To determine the volume of gas collected at standard temperature and pressure (STP) after passing dry ammonia over heated copper oxide, we need to analyze the chemical reaction and the data provided. The reaction between ammonia (NH3) and copper oxide (CuO) can be summarized as follows:
The Reaction Process
When ammonia is heated in the presence of copper oxide, a reduction reaction occurs. The ammonia reduces the copper oxide to copper while itself being oxidized to nitrogen gas and water vapor. The balanced chemical equation for this reaction is:
- 2 NH3(g) + 3 CuO(s) → 3 Cu(s) + N2(g) + 3 H2O(g)
This indicates that for every 2 moles of ammonia, 1 mole of nitrogen gas is produced. The water vapor produced will condense and can be removed from the gas mixture, leaving nitrogen gas.
Calculating the Amount of Gas Produced
Given that the gain in weight of anhydrous calcium chloride (CaCl2) is 0.06 g, we can use this information to find the amount of water produced, as CaCl2 is used to absorb moisture. The molar mass of water (H2O) is approximately 18 g/mol. To find the moles of water absorbed by CaCl2, we can use the formula:
- Moles of H2O = Mass of H2O / Molar Mass of H2O
Substituting the values:
- Moles of H2O = 0.06 g / 18 g/mol ≈ 0.00333 mol
Relating Water to Nitrogen Production
From the balanced equation, we see that for every 2 moles of NH3, 1 mole of N2 is produced. Since water is produced in the reaction, we can relate the moles of water to the moles of nitrogen gas produced. The stoichiometry shows that 3 moles of water correspond to 1 mole of nitrogen gas. Therefore:
- 0.00333 mol H2O × (1 mol N2 / 3 mol H2O) = 0.00111 mol N2
Calculating the Volume of Nitrogen Gas at STP
At standard temperature and pressure (0 degrees Celsius and 1 atm), 1 mole of any ideal gas occupies 22.4 liters. Thus, we can calculate the volume of nitrogen gas produced:
- Volume of N2 = Moles of N2 × 22.4 L/mol
Substituting the moles of nitrogen gas we calculated:
- Volume of N2 = 0.00111 mol × 22.4 L/mol ≈ 0.0248 L
Converting this to milliliters (1 L = 1000 mL), we find:
Final Thoughts
In summary, after passing dry ammonia over heated copper oxide and collecting the resulting gases, the volume of nitrogen gas collected at STP is approximately 24.8 mL. This process illustrates the principles of stoichiometry and gas laws in chemistry, showcasing how we can derive meaningful data from experimental observations.
