Question

A direct-current power supply of low voltage (less than 10 volts) has lost the markings that indicate which output terminal is positive and which is negative. A chemist suggests that the power supply terminals be connected to a pair of platinum electrodes that dip into 0.1-molar KI solution. Which of the following correctly identifies the polarities of the power supply terminals?

(A) A gas will be evolved only at the positive electrode.
(B) A gas will be evolved only at the negative electrode.
(C) A brown color will appear in the solution near the negative electrode.
(D) A metal will be deposited on the positive electrode.
(E) None of the methods above will identify the polarities of the power supply terminals.

Answer 1

A

Step-by-step explanation:

As electrolysis progresses, the iodide ion migrates towards the anode (positive electrode) and is discharged as iodine gas while the metal migrates towards the cathode (negative electrode). The evolution of gas at the positive electrode signifies the reaction:

2I-=I2 +2e