Cations
Cards (7)
- They are positively charged ions with a +1 charge or more
- Testing for group 2 cations
- Place 10 drops of a group 2 compound in a test tube (0.1moldm-3)
- Add 10 drops of 0.6moldm-3 of NaOH to test tube
- Record observations
- Add an excess of NaOH
- Record results
- Results for testing group 2 cationswith NaOHAfter adding NaOH (not an excess)Barium - stays colourlessCalcium - colourless to slight white precipitateMagnesium - colourless to slight white precipitateStrontium - colourless to slight white precipitateAfter adding excess of NaOHBarium - stays colourlessCalcium - still has a slight white precipitateMagnesium - slight white precipitate to white precipitateStrontium - still has a slight white precipitate
- How to distinguish between calcium and strontium?
- Place 10 drops of the group 2 compounds in a test tube
- Add 10 drops of sulfuric acid (1.00 moldm-³)
- Record observations
- Then add an excess of sulfuric acid
Strontium would have a white precipitate and calcium would have a slight white precipitate - Results for testing group 2 cations with sulfuric acidAfter adding 10 drops of sulfuric acid
- Barium - Colourless to white precipitate
- Calcium - Colourless to slight white precipitate
- Magnesium - Colourless to slight white precipitate
- Strontium - Colourless to white precipitate
After adding excess of sulfuric acid- Barium - Colourless to white precipitate
- Calcium - Colourless to slight white precipitate
- Magnesium - Colourless to Colourless
- Strontium - Colourless to white precipitate
- How to test for ammonium ions (NH4+)
- Place 10 drops of ammonium compound (e.g. NH4Cl ) into a test tube
- Add 10 drops of NaOH into test tube and shake
- Warm the test tube
- Place damp red litmus paper at the top of the test tube
- If it turns blue then ammonium ions are present
- Adding ammonium solution to any of the group 2 hydroxide only Magnesium hydroxide reacts and produces a white precipitate.