Suppose that 0.473 g of an unknown gas that occupies 200. mL at 1.81 atm and 25 8C was analyzed and found to contain 0.414 g of nitrogen and 0.0591 g of hydrogen. (a) What is the molecular for- mula of the compound

Respuesta :

The molecular formula of the compound is N₂H₄

we'll begin by calculating the number of mole of the unknown gas. This can be obtained as follow:

Volume (V) = 200 mL = 200 / 1000 = 0.2 L

Pressure (P) = 1.81 atm

Temperature (T) = 25 °C = 25 + 273 = 298 K

Gas constant (R) = 0.0821 atm.L/Kmol

Number of mole (n) =?

PV = nRT

1.81 × 0.2 = n × 0.0821 × 298

0.362 = n × 24.4658

Divide both side by 24.4658

[tex]n \: = \frac{0.362}{24.4658} [/tex]

n = 0.0148 mole

  • Next, we shall determine the molar mass of the compound.

mole of compound = 0.0148 mole

mass of compound = 0.473 g

molar mass of compound =?

[tex]molar \: mass \: = \frac{mass}{mole} \\ \\ molar \: mass \: = \frac{0.473}{0.0148} \\ \\ [/tex]

Molar mass of compound = 31.96 g/mol

  • Next, we shall determine the empirical formula of the compound.

Nitrogen (N) = 0.414 g

Hydrogen (H) = 0.0591 g

Empirical formula =?

Divide by their molar mass

N = 0.414 / 14 = 0.0296

H = 0.0591 / 1 = 0.0591

Divide by the smallest

N = 0.0296 / 0.0296 = 1

H = 0.0591 / 0.0296 = 2

Therefore, the empirical formula of the compound is NH₂

  • Finally, we shall determine the molecular formula of the compound. This can be obtained as follow:

Molar mass of compound = 31.96 g/mol

Empirical formula = NH₂

Molecular formula = ?

Molecular formula = Empirical formula × n = Molar mass

[NH₂]n = 31.96

[14 + (2×1)]n = 31.96

16n = 31.96

Divide both side by 16

n = 31.96 / 16

n = 2

Molecular formula = [NH₂]n

Molecular formula = [NH₂]₂

Molecular formula = N₂H₄

Thus, the molecular formula of the compound is N₂H₄

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