Test for Cations and Anions

Describe the flame test

1. place the nichrome wire in hydrochloric acid

2. clean inroaring flame

3. repeat 1&2 until the flame no longer changes colour

4. dip the wire in sample salt and put it in a flame

5. observe colour

NOTE: use distilled water to avoid contamination with Na+ ions

The colour of the flame when… Na+ (sodium)

yellow orange

The colour of the flame when… K+ (potassium)

lilac

The colour of the flame when… Cu 2+ (copper)

blue green

The colour of the flame when… Li (lithium)

crimson red

Describe the test for transition metals

1. add NaOH, sodium hydroxide (aq)

2. observe the colour of precipitate

The colour of the percipitate when… Cu 2+

blue

The colour of the precipitate when… Fe 2+

green→red brown

The colour of precipitate when… Fe 3+

red brown

The colour of precipitate when…

• Zn 2+

• Ca 2+

• Mg 2+

• Al 2+

white

Describe the test for ammonium ions

1. add NaOH, sodium hydroxide

2. gently heat in a water bath

3. hold red litmus paper over test tube (*do not dip)

4. if it turns blue, positive for NH3

Describe the test for carbonate ions

1. add dilute acids

2. check for effervescenes

3. bubble the gas throght lime water

4. if it turns milkey, poritive for Ca3 2-

Describe the test for sulfate ion

1. add a few drops of BaCl2 (barium chloride) solution

2. observe if the solution turns milkey (if any white precipitate forms)

3. milkey, then positive for SO4 2-

Describe the test for nitrate ion

1. add NaOH (sodium hydroxide) and Al (s) powder

2. heat gently in water bath

3. then test for ammonia

Describe the test for halides (negatively charged halogens)

1. acidify with dilute HNO3 (nitric acid)

2. add a few drops of AgNO3 (silver nitrate)

3. observe colour if…

   white… Cl-, chloride

   cream… Br-, bromide

   yellow… I-, iodide