Tests for Cations

Question 1

what colour flame does lithium (Li+) have?

Answer 1

red

Question 2

what colour flame does sodium (Na+) have?

Answer 2

yellow

Question 3

what colour flame does potassium (K+) have?

Answer 3

lilac

Question 4

what colour flame does calcium (Ca2+) have?

Answer 4

orange-red

Question 5

what colour flame does copper (Cu2+) have?

Answer 5

blue-green

Question 6

how to do a flame test

Answer 6

1. clean a platinum wire loop by dipping in dilute hydrochloric acid and then holding it in a flame
2. once you hold the loop in the flame and it burns without any colour you can dip into the sample you want to test
3. heat in roaring clear blue Bunsen flame

Question 7

what do flame tests test for?

Answer 7

metal ions

Question 8

how to do a sodium hydroxide test

Answer 8

1. dissolve the sample in water
2. add a few drops of sodium hydroxide to the solution
3. if you get a coloured insoluble hydroxide you can tell which metal was in the compound

Question 9

what precipitate colour does copper(II) (Cu2+) form?

Answer 9

blue

Question 10

what is the ionic formula for copper(II) (Cu2+)?

Answer 10

Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)

Question 11

what precipitate colour does iron(II) (Fe2+) form?

Answer 11

green

Question 12

what is the ionic formula for iron(II) (Fe2+)?

Answer 12

Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)

Question 13

what precipitate colour does iron(III) (Fe3+) form?

Answer 13

brown

Question 14

what is the precipitate formula from iron(III) (Fe3+)?

Answer 14

Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)

Question 15

ammonia test

Answer 15

1. add sodium hydroxide to the sample solution
2. test the gas given off with damp red litmus paper
   NOTE: the litmus paper must be damp so the ammonia gas can dissolve and make the colour change
3. if ammonia is present, the paper will turn blue