Question

Aqueous solution of Mohr's salt gives a positive test for:

• A. Fe\(^{2+}\)
• B. NH\(_4^+\)
• C. SO\(_4^{2-}\)
• D. All of these

Hint:

Mohr's salt is a useful reagent in analytical chemistry, especially for detecting iron(II) ions and performing sulfate ion tests. It is commonly used in titrations for determining the concentration of iron(II) in samples.

Answer 1

The Correct Option is D

Mohr's Salt is chemically known as ammonium iron(II) sulfate and has the formula (NH₄)₂Fe(SO₄)₂·6H₂O. When it dissolves in water, it dissociates into its constituent ions:

(NH₄)₂Fe(SO₄)₂·6H₂O → 2NH₄⁺ + Fe²⁺ + 2SO₄^2- + 6H₂O

Thus, an aqueous solution of Mohr's salt contains Fe²⁺, NH₄⁺, and SO₄^2- ions. Each of these ions can be tested for positively:

• Fe²⁺ Test: Adding potassium ferricyanide, a blue precipitate (Turnbull's Blue) forms.
• NH₄⁺ Test: Adding NaOH and heating releases ammonia gas, detected by its smell or by turning moist red litmus paper blue.
• SO₄^2- Test: Adding BaCl₂, a white precipitate of BaSO₄ forms.

Thus, an aqueous solution of Mohr's salt gives a positive test for all three ions: Fe²⁺, NH₄⁺, and SO₄^2-.