Item I:-Choose the best answer for the following questions from the given alternative and write your answer. (0.5 pt. each)
1. The -------------- functional group of organic molecules may be represented in a less detailed manner by condensed structural formulas.
A. Alkene B. Alkane C. Aromatic D. Alkyne
2. Which of the following alkane is liquid at room temperature?
A. C8H18 B. C3H8 C. C14H30 D. C4H8
3. One of the following is true about substitution reaction of alkane?
A. Carbon-carbon bonds are broken in these reactions.
B. One or more of the alkane’s hydrogen atoms is replaced with a different atom.
C. Hybridization of the carbon atoms does change.
D. All of the above
4. Of the following is the simplest alkene?
A. C3H6 B. C2H8 C. C4H6 D. C2H4
5. Alkenes are much more reactive than alkanes because
A. The C=C moiety is a reactive functional group.
B. A π bond, being a stronger bond, is disrupted much more easily than a σ bond.
C. Alkenes have bond angels 180⁰ D. None of the above
6. Which one of the following functional group have carbonyl group
A. Aldehyde B. Alcohol C. Alkyne D. Ether
7. Amines are weak bases due to……..
A. Found in a wide variety of compounds.
B. The lone pair of electrons on their nitrogen atoms
C. Nitrogen atoms connected to the carbon atom of a carbonyl group.
D. The hydrogen atom in the functional group of amines will react with a base to form an ionic salt:
Item II:-Write short and precise answer for the following questions.
1. Draw the skeletal structures for the following molecules. (0.5 pt.)
2. Alcohols A, B and C all have the composition C4H10O. Molecules of alcohol A contain a branched carbon chain and can be oxidized to an aldehyde; molecules of alcohol B contain a linear carbon chain and can be oxidized to a ketone; and molecules of alcohol C can be oxidized to neither an aldehyde nor a ketone. Write the Lewis structures of these molecules. (1 pt.)
3. Write the IUPAC name of the following compound (0.5 pt. each)
4. Draw the structure for the following named compounds (0.5 pt. each)
A. 3-Methylhept-2,5-diene
B. 2-Bromocyclopentanol
C. 4-Chloro-2-methylhexanoic acid
D. 2,3,5-Trimethylphenol
E. Hex-2-en-4-yne
5. Define the following terms clearly and neatly (0.25pt each)
a) Salt bridge and its function
b) Standard cell potential
c) Faraday’s 1st and 2nd law of electrolysis.
d) Battery
e) Fuel cell
f) Preferential discharge and factors affecting it
6. Compare and contrast the following terms (0.5pt)
a) Electrolytic (Voltic cell) and galvanic cell
b) Types of cell (Primary and secondary cell)
7. Write the anode the cathode and cell reaction for the following (0.25pt each)
a) Copper (II) Sulphate (using inert electrode)
b) Dilute sulphuric acid Solution
c) concentrated sodium chloride solution (brine solution)
d) Dilute Sodium Chloride Solution
8. What is the effect of change in the concentration of reactants on cell potential? Support with equation? (0.5pt)
9. Aluminum metal displaces zinc (II) ion from aqueous solution. Write (0.25pt)
(a) oxidation half-cell reaction
(b) Reduction half-cell reaction
(c) overall cell reaction
(d) the cell diagram for which this reaction occurs.
10. A Galvanic cell consists of a Mg electrode in 1.0 M Mg (NO3)2 solution and a Ag electrode in 1.0 M AgNO3 solution. Calculate the standard cell potential (emf) of this cell at 25°C (0.5pt)
11. Given E° =2.12V, determine standard Gibbs energy change (∆Go) of the following rxn? (1pt)
Zn(s) +Cl2 (g, 1bar) ZnCl2(aq,1M)
12. Will aluminum metal displace Cu2+ ion from aqueous solution? That is, will a spontaneous reaction occur in the forward direction for the following reaction (1pt)
2Al(s) + 3Cu2+ (1M) = 3Cu(s) + 2Al3+ (1M)
13. Calculate the mass of copper deposited by the electrolysis of copper (II) sulphate solution placed in series with a silver nitrate solution, when 0.108 g of silver is being deposited (1pt)
14. Predict whether the following reaction would proceed spontaneously as written at 298 K:
Co(s) + Fe2+ (aq) Co2+ (aq) + Fe(s)
given that [Co2+] = 0.25 M and [Fe2+] = 0.94 M. (1pt)
15. List at list five industrial applications of electrochemistry and explain briefly (0.5pt)
Item I:
1. B. Alkane
2. B. C3H8
3. B. One or more of the alkane’s hydrogen atoms is replaced with a different atom.
4. D. C2H4
5. A. The C=C moiety is a reactive functional group.
6. A. Aldehyde
7. B. The lone pair of electrons on their nitrogen atoms
Item II:
1. Skeletal structures:
A. CH3-CH2-CH2-CH3
B. CH3-CH2-CH2-OH
C. CH3-CH(CH3)-OH
2. Lewis structures:
A. CH3-CH(CH3)-CHO
B. CH3-CH2-CH2-CO-CH3
C. CH3-CH(CH3)-CH2-OH
3. IUPAC names:
A. 2-Methylhexane
B. 2-Bromocyclopentanol
C. 4-Chloro-2-methylhexanoic acid
D. 2,3,5-Trimethylphenol
E. 4-Hex-1-en-4-yne
5. Definitions:
a) A salt bridge is a structure that connects the two half-cells in a galvanic cell, allowing ions to flow and maintain electrical neutrality.
b) Standard cell potential is the voltage difference between two half-cells at standard conditions.
c) Faraday's first law states that the amount of substance deposited or liberated during electrolysis is directly proportional to the quantity of electricity passed through it. Faraday's second law states that the masses of different substances liberated by the same quantity of electricity are in the ratio of their equivalent masses.
d) A battery is a device that converts chemical energy into electrical energy through electrochemical reactions.
e) A fuel cell is a device that converts the chemical energy of a fuel and oxidant directly into electrical energy.
f) Preferential discharge is the phenomenon where certain ions in a solution discharge at the electrodes preferentially due to factors like electrode potential and concentration of ions.
6. Comparisons:
a) Electrolytic cells require an external source of electrical energy to drive non-spontaneous reactions, while galvanic cells produce electrical energy from spontaneous redox reactions.
b) Primary cells are non-rechargeable, whereas secondary cells are rechargeable.
7. Anode, cathode, and cell reactions:
a) Anode: Cu -> Cu2+ + 2e-
Cathode: 2e- + 2Cl- -> Cl2 + 2e-
Overall cell reaction: Cu + 2Cl- -> Cu2+ + Cl2
b) Anode: 2H2O -> O2 + 4H+ + 4e-
Cathode: 4H+ + 4e- -> 2H2
Overall cell reaction: 2H2O -> O2 + 2H2
c) Anode: 2Cl- -> Cl2 + 2e-
Cathode: 2H2O + 2e- -> H2 + 2OH-
Overall cell reaction: 2NaCl + 2H2O -> Cl2 + 2NaOH + H2
d) Anode: 2Cl- -> Cl2 + 2e-
Cathode: 2H2O + 2e- -> H2 + 2OH-
Overall cell reaction: 2NaCl + 2H2O -> Cl2 + 2NaOH + H2
8. Change in concentration of reactants affects cell potential according to the Nernst equation:
Ecell = E°cell - (0.0592/n) * log(Q)
Where Q is the reaction quotient and n is the number of moles of electrons exchanged.
9. Aluminum displacement reaction:
a) 2Al -> 2Al3+ + 6e-
b) 3Cu2+ + 6e- -> 3Cu
c) 2Al + 3Cu2+ -> 2Al3+ + 3Cu
d) Al | Al3+ || Cu2+ | Cu
10. Standard cell potential calculation:
E°cell = E°cathode - E°anode
E°cell = 0.80V - (-2.37V)
E°cell = 3.17V
11. Standard Gibbs energy change calculation:
∆Go = -n * F * E°cell
∆Go = -2 * 96485 * 2.12
∆Go = -407.216 kJ/mol
12. Aluminum will displace Cu2+:
2Al + 3Cu2+ -> 3Cu + 2Al3+
13. Mass of copper deposited:
1 mole of Ag deposited corresponds to 1 mole of Cu deposited.
Molar mass of Cu = 63.55 g/mol
Therefore, 0.108 g of Cu will be deposited.
14. Spontaneous reaction determination:
Calculate the cell potential using the Nernst equation to determine spontaneity.
15. Industrial applications of electrochemistry:
- Electroplating
- Corrosion prevention
- Production of chemicals like chlorine and sodium hydroxide
- Batteries and fuel cells
- Electrolysis for metal extraction.