Molecular mass is the sum of the atomic masses of all the atoms in a molecule and it's found by using the periodic table to identify each element's atomic mass and then adding them together based on the molecule's formula.
Understanding Molecular Mass
Molecular mass, also known as molecular weight, represents the mass of a single molecule. It's crucial for various calculations in chemistry, such as determining the amount of a substance needed for a reaction. The unit for molecular mass is atomic mass units (amu) or Daltons (Da).
How to Calculate Molecular Mass
Here's a step-by-step guide:
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Identify the Chemical Formula: Determine the chemical formula of the molecule. This formula tells you which elements are present and how many atoms of each element are in the molecule. For example, water is H2O, meaning it has two hydrogen atoms and one oxygen atom.
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Find the Atomic Masses: Look up the atomic mass of each element in the molecule on the periodic table. Atomic mass is typically found below the element symbol.
- Hydrogen (H): Approximately 1.01 amu
- Oxygen (O): Approximately 16.00 amu
- Nitrogen (N): Approximately 14.01 amu
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Multiply and Add: Multiply the atomic mass of each element by the number of atoms of that element present in the molecule. Then, add up these values to get the molecular mass.
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For water (H2O):
(2 x Atomic mass of H) + (1 x Atomic mass of O) = (2 x 1.01 amu) + (1 x 16.00 amu) = 2.02 amu + 16.00 amu = 18.02 amu -
For ammonia (NH3):
(1 x Atomic mass of N) + (3 x Atomic mass of H) = (1 x 14.01 amu) + (3 x 1.01 amu) = 14.01 amu + 3.03 amu = 17.04 amu
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Example Calculation
Let's calculate the molecular mass of carbon dioxide (CO2):
- Chemical Formula: CO2
- Atomic Masses (from the periodic table):
- Carbon (C): 12.01 amu
- Oxygen (O): 16.00 amu
- Calculation:
(1 x Atomic mass of C) + (2 x Atomic mass of O) = (1 x 12.01 amu) + (2 x 16.00 amu) = 12.01 amu + 32.00 amu = 44.01 amu
Therefore, the molecular mass of CO2 is 44.01 amu.
