Concentrated sodium chloride solution is electrolyzed using mercury cathode and graphite anode. The products at the anode and the cathode respectively are
hydrogen and chlorine
chlorine and hydrogen
chlorine and sodium
sodium and chlorine
Explanation
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sodium will form almagam at the cathode preventing H+ from discharging
Cl- will be discharged because of its concentration and closeness to OH-
According to what I've read, The conditions are specific; It is a concentrated solution so the sodium and chlorine both have a chance to be reduced; in this case chlorine is liberated at the anode instead of oxygen gas.
Meanwhile at the cathode; with the use of other materials the liberated product ought to be hydrogen, however the anode used is mercury which sodium is very reactive with to form sodium amalgam, therefore it is reduced instead of the hydrogen.
This is not an aqueous soln or dilute... How can u say B
It is a Conc Nacl therefore the answer should be C
A eletrólise pode ser complicada porque os produtos dependem não apenas dos produtos químicos envolvidos, mas também da natureza dos eletrodos utilizados.
Nesta questão específica, cloreto de sódio concentrado (salmoura)
Electrolysis can be tricky because the products depend not just on the chemicals involved, but also on the nature of the electrodes used.
In this specific question, concentrated sodium chloride (brine) is being electrolyzed. The ions present are Na^{+}, Cl^{-}, H^{+}, and OH^{-}.
Why Option C is actually the Correct Answer
There seems to be an error in the answer key shown in your image. In standard chemistry (specifically the Castner-Kellner process), using a mercury cathode changes the rules of discharge.
At the Anode (Graphite): Chloride ions (Cl^{-}) are in high concentration. They are discharged to form Chlorine gas.
At the Cathode (Mercury): Normally, H^{+} would be discharged because it is lower in the electrochemical series than Na^{+}. However, mercury has a very high overvoltage for hydrogen. This makes it extremely difficult for hydrogen gas to form. Instead, Sodium ions (Na^{+}) are discharged.
The Result: The sodium metal dissolves in the mercury to form sodium amalgam (Na/Hg).
Therefore, the products at the anode and cathode respectively are Chlorine and Sodium.
Breakdown of the Options
Option B: Chlorine and Hydrogen
This is what happens when you use inert electrodes (like platinum or carbon/graphite) for both the anode and cathode.
Anode: Cl^{-} is discharged (Chlorine gas).
Cathode: H^{+} is discharged because it is less electropositive than sodium (Hydrogen gas).
Why it's wrong here: The presence of the mercury cathode specifically prevents hydrogen from discharging, favoring sodium instead.
Option C: Chlorine and Sodium
This is the correct result for this specific setup.
Anode: Cl^{-} ions lose electrons to become chlorine gas.
Cathode: Due to the mercury electrode's properties, Na^{+} ions gain electrons to become sodium metal (which then forms an amalgam with the mercury).
Summary Table for Brine ElectrolysisElectrode Type Anode Product Cathode Product
Inert (Graphite/Platinum) Chlorine gas Hydrogen gas
Mercury Cathode Chlorine gas Sodium
Electrode Type Anode Product Cathode Product
Inert (Graphite/Platinum) Chlorine gas Hydrogen gas
Mercury Cathode Chlorine gas Sodium
no i disagree with the answer
Na+ is discharged preferentially because hydrogen creates a high over voltage at the mercury cathode which prevent its ion being discharged
so the correct answer is D
Electrolysis of Concentrated Sodium Chloride Solution
When concentrated sodium chloride (NaCl) solution is electrolyzed using a mercury cathode and a graphite anode, the products formed at the electrodes are determined by the specific conditions and electrode materials:
Products at the Electrodes
- At the Anode (Graphite): Chlorine gas (Cl₂) is produced due to the oxidation of chloride ions (Cl⁻) in the solution. The reaction is 2Cl⁻ → Cl₂ + 2e⁻.
- At the Cathode (Mercury): Sodium (Na) is deposited into the mercury, forming an AMALGAM, rather than hydrogen being produced. This is because the mercury cathode facilitates the reduction of sodium ions (Na⁺) over water reduction to hydrogen. The reaction is Na⁺ + e⁻ → Na.
Conclusion
Given the use of a mercury cathode, which allows for the preferential discharge of sodium ions over hydrogen ions, the products of the electrolysis are chlorine gas at the anode and sodium (which forms an amalgam with mercury) at the cathode.
The best answer is C
sorry the correct answer is C..Na will discs preferencetially because I of high voltage of H+ on Mercury cathode
My school team... you pipo are truly trying😂😂
I was scared when I saw that the answer was not D...
Please review this...
Hg prefers to discharge Na while Concentration of Cl ions favours its discharge too...
Greetings, The Myschool Team.
The correct answer is C(chlorine and sodium) and not B(chlorine and hydrogen). The bone of contention hinges on the product formed at the cathode. Ordinarily, hydrogen would be evolved at the cathode. However, due to the fact mercury electrode is used, sodium would be discharged, as it would associate with mercury to form Na/Hg amalgam which is preferentially formed. In this case, the nature of electrode plays a role. Thus, the correct answer is C(chlorine and sodium) and not B(chlorine and hydrogen). Thank you.
Correct answers is option C. Chlorine and Sodium. This is because nature of the electrode which is mercury cathode, affects the discharge of ions by having affinity for Sodium ions.
When a concentrated sodium chloride (NaCl) solution is electrolyzed using a mercury cathode and a graphite anode, the reactions at the electrodes are as follows:
At the anode (Graphite) - Oxidation occurs:
Chloride ions (Cl⁻) are oxidized to chlorine gas (Cl₂):
2Cl⁻ \rightarrow Cl₂ (g) + 2e⁻
2Cl
−
→Cl
2
(g)+2e
−
Product at the anode: Chlorine gas (Cl₂).
At the cathode (Mercury) - Reduction occurs:
Sodium ions (Na⁺) are reduced and form a sodium amalgam (Na-Hg) because mercury dissolves sodium:
Na⁺ + e⁻ \rightarrow Na (amalgam)
Na
+
+e
−
→Na(amalgam)
Product at the cathode: Sodium amalgam (Na-Hg).
Final Answer:
Anode product: Chlorine gas (Cl₂)
Cathode product: Sodium amalgam (Na-Hg)
