Question

Nickel can combine with carbon monoxide to form a compound that has the chemical formula Ni(CO)n, where n is a whole number. This compound is a gas at 75 C. In an effusion experiment at 75 C, 12.1 mL of this compound escapes through the pinhole in 10.0 minutes. Under the same conditions, 11.9 mL of carbon dioxide effuses in 5.0 minutes. Using this information, determine the chemical formula of the unknown compound.

Answer 1

Ans. It’s assumed that both the gases behave ideally under given conditions. The experiment is conducted as same temperature.

Now,

Rate of effusion of CO = Vol. of CO effusing per unit time

                                                = 11.9 mL/ 5.0 min

                                                = 2.38 mL min^-1

Rate of effusion of Ni(CO)n = 12.1 mL/ 10.0 min = 1.21 mL min^-1

# Calculation of molar mass of Ni(CO)n using Graham’s law:

# Calculation of molecular formula of Ni(CO)n:

Total mass of the compound per mol =

(1 mol x molar mass of Ni) + (n mol x molar mass of Co)

Or, 108.375 g = (1 mol x 58.693 g mol^-1) + (n mol x 28.0104 g mol^-1)

Or, 108.375 g – 58.693 g = (n mol x 28.0104 g mol^-1)

Or, 49.682 g / 28.0104 g = n

Or, n = 1.77 = 2.0 (rounded off to nearest whole number)

            Thus, n = 2

Therefore, chemical formula of the compound = Ni(CO)₂