Question

Molecular formula for alkane having molecular mass 142

Answer 1

alkanes General molecular formula is C(n)H(2n+2) where n is no. of carbon atoms now using it to calculate mass that it
12 is mass of carbon and 1 is of hygrogen.
total given mass is 142. now then
12n +1(2n+2) = 142.
14n +2 = 142
14n = 140
n= 10.
thus Decane is the answer.

Answer 2

Given:

An alkane has a molecular mass of 142.

To find:

We have to find the molecular formula.

Solution:

The general formula of an alkane is $C_nH_{2n+2}$.

The atomic mass of the C atom is 12 and the atomic mass of the H atom is 1.

Thus the general molecular mass of alkane is-

12n+(n+2)×1

This is equal to 142.

So, we can write-

$12n + n + 2 = 142 \\ 14n = 140 \\ n = 10$

The value of n is 10.

Hence the molecular formula of the alkane is $C_{10}H_{12}$.