Comparing nitrogen content and soil pH effects of ammonium fertilizers

Steps:

• Calculate %N in NH4NO3: molar mass 80 g/mol, nitrogen 28 g/mol, so (28/80) × 100 = 35%.
• Calculate %N in (NH4)2SO4: molar mass 132 g/mol, nitrogen 28 g/mol, so (28/132) × 100 ≈ 21%.
• Both salts contain NH4+ ions, which hydrolyze (NH4+ + H2O ⇌ NH3 + H3O+) to produce H3O+, acidifying neutral soil and decreasing pH equally.
• Thus, %N by mass decreases from NH4NO3 to (NH4)2SO4, while pH effect is the same (decrease).

Why A is correct:

• A identifies the decrease in %N by mass when comparing NH4NO3 (35%) to (NH4)2SO4 (21%), matching molar mass calculations.

Why the others are wrong:

• B incorrectly states ammonium nitrate increases pH, but it decreases pH via NH4+ hydrolysis.
• C misattributes pH decrease solely to ammonium sulfate, ignoring the shared NH4+ effect.
• D wrongly claims ammonium sulfate increases pH, contradicting acidification by hydrolysis.

Final answer: A