- Food is tested for purity and safety in chemical analysis.
- Qualitative analysis checks the type of substances in the sample.
- Quantitative analysis measures the amount of the substances in the sample.
- Water sometimes contains ionic compounds which are made of cations and anions.
- An analyst must test for each ion to identify an unknown ionic compound. Both anion and cation must be identified.
- Ion tests must only give one positive result to identify the compound.
- Flame tests can detect some cations.
- Symbol: Ca2+
- Flame colour: Brick red
- Symbol: Na+
- Flame colour: Yellow
- Symbol: K+
- Flame colour: Lilac
- Symbol: Cu2+
- Flame colour: Green/Blue
- Sodium hydroxide can be added to the solution to find the unknown cations
- Many metal hydroxides are insoluble so a precipitation reaction can occur.
- The precipitate formed can identify the ion.
- Symbol: Al3+(aq)
- Effect: White precipitate
- Symbol: Ca2+(aq)