Answer to Question #154438 in Inorganic Chemistry for Ash

Question

A 0. 750 g sample of gas PX3 is in a sealed 542 mL bulb at 26 and 1.00 atm of pressure. identify element X and name the gas.

Answer 1

mass of sample = 0.750g

V = 542mL = 542 × 10^-6 m³

T = 26°C = 273K + 26 = 299K

P = 1.00atm = 101325Nm^-2

Using the Ideal gas law,

PV = nRT

101325 × 542 × 10^-6 = n × 8.314 × 299

n = $\dfrac{101325×542×10^{-6}}{8.314×299} = 0.0221$

Therefore the sample of gas with a mass 0.750g contains 0.0223 moles of the compound

0.0221 moles = 0.750g

1 mole = x

x = $\dfrac{0.750}{0.0221}$g/mol = 33.94g/mol

PX₃ = 33.94g/mol

30.97g/mol + (3 × X) = 33.94g/mol

3x = 2.97g/mol

x = 0.99g/mol

The only element with that small a molar mass is Hydrogen. Therefore, x = Hydrogen

Since x = H, the chemical formula for the chemical compound is PH₃ which is another name for Phosphine with an IUPAC name Phosphane.