When chromium metal is added to nitric acid, the following reaction takes place Cr (s) + 6 HNO₃ (aq) → Cr(NO₃)₃ (aq) + 3 H₂O (l) + 3 NO₂ (g) Calculate the volume of NO₂ gas (in L) collected over...

Question

When chromium metal is added to nitric acid, the following reaction takes place Cr (s) + 6 HNO₃ (aq) → Cr(NO₃)₃ (aq) + 3 H₂O (l) + 3 NO₂ (g) Calculate the volume of NO₂ gas (in L) collected over water at 40.0 °C when 11.1 g of chromium is added to excess nitric acid if the total pressure is 675.0 torr. The vapor pressure of water at 40.0 °C is 55.3 torr.

Answer 1

Cr (s) + 6 HNO₃ (aq) ==> Cr(NO₃)₃ (aq) + 3 H₂O (l) + 3 NO₂ (g) ... balanced equation

To find the volume of NO2 formed, we must first find the moles of NO₂ produced and then use the ideal gas law to find the volume under the conditions of the experiment.

moles NO₂ formed:

11.1 g Cr x 1 mol Cr / 52.0 g x 3 mol NO₂ / 1 mol Cr = 0.640 mols NO₂ produced

Volume of NO₂ produced:

Use the ideal gas law ... PV = nRT

P_NO2 = total pressure - pressure of H₂O = 675 torr - 55.3 torr = 619.7 torr x 1 atm/760 torr = 0.815 atm

V = volume in L = ?

n = moles = 0.640

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 40C + 273 = 313K

Solving for V, we have ...

V = nRT/P = (0.640)(0.0821)(313) / 0.815)

V = 20.2 L