The mass of ammonium dihydrogen phosphate in compound fertilizer is100 kg× 21+2+2 = 40kg.
The mass of potassium chloride in compound fertilizer is100 kg× 21+2+2 = 40kg.
B: B: The mass of nitrogen in 20kg ammonium nitrate is 20kg×14× 280x100% = 7kg.
The mass of nitrogen in 40kg of ammonium dihydrogen phosphate is 40 kg×1415×100% ≈ 4.9 kg.
Only ammonium nitrate and ammonium dihydrogen phosphate contain nitrogen in compound fertilizer, so the mass of nitrogen in compound fertilizer is 7kg+4.9kg= 1 1.9kg.
Therefore, the mass fraction of nitrogen in compound fertilizer is11.9 kg100 kg×100% =11.9%.
The mass of phosphorus in 40kg ammonium dihydrogen phosphate is 40kg× 3115x100% ≈10.8kg. ..
Only ammonium dihydrogen phosphate contains phosphorus in compound fertilizer, so the mass fraction of phosphorus in compound fertilizer is10.8kg100kg×100% =10.8%.
The mass of potassium in 40 kg of potassium chloride is 40 kg× 39 74.5×100% ≈ 20.9 kg.
Only potassium chloride contains potassium in compound fertilizer, so the mass fraction of potassium in compound fertilizer is 20.9 kg100 kg×100% = 20.9%.
(2) Ammonium ion in ammonium sulfate is easy to be absorbed, but sulfate ion is not easy to be absorbed, so when ammonium sulfate is applied, it is easy to make the soil more acidic, which is not conducive to the growth of crops; Ammonium ion and nitrate ion in ammonium nitrate are easily absorbed by crops, and have less influence on soil than ammonium sulfate, so ammonium nitrate is suitable for acidic soil.
Answer: (1) Answer: 20kg needs ammonium nitrate; 40kg needs ammonium dihydrogen phosphate; Potassium chloride 40kg. Is necessary.
B: the mass fraction of nitrogen in compound fertilizer is11.9%; The mass fraction of phosphorus in compound fertilizer is10.8%; The mass fraction of potassium in compound fertilizer is 20.9%.
(2) Ammonium nitrate is suitable for acid soil; The reason is that ammonium ion in ammonium sulfate is easy to be absorbed, and sulfate ion is not easy to be absorbed, so it is easy to make the soil more acidic when ammonium sulfate is applied, which is not conducive to the growth of crops; Ammonium ion and nitrate ion in ammonium nitrate are easily absorbed by crops and have less influence on soil than ammonium sulfate.