Qualitative Analysis Team Experiment I

Southern Utah University

Chemistry Olympics

Qualitative Analysis Team Experiment I:

The goal: to identify Five unknown cations (positive ions) by reacting them with sodium hydroxide aqueous solution.

Each team will be given Five dropper bottles, each containing an aqueous solution of one of the Ions listed below. The members of the team determine which solution is in each bottle by a procedure limited to adding sodium hydroxide solution to the unknown aqueous solutions. (Students are not to touch, smell, or taste the solutions). Each team is supplied with an eight well spot plate, a wash bottle and a data sheet.

Winning teams (1st, 2nd, and 3rd place will be selected on the bases of the time required to make the correct assignments.

The Five unknown solutions are:

Ca2+(aq)

Al3+(aq)

Cu2+(aq)

Fe2+(aq)

Fe3+(aq)

Procedure:

Place 20 drops of the unknown solution into a test tube. Add sodium hydroxide solution dropwise, and observe the result. In each case a precipitate will form in the test tube. By recognizing the physical properties (color, maturity, …) of the precipitate you will be able to identify the unknown Ion.

Observations:

Ca2+(aq) Forms white precipitate. Ca2+(aq) + 2OH-(aq) ® Ca(OH)2(s)

Al3+(aq) Forms white precipitate. Al3+(aq) + 3OH-(aq) ® Al(OH)3(s)

This precipitate will dissolve upon addition of excess NaOH(aq) to it.

Cu2+(aq) Forms blue gelatinous precipitate. Cu2+(aq) + 2OH-(aq) ® Cu(OH)2(s)

Fe2+(aq) Forms dark green gelatinous precipitate. Fe2+(aq) + 2OH-(aq) ® Fe(OH)2(s)

Fe3+(aq) Forms red/brown (rust) gelatinous precipitate. Fe3+(aq) + 3OH-(aq) ® Fe(OH)3(s)