Electrochemistry

Step 1: Understanding Electrode Polarity:
The negative electrode is the Cathode. Cations (positively charged ions) are attracted to the cathode to undergo reduction.

Step 2: Identifying the Cation:
In molten aluminium oxide (Al_2O_3), the cation is Al^3+.

Step 3: Describing the Cathode Reaction:
At the cathode, aluminium ions gain three electrons each to form neutral aluminium atoms: [ Al^3+ + 3e^- Al ] This is a reduction reaction.

Step 4: Final Answer:
Reaction 1 is the correct cathode reaction.

Step 1: Understanding Water Electrolysis:
The decomposition of water into its constituent gases is represented by the equation: [ 2H_2O (l) 2H_2 (g) + O_2 (g) ]

Step 2: Evaluating the Assertion:
From the balanced equation, 2 volumes of Hydrogen are produced for every 1 volume of Oxygen. Thus, Assertion (A) is True.

Step 3: Evaluating the Reason:
Water (H_2O) consists of Hydrogen and Oxygen in a ratio of 2:1 by volume (and 1:8 by mass). Reason (R) states the ratio is 1:2, which is False.

Step 4: Final Answer:
Assertion (A) is true but Reason (R) is false.

(a) Cathode Reaction: The silver ions migrate to the spoon (cathode) and gain electrons to deposit as metal. [ Ag^+ + e^- Ag(s) ]

(b) Reason for avoiding (AgNO_3): Silver nitrate is a strong electrolyte and causes very rapid migration of ions. This leads to an uneven, loose, and non-uniform coating. Sodium argentocyanide (Na[Ag(CN)_2]) provides a slow and steady supply of silver ions, ensuring a smooth and firm plate.

(c) Why AC is not used: Alternating current (AC) reverses polarity periodically. This would cause the metal to deposit during one half-cycle and dissolve back into the solution during the next, resulting in no net electroplating.

(d) Observation at Anode: The silver block (anode) gradually decreases in size/mass as silver atoms lose electrons and enter the solution as ions (Ag Ag^+ + e^-).