The molecular mass of the organic compound described is 78. This specific value, along with its elemental composition, helps identify and characterize the compound.
Understanding Molecular Mass
Molecular mass represents the sum of the atomic masses of all atoms present in a molecule. It is a fundamental property of any chemical compound, especially organic compounds, which are primarily composed of carbon and hydrogen, often with oxygen, nitrogen, and other elements. Knowing the molecular mass is crucial for:
- Identification: It helps in narrowing down the possible chemical structures of an unknown compound.
- Stoichiometry: Essential for calculating quantities in chemical reactions.
- Properties: Influences physical properties like boiling point, melting point, and density.
Determining Molecular Mass and Composition
For a specific organic compound, its molecular mass is an exact value. Complementing this, the elemental composition — the percentage by mass of each element in the compound — provides critical insight into its makeup.
Consider an organic compound with a molecular mass of 78. Its elemental composition reveals it consists of:
- 92.4% Carbon (C)
- 7.6% Hydrogen (H)
This information allows chemists to determine the compound's empirical formula (the simplest whole-number ratio of atoms) and then, using the molecular mass, the exact molecular formula (the actual number of atoms of each element in a molecule).
Example: A Specific Organic Compound
Let's examine the details of this particular organic compound:
| Property | Value |
|---|---|
| Molecular Mass | 78 |
| Carbon Content | 92.4% |
| Hydrogen Content | 7.6% |
To illustrate how this data is used, we can deduce the molecular formula:
- Assume a 100 g sample: This means there are 92.4 g of Carbon and 7.6 g of Hydrogen.
- Convert mass to moles:
- Moles of Carbon (C) = 92.4 g / 12.01 g/mol ≈ 7.70 mol
- Moles of Hydrogen (H) = 7.6 g / 1.008 g/mol ≈ 7.54 mol
- Find the simplest mole ratio (Empirical Formula): Divide each mole value by the smallest number of moles (7.54).
- C: 7.70 / 7.54 ≈ 1.02 ≈ 1
- H: 7.54 / 7.54 ≈ 1
- The empirical formula is CH.
- Calculate Empirical Formula Mass: The mass of (CH) is approximately 12.01 + 1.008 = 13.018 g/mol.
- Determine the Molecular Formula: Divide the given molecular mass by the empirical formula mass.
- n = Molecular Mass / Empirical Formula Mass = 78 / 13.018 ≈ 5.99 ≈ 6
- Multiply the subscripts in the empirical formula by 'n'. Thus, the molecular formula is (CH)6 or C₆H₆.
This specific organic compound with a molecular mass of 78 and the given composition is benzene, a well-known aromatic hydrocarbon. You can learn more about how empirical and molecular formulas are determined from chemical composition at educational resources like Khan Academy.
Importance in Organic Chemistry
The exact molecular mass, combined with precise elemental composition, is a cornerstone of organic chemistry. It allows scientists to:
- Synthesize specific compounds: By ensuring the correct proportions of reactants.
- Analyze unknown substances: Essential in fields like forensic science, environmental monitoring, and drug discovery.
- Develop new materials: Tailoring molecular structure to achieve desired properties.
Understanding these foundational concepts is key to grasping the vast and intricate world of organic chemistry.
