3.55 moles #H_2# (g), 1.25 moles #CO# (g), and an unknown number of moles #N_2# (g) were placed into a 5.00 L flask at #25.0^oC#. Given the density of this gas mixture to be 19.92 g/L, how many moles of #N_2# were in the flask?

Question

What is the total pressure, in atm, inside the flask?

Caleb Adams · Accepted Answer

2.05 mol.

Determine the mass of the gas mixture first. Density is equal to mass / volume. #mass = density xx volume# #mass = 19.92 \ g/L xx 5.00 \ L# #mass = 19.92 \ g/cancel(L)xx 5.00 \ cancel(L)# #mass = 99.6 \ g# The above mass is the mass of the gas mixture (#m_(mix)#). It includes the masses of #N_2 , H_2 # and #CO#. #color (red) (m_(mix) = m_(N_2) + m_(H_2) + m_(CO))# #----------------# #underbrace(m_(N_2) = ???)# #m_(H_2) = n_(H_2) xx MM_(H_2)# #m_(H_2) = 3.55 \ mol. xx 2.016 \ g/(mol.)# #m_(H_2) = 3.55 \ cancel(mol.)xx 2.016 \ g/(cancel(mol.))# #underbrace(m_(H_2) = 7.16 \ g)# #m_(CO) = n_(CO) xx MM_(CO)# #m_(CO) = 1.25 \ mol. xx 28.01 g/(mol.)# #m_(CO) = 1.25 \ cancel(mol.) xx 28.011 g/(cancel(mol.))# #underbrace (m_(CO) = 35.0 \ g)# #m_(N_2) = m_(mix) -{ m_(H_2) + m_(CO)}# #m_(N_2) = 99.6 \ g - { 7.16 \ g +35.0 \ g}# #underbrace (m_(N_2) = 57.4 \ g)# Once the mass of #N_2# is determined, find the number of moles. #n_(N_2) = (m_(N_2))/ (MM_(N_2))# #n_(N_2) = (57.4 \ g)/ (28.02 \ g.mol.^-1)# #n_(N_2) = (57.4 \ cancel(g))/ (28.02 \ cancel(g).mol.^-1)# #n_(N_2) = 2.05 \ mol.#

Avery Adams · Answer

undefined To find the number of moles of N2 in the flask, we first need to find the total mass of the gas mixture using the given density. Then, we can subtract the masses of the known gases (H2 and CO) to find the mass of N2. Finally, we can convert the mass of N2 to moles using its molar mass.

Total mass of gas mixture = Density * Volume
                             = 19.92 g/L * 5.00 L
                             = 99.6 g

Mass of H2 = 3.55 moles * molar mass of H2
           = 3.55 moles * 2.016 g/mol
           ≈ 7.16 g

Mass of CO = 1.25 moles * molar mass of CO
           = 1.25 moles * 28.01 g/mol
           ≈ 35.01 g

Mass of N2 = Total mass of gas mixture - Mass of H2 - Mass of CO
           = 99.6 g - 7.16 g - 35.01 g
           ≈ 57.43 g

Now, we can convert the mass of N2 to moles:

Moles of N2 = Mass of N2 / molar mass of N2
            ≈ 57.43 g / (2 * 14.01 g/mol)
            ≈ 2.05 moles

So, there were approximately 2.05 moles of N2 in the flask.