Appendix 2: Qualitative chemical analysis: Chemical tests for cations
Appendix 2: Teacher notes - outputs of the lesson
Task 1
Completed tables for Task 1 are given below.
Table 1 Qualitative data from reactions of positively charged metal ions in solution with a solution of dilute sodium hydroxide.
|
Cations |
Add a few drops of NaOH |
Add large excess of NaOH |
|
Zn2+ |
White precipitate forms (gelatinous)
|
Precipitate redissolves |
|
Ca2+ |
White precipitate forms
|
No change |
|
Al3+ |
White precipitate forms (gelatinous)
|
Precipitate redissolves |
|
Pb2+ |
White precipitate forms
|
Precipitate redissolves |
|
Cu2+ |
Pale blue precipitate forms (gelatinous) |
No change |
|
Fe2+ |
Green precipitate (gelatinous)
|
No change |
|
Fe3+ |
Reddish-brown precipitate (gelatinous) |
No change |
Table 2 Qualitative data from reactions of positively charged metal ions in solution with a solution of dilute ammonia.
|
Cations |
Add a few drops of NH3(aq) |
Add large excess of NH3(aq) |
|
Zn2+ |
White precipitate forms (gelatinous) |
Precipitate redissolves |
|
Ca2+ |
No precipitate forms
|
No precipitate formed |
|
Al3+ |
White precipitate forms (gelatinous) |
No change |
|
Pb2+ |
White precipitate forms
|
No change |
|
Cu2+ |
Pale blue precipitate forms (gelatinous) |
Precipitate redissolves |
|
Fe2+ |
Green precipitate (gelatinous)
|
No change |
|
Fe3+ |
Reddish brown precipitate (gelatinous) |
No change |
Task 2
The application will allocate four random unknown samples of metal ions in solution to each student. The colour of some unknown solutions may provide a clue in the identification of a metal ion. However, you should ask your students to always carry out the chemical tests to conclusively confirm which metal ion is present.
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