When pH = 2
[H+] = _____________M
pOH = ____________
[OH-] = ____________M
When pOH = 8
[OH-] = ___________ M
pH = _____________
[H+] = ____________ M
[H+] = 1.0 x 10-3 M What is the [OH-]?
-
More Practice (HW)
1. What is the pH of a solution with a [H+] of 10-8 M?
2. What is the pOH of a solution with a [OH-] of 10-11 M?
3. What is the pH of a solution with a [OH-] of 10-2 M?
4. What is the pOH of a solution with a [H+] = 10-5 M?
5. Which is more acidic, a solution with a pH of 6 or one
with a pH of 9?
6. Which is more basic, a solution with a pOH of 7 or one
with a pOH of 12?
7. Which is more acidic, a solution with a pH of 5 or one
with a pOH of 10?
8. Which is more basic, a solution with a pH of 8 or one
with a pOH of 12?
-
More Practice
1. What is the pH of a solution with a [H+] of 10-8 M? 8
2. What is the pOH of a solution with a [OH-] of 10-11 M? 11
3. What is the pH of a solution with a [OH-] of 10-2 M? 12
4. What is the pOH of a solution with a [H+] = 10-5 M? 9
5. Which is more acidic, a solution with a pH of 6 or one
with a pH of 9? pH of 6
6. Which is more basic, a solution with a pOH of 7 or one
with a pOH of 12? pOH of 7
7. Which is more acidic, a solution with a pH of 5 or one
with a pOH of 10? pOH of 10
8. Which is more basic, a solution with a pH of 8 or one
with a pOH of 12? pH of 8
-
More Practice
9. Stomach contents can have a pH of 3.
Are stomach contents acidic, basic or neutral?
10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral?
11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic?
12. Acid precipitation is often a problem in industrialized areas.
What might you expect the pH of acid rain to be?
-
More Practice
9. Stomach contents can have a pH of 3. Are stomach contents acidic, basic or neutral? acidic
10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral? neutral
11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic?
slightly acidic
12. Acid precipitation is often a problem in industrialized areas.
What might you expect the pH of acid rain to be? < 6
-
Warm up
1. Write formulas for the following acids:
a) hydroiodic acid
b) chlorous acid
c) chloric acid
d) perchloric acid (Honors)
e) hypochlorous acid (Honors)
f) phosphoric acid
g) phosphorous acid
-
Warm up
1. Write formulas for the following acids:
a) hydroiodic acid HI
b) chlorous acid HClO2
c) chloric acid HClO3
d) perchloric acid HClO4 (Honors)
e) hypochlorous acid HClO (Honors)
f) phosphoric acid H3PO4
g) phosphorous acid H3PO3 (Honors)
-
Warmup
What is the pH of a solution of nitric acid (strong acid) that has a concentration of 10-4 M?
What is its pOH?
Concentration of OH-?
-
Warmup
What is the pH of a solution of nitric acid (strong acid) that has a concentration of 10-4 M?
4
What is its pOH?
10
Concentration of OH-?
10-10 M
-
Acid-base Indicators
• Acid-base indicator = a weak acid or base that
undergoes dissociation in a known pH range.
• In this range, the acid (base) is a different
color from its conjugate base (or acid).
• Universal indicator (UI) = a mixture of
indicators that shows a range of colors over a
wide range of pH values
-
Intro to pH Serial Dilution Lab
• Overview: you will create a pH scale (1 to 14) by serial dilutions, then test acid-base indicators.
Serial Dilutions
1 drop 1 M HCl + 9 drops dH2O = 10X dilution
i.e. 1M 0.1 M, which is pH = 1
1 drop 0.1 M HCl + 9 drops dH2O = 10X dilution
i.e. 0.1M 0.01 M 10-2 M, which is pH = 2
-
Intro to pH Serial Dilution Lab
Safety: apron and goggles
Complete the pre-lab questions on the first page before you go into lab
Work on your own
-
Intro to pH Serial Dilution Lab
Begin with UI, then choose at least two other acid-base indicators to test.
Use dH2O dropper bottle for the 9 drops of water per well.
Be sure to rinse pipet with dH2O between dilutions.
Collect this dH2O into a beaker from the carboys by the windows.
Rinse and dry wellplates/spot plates between runs (use dH2O).
-
Neutralization Reactions
When a strong acid reacts with a strong base, the net ionic equation is…
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
© 2009, Prentice-Hall, Inc.
-
Neutralization Reactions
When a strong acid reacts with a strong base, the net ionic equation is…
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq)
Na+ (aq) + Cl- (aq) + H2O (l)
© 2009, Prentice-Hall, Inc.
-
Neutralization Reactions
When a strong acid reacts with a strong base, the net ionic equation is…
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq)
Na+ (aq) + Cl- (aq) + H2O (l)
H+ (aq) + OH- (aq) H2O (l)
© 2009, Prentice-Hall, Inc.
-
Titration
Titration is an
analytical
technique in
which one can
calculate the
concentration
of a solute in
a solution.
© 2009, Prentice-Hall, Inc.
-
Titration
= A method of volumetric analysis in which a volume of one
reagent is added to a known volume of another reagent
slowly from a buret until an end point is reached. If
one of the solutions has a known concentration, the
concentration of the other can be calculated, via
stoichiometry.
© 2009, Prentice-Hall, Inc.
-
Titration
Standard solution = reagent solution of knownconcentration
Titrant = reagent solution of unknownconcentration
Equivalence point = the point at which stoichiometrically equivalent quantities are brought together
End point = color change (v. close to equivalence point)
© 2009, Prentice-Hall, Inc.
-
Change in appearance of a solution containing
phenolphthalein as base indicator
© 2009, Prentice-Hall, Inc.
-
Titration
© 2009, Prentice-Hall, Inc.
-
Example Titration
Predict the number of mL of ~0.10 M NaOH needed to
neutralize 10.0 mL of 0.25 M HCl.
We want to know the exact molarity of the NaOH
solution.
© 2009, Prentice-Hall, Inc.
-
Titration Practice Problems
Remember: Moles are
central!1. In the titration of 35 mL of liquid drain cleaner
containing NaOH, 50. mL of 0.40 M HCl must be added
to reach the equivalence point. What is the molarity
of the base in the cleaner?
(0.57 M)
© 2009, Prentice-Hall, Inc.
-
Titration Practice Problems
Remember: Moles are
central!2. A 20.0 mL sample of an HCl solution is titrated with
27.4 mL of a standard solution of Ba(OH)2.
The concentration of the standard is 0.0154 M. What
is the molarity of the HCl?
(0.0422 M)
© 2009, Prentice-Hall, Inc.
-
Strength of Acids and Bases
Strong acid or base – ionizes/dissociates completely in water
[H+] or [OH-] = conc. of acid or base. e.g. HCl, NaOH.
5 units of acid – 5 out of 5 dissociated
H+ Cl- H+ Cl- H+ Cl- H+ Cl- H+ Cl-
Weak acid or base – ionizes/dissociates only partially in water
[H+] or [OH-] < conc. of acid or base. e.g. HC2H3O2, NH35 units – only 1 out of 5 dissociated
HC2H3O2 HC2H3O2 HC2H3O2 HC2H3O2 H+ C2H3O2
-
-
Practice
The diagrams below represent aqueous
solutions of three acids (HX, HY, and HZ)
with water molecules omitted for clarity.
Rank them from strongest to weakest.
© 2009, Prentice-Hall, Inc.
-
Strengths of Acids and Bases
Strong concentrated
Weak dilute
A concentrated weak acid (or base) may have the same pH as a dilute strong acid (or base).
-
Strong vs. Weak Demo
Strong acid:
HCl + H2O Cl- + H3O
+
1.0 x 10-2 M ? M
pH = ?
Weak acid:
HC2H3O2 + H2O ↔ C2H3O2- + H3O
+
1.0 x 10-2 M ? M
pH = ?
Strong base:
NaOH + H2O Na+ + OH-
1.0 x 10-2 M ? M
pH = ?
Weak base:
NH3 + H2O ↔ NH4+ + OH-
1.0 x 10-2 M ? M
pH = ?
-
Strong and Dilute vs. Weak and Concentrated
Acids:
Strong HCl Weak HC2H3O2 Weak HC2H3O2
Dilute Dilute Conc 100 x
0.01 M 0.01 M 1M
pH = pH = pH =
Bases:
Strong NaOH Weak NH3 Weak NH3
Dilute Dilute Conc 100 x
0.01M 0.10 M 1M
pH = pH = pH =
-
Warmup
Compare strong acids with weak acids. Use
concentration, extent of ionization, and pH in your
answer.
-
Warmup
Compare strong acids with weak acids. Use concentration,
extent of ionization, and pH in your answer.
Strong acids ionize completely in water, so the concentration
of H+ is the same as the compound itself. A weak acid of
equal concentration (molarity) will have a lower
concentration of H+, and thus a higher pH.
-
What do you think?
Table salt
Vinegar
Rubbing alcohol
Window Cleaner
Distilled water
Lemon juice
Soap
Drain cleaner
Applesauce
Blood
Are the following acidic, basic or neutral?
What is the difference between a strong acid and a concentrated acid?
A weak acid and a dilute acid?
-
Brønsted-Lowry Acids and Bases (1923)
Acid: H+ (proton) donor
Base: H+ (proton) acceptor
HCl + H2O H3O+ + Cl-
acid base conjugate conjugate
acid base
-
Brønsted-Lowry Acids and Bases (1923)
NH3 + H2O D NH4+ + OH-
ammonia water ammonium ionhydroxide ion
(B-L base) (B-L acid) (B-L acid) (B-L base)
base acid conjugate acid conjugate base
-
Conjugate Acid-Base Pairs
Conjugate acid = species produced when a base accepts a hydrogen ion from an acid
Conjugate base = species that results when an acid donates a hydrogen ion to a base
-
Identify the conjugate acid-base pairs:
HClO + H2O D ClO- + H3O
+
HS- + H2O D H2S + OH-
HPO42- + H2O D H2PO4
- + OH-
HPO42- + H2O D PO4
3- + H3O+
An amphoteric compound is able to act as either an
acid or a base. Which compounds in the above
equations are amphoteric?