ion testing Flashcards
Describe how to carry out a flame test to test for ions
Clean a nichrome wire using hydrochloric acid
Turn the bunsen burner onto the blue flame
Dip the wire into the substance being tested
Place the wire in the flame and record the colour
Colour of the flame test on lithium
Crimson
Colour of the flame on sodium
Yellow
Colour of the flame on potassium
Lilac
Colour of the flame on Calcium
Orange-red
Colour of the flame on copper
Blue-green
Why must the nichrome wire be cleaned first before carrying out a flame test?
To remove any unwanted ions that might obscure the colour of the flame
What is a precipitate
An insoluble solid suspended in a liquid
What colour precipitate forms when sodium hydroxide reacts with calcium
White
What colour precipitate forms when sodium hydroxide reacts with copper (II)
Blue
What colour precipitate forms when sodium hydroxide reacts with iron (II)
Green
What colour precipitate forms when sodium hydroxide reacts with iron(III)
Brown
What colour precipitate forms when sodium hydroxide reacts with aluminium
White, but with excess NaOH, the precipitate re-dissolves to form a colourless solution
What is observed when sodium hydroxide reacts with ammonium ions?
A pungent-smelling gas is produced (NH3) which will turn damp red litmus paper blue
How could you distinguish between two solutions containing aluminium ions and calcium ions?
Add excess sodium hydroxide. Both will form white precipitates initially. The precipitate formed from aluminium ions will re-dissolve to form a colourless solution.