Question

A 0.465 g sample of an unknown compound occupies 245 ml at 298 k and 1.22 atm. what is the molar mass of the unknown compound?

a.26.3 g/mol
b.33.9 g/mol
c.12.2 g/mol
d.38.0 g/mol
e.81.8 g/mol

Answer 1

Answer: Option (d) is the correct answer.

Step-by-step explanation:

It is know that for an ideal gas PV = nRT

where P = pressure

V = volume

n = number of moles =
`(mass)/(molar mass)`

R = gas constant = 0.082
`L atm K^(-1) mol^(-1)`

T = temperature

Therefore, put the given values in the formula above as follows.

PV = nRT

or, PV =
`(mass)/(molar mass)RT`

`1.22 atm * 0.245 L = (0.465 g)/(molar mass) * 0.082 L atm K^(-1) mol^(-1) * 298 K`

molar mass = 38.12 g/mol

= 38.0 g/mol (approx)

Therefore, we can conclude that the molar mass of the unknown compound is 38.0 g/mol.

Answer 2

we can find the number of moles of gas using the ideal gas law equation

PV = nRT

where P - pressure - 1.22 atm

V - volume - 0.245 L

n - number of moles

R - gas constant - 0.08206 L.atm/mol.K

T - temperature - 298 K

substituting the values in the equation

1.22 atm x 0.245 L = n x 0.08206 L.atm/mol.K x 298 K

n = 0.0122 mol

molar mass of compound = mass present / number of moles therefore molar mass = 0.465 g / 0.0122 mol = 38.1 g/mol
the answer is d) 38.0 g/mol