Problem 57 - Chemistry The Molecular Nature of Matter

Question

Write the chemical formulas for (a) methane, (b) ethane, (c) propane, and (d) butane. Give one practical use for each of these hydrocarbons.

Step-by-Step Solution

Answer

The chemical formulas are (a) methane: CH4, (b) ethane: C2H6, (c) propane: C3H8, and (d) butane: C4H10. Methane is used for heating, ethane for making plastics, propane for heating and engines, and butane for lighters and stoves.

Step 1: Identify the Prefix for Hydrocarbon Chains

The prefixes meth-, eth-, prop-, and but- correspond to the number of carbon atoms in the hydrocarbon chain: 1, 2, 3, and 4 respectively.

Step 2: Determine the Suffix for Single Bonds

Since these hydrocarbons are alkanes, they have single bonds between carbon atoms, which is denoted by the suffix -ane.

Step 3: Write the Molecular Formulas

Combine the prefixes and the suffix to write the molecular formula. Methane has one carbon, so its formula is CH4. Ethane has two carbons, so its formula is C2H6. Propane has three carbons, so its formula is C3H8. Butane has four carbons, so its formula is C4H10.

Step 4: Identify Practical Uses

Methane is used as a fuel for cooking and heating. Ethane is used in the production of ethylene for making plastics. Propane is used in heating, cooking, and as a fuel for engines. Butane is used as a fuel in lighters and portable stoves.

Key Concepts

Alkane Molecular Structure

Alkanes form a fundamental group of hydrocarbons in organic chemistry characterized by their simple structure and single covalent bonds. Each carbon atom in an alkane has four bonds. When bonded with hydrogen, the formula for alkanes follows a general pattern: \( C_nH_{2n+2} \), where \( n \) is the number of carbon atoms.

Starting with methane, the simplest alkane with one carbon atom (\( C_1H_{2(1)+2} = CH_4 \) ), we then increase the carbon chain by one to determine the chemical formulas for ethane, propane, and butane. Ethane (\( C_2H_{2(2)+2} = C_2H_6 \) ), propane (\( C_3H_{2(3)+2} = C_3H_8 \) ), and butane (\( C_4H_{2(4)+2} = C_4H_{10} \) ).

Visualization: Imagine a string of pearls where each pearl is a carbon atom. The chain has a certain number of pearls, and each pearl connects with single lines (representing single bonds) to four neighbors—other pearls (carbons) or smaller beads (hydrogens).

Organic Chemistry Nomenclature

Naming organic compounds is an essential skill in chemistry. The names of alkanes are derived by combining a prefix that indicates the number of carbon atoms with the suffix '-ane' to signify that the compounds are alkanes. For example, 'meth-' signifies one carbon, 'eth-' signifies two, 'prop-' signifies three, and 'but-' signifies four.

For the compounds in our exercise, 'methane' represents a one-carbon alkane, 'ethane' a two-carbon, 'propane' a three-carbon, and 'butane' a four-carbon alkane. This system of nomenclature allows chemists to derive the structure of the compound from its name and vice versa. This standardized naming convention greatly facilitates the study and communication of organic compounds within the scientific community.

Practical Uses of Hydrocarbons

Hydrocarbons are not just academic, they are indispensable in daily life. Methane, known chiefly as natural gas, is used extensively for domestic cooking and heating due to its clean-burning nature. Ethane, less commonly known to the public, is a vital petrochemical feedstock, cracking it produces ethylene, a precursor for polyethylene plastic manufacturing.

Propane's versatility sees it as a fuel for barbecue grills, to power engines, and in residential heating systems. Portable and readily available, it's a popular energy source. Butane finds its niche mainly as a lighter fuel and in portable camping stoves due to its ease of liquefaction and transportability. These practical applications of hydrocarbons illustrate their critical role in modern technology and industry, making an understanding of their chemistry highly relevant.