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Molten Sodium Chloride Electrolysis
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1
Question
Which species is reduced at the cathode during electrolysis of molten sodium chloride?
Page 3
Answer
\$Na^+\$ is reduced to elemental sodium: \$2Na^+ + 2e^- \rightarrow 2Na\$.
2
Question
Which species is oxidized at the anode during electrolysis of molten sodium chloride?
Page 3
Answer
\$Cl^-\$ is oxidized to chlorine gas: \$2Cl^- \rightarrow Cl_2 + 2e^-\$.
3
Question
Write the overall chemical equation for the electrolysis of molten sodium chloride.
Page 3
Answer
\$2NaCl \rightarrow 2Na + Cl_2\$ (electricity is required to drive this non-spontaneous reaction).
4
Question
In the external circuit of the electrolytic cell, which direction do electrons flow during electrolysis of molten NaCl?
Page 3
Answer
Electrons flow from the anode to the cathode through the external circuit (produced at the anode, consumed at the cathode).
5
Question
Which direction do \$Na^+\$ ions move inside molten NaCl during electrolysis and why?
Page 3
Answer
\$Na^+\$ ions migrate toward the cathode so they can gain electrons and be reduced to \$Na\$.
6
Question
Which direction do \$Cl^-\$ ions move inside molten NaCl during electrolysis and why?
Page 3
Answer
\$Cl^-\$ ions migrate toward the anode so they can lose electrons and be oxidized to \$Cl_2\$.
7
Question
Define the anode and cathode in the context of the molten NaCl electrolytic cell.
Page 3
Answer
Anode: the electrode where oxidation occurs (chloride ions oxidize to \$Cl_2\$). Cathode: the electrode where reduction occurs (sodium ions reduce to \$Na\$).
8
Question
In an electrolytic cell performing molten NaCl electrolysis, which electrode is connected to the positive terminal of the external power supply?
Page 3
Answer
The anode is connected to the positive terminal of the power supply; the cathode is connected to the negative terminal.
9
Question
What physical products appear at the cathode and anode during electrolysis of molten NaCl?
Page 3
Answer
At the cathode: molten elemental sodium (liquid metal). At the anode: chlorine gas bubbles (\$Cl_2\$).
10
Question
Why must sodium chloride be molten (or dissolved) to undergo electrolysis?
Page 3
Answer
Molten (or dissolved) sodium chloride provides mobile ions (\$Na^+\$ and \$Cl^-\$) that can migrate to the electrodes and conduct current; solid ionic crystals do not allow ion mobility.
11
Question
How many electrons are transferred in the pair of half-reactions for the electrolysis of two moles of NaCl to give \$2Na\$ and \$Cl_2\$?
Page 3
Answer
Two electrons are transferred: the anode half-reaction releases 2 e^- (\$2Cl^- \rightarrow Cl_2 + 2e^-\$) and the cathode half-reaction consumes 2 e^- (\$2Na^+ + 2e^- \rightarrow 2Na\$).
12
Question
Describe the change in oxidation number for sodium and chlorine during the electrolysis of molten NaCl.
Page 3
Answer
Sodium: oxidation number changes from +1 in \$Na^+\$ to 0 in \$Na\$ (reduction). Chlorine: oxidation number changes from -1 in \$Cl^-\$ to 0 in \$Cl_2\$ (oxidation).