Problem 78 - Chemistry: The Central Science

Question

(a) What do ethane and ethanol have in common? (b) How does 1-propanol differ from propane?

Step-by-Step Solution

Answer

(a) Ethane and ethanol both have 2 carbon atoms and have similar structural features with an ethyl (C2H5) molecule as the base structure. (b) 1-propanol (CH3CH2CH2OH) has an OH functional group (hydroxyl), making it an alcohol, while propane (CH3CH2CH3) has no functional groups and is an alkane. Additionally, 1-propanol has one more oxygen atom and one less hydrogen atom in its molecular formula compared to propane.

Step 1: Identifying the structures of ethane and ethanol

Ethane is an alkane, which means it consists only of carbon and hydrogen atoms and has only single bonds. Its molecular formula is C2H6 and its structure is CH3CH3. Ethanol is an alcohol, which means it consists of carbon, hydrogen, and an OH group (hydroxyl group). Its molecular formula is C2H5OH and its structure is CH3CH2OH.

Step 2: Identifying the common feature between ethane and ethanol

Both ethane and ethanol have the same number of carbon atoms (2 carbon atoms) and have similar structural features with hydrocarbon chains. This is the main common feature, as both have an ethyl (C2H5) molecule as the base structure.

Step 3: Identifying the structures of 1-propanol and propane

1-propanol is an alcohol that consists of carbon, hydrogen, and an OH group. Its molecular formula is C3H7OH, and its structure is CH3CH2CH2OH. Propane is an alkane meaning it consists only of carbon and hydrogen atoms and has only single bonds. Its molecular formula is C3H8, and its structure is CH3CH2CH3.

Step 4: Comparing 1-propanol and propane

The main difference between 1-propanol and propane lies in the functional group they possess. 1-propanol has an OH functional group (hydroxyl), making it an alcohol, while propane does not have any functional groups and is an alkane. Additionally, 1-propanol has one more oxygen atom and one less hydrogen atom in its molecular formula compared to propane.

Key Concepts

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties, no matter what they are attached to. They are the active part of the molecule and often determine how a molecule reacts with other substances. In organic chemistry, recognizing functional groups helps to predict reactivity and properties of organic compounds.

• A key functional group in this context is the hydroxyl group (OH), which defines alcohols like ethanol and 1-propanol.
• The presence of functional groups like OH provides chemical functionality beyond what is possible with just carbon and hydrogen atoms alone.
• For example, ethanol has a hydroxyl group, making it an alcohol, whereas ethane lacks such a functional group, classifying it as an alkane.

Alkanes

Alkanes are the simplest family of hydrocarbons and are often referred to as saturated hydrocarbons due to their single bonds between carbon atoms. These compounds are made up entirely of carbon and hydrogen atoms. They follow the general molecular formula \\( C_nH_{2n+2} \).

• They are characterized by their simple arrangement, consisting solely of single carbon-carbon bonds.
• Alkanes are relatively inert, which means they don’t react easily with other substances and are typically nonpolar.
• Examples such as ethane (C2H6) and propane (C3H8) indicate how the lengths of carbon chains can increase while maintaining the alkane structure.

Alcohols

Alcohols are a category of organic compounds formed when a hydroxyl group (OH) is attached to a saturated carbon atom in a hydrocarbon chain. This makes the alcohols more polar compared to alkanes and gives them distinct properties like higher boiling points.

• Alcohols, like ethanol (C2H5OH) and 1-propanol (C3H7OH), have diverse applications due to their ability to dissolve in water.
• The presence of the hydroxyl group leads to different chemical reactivity and physical properties compared to alkanes of similar molecular size.
• Alcohols can engage in hydrogen bonding, which increases their boiling and melting points relative to alkanes.

Hydrocarbon Chains

Hydrocarbon chains form the backbone of organic molecules and consist solely of hydrogen and carbon atoms connected by single, double, or triple bonds. The simplest form is in alkanes, which contain only single bonds.

• Ethane and ethanol share a common hydrocarbon backbone, although ethanol includes an additional functional group (hydroxyl) attached to it.
• The structure and length of the hydrocarbon chain affect the chemical properties and types of reactions the molecule can undergo.
• In the comparison between 1-propanol and propane, the primary difference lies in the attachment of the functional group to the hydrocarbon chain.