Question

Molecular weight of alkane found to be 142 suggest its molecular formula

Answer 1

using the formula of alkane C(n) H(2n+2), we can easily find molecular formula of any alkane , its molecular weight is 142 , so it is C10H22

Answer 2

Molecular formula for the alkane with molecular weight is $C_{10}H_{22}$

• The general formula for alkane is $C_nH_{2n+2}$.
• As the molecular weight is given as 142, to find the molecular formula, following the value of the 'n' must be identified through the following step:

Molecular formula = Molecular weight

12n + 2n+2 = 142       ∵(Mass of carbon is 12 and hydrogen is 1)

14n + 2 = 142

14n = 142 - 2

14n = 140

n = $\frac{140}{10}$

n = 10

• When the value of n is substituted in general formula of alkane, it gives $C_{10}H_{20+2} = C_{10}H_{22}$.
• Thus for alkane with molecular weight 142, the molecular formula was identified as $C_{10}H_{22}$.

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