Calculate The Molecular Weight of The Following Compounds
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The molecular weight of a compound is the sum of the atomic weights of all the atoms in its molecular formula. This calculation is essential for chemistry, biochemistry, and pharmaceutical applications where precise measurements are required.
How to Calculate Molecular Weight
To determine the molecular weight of a compound, follow these steps:
- Identify the molecular formula of the compound.
- Break down the formula into individual elements and their quantities.
- Find the atomic weight of each element from the periodic table.
- Multiply each element's atomic weight by its quantity in the formula.
- Sum all the values to get the molecular weight.
Remember that molecular weight is different from molar mass. Molecular weight is calculated based on the atoms present, while molar mass includes the molecular weight plus the average mass of isotopes.
Molecular Weight Formula
The molecular weight (MW) of a compound can be calculated using the following formula:
Where:
- Σ (Sigma) represents the sum of all elements in the compound
- Number of atoms of each element is the count from the molecular formula
- Atomic weight of each element is taken from the periodic table
Worked Example
Let's calculate the molecular weight of glucose (C6H12O6):
- Carbon (C): 6 atoms × 12.01 g/mol = 72.06 g/mol
- Hydrogen (H): 12 atoms × 1.01 g/mol = 12.12 g/mol
- Oxygen (O): 6 atoms × 16.00 g/mol = 96.00 g/mol
Total molecular weight = 72.06 + 12.12 + 96.00 = 180.18 g/mol
Note: The actual molecular weight of glucose is approximately 180.16 g/mol, showing the precision of this calculation method.
Common Compound Weights
Here are the molecular weights of some common compounds:
| Compound | Formula | Molecular Weight (g/mol) |
|---|---|---|
| Water | H2O | 18.02 |
| Sucrose (Table Sugar) | C12H22O11 | 342.29 |
| Ethanol | C2H5OH | 46.07 |
| Acetic Acid | C2H4O2 | 60.05 |
| Methanol | CH3OH | 32.04 |
Frequently Asked Questions
What is the difference between molecular weight and molar mass?
Molecular weight is the sum of the atomic weights of all atoms in a molecule, while molar mass includes the average mass of isotopes. For most practical purposes, these values are very close.
How accurate is the molecular weight calculation?
The calculation is highly accurate when using precise atomic weights from the periodic table. Small variations may occur due to isotopic distribution.
Can I use this calculator for polymers?
Yes, you can calculate the molecular weight of polymers by summing the weights of their repeating units and considering the degree of polymerization.
What if I don't know the exact formula?
You can estimate the molecular weight by knowing the approximate composition of the compound. For precise results, always use the exact molecular formula.