Calculate The Molar Mass for Each of The Following:
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The molar mass of a chemical compound is the mass of one mole of that substance. It's calculated by summing the atomic masses of all atoms in the compound's molecular formula. This calculation is essential for stoichiometry, solution preparation, and chemical reaction analysis.
How to Calculate Molar Mass
To calculate the molar mass of a compound:
- Write down the molecular formula of the compound
- Identify the number of each type of atom in the formula
- Find the atomic mass of each element from the periodic table
- Multiply each atomic mass by the number of atoms of that type
- Sum all the values to get the molar mass
For example, to calculate the molar mass of water (H₂O):
- Hydrogen (H) has an atomic mass of 1.008 g/mol
- Oxygen (O) has an atomic mass of 15.999 g/mol
- There are 2 hydrogen atoms and 1 oxygen atom in water
- Calculation: (2 × 1.008) + (1 × 15.999) = 18.015 g/mol
Molar Mass Formula
Molar Mass = Σ (Number of atoms of each element × Atomic mass of each element)
The molar mass is expressed in grams per mole (g/mol). The atomic masses used are from the standard periodic table, typically based on carbon-12 with a mass of exactly 12.000 atomic mass units (u).
Worked Example
Let's calculate the molar mass of sodium chloride (NaCl):
- Molecular formula: NaCl
- Atomic masses:
- Sodium (Na): 22.990 g/mol
- Chlorine (Cl): 35.453 g/mol
- Number of atoms:
- 1 sodium atom
- 1 chlorine atom
- Calculation: (1 × 22.990) + (1 × 35.453) = 58.443 g/mol
The molar mass of sodium chloride is 58.443 g/mol.
Common Compound Molar Masses
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water | H₂O | 18.015 |
| Sucrose (Table Sugar) | C₁₂H₂₂O₁₁ | 342.297 |
| Ethanol | C₂H₅OH | 46.069 |
| Calcium Carbonate | CaCO₃ | 100.087 |
| Glucose | C₆H₁₂O₆ | 180.156 |
Frequently Asked Questions
What is the difference between molecular mass and molar mass?
Molecular mass refers to the mass of a single molecule, while molar mass is the mass of one mole (6.022 × 10²³ molecules) of that substance. Molar mass is typically used in chemical calculations.
How do I find the atomic mass of an element?
You can find atomic masses in the periodic table. They are typically listed below each element's symbol and are usually based on the most stable isotope of that element.
Why is molar mass important in chemistry?
Molar mass is crucial for stoichiometry calculations, determining solution concentrations, and understanding reaction quantities. It helps chemists predict how much product will form from given reactants.