2.49g of ammonia at STP occupies a volume of 2.48 `dm^3` calculate the molar mass of ammonia.

Options

A. 11.2g/mol
B. 22.5g/mol
C. 25g/mol
D. 16.5g/mol

Explanation

To calculate the molar mass of ammonia (NH₃) given that 2.49 g of ammonia occupies a volume of 2.48 dm³ at STP, we can follow these steps:

### Step 1: Understand the relationship between volume and moles at STP
At standard temperature and pressure (STP), one mole of any ideal gas occupies a volume of 22.4 liters (or 22.4 dm³).

### Step 2: Convert the volume from dm³ to liters
Since the volume is already given in dm³, we can directly use it:
- Volume of ammonia = 2.48 dm³

### Step 3: Calculate the number of moles of ammonia
Using the relationship that 1 mole of gas occupies 22.4 liters at STP, we can calculate the number of moles (n) of ammonia using the formula:
\[ n = \frac{\text{Volume}}{22.4 \, \text{L}} \]

Substituting the values:
\[ n = \frac{2.48 \, \text{L}}{22.4 \, \text{L/mol}} \]

Calculating this gives:
\[ n = 0.1107 \, \text{mol} \]

### Step 4: Calculate the molar mass of ammonia
The molar mass (M) can be calculated using the formula:
\[ M = \frac{\text{mass}}{\text{number of moles}} \]

Substituting the values we have:
\[ M = \frac{2.49 \, \text{g}}{0.1107 \, \text{mol}} \]

Calculating this gives:
\[ M \approx 22.49 \, \text{g/mol} \]

### Step 5: Round the molar mass to appropriate significant figures
The molar mass of ammonia is approximately 22.5 g/mol when rounded to three significant figures.

### Final Answer
The molar mass of ammonia (NH₃) is approximately **22.5 g/mol**.

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