Transcript Chem 109 A - University of California, Santa Barbara

Chem 109 A
Chapter 2
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Web-site: http://clas.sa.ucsb.edu/staff/terri/
Ch.2
1. Show the equation using Kekule structures for the reaction
between ammonium ion (NH4+) and methoxide ion (CH3O-).
a. Label the conjugate pairs
b. Circle the stronger acid
c. Calculate the approximate Keq
d. Which direction does the equilibrium lie?
Compound
pKa
CH3OH
17
NH4+
11
Ch. 2
As acid strength ↑
Ka ↑
pKa ↓
conjugate base strength ↓
Ch.2
2. Show the equation using Kekule structures for the reaction
between acetate ion (CH3COO-) and protonated ethanol
(CH3CH2OH2+).
a. Label the conjugate pairs
b. Circle the stronger acid
c. Calculate the approximate Keq
d. Which direction does the equilibrium lie?
Compound
pKa
CH3COOH
4.76
CH3CH2OH2+
-2.4
Ch. 2
3. What is the resulting pH if 5 moles of ammonia were mixed
with 5 moles of ammonium chloride (pKa = 9.4)? What is the
pH if the molar ratio was 1:10 or 100:1 respectively?
Ch.2
4. For the following pairs predict the stronger acid. Explain your
reasoning.
a. HF or HCl
b. H2S or H2O
c. HF or H2O
d. CH3OH or CF3OH
e. CH3(CH2)2CH(Cl)OH or CH3CH(Cl)(CH2)2OH
f. CH3OH or HCO2H
g. HC≡CH or H2C=CH2
h. CH3NH2 or CH3NH3+
Ch. 2
Comparing Relative Acid Strength
Are the acidic hydrogens on the same element?
1. No
A. Same period elements => acid strength increases with increasing
electronegativity
B. Different period elements => acid strength increases with increasing atomic
radius
2. Yes
A. Formal charge => Acid strength increases with increasing charge
B. Hybridization => Acid strength increases with increasing s character
C. Resonance => Acid strength increases with withdrawing electrons via
delocalization
D. Induction => Acid strength increases with withdrawing electrons due to
induction
Ch. 2
5. Predict the stronger base.
A. NH3 or PH3
B. CH3O- or CF3OC. CH3OCH3 or CH3COCH3
D. CH3O- or CH3NH-
Ch. 2
5. What pH would allow the following to dissolve best in water
verses hexane?
A. Aliphatic carboxylic acid
B. Aliphatic amine
C. Aliphatic alcohol
Ch. 2
6. You are planning to synthesize a compound and one of the
by-products is hydroxide. If you wanted to maintain a pH of 4.2
would it be better to use a formic acid (pKa = 3.75)/formate
buffer or acetic acid (pKa = 4.76)/acetate buffer?
End of Chapter 2
Ch. 3
1. Give the following a systematic name and common name (if
possible):
Ch. 3
2. Draw the following compounds and assign a systematic
name:
a. sec-butyl iodide
b. isoheptane
c. tert-butyl isopentyl ether
d. pentyl alcohol
e. cyclobutyldimethylamine
Ch. 3
3. What is more soluble in water?
a. Methanol or ethanol
b. Propylamine or trimethylamine
Ch. 3
4. What has a higher boiling point?
a. butane or pentane
b. pentane or neopentane
c. ethanol or dimethyl ether
d. butylamine or dimethylethylamine
e. flourocyclohexane or bromocyclohexane
Ch. 3
5. Determine if the following alcohols primary, secondary or
tertiary:
a. 2-methyl-2-pentanol
b. 3-ethyl-1-hexanol
c. cyclopropanol
Ch. 3
6. Determine if the following amines primary, secondary or
tertiary:
a. Cyclopentanamine
b. N,N-diethyl-2-butanamine
c. butylisobutylpentylamine
Ch. 3
7. Draw the conformations of pentane considering rotation
about the C2-C3 bond. Label the structures relative
energy/stability. Draw an energy diagram that corresponds
with your drawings.
Ch. 3
8. Draw the two chair conformers for bromocyclohexane and
determine which isomer is more stable. Explain your
reasoning.
Ch. 3
9. Which geometric isomer is more stable; cis or trans 1,3dimethylcyclohexane?
Ch. 3
10. Draw the chair conformers for 1-isopropyl-3methylcyclohexanol. Which structure is more stable?
Ch. 3