The electrolysis of an aqueous solution of potassium iodide, KI, results in the

Question

The electrolysis of an aqueous solution of potassium iodide, KI, results in the formation of hydrogen gas at the cathode and iodine at the anode. A sample of 80.0 milliliters of a o.150 molar solution of KI was electrolyzed for 3.00 minutes, using a constant current. At the end of this time, the 2 produced was titrated against a 0.225 molar solution of sodium thiosulfate, which reacts with iodine according to the equation below. The end point of the titration was reached when 37.3 milliliters of the Na.S,O, solution had been added. 12 + 2 S,032-21. + S4062. (a) How many moles of 12 was produced during the electrolysis? The hydrogen gas produced at the cathode during the electrolysis was collected over water at 25°C at a total pressure of 752 millimeters of mercury. Determine the volume of hydrogen collected. (The vapor pressure of water at 25°C is 24 millimeters of mercury.) (b)

Explanation / Answer

(b) Write down the cathode and the anode reactions:

Cathode: H2O (aq) -------> H+ (aq) + OH- (aq)

2 H+ (aq) + 2 e- -------> H2 (g)

Anode: KI (aq) -------> K+ (aq) + I- (aq)

2 I- (aq) -------> I2 (s) + 2 e-

The overall reaction is

2 H+ (aq) + 2 I- (aq) -------> H2 (g) + I2 (s)

As per the stoichiometric equation,

1 mole H2 = 1 mole I2.

Therefore, mole(s) H2 produced at the cathode = mole(s) I2 produced at the anode = 0.0042 mole.

Use the ideal gas law: P*V = n*R*T

where P = pressure of H2 and T = temperature of H2 gas.

The pressure of H2 is 752 mmHg and the water vapor pressure is 24 mmHg; therefore, the pressure of dry H2 is (752 – 24) mmHg = 728 mmHg = (728 mmHg)*(1 atm/760 mmHg) = 0.9579 atm; T = 25°C = (25 + 273)K = 298 K.

Plug in values and obtain

(0.9579 atm)*V = (0.0042 mole)*(0.082 L-atm/mol.K)*(298 K)

====> V = 0.10714 L = (0.10714 L)*(1000 mL/1 L) = 107.14 mL (ans).

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.