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How to Find the Molar Mass of a Compound?

Published in Molar Mass Calculation 3 mins read

The molar mass of a compound is found by summing the atomic masses of all the atoms in its chemical formula.

Steps to Calculate Molar Mass:

Here’s a detailed breakdown of how to calculate the molar mass of a compound, using the example of carbon dioxide (CO₂) from the reference:

  1. Identify the Chemical Formula: Determine the chemical formula of the compound. For example, carbon dioxide is CO₂.

  2. List the Elements and their Number: Identify the elements present and the number of atoms of each element. In CO₂, we have:

    • One carbon atom (C)
    • Two oxygen atoms (O)

  3. Find the Atomic Masses: Look up the atomic mass of each element on the periodic table.

    • Carbon (C) has an atomic mass of approximately 12.01 atomic mass units (amu).
    • Oxygen (O) has an atomic mass of approximately 16.00 amu.

  4. Multiply Atomic Mass by Number of Atoms: Multiply the atomic mass of each element by the number of its atoms present in the compound.

    • Carbon: 1 atom * 12.01 amu/atom = 12.01 amu
    • Oxygen: 2 atoms * 16.00 amu/atom = 32.00 amu

  5. Add the Results Together: Sum the results from the previous step to obtain the molar mass.

    • Molar mass of CO₂: 12.01 amu + 32.00 amu = 44.01 amu
    • The molar mass is generally expressed in grams per mole (g/mol). Therefore the molar mass of CO₂ is approximately 44.01 g/mol as mentioned in the reference "...so the molar mass of carbon dioxide is 44.01 grams per mole".

Example: Silicon Tetrafluoride (SiF₄)

Let’s apply the same method to silicon tetrafluoride (SiF₄), as also mentioned in the provided reference.

  • Elements and Atoms:

    • One silicon atom (Si)
    • Four fluorine atoms (F)

  • Atomic Masses:

    • Silicon (Si) has an atomic mass of approximately 28.09 amu.
    • Fluorine (F) has an atomic mass of approximately 19.00 amu.

  • Calculation:

    • Silicon: 1 * 28.09 amu = 28.09 amu
    • Fluorine: 4 * 19.00 amu = 76.00 amu

  • Molar Mass of SiF₄:

    • 28.09 amu + 76.00 amu = 104.09 amu
    • Therefore, the molar mass of SiF₄ is 104.09 g/mol.

Summary Table

Compound Chemical Formula Atoms Atomic Masses (amu) Molar Mass (g/mol)
Carbon Dioxide CO₂ 1 C, 2 O C: 12.01, O: 16.00 44.01
Silicon Tetrafluoride SiF₄ 1 Si, 4 F Si: 28.09, F: 19.00 104.09

Key Points:

  • Molar mass is expressed in grams per mole (g/mol).
  • Atomic masses can be found on the periodic table.
  • This process can be used for any compound, regardless of the number of elements or atoms it contains.

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