test for positive ions Flashcards
How does a person carry out a flame test for positive ions?
- put a small amount of the compound to be tested in a nichrome wire loop
- then hold the loop in the roaring blue flame of a Bunsen burner
- use the colour of the Bunsen flame to identify the metal ion in the compound
Why should the wire loop be dipped in concentrated hydrochloric acid and heated first? What should happen next?
To clean it. Then it should be dipped in the acid again before dipping it in the metal compound
What colour flame does lithium burn with?
crimson
What colour flame does sodium burn with?
yellow
What colour flame does potassium burn with?
lilac
What colour flame does calcium burn with?
brick red
What colour flame does barium burn with?
apple green
If a compound pound produces a white precipitate after reacting with sodium hydroxide solution, what positive ions might it contain?
Aluminum (Al3+), calcium (Ca2+) or magnesium (Mg2+) ions
What can be done to a compound with positive ions to identify it as containing aluminum ions?
If more and more sodium hydroxide solution is added, then the precipitate dissolves
How can calcium and magnesium ions be distinguished?
A flame test has to be done. Calcium ions give a brick red flame but magnesium ions produce no colour at all
What do some metal ions form when reacted with sodium hydroxide solution?
They form a coloured precipitate
What is the colour of the precipitate formed when sodium hydroxide solution is added to a substance containing copper (II) ions?
Blue
What is the colour of the precipitate formed when sodium hydroxide solution is added to a substance containing iron (II) ions?
Green
What is the colour of the precipitate formed when sodium hydroxide solution is added to a substance containing copper (III) ions?
Brown
