Question

An organic compound is 61.5% C, 2.56% H and 35.9% N by mass. 2.00 grams of this gas is entered into a 300.0 mL flask and heated to 228 degrees C. At these conditions, the gas exerts a pressure of 2670 torr. Find the empirical formula.

Answer 1

Answer:

C₄H₂N₂

Explanation:

First we calculate the moles of the gas, using PV=nRT:

P = 2670 torr ⇒ 2670/760 = 3.51 atm

V = 300 mL ⇒ 300/1000 = 0.3 L

T = 228 °C ⇒ 228 + 273.16 = 501.16 K

• 3.51 atm * 0.3 L = n * 0.082atm·L·mol⁻¹·K⁻¹ * 501.16 K

• n = 0.0256 mol

Now we calculate the molar mass of the compound:

• 2.00 g / 0.0256 mol = 78 g/mol

Finally we use the percentages given to calculate the empirical formula:

• C ⇒ 78 g/mol * 61.5/100 ÷ 12g/mol = 4

• H ⇒ 78 g/mol * 2.56/100 ÷ 1g/mol = 2

• N ⇒ 78 g/mol * 35.9/100 ÷ 14g/mol = 2

So the empirical formula is C₄H₂N₂