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Q-8
ADVANCE STUDY ASSIGNMENT
1.
What is the difference between an electrolytic cell and a voltaic cell?
Answer:
In an electrolytic cell, electrical energy is used to produce a nonspontaneous chemical
change. In a voltaic cell, a spontaneous chemical reaction is used to produce electrical
energy.
2.
What is the purpose of the filter paper saturated with KNO3 between half-cells? Why is a salt bridge
essential to the voltaic cell? What would happen if the KNO3 were omitted?
Answer: Salt bridge provides electrical contact between the half-cells without physical mixing and
maintains ion charge neutrality in each cell. Without KNO3, the potential difference
between the cells cannot be measured.
3.
Refer to Fig. 1. Label the anode, the cathode, and the electrode where reduction occurs. Indicate
the direction of electron flow in the external circuit. Write the equation for the half-reaction that
occurs at each electrode.
4.
Why would an inert graphite electrode be used in the C
(graphite)
/(I
-
, I2, I3
-
) half-cell?
Answer: An inert electrode is needed because an I
2(s)
electrode does not conduct.
5.
CH2Cl2 is colorless. What is the color of I2 dissolved in CH2Cl2?
Answer: purple.
6.
A student added 1 mL of CH2Cl2 into a test tube with 1 mL of KI. Then a few crystals of a metal
salt, MNO3, was added and the mixture shaken.
a) If the M oxidizes the I
-
, what color would the CH2Cl2 be?
Answer: purple.
b) What color would the CH2Cl2 be if the M
+
does not react with the I
-
?
Answer: colorless.
Why?
REAGENTS AND EQUIPMENT
Metal strips
24-well plate
Standard metal salt solutions (1.0 M)
CH2Cl2 (dichloromethane)
Cl2 (as chlorine water)
1.0 M KNO3 (potassium nitrate)
Br2 (as bromine water)
graphite electrode
I2 {as iodine-triiodide solution, (I
-
, I2, I3
-
)}
voltmeter and electrode leads
Cl
-
(as 0.10 M KCl)
emery cloth or sand paper
Br
-
(as 0.10 M KBr)
filter paper
