Tests for Positive Ions (Cations)

What is the chemical formula of the precipitate formed when FeCl3 reacts with ammonium hydroxide?

What is the purpose of adding 6M HCl to the solution containing the red-brown precipitate in the Fe3+ test?

Which of the following is NOT a characteristic of the test for Ca2+?

What is the purpose of adding ammonia to the solution containing Ca(NO3)2 in the Ca2+ test?

In both tests, what is the purpose of using a clean dry tube?

Tests for Positive lons (Cations)

A. Test for Fe³⁺

Ferric ions react with ammonium hydroxide to form a red-brown precipitate of ferric hydroxide.
The chemical reaction is Fe³⁺ + 3OH⁻ → Fe(OH)₃↓ (red-brown ppt)
This precipitate can be confirmed by adding 6M HCl, which causes the red-brown precipitate to dissolve.

Procedure

Add 1 mL of 0.1 M FeCl₃ solution into a clean dry test tube.
Add 0.5 mL of ammonium hydroxide and observe the formation of the red-brown precipitate.
Add 0.5 mL of 6M HCl and shake to observe the disappearance of the red precipitate.

B. Test for Ca²⁺

A calcium-containing solution reacts with ammonium oxalate in an alkaline medium to form a white precipitate of calcium oxalate.
The chemical reaction is Ca(NO₃)₂ + (NH₄)₂C₂O₄ → CaC₂O₄↓ + 2NH₄NO₃
Calcium oxalate is a white precipitate.

Procedure

Add 1 mL of drops of 0.1M Ca(NO₃)₂ solution into a clean dry test tube.
Add 0.5 mL of 6M ammonia and shake gently.
Add 0.5 mL of (NH₄)₂C₂O₄ and observe the formation of the white calcium oxalate precipitate.

This quiz covers the procedures for identifying positive ions, specifically Ferric (Fe³⁺) and Calcium (Ca²⁺) cations. Participants will learn about the chemical reactions involved and the resultant precipitates formed. Test your understanding of these important procedures in analytical chemistry.