Respuesta :
Answer:
The molecular formula = N2O4 (option D)
Explanation:
Step 1: Data given
Compound has 30.4 % N and 69.6 % O
Mass of the sample = 5.25 grams
Volume = 1L
Pressure = 958 mmHg = 1.26 atm
Temperature = -4°C = 269 Kelvin
Molar mass of N = 14 g/mol
Molar mass of O = 16 g/mol
Step 2: Calculate mass of N
Mass of N = 5.25 grams * 0.304 = 1.596 grams
Step 3: Calculate mass of O = 5.25 grams * 0.696 = 3.654 grams
Step 4: Calculate number of moles N
Number of moles = Mass of N/ Molar mass of N
Moles of N = 1.596 grams / 14g/mol
Moles of N = 0.114 moles
Step 5: Calculate moles of O
Moles O = 3.654 grams /16 g/mol
Moles 0 = 0.2884 moles
Step 6: Divide number of moles by the smallest number of mol
N : 0.114 / 0.114 = 1
O: 0.2284 / 0.114 = 2
⇒ This means the empirical formule = NO2
Step 7: Calculate number of moles of 5.25 g sample via gas law:
p*V = nRT
with p = the pressure = 1.26 atm
with v = 1.00 L
with n = the number of moles = TO BE DETERMINED
with R = the gasconstant = 0.08206 L*atm/ K*mol
with T = the temperature = 269 K
n = p*V/R*T
n = (1.26*1L)/(0.08206*269)
n = 0.057 mol
Step 8: Calculate molar mass of the gas
This means 5.25 grams of the gas = 0.057 moles
So 1 mol = 5.25 / 0.057 = 92.11 g/mol
Step 9: Calculate molar mass of the empirical formula
The empirical formule NO2 has a molar mass of 46 g/mol
Step 10: Calculate molecular formula
92.11 / 46 = 2
This means the empirical formula should be multiplied by 2
2(NO2) = N2O4
The molecular formula = N2O4
