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NaOH molar mass (sodium hydroxide)
The naoh molar mass is the mass of one mole of sodium hydroxide, determined from the compound’s chemical formula and periodic-table atomic masses.
Key idea: For a compound, molar mass equals the sum of each element’s atomic mass multiplied by its subscript in the formula.
Step 1: Read the formula and count atoms
Sodium hydroxide has formula NaOH. The subscripts are implicit:
- Na: 1 atom
- O: 1 atom
- H: 1 atom
Step 2: Look up atomic masses (periodic table)
Typical periodic-table values (rounded reasonably) are: Na ≈ 22.99, O ≈ 16.00, H ≈ 1.008 (in g/mol per atom in the formula).
| Element | Atoms in NaOH | Atomic mass (g/mol) | Contribution (g/mol) |
|---|---|---|---|
| Na | 1 | 22.99 | \(1 \times 22.99 = 22.99\) |
| O | 1 | 16.00 | \(1 \times 16.00 = 16.00\) |
| H | 1 | 1.008 | \(1 \times 1.008 = 1.008\) |
Step 3: Add contributions to get the NaOH molar mass
\[ M(\mathrm{NaOH}) = (1)\,M(\mathrm{Na}) + (1)\,M(\mathrm{O}) + (1)\,M(\mathrm{H}) \]
\[ M(\mathrm{NaOH}) = 22.99 + 16.00 + 1.008 = 39.998 \ \text{g/mol} \approx 40.00 \ \text{g/mol} \]
Therefore, the NaOH molar mass ≈ 40.00 g/mol. The same numerical value is often called the formula mass (or molecular weight) depending on context.
Common checks and a quick application
- Unit check: atomic masses add to give g/mol, the standard unit for molar mass.
- Reasonableness: sodium (≈23) plus oxygen (≈16) already totals ≈39, so the final value should be near 40.
- Using molar mass: converting between moles and grams uses \(m = n \times M\). For example, \[ m = (2.50\ \text{mol}) \times (40.00\ \text{g/mol}) = 100.0\ \text{g}. \]
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