Cations Flashcards
What are cations?
positive ions
Give an example of a cation.
Na+ or Ca2+
Give a test for cations that involve the alkali metals
flame tests
Describe the flame tests for cation ions (In this case metal ions)
Clean a platinum wire loop by dipping it in DILUTE HYDROCHLORIC ACID and then holding it in a flame, once the you hold in the loop in the flame and IT BURNS WITHOUT ANY COLOUR you can dip it into the sample you want to test and then put it back in the flame and observe the new COLOUR OR THE FLAME.
What colour does potassium burn with?
lilac
What colour does sodium burn with?
yellow-orange
what colour does calcium burn with?
brick red
what colour does lithium burn with?
crimson - red
With what do some metals form a colour precipitate
sodium hydroxide (NaOH)
Describe the sodium hydroxide test.
Add a few drops of SODIUM HYDROXIDE SOLUTION to a solution of your unknown compund. If you get a COLOUR PRECIPITATE you can tell which metal was in the compound.
What is the coloured precipitate and how is it formed?
insoluable metal hydroxide, it is formed by the metal ions reacting with the sodium hydroxide.
what is the coloured precipitate for copper?
blue
what is the coloured precipitate for iron (ll)?
sludgy green
what is the coloured precipitate for iron (lll)?
reddish brown
what is the equation for copper when reacted with sodium hydroxide?
Cu2+ (charge two +) + (aq) + 2OH- (aq) > Cu(OH)2
