The mass of 11.2 L of ammonia gas at STP is

Options

A. 8.5 g
B. 85 g
C. 17 g
D. 1.7 g

Explanation

To find the mass of 11.2 L of ammonia gas (NH₃) at Standard Temperature and Pressure (STP), we can follow these steps:

### Step 1: Understand the relationship between volume and moles at STP
At STP (Standard Temperature and Pressure), 1 mole of any ideal gas occupies 22.4 liters.

### Step 2: Calculate the number of moles in 11.2 L of NH₃
To find the number of moles of NH₃ in 11.2 L, we can use the formula:
\[ \text{Number of moles} = \frac{\text{Volume of gas at STP}}{\text{Volume of 1 mole at STP}} = \frac{11.2 \, \text{L}}{22.4 \, \text{L/mol}} = 0.5 \, \text{moles} \]

### Step 3: Determine the molar mass of ammonia (NH₃)
The molar mass of ammonia can be calculated as follows:
- Nitrogen (N) has an atomic mass of 14 g/mol.
- Hydrogen (H) has an atomic mass of 1 g/mol, and there are three hydrogen atoms in ammonia.

Thus, the molar mass of NH₃ is:
\[ \text{Molar mass of NH₃} = 14 + (3 \times 1) = 14 + 3 = 17 \, \text{g/mol} \]

### Step 4: Calculate the mass of NH₃
Now that we have the number of moles and the molar mass, we can find the mass of NH₃ using the formula:
\[ \text{Mass} = \text{Number of moles} \times \text{Molar mass} \]
Substituting the values:
\[ \text{Mass} = 0.5 \, \text{moles} \times 17 \, \text{g/mol} = 8.5 \, \text{grams} \]

### Final Answer
The mass of 11.2 L of ammonia gas at STP is **8.5 grams**.

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