Tests for Positive Ions Flashcards
What do flame tests identify?
Metal ions
What colour flame is Lithium, Li⁺?
Crimson
What colour flame is Sodium, Na⁺?
Yellow
What colour flame is Potassium, K⁺?
Lilac
What colour flame is Calcium, Ca²⁺?
Red
What colour flame is Barium, Ba²⁺?
Green
How do you flame test a compound?
Dip a clean wire loop into a sample of the compound and put the wire loop in the clear blue part of the Bunsen flame.
Make sure the wire loop is really clean by dipping it into hydrochloric acid and rinsing it with distilled water
Some metals form a [ ] NaOH
coloured precipitate
Many metal hydroxides are [ ] and precipitate out of solution when formed. Some of these [ ] have a characteristic colour.
insoluble
hydroxides
What is the process of finding a compound by looking at the colour of the precipitate?
You add a few drops of sodium hydroxide solution to a solution of your mystery compound. If you get a coloured insoluble hydroxide you can then tell which metal was in the compound
What is the colour of the precipitate and the ionic reaction (symbols) of Calcium, Ca²⁺?
White
Ca²⁺ (aq) + 2OH⁻ (aq) -> Ca(OH)₂ (s)
What is the colour of the precipitate and the ionic reaction (symbols) of Copper (II), Cu²⁺?
Blue
Cu²⁺ (aq) + 2OH⁻ (aq) -> Cu(OH)₂ (s)
What is the colour of the precipitate and the ionic reaction (symbols) of Iron (II), Fe²⁺?
Green
Fe²⁺ (aq) + 2OH⁻ (aq) -> Fe(OH)₂ (s)
What is the colour of the precipitate and the ionic reaction (symbols) of Iron (III), Fe³⁺?
Brown
Fe³⁺ (aq) + 3OH⁻ (aq) -> Fe(OH)₃ (s)
What is the colour of the precipitate and the ionic reaction (symbols) of Aluminium, Al³⁺?
White at first. But then it redissolves in excess NaOH to form a colourless solution
Al³⁺ (aq) + 3OH⁻ (aq) -> Al(OH)₃ (s)
Then Al(OH)₃ (s) + OH⁻ (aq) -> Al(OH)₄⁻ (aq)
