Answer :
(b) If the addition of dilute hydrochloric acid followed by aqueous barium chloride to an aqueous solution of Mohr's salt results in a white precipitate, this suggests the presence of sulfate ions (SO₄²⁻) since barium sulfate (BaSO₄) is a well-known white precipitate that forms under these conditions. Thus, the identity of the white precipitate is barium sulfate (BaSO₄).
(c)
(1) Mohr's salt is a double salt that contains the ions of ferrous sulfate (FeSO₄) and ammonium sulfate ((NH₄)₂SO₄) in a complex. So, the two individual salts that are mixed together to make Mohr's salt are:
salt 1: Ferrous sulfate (FeSO₄)
salt 2: Ammonium sulfate ((NH₄)₂SO₄)
(ii) Let's now calculate the relative formula mass (also known as molar mass) of each of these salts.
For ferrous sulfate (FeSO₄), the relative atomic masses are:
- Fe: 55.845
- S: 32.065
- O: 15.999 (four oxygens)
The relative formula mass of ferrous sulfate (FeSO₄) is:
= (1 × 55.845) + (1 × 32.065) + (4 × 15.999)
= 55.845 + 32.065 + 63.996
= 151.906 amu
For ammonium sulfate ((NH₄)₂SO₄), the relative atomic masses are:
- N: 14.007 (two nitrogens)
- H: 1.008 (eight hydrogens)
- S: 32.065
- O: 15.999 (four oxygens)
The relative formula mass of ammonium sulfate ((NH₄)₂SO₄) is:
= (2 × 14.007) + (8 × 1.008) + (1 × 32.065) + (4 × 15.999)
= 28.014 + 8.064 + 32.065 + 63.996
= 132.139 amu
Relative formula mass of salt 1 (FeSO₄): 151.906 amu
Relative formula mass of salt 2 ((NH₄)₂SO₄): 132.139 amu
*amu refers to atomic mass units
