Testing for positive ions (group 2)

Question 1

Flame test for Group 2 ions

Answer 1

1) dip a nichrome wire loop into Hydrochloric acid
2) Then dip the wire loop into an unknown compound
3) hold the loop in the blue flame in the bunsen burner
4) observe colour change

calcium- Brick red Ca2+

Strontium - red Sr2+

barium- Pale green Ba2+

Question 2

using sodium hydroxide to test for group 2 ions

Answer 2

1) Add NaOH to a test tube drop wise containing the metal ion solution, and observe the precipitate that forms
2) Keep adding the NaOH until it is in excess, and record any changes you see.

Mg2+ with NaOH= slightly white precipitate
Ca2+ with NaOH= slightly white precipitate
Sr2+ with NaOH= slightly white precipitate
Ba2+= No change

EXCESS:
Mg2+= white precipitate
Ca2+= slightly white precipitate
Sr2+= Slightly white precipitate
Ba2+= No change

Question 3

Testing for ammonium ions (NH4+) with red litmus paper

Answer 3

1) if ammonia is present litmus paper turns BLUE

- litmus paper needs to be damp so the NH3 can dissolve

Question 4

Testing for ammonium ions (NH4+) using NaOH

Answer 4

1 )Add NaOH to test tube containing a substance and gently HEAT the mixture.

2) If AMMONIA GAS is given off (NH3), then ammonium ions are present (NH4+)

NH4+ + OH- –> NH3 + H2O