Use the vapour pressures (at 25 °C) of the pure substances below to answer the f

Question

Use the vapour pressures (at 25 °C) of the pure substances below to answer the following questions.

1. Determine the partial pressure (in kPa) of 3-methyl-1-pentene (C6H12) in the vapour phase (at 25 °C) over a solution for which the mole fraction of diiodomethane (CH2I2) is 0.170. Report your answer to three significant figures in scientific notation.



2.99×101 kPa

2. A solution of diiodomethane (CH2I2) and 3-methyl-1-pentene (C6H12) is prepared by adding 3.15 g of diiodomethane to 5.63 g of 3-methyl-1-pentene. Determine the mole fraction of diiodomethane in the vapor phase (at 25 °C). Report your answer to three significant

Substance P* (kPa) diiodomethane (CH2I2) 0.172 3-methyl-1-pentene (C6H12) 36

Explanation / Answer

Given that;

the mole fraction of diiodomethane (CH2I2) is 0.170

thus the mole fraction of 3-methyl-1-pentene (C6H12) = 1-0.170= 0.830

Substance

P* (kPa)

diiodomethane (CH2I2)

0.172

3-methyl-1-pentene (C6H12)

36

Partial pressure (in kPa) of 3-methyl-1-pentene (C6H12) in the vapor phase= mole fraction * vapor pressure of pure substance

= 0.830 *36 kPa = 2.99*10^1 kPa

2

Number of moles = amount in g/ molar mass

diiodomethane (CH2I2): mole s= 3.15 g/ 267.84 g/mol

= 0.0118 moles

3-methyl-1-pentene , moles = 5.63 g/ 84.162g/ mole

= 0.0668 moles

Mole fraction; diiodomethane: number of moles diiodomethane/ total moles

= 0.0118 /0.0118+ 0.0668

= 0.0118/0.0786

= 0.15

thus the mole fraction of 3-methyl-1-pentene (C6H12) = 1-0.150= 0.850

Substance

P* (kPa)

diiodomethane (CH2I2)

0.172

3-methyl-1-pentene (C6H12)

36

Partial pressure (in kPa) of 3-methyl-1-pentene (C6H12) in the vapor phase= mole fraction * vapor pressure of pure substance

= 0.850 *36 kPa = 3.06*10^1 kPa

Partial pressure (in kPa) of diiodomethane (CH2I2) = 0.150* 0.172

=0.0258 kPa

Total pressure = 3.06*10^1 kPa +0.0258 kPa = 30.63 kPa

Mole fraction in vapor = pressure of pure substance / total pressure

diiodomethane (CH2I2)= 0.172 /30.6

= 5.62*10^-3

3-methyl-1-pentene (C6H12)= 1.00- 5.62*10^-3

=0.994

Substance

P* (kPa)

diiodomethane (CH2I2)

0.172

3-methyl-1-pentene (C6H12)

36

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