Question

Question #1fd4c

Answer 1

The molecular formula is `C_4H_10`

Explanation:

`n= V/24 = 9.6/24 = 0.4mol`

`Mr = M/n = 23.2/0.4 = 58 gmol^-1`

Since the formula mass of `C_2H_5` is 29, it follows that the molecule contains `58/29`, or `2` times the number of atoms.

Hence, the molecular formula is `C_4H_10`, which is butane.

Answer 2

The molecular formula is `"C"_4"H"_10`, which is probably butane.

Explanation:

We have `"C"_2"H"_5` as the empirical formula. We must find its molar mass. To do so, we need to know how many moles of it evaporated. Use the Ideal Gas Law:

`PV=nRT`, and here:

`P=1"atm"`

`V=9.6"L"`

`R=0.0821"L atm K"^-1"mol"^-1`

`T=293.15"K"`.

To solve for `n`, moles, we rearrange:

`n=(PV)/(RT)`, and inputting:

`n=(1*9.6)/(293.15*0.0821)`

`n=0.399"mol"~~0.4"mol"`

Another formula for moles is `n=m/M`, where `m` is the mass and `M` the molar mass.

Rearranging to solve for `M`, we get:

`M=m/n`

We have `m=23.2"g"`. Inputting:

`M=23.2/0.399`

`M=58.16"g/mol"`

We must calculate the molar mass of the empirical formula:

`M_e=(12*2)+(1*5)`

`M_e=29"g/mol"`

We see a `2:1` ratio.

Therefore, the molecular formula is `"C"_4"H"_10`, which is probably butane.