The active mass of 7.0 g of nitrogen in a 2.0 L container would be

Options

A. 0.25
B. 0.125
C. 0.5
D. `14.0`

Answer

To find the active mass (or concentration) of nitrogen gas (N₂) in a 2.0 L container when 7.0 g of nitrogen is present, we can follow these steps:

### Step 1: Calculate the number of moles of nitrogen (N₂)
To calculate the number of moles, we use the formula:

\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]

The molar mass of nitrogen (N₂) is calculated as follows:
- The atomic mass of nitrogen (N) is approximately 14 g/mol.
- Therefore, the molar mass of N₂ = 2 × 14 g/mol = 28 g/mol.

Now, substituting the values:
\[ \text{Number of moles of N₂} = \frac{7.0 \text{ g}}{28 \text{ g/mol}} = 0.25 \text{ moles} \]

### Step 2: Calculate the concentration (C) of nitrogen
The concentration (C) is calculated using the formula:

\[ C = \frac{\text{Number of moles}}{\text{Volume (L)}} \]

We have already calculated the number of moles (0.25 moles) and the volume of the container is 2.0 L. Now substituting these values into the formula:

\[ C = \frac{0.25 \text{ moles}}{2.0 \text{ L}} = 0.125 \text{ moles/L} \]

### Step 3: Conclusion
The concentration of nitrogen gas in the container is 0.125 moles/L, which can also be referred to as 0.125 M (molarity).

### Final Answer:
The active mass (concentration) of 7.0 g of nitrogen in a 2.0 L container is **0.125 M**.

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