Question Video: Understanding Why Ethane Is a Member of the Homologous Series of Alkanes but Methanol Is Not | Nagwa Question Video: Understanding Why Ethane Is a Member of the Homologous Series of Alkanes but Methanol Is Not | Nagwa

Question Video: Understanding Why Ethane Is a Member of the Homologous Series of Alkanes but Methanol Is Not Chemistry

Why is ethane a member of the homologous series of alkanes, but methanol is not?

02:54

Video Transcript

Why is ethane a member of the homologous series of alkanes, but methanol is not? (A) Ethane has two carbon atoms, but methanol only has one. (B) Ethane is a gas, but methanol is a liquid. (C) Ethane is obtained from crude oil. (D) Ethane has a smaller molecular mass. (E) Ethane contains the same functional group as other alkanes.

Let us start by discussing what a homologous series is. A homologous series is a family of compounds that have the same functional group. One general formula can describe all members of a homologous series. Each molecule in the series differs from the next by a simple structural unit such as the -CH2 unit.

The members of a homologous series usually have similar chemical properties because they have the same functional group. Alkanes are a series of saturated hydrocarbons that only include carbon and hydrogen covalently bonded together with only single bonds. All straight-chain alkanes have the same functional group because they are of a single homologous series. They also have somewhat similar chemical properties. All straight-chain alkane compounds have the formula C𝑛H2𝑛+2, where 𝑛 represents the number of carbon atoms. Ethane has the chemical formula C2H6. We can test to see if it is an alkane. All we need to do is to determine if it has the general formula C𝑛H2𝑛+2.

We should first state that ethane has two carbon atoms and six hydrogen atoms. To determine if ethane is an alkane, we substitute 𝑛 with the number of carbon atoms in ethane. Then, we substitute 𝑛 into C𝑛H2𝑛+2 and get C2H2(2)+2. This formula simplifies to C2H6. So, we can see that ethane is an alkane because it has the same general formula and the same functional group as other alkanes.

Methanol has the formula CH3OH, and this does not match the general formula of an alkane. As you can see, methanol contains the hydroxyl group -OH. This means that it belongs to the homologous series of alcohols. Ethane and methanol do not have the same general formula or the same functional group.

So, the correct answer is (E). Ethane contains the same functional group as other alkanes.

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