This question is about ammonia and fertilisers - AQA - GCSE Chemistry - Question 2 - 2016 - Paper 2

To find the percentage by mass of nitrogen in ammonia, we first determine the molar mass of NH₃:

• Nitrogen (N): 1 × 14 = 14 g/mol
• Hydrogen (H): 3 × 1 = 3 g/mol
• Molar mass of NH₃ = 14 g/mol + 3 g/mol = 17 g/mol.

Now, the percentage by mass of nitrogen is given by:

[ \text{Percentage of N} = \left( \frac{\text{mass of N}}{\text{molar mass of NH}_3} \right) \times 100 = \left( \frac{14}{17} \right) \times 100 \approx 82.35%. ]

The pH of a neutral solution is 7.

The correct equation for a neutralisation reaction is H⁺ + OH⁻ → H₂O.

The salt produced when ammonia reacts with hydrochloric acid is ammonium chloride (NH₄Cl).

Based on the graphs A, B, and C, farmers should use around 200 kg of ammonium nitrate per hectare. This amount maximizes crop yield as seen in Graph A, while Graph B indicates that profit remains stable beyond this point. Additionally, Graph C shows that using more than 200 kg leads to increased runoff, which could contribute to environmental concerns.