Question

(a) What is a hydrocarbon? (b) Butane is the alkane with a chain of four carbon atoms. Write a structural formula for this compound and determine its molecular and empirical formulas.

Short answer

(a) A hydrocarbon is an organic compound consisting of only hydrogen and carbon atoms. They can be classified as alkanes, alkenes, or alkynes based on the types of carbon-carbon bonds present. (b) Butane has a molecular formula of \(C_4H_{10}\) and its structural formula is shown below: H H H H | | | | C-C-C-C | | | | H H H H As the ratio of carbon to hydrogen atoms is already in whole numbers (4:10), the empirical formula for butane is also \(C_4H_{10}\).

Step-by-step solution

Part (a): Definition of Hydrocarbon

A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon atoms. These compounds can be classified into different categories, such as alkanes, alkenes, and alkynes, based on the types of carbon-carbon bonds present in them.

Part (b): Butane's Structural Formula

Butane is an alkane, which means it has only single carbon-carbon bonds. Given that it has four carbon atoms in its chain (n=4), we can write its structural formula as follows: Butane: \(C_4H_{10}\) Structural formula: H H H H | | | | C-C-C-C | | | | H H H H

Part (b): Butane's Molecular Formula

The molecular formula represents the actual number of atoms of each element in a molecule of the compound. Since butane has four carbon atoms and ten hydrogen atoms, its molecular formula is \(C_4H_{10}\).

Part (b): Butane's Empirical Formula

The empirical formula is the simplest whole number ratio of the atoms of each element in a compound. In butane's molecular formula, \(C_4H_{10}\), the ratio of carbon to hydrogen atoms is 4:10 or 2:5 when simplified. However, since empirical formulas require whole numbers, the empirical formula for butane is the same as its molecular formula: \(C_4H_{10}\).

Key concepts

Organic Chemistry

Organic chemistry is a branch of chemistry that focuses on carbon-based compounds. This field studies compounds that contain carbon atoms bound to hydrogen, oxygen, nitrogen, or other elements.
The versatile carbon atom can form stable bonds with many different elements, leading to a wide array of compounds.
Organic chemistry is essential to understanding biomolecules, plastics, fuels, and many everyday chemicals.

• Carbon forms four covalent bonds allowing for complex structures.
• Hydrocarbons are the simplest form, consisting only of carbon and hydrogen.
• The study of organic chemistry helps explain processes like digestion and metabolism.

Understanding organic chemistry principles is crucial for advances in biochemistry, medicine, and environmental science.

Alkanes

Alkanes are a type of hydrocarbon characterized by only single bonds between their carbon atoms. They follow the general formula, \(C_nH_{2n+2}\).
This class of compounds is known as saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can attach to the carbon chain.

• Alkanes are also called paraffins.
• They exhibit relatively low reactivity compared to other hydrocarbon classes like alkenes and alkynes.
• Common examples include methane, ethane, propane, and butane.

Alkanes are typically found in natural gas and petroleum. Their primary uses include fuels and as starting materials in chemical synthesis.

Molecular Formula

A molecular formula indicates the exact number and types of atoms in a single molecule of a compound. It provides a straightforward representation of how many of each type of atom are present.
For example, the molecular formula for butane is \(C_4H_{10}\). This shows that butane contains four carbon atoms and ten hydrogen atoms.

• Molecular formulas provide insight into the composition but not the structure.
• They are crucial for determining molecular mass and stoichiometry.
• Molecular formulas are used in calculating reactant and product amounts in chemical reactions.

While molecular formulas tell us the quantity of each atom, they do not show how the atoms are connected. For structural information, other types of formulas are needed.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of elements in a compound. It shows the proportion but not the actual number of atoms.
In butane, with a molecular formula of \(C_4H_{10}\), the subscript ratio is simplified to 2:5, remaining the same as its molecular formula.

• Empirical formulas are useful for comparing relative compositions.
• They are often derived from experimental data like combustion analysis.
• Empirical formulas may match or differ from molecular formulas.

Empirical formulas provide a quick way to understand a compound's basic composition, which is especially useful in chemical analysis and understanding formulas in their simplest form.