2g) Tests for ions and gases

Flame tests for metal ions:

• dip in HCl
• Heat in flame 
• Clean
• dip in crystals 
• place on burnsen burner flame 
• identify colour 

+-------------+-----------+---------------------+
| Metal ions  |           | Flame test colour   |
+-------------+-----------+---------------------+
| Li+         | Lithium   | Brick red/ Crimson  |
+-------------+-----------+---------------------+
| Na+         | Sodium    | Yellow              |
+-------------+-----------+---------------------+
| K+          | Potassium | Purple/Lilac        |
+-------------+-----------+---------------------+
| Ca3+        | Calcium   | Brick red           |
+-------------+-----------+---------------------+

Tests for gases

+--------------------+------------------------+----------------------------+
| Hydrogen H2        | Light                  | Burns with a 'squeaky pop' |
+--------------------+------------------------+----------------------------+
| Oxygen O2          | glowing splint         | Relights                   |
+--------------------+------------------------+----------------------------+
| Carbon Dioxide CO2 | Limewater              | Makes it go cloudy/milky   |
+--------------------+------------------------+----------------------------+
| Ammonia NH3        | Damp red litmus paper  | turns blue                 |
+--------------------+------------------------+----------------------------+
| Chlorine Cl2       | Damp blue litmus paper | turns red                  |
+--------------------+------------------------+----------------------------+

Tests for cations:

+------+---------------+----------------------------------------+
| NH4+ | Add NaOH (aq) | NH3 released;test --> damp red litmus  |
|      |               | paper goes blue                        |
+------+---------------+----------------------------------------+

+-------+-----------+------------------------+
| Cu2+  | Add NaOH  | Pale blue precipitate  |
+-------+-----------+------------------------+
|       | Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) |
+-------+------------------------------------+

+-------+-----------+-------------------------+
| Fe2+  | Add NaOH  | Dirty green precipitate |
+-------+-----------+-------------------------+
|       | Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s)  |
+-------+-------------------------------------+

+-------+------------+-----------------------+
| Fe3+  | Add NaOH   | Red-brown precipitate |
+-------+------------+-----------------------+
|       | Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s) |
+-------+------------------------------------+

Tests for anions:

+-------+-------------------------------+-------------+
| Ion   |                               | Precipitate |
+-------+-------------------------------+-------------+
| Cl-   | dilute nitric acid. Add AgNO3 | white       |
+-------+-------------------------------+-------------+
|       |        Ag+(aq) + Cl-(aq) --> AgCl(s)        |
+-------+---------------------------------------------+
| Br-   | dilute nitric acid. Add AgNO3 | cream       |
+-------+-------------------------------+-------------+
|       |        Ag+(aq) + Br-(aq) --> BrAg(s)        |
+-------+---------------------------------------------+
| I-    | dilute nitric acid. Add AgNO3 | yellow      |
+-------+-------------------------------+-------------+
|       |         Ag+(aq) + I-(aq) --> AgI(s)         |
+-------+---------------------------------------------+
| SO42- | Acidify with HCL. Add BaCl2   | white       |
+-------+-------------------------------+-------------+
|       |      Ba2+(aq) + SO42-(aq) --> BaSO4(s)      |
+-------+---------------------------------------------+
| CO32- | Add acid, CO2 is released.    | milky       |
|       | Bubble through limewater      |             |
+-------+-------------------------------+-------------+