In this experiment what type of chemical reaction is occurring to produce H_2 at

Question

In this experiment what type of chemical reaction is occurring to produce H_2 at the cathode? What process is occurring at the anode? Why is H_2SO_4 present in the electrolysis solution? When an aqueous NaCl solution is electrolyzed, how many faradays need to be transferred at the anode to release 0.100 mol of C1_2 gas? How long must a current of 0.50 A pass through a sulfuric acid solution to liberate 0.200 L of H_2 gas at STP? A current of 3.00 A was passed through a solution of sulfuric acid for 20 minutes. The hydrogen was collected at 20 degree C and 640.0 mm Hg and was found to occupy a volume of 534 mL, How many coulombs (C = A times s) were passed through the solution? How many electrons were passed through the solution? How many moles of H_2 were produced? What is the value of Avogadro's number, N?

Explanation / Answer

1)

Faradays need to be transfered at the anode to release 0.100mol of Cl2 gas.

Cathode (reduction): Na+ + e- = Na

Anode (oxidation): 2 Cl- = Cl2 + 2 e-

2 Cl- + 2 Na+ -------> Cl2 + 2 Na

Faraday is charge of one mole of electron which is 96 485.3329 coulombs.

So one mole of electron (Faraday) produces one mole of Na and half mole of Cl2

2 moles of electron = 1 mol of Cl2

0.100 mol of Cl2 = 0.100 x 2 moles of electron.

0.100 mol of Cl2 = 0.200 moles of electron.

1 mol = 6.0221415 x 1023

0.200 mol = 0.200 x 6.0221415 x 1023

= 1.2044283 x 1023

1 Faraday = 1.60217653 x 10-19 x 6.0221415 x 1023

So 1.2044283 x 1023 corresponds to 1.60217653 x 10-19 x 1.2044283 x 1023 = 19297.067 columbs

1 Faraday = 96 485.3329 coulombs.

(1/96 485.3329) Faraday = 1 coulomb

19297.067 coulombs = 19297.067 / 96 485.3329 = 0.199 faradays.

2)

Sulphuric acid electrolysis

Current = Charge / Second.

Number of moles of H2

PV = nRT

n = 1 atm x 0.200 L / 8.205 74 × 10 2 L atm K 1 mol 1 x 298 K

n = 0.0081789 mol

it takes 2 moles electron to from one mol of H2

1 mol of H2 = 2 mol of electron

0.0081789 mol of H2 = 0.0081789 x 2 mol of electron

= 0.0163578 mol of electron.

1 mol = 6.0221415 x 1023

0.0163578 mol = 0.0163578 x 6.0221415 x 1023

= 9.85089 x 1021

1 Faraday = 1.60217653 x 10-19 C x 6.0221415 x 1023

= 1.60217653 x 10-19 x 9.85089 x 1021

= 1578.28 C

Time required is

1578.28 C / 0.50 C s-1 = 3156.56 seconds or 0.87 hours

3)

PV = nRT

Given

P = 640 mmHg(Torr)

T = 20 oC

V = 534 x 10-3 L

n = PV / RT

n = 640 Torr x 534 x 10-3 L / (1 62.364 L Torr K 1 mol 1)(R in terms of L and Torr) x (273+20) K

n = 0.007183 mol

Number of moles of H2 produced is 0.007183

Current = Charge / Time

Given

Time = 20 min

Current = 3.00 A

Charge = Current x Time

Charge = 3.00 C / s x (20 x60) s

Charge = 3.00 C / s x 1200 s

Charge = 3600 C

We know that it takes 2 moles electron to from one mol of H2

1 mol of H2 = 2 mol of electron

Then

0.007183 mol of H2 = 2 x 0.007183 mol of electron

Number of moles of electron is 0.014366

The value of Avagadro number is 6.0221415 x 1023

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