Question

for anions pre lab

3-Describe what kind of chemical reaction will take place for each of the following screening tests and provide an example for each one. For example, you might say “Test five will involve an oxidation-reduction reaction. For example: Fe + H2SO4 → H2 + Fe3+ + SO42-”.

Reaction with silver nitrate

Reaction with calcium and barium

Reaction with Permanganate

Reaction with sulfuric acid

Answer 1

1) Test with silver nitrate (AgNO3):

Formation of a white precipitate with AgNO3 confirms the presence of halide anions (Cl-, Br-,I-). This is a precipitation reaction

Ag⁺(aq) + Cl^-(aq) ------ AgCl (s)

2) Test with Calcium and Barium:

Formation of a white precipiate with Ca and Ba solutions (CaCl2 or BaCl2) indicates the presence of sulphate ions, SO4^2-

Ba²⁺(aq) + SO4^2-(aq) ----- BaSO4 (s)

3) Test with permanganate (KMnO4):

Halides and oxalate (C2O4^2-) anions undergo a redox (reduction oxidation) with KMnO4. This results in the decolorisation of KMnO4 solution followed by evolution of halogen gas or CO2 in the case of oxalate anions.

4) Test with H2SO4:

This is agin a redox reaction for detecting the presence of halide and oxalate ions. formation of white fumes, brown vapors or violet vapors suggests the presence of Cl-, Br- or I- respectively. If a colorless gas (CO2) is evolved which turns lime water milky, then it suggests the presence of oxalate ion.