Electrolysis is a process that can split water into hydrogen gas and oxygen gas. If 27.1 g of water are split, what is the resulting mole fraction of hydrogen gas? Of oxygen gas? If the gases are in a 12.2 L container at standard temperature, what is the partial pressure of the hydrogen gas? Of oxygen gas?

Respuesta :

Answer:

  • 1. mole fraction of hydrogen gas: 0.667
  • 2. Mole fraction of oxygen gas: 0.333
  • 3. Partial pressure of the hydrogen gas: 2.764 atm
  • 4. Partial pressure of oxygen gas: 1.382 atm

Explanation:

1. Chemical equation of electrolysis

a) Word equation:

  • Water  → hydrogen gas + oxygen gas

b) Balanced chemical equation:

           [tex]2H_2O(l)\rightarrow 2H_2(g)+O_2(g)[/tex]

c)  Mole ratios:

          [tex]2molH_2O(l):2molH_2(g):1molO_2(g)[/tex]

2.  Number of moles of water

i) Formula: Number of moles = mass in grams/molar mass

ii) Molar mass of water: 18.015g/mol

iii) Mass: 27.1 g

iv) Substitute and compute:

  • Number of moles = 27.1g / 18.015g = 1.504mol

3.  Mol fraction of hydrogen gas:

a) Number of moles of hydrogen gas:

Using the theoretical mol ratio of hydrogen to water, 2 moles of water produce 2 moles of hydrogen gas. Then, 1.504 mol of water produce 1.504 mol of hydrogen gas.

  • 1.504 mol H₂(g)

b) Number of moles of oxygen gas:

Using the theoretical mol ratio, 2 moles of water produce 1 mole of oxygen gas. The, 1.504 mol of water produce half of 1.504 mol = 0.752 moles of oxygen gas.

  • 0.752 mol O₂(g)

c) Mole fraction: [tex]X_A[/tex]

i) Formula: [tex]X_A=\dfrac{\text{moles of A}}{\text{total number of moles}}[/tex]

ii) For hydrogen:

               [tex]X_H_2=\dfrac{1.50mol}{1.504mol+0.725mol}[/tex]

               [tex]X_H_2=0.667[/tex]

4. Mole fraction of oxygen gas

The mole fraction of all the components of a mixture adds up 1.

The mole fraction of O₂ = 1 - 0.667 = 0.333

5. Partial pressure of the hydrogen gas

i) Calculate the total pressure

  • Use ideal gas equation:

          [tex]pV=nRT[/tex]

         [tex]p=\dfrac{nRT}{V}[/tex]

Substitute:

  • n = 2.256mol
  • R = 0.08206amt-liter/K-mol
  • T = 273.15K

          [tex]p=\dfrac{2.256atm\times 0.08206(atm\cdot liter/K\cdot mol)\times 273.15K }{12.2liter}\\\\\\p=4.146atm[/tex]

ii) Partial pressure

  • Formula:

[tex]\text{Partial pressure of A}=X_A\times \text{Total pressure}[/tex]

  • Substitute and compute:

       [tex]\text{Partial pressure of }H_2=0.667\times 4.146atm=2.764atm[/tex]

6. Partial pressure  oxygen gas

        [tex]\text{Partial pressure of }O_2=0.333\times 4.146atm=1.382atm[/tex]

1. Mole fraction of hydrogen gas: 0.667

2. Mole fraction of oxygen gas: 0.333

3. Partial pressure of the hydrogen gas: 2.764 atm

4. Partial pressure of oxygen gas: 1.382 atm

Chemical equation of electrolysis:

a) Word equation:

Water  → hydrogen gas + oxygen gas

b) Balanced chemical equation:

[tex]2H_2O--- > 2H_2(g)+O_2(g)[/tex]

     

Number of moles of water

Number of moles = mass in grams/molar mass

Molar mass of water: 18.015g/mol

Mass: 27.1 g

On substituting the values:

Number of moles = 27.1g / 18.015g = 1.504mol

Mol fraction of hydrogen gas:

a) Number of moles of hydrogen gas:

Using the theoretical mol ratio of hydrogen to water, 2 moles of water produce 2 moles of hydrogen gas. Then, 1.504 mol of water produce 1.504 mol of hydrogen gas.

1.504 mol H₂(g)

b) Number of moles of oxygen gas:

Using the theoretical mol ratio, 2 moles of water produce 1 mole of oxygen gas. The, 1.504 mol of water produce half of 1.504 mol = 0.752 moles of oxygen gas.

0.752 mol O₂(g)

c) Mole fraction:

For hydrogen: 1.50 mol / 1.504+0.725 mol

Mol fraction of hydrogen = 0.667

Mole fraction of oxygen gas

The mole fraction of all the components of a mixture adds up 1.

The mole fraction of O₂ = 1 - 0.667 = 0.333

Partial pressure of the hydrogen gas

i) Calculate the total pressure

Use ideal gas equation:

PV= nRT        

where,

n = 2.256mol

R = 0.08206amt-liter/K-mol

T = 273.15K

P= (2.256 * 0.08206*273.15 )/ 12.2

P= 4.126 atm

Partial pressure of A = XA * Total pressure

Partial pressure of hydrogen gas = 0.667 * 4.146 = 2.764

Partial pressure oxygen gas =  0.333*4.146 = 1.382 atm

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