Question

What is the molecular weight of chloroform if \[0.025mol\] weighs \[3.28gms\] ?
A) \[0.0076gm\]
B) \[0.082gm\]
C) \[131.2gm\]
D) None of the above

Answer 1

Hint: We have to remember that the chloroform is an organic compound having molecular formula \[CHC{l_3}\].The molar mass of $CHC{l_3}$ is $119.38g/mol$.

Complete step by step answer:
We need to remember that the number of molecules is equal to the given weight of a compound divided by the molecular weight of a compound.
\[n = \dfrac{m}{M}\]
Where,
n=no. of moles
m=given weight of a compound
M=molecular weight of a compound
To find the molecular weight of chloroform in this question will be as follows:
Let M be x i.e. the molecular weight of chloroform
Given data contains
$m = 3.28gm$
$n = 0.025mol$
\[n = \dfrac{m}{M}\]
Now we can substitute the known values we get,
\[0.025 = \dfrac{{3.28}}{x}\]
$x = \dfrac{{3.28}}{{0.025}}$
On simplification we get,
$x = 131.2gm$

Option A) this is an incorrect option as this value comes no. of moles is divided to the given weight of chloroform which is an incorrect formula to calculate no. of moles.
Option B) This is an incorrect option as this value comes when we multiply no. of moles with given weight of chloroform which is an incorrect formula to find the molecular weight of this compound.
Option C) this is a correct option as \[131.2gm\] is the molecular weight of chloroform if the no. of moles is equals to \[0.025mol\] and the given weight is $3.28gm$ as solved above. As no. of moles is equal to given weight divided by molecular weight.
Option D) this is an incorrect option as we got option C as the correct option.

Hence, the correct answer is, ‘Option C’.

Note: We have to remember that the molar mass of chloroform is used when we need to calculate no. of moles and the given mass is always given if we need to find the no. of moles.