Alkanes have the general molecular formula CnH₂n+2. Thus, when n = 1, the alkane is CH₄, when n = 2, the alkane is C₂H₆ etc. If an alkane has a molar mass between 140 and 150, this alkane is ________.

Question

Quizplus · Accepted Answer

To find the alkane with a molar mass between 140 and 150, we need to first find the range of possible values for n in the formula CnH₂n+2:

Let M be the molar mass of the alkane.

M = n(12.01 g/mol) + (2n + 2)(1.01 g/mol) 
M = 14.02n + 2.02

Solving for n: 
140 g/mol ≤ 14.02n + 2.02 ≤ 150 g/mol 
137.98 g/mol ≤ 14.02n ≤ 147.98 g/mol 
9.83 ≤ n ≤ 10.54

Therefore, the alkane with a molar mass between 140 and 150 has a value of n between 9.83 and 10.54.

The only option that fits this criteria is C, which corresponds to an alkane with 10 carbon atoms (n = 10) and 22 hydrogen atoms.

Alkanes Have the General Molecular Formula CnH₂n+2