Current is applied to an aqueous solution of lithium sulfide. What is the cathode and what is the anode?
cathode: H2 (g)
anode: S(s)
Oh, shocking! When current is applied to an aqueous solution of lithium sulfide, the positive lithium ions (Li+) will be attracted to the negative electrode, which is the cathode. And the negative sulfide ions (S2-) will be drawn to the positive electrode, which we call the anode. Opposites sure do attract in this electrifying romance!
In order to determine the cathode and anode in an electrochemical cell, we need to consider the reduction and oxidation processes that occur during the electrochemical reaction.
Lithium sulfide (Li2S) is an ionic compound composed of lithium cations (Li+) and sulfide anions (S2-). When this compound is dissolved in water to form an aqueous solution, it dissociates into lithium ions and sulfide ions. The reduction and oxidation processes can be identified by analyzing the standard reduction potentials (E°) of the species involved.
For the reduction process:
- Lithium ions (Li+) have a lower reduction potential compared to sulfide ions (S2-). As a result, lithium ions can be reduced at the cathode.
For the oxidation process:
- Sulfide ions (S2-) have a higher reduction potential compared to lithium ions (Li+). Therefore, sulfide ions are oxidized at the anode.
Based on this information, the cathode is where reduction occurs (lithium ions), and the anode is where oxidation occurs (sulfide ions).
To determine the cathode and anode in this scenario, we first need to understand the basics of an electrochemical cell. An electrochemical cell consists of two electrodes immersed in an electrolyte solution. The electrode where reduction occurs is called the cathode, while the electrode where oxidation occurs is called the anode.
In the case of an aqueous solution of lithium sulfide (Li2S), we need to identify the species that can undergo reduction (gain electrons) and the species that can undergo oxidation (lose electrons).
Lithium sulfide can dissociate in water to form lithium ions (Li+) and sulfide ions (S2-). In this case, the sulfide ion (S2-) is more likely to undergo oxidation, while the lithium ion (Li+) is more likely to undergo reduction.
At the cathode, reduction takes place. Since the lithium ions (Li+) can gain electrons according to the reduction half-reaction,
Li+ + e- → Li
the cathode will have lithium ions being reduced to form lithium metal (Li).
At the anode, oxidation occurs. Since the sulfide ions (S2-) can lose electrons according to the oxidation half-reaction,
S2- → S + 2e-
the anode will have sulfide ions being oxidized to form sulfur (S).
Therefore, in this electrochemical cell with an aqueous solution of lithium sulfide, the cathode is where lithium metal (Li) is formed, and the anode is where sulfur (S) is formed.