Question

What is the molecular mass of a compound if 560mL have a mass of 1.10g at STP?

Answer 1

Assuming that your compound is a gas, then the answer should be 44.053 g/mol.

Explanation:

Since the volume, temperature and pressure of the unknown compound is given, I'm going to assume that it is a gas (although these given are applicable to liquid compounds as well).

So the given are: m = 1.10 g; V = 560 mL or `color (orange) (0.560 L)`; T = `0^@C` or `color (orange) (273.15 K)`; P = `760 "mmHg"` or `color (orange) (1 "atm")`

Based on the given, we can use the Ideal Gas Equation (where the gas constant, R is equal to `0.0821 (L*atm)/(mol*K)`) to determine the number of moles the unknown compound has, then subsequently, its molecular mass.

`PV` = `nRT`

thus,

`n` = `(PV)/(RT)`

`n` = `(1 cancel "atm" * 0.56 cancel L)/(0.0821 cancel (L* cancel atm)/(mol* cancel K) * (273.15 cancel K)`

`n` = `0.02497 "mol"`

Since molar mass is defined as weight of substance over the number of moles substance or

`MM` = `("g substance")/("mol substance")`

then,

`MM` = `("1.10 g")/("0.02497mol")`

`MM` = `44.053 g/(mol)`