1.1. Ammonia produced from the Haber process is used as a raw material to make fertilisers.

Ammonium sulfate is a common fertiliser that can be made in the laboratory by the titration of ammonia solution with sulfuric acid.

A student followed the method below to make ammonium sulfate.

Explain why the student used litmus paper instead of adding an indicator to the ammonia solution to find the end point.

1.2. The balanced symbol equation for the neutralisation of ammonia solution with sulfuric acid is:

   2NH₃ (aq)   +   H₂SO₄ (aq)   →    (NH₄)₂SO₄ (aq)

The student carried out the titration to make the fertiliser, ammonium sulfate.

They found that 23.45 cm³ of 1 mol/dm³ sulfuric acid was needed to neutralise 25.0 cm³ of ammonia solution.

Calculate the concentration of the ammonia solution.

Give your answer to three significant figures.

1.3. Urea is another compound used by farmers. Urea is made from ammonia in the reaction below.

2NH₃ + CO₂ $\rightleftharpoons$ NH₂CONH₂ + H₂O

Compare the atom economy of urea for this reaction with the atom economy of ammonium sulfate in the reaction between sulfuric acid and ammonia.

Relative atomic masses (A_r): H = 1;  C = 12;  N = 14;  O = 16;  S = 32

1.4. Ammonium nitrate, NH₄NO₃ is another fertiliser made from ammonia. 

Fertilisers containing nitrogen are also known as nitrogenous fertilisers.

Calculate the percentage by mass of nitrogen for ammonium nitrate and ammonium sulfate, (NH₄)₂SO₄, to determine which fertiliser is the best nitrogenous fertiliser.

Relative atomic masses (A_r):  H = 1;  N = 14;  O = 16;  S = 32