Question

Which process occurs in the electrolysis of an aqueous solution of nickel chloride at nickel anode? (a) \(\mathrm{Ni} \rightarrow \mathrm{Ni}^{2+}+2 \mathrm{e}^{-}\) (b) \(\mathrm{Ni}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Ni}\) (c) \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}\) (d) \(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}\)

Short answer

The process that occurs in the electrolysis of an aqueous solution of nickel chloride at nickel anode is (c) the oxidation of chloride ions, resulting in the formation of chlorine gas.

Step-by-step solution

Understand the Electrolysis Process

Electrolysis is the process of causing a chemical reaction to occur by passing an electric current through a substance. In the electrolysis of an aqueous solution of nickel chloride (NiCl2), there are two possible reactions at the anode: oxidation of nickel (Ni) and oxidation of chloride ions (Cl-).

Identify the Anode Reaction

The anode is the electrode where oxidation occurs. In an electrolytic cell, positive metal ions are reduced at the cathode, while at the anode, either the metal goes into solution by oxidation (if the electrode is active) or the anions in the solution are oxidized. Since the anode in this case is made of nickel, we must determine whether the nickel or the chloride ions are oxidized.

Determine the Reaction at a Nickel Anode

Considering that nickel is a less reactive metal, it's more likely for the chloride ions to be oxidized at the anode rather than the nickel itself. Therefore, the oxidation of chloride ions to form chlorine gas is the expected reaction. This is option (c).

Key concepts

Understanding the Electrolysis Process

Electrolysis is a fascinating and widely-used chemical process where electric current triggers a non-spontaneous chemical reaction. This process is pivotal in numerous industrial applications, including electroplating, purifying metals, and generating chemicals like chlorine and hydrogen. In essence, electrolysis involves an electrochemical cell with two electrodes immersed in an electrolyte solution. When voltage is applied, ions in the solution move towards the electrodes, where reduction and oxidation reactions occur. The cathode, which attracts cations, is the site of reduction, while the anode, which attracts anions, is where oxidation takes place.

During electrolysis, it's essential to distinguish between the electrodes involved. The positive electrode, or anode, supports the oxidation reaction - atoms or ions lose electrons here. On the other hand, the negative electrode, or cathode, sees reduction - atoms or ions gain electrons. The type of ions present in the solution and the nature of the electrode material profoundly influence the actual reactions that occur.

Details of Anode Oxidation Reaction

At the anode, oxidation reactions are key to the electrolytic process, as they involve the loss of electrons from chemical species. Oxidation can occur with either metal atoms from the electrode or with anions from the electrolyte. Normally, if the electrode material is more reactive, it tends to oxidize and dissolve into the solution. If the electrode is less reactive or 'inert', the anions from the electrolyte are likely to be oxidized instead.

In an aqueous solution, if the electrolyte contains ions from a reactive metal, such as sodium or magnesium, they will not oxidize at the anode. Instead, water molecules will decompose, leading to the production of oxygen and protons. However, with less reactive electrode materials, such as platinum or graphite, the anions (like sulfate or chloride ions) are more likely to be oxidized. This dynamic is essential for predicting the products of electrolysis and ensuring the desired reactions occur within industrial processes.

Nickel Chloride Electrolysis Breakdown

The specific case of aqueous nickel chloride (NiCl2) electrolysis involves the conductive solution of NiCl2 surrounded by a nickel anode and typically a less reactive cathode. Considering nickel's position in the reactivity series and its tendency not to readily oxidize in an electrolytic setup, the anode reaction predominantly features the oxidation of chloride ions (Cl-) over the oxidation of nickel itself. This reaction can be summarized with the equation:
\[2 \mathrm{Cl}^- \rightarrow \mathrm{Cl}_{2(g)} + 2e^-\].

Chloride ions give up their electrons to become chlorine gas, which bubbles off at the anode. Meanwhile, at the cathode, nickel ions in the solution can gain electrons to form solid nickel, or if the concentration of hydrogen ions is high enough and the potential is suitable, hydrogen evolution may occur instead. On passing a sufficient electric current, nickel ions can also be reduced to metallic nickel, completing the electrolysis process:
\[\mathrm{Ni}^{2+} + 2e^- \rightarrow \mathrm{Ni(s)}\].

This understanding enables accurate prediction of the electrolysis outcomes and ensures effective application in tasks such as metal refining and electroplating.