What is the number of moles of 'He' in 104 g of helium gas?
26
Calculating Moles of Helium Gas
Let's figure out how to find the number of moles of 'He' in 104 g of helium gas. This type of question involves using the relationship between mass, molar mass, and the number of moles.
Understanding Moles and Molar Mass
- A mole is a unit of amount of substance. It's a specific number of particles (like atoms, molecules, or ions), similar to how a "dozen" is 12.
- The molar mass of an element or compound is the mass of one mole of that substance. For elements, the molar mass in grams per mole (g/mol) is numerically equal to its atomic mass in atomic mass units (amu).
- For Helium (He), the atomic mass is approximately 4 amu. Therefore, the molar mass of Helium gas (which exists as individual He atoms) is 4 g/mol. This means 1 mole of Helium atoms weighs 4 grams.
Formula for Calculating Moles
The number of moles can be calculated using the following formula:
\(\text{Number of moles} = \frac{\text{Given mass}}{\text{Molar mass}}\)
Applying the Formula to Helium
We are given:
- Given mass of Helium = 104 g
- Molar mass of Helium (He) = 4 g/mol
Now, let's plug these values into the formula:
\(\text{Number of moles of He} = \frac{104 \text{ g}}{4 \text{ g/mol}}\)
\(\text{Number of moles of He} = 26 \text{ mol}\)
So, 104 g of helium gas contains 26 moles of Helium atoms.
Step-by-Step Calculation
- Identify the given mass of the substance (Helium). Mass = 104 g.
- Find the molar mass of the substance (Helium). Molar mass of He = 4 g/mol.
- Use the formula: Number of moles = Mass / Molar mass.
- Calculate: \(\frac{104}{4} = 26\).
- State the final answer with the correct unit (moles). The number of moles of He is 26 mol.
Revision Table: Moles Calculation
| Concept | Definition/Value | Unit |
|---|---|---|
| Given Mass | 104 | g |
| Molar Mass of He | 4 | g/mol |
| Formula | Mass / Molar Mass | - |
| Calculated Moles | 26 | mol |
Additional Information: Moles and Atoms
- One mole of any substance contains Avogadro's number of particles. Avogadro's number is approximately \(6.022 \times 10^{23}\).
- Therefore, 26 moles of Helium contain \(26 \times 6.022 \times 10^{23}\) Helium atoms.
- The concept of moles is fundamental in chemistry for relating microscopic properties (like the mass of a single atom or molecule) to macroscopic properties (like the mass of a sample).
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