5.2.4 - cation tests

Question 1

what are cations

Answer 1

positive ions

Question 2

how to do a flame test:

Answer 2

1) dip a piece of nichrome/platinum wire into hydrochloric acid
(acid cleans the wire)

2) dip the wire into a sample of solid or solution

3) place tip of wire into a bunsen burner

Question 3

what colour does lithium (Li+) flame turn

Answer 3

red

Question 4

what colour does sodium (Na+) flame turn

Answer 4

yellow

Question 5

what colour does potassium (K+) flame turn

Answer 5

lilac

Question 6

what colour does calcium (Ca2+) flame turn

Answer 6

orange-red

Question 7

what colour does copper (Cu2+) flame turn

Answer 7

blue-green

Question 8

what do we use sodium hydroxide (NaOH) to test for

Answer 8

Cu2+, Fe2+ and Fe3+

-> if any of these are present, a metal hydroxide precipitate forms

Question 9

how to conduct an NaOH test

Answer 9

1) dissolve sample in water
2) add a few drops of NaOH(aq)

Question 10

what is the precipitate colour and formula for the metal cation Cu2+

Answer 10

colour - blue
formula - Cu(OH)2

Question 11

what is the precipitate colour and formula for the metal cation Fe2+

Answer 11

colour - green
formula - Fe(OH)2

Question 12

what is the precipitate colour and formula for the metal cation Fe3+

Answer 12

colour - brown
formula - Fe(OH)3

Question 13

how do we test for ammonium ions

Answer 13

using sodium hydroxide (NaOH)

Question 14

how to conduct an ammonium test

Answer 14

1) dissolve the sample in water
2) add some NaOH(aq) and warm it
3) test the gas evolved with damp red litmus paper

if ammonium ions are present the litmus paper will turn blue