Tests for ions · Grade 10
In Grade 10 you learn: flame tests.
Metal ions can be found with flame tests and by adding sodium hydroxide solution to see the color of the precipitate. Negative ions have their own tests: carbonates fizz with acid, halides give colored precipitates with silver nitrate, and sulfates give a white precipitate with barium chloride. Using one test for each ion identifies a salt.
Key facts
- Flame tests: lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper green.
Worked examples
Example 1
What color flame do lithium ions give in a flame test?
Answer: crimson
Example 2
Why is the wire for a flame test cleaned in acid first?
Answer: to remove any metal ions left from earlier tests
Example 3
A compound gives a yellow flame in a flame test. Which metal ion does it contain?
Answer: sodium ions
Example 4
Why can a flame test be hard to read for a mixture of metal ions?
Answer: one color can hide another