Calculating Nitrogen Content

Farmers add ammonium sulfate to the soil. What is the purpose of this?

• A. To add sulfur to the soil.

• B. To add nitrogen to the soil.

• C. To neutralise excess acid in the soil.

• D. To destroy excess lime in the soil.

What are the essential elements found in KNO₃ which can help in plant growth?

• A. Nitrogen and Oxygen

• B. Phosphorus and Nitrogen

• C. Potassium and Nitrogen

• D. Potassium and Oxygen.

Which compound when reacted with sulfuric acid produces a product which is used as a fertiliser?

• A. ammonia

• B. calcium carbonate

• C. calcium hydroxide

• D. sodium hydroxide

Which substance has the highest percentage by mass of nitrogen?

• A. NH₄NO₃

• B. (NH₃)₂SO₄

• C. CO(NH₂)₂

• D. (NH₄)₃PO₄

All ammonium salts on heating with sodium hydroxide produce ammonia gas.

From which ammonium salt can the greatest mass of ammonia be obtained?

• A. 0.5 mol (NH₄)₃PO₄

• B. 0.5 mol (NH₄)₂SO₄

• C. 1.0 mol NH₄Cl

• D. 1.0 mol NH₄NO₃

6. Farmers that grow vegetable oil crops often use large quantities of ammonium nitrate fertlisers, NH₄NO₃.

a) Calculate the percentage by mass of nitrogen in ammonium nitrate.

% By mass = _________________

[Mark: 1]

b) A sample of ammonium phosphate can be produced by the reaction of aqueous ammonia and phosphoric acid.

3NH₃(aq) + H₃PO₄(aq) --> (NH₄)₃PO₄(aq)

25.0 cm³ of 1.25 mol/dm³ phosphoric acid is neutralised by 45.3 cm³ of aqueous ammonia.

i) Calculate the concentration, in mol/dm³, of the ammonia used.

Concentration of ammonia = ____________ mol / dm³

[Mark: 3]

ii) Show, by calculation, that 4.66 g of ammonium phosphate would be produced. Assume that the yield is 100%. [Mr: (NH₄)₃PO₄, 149]

[Mark: 1]

iii) In practice, the actual mass of ammonium phosphate produced is 2.93 g. Calculate the percentage yield of ammonium phosphate.

Percentage yield = ____________ %

[Mark: 1]

7) Urea is a white solid with the formula CO(NH₂)₂. The compound is used as a fertiliser.

a) Which important element is added to the soil by urea?

[Mark: 1]