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A sample of oxygen gas is collected over water at 25°C and a total pressure of 644 torr. The volume of the gas collected is 500.0 mL. What mass of oxygen is collected? The vapor pressure of water at 25°C is 23.8 torr.

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onyebuchinnaji

The mass of oxygen gas sample collected over water is 0.544 g.

The given parameters;

  • temperature of the oxygen gas, t = 25 °C
  • total pressure of the gas, P = 644 torr
  • volume of the gas, V = 500 mL
  • vapor pressure = 23.8 torr
  • molar mass of oxygen gas = 32 g/mol

The number of moles of the gas collected is calculated by using ideal gas equation as follows;

PV = nRT

where;

  • R is the ideal gas constant = 62.36 L.torr/mol.K
  • P is the pressure of the gas = 644 torr - 23.8 torr = 620.2 torr
  • T is the temperature of the gas = 25 + 273 = 298 K
  • V is the volume of the gas = 500 mL = 0.5 L

The number of moles of the  gas is calculated as follows;

[tex]n = \frac{PV}{RT} \\\\n = \frac{620.2 \times 0.5}{62.36 \times 298} \\\\n = 0.017 \ mol[/tex]

The mass of oxygen gas collected is calculated as follows;

m = 0.017 (32 g/mol)

m = 0.544 g

Thus, the mass of oxygen gas sample collected over water is 0.544 g.

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