2(h) Chemical Tests Flashcards
Test for Oxygen
Insert glowing splint into test tube
Positive result: Relights
Test for Hydrogen
Lit splint in test tube
Positive result: Burns with squeaky pop -> hydrogen in air reacts with oxygen to form water
Test for Carbon Dioxide
Bubble gas through limewater
Positive Result: colourless -> cloudy (calcium carbonate white precipitate)
What is Limewater
Calcium Hydroxide
Test for Chlorine gas
Damp blue litmus paper
Positive Result: Red then bleach white
Test for Ammonia
Damp red litmus paper
Positive Result: Blue
How to chemically clean wire for flame test
Dip nichrome wire in concentrated HCl
Put wire in hot part of blue roaring flame of bunsen burner
Repeat till flame burns cleanly
How to carry out a flame test
Dip nichrome wire in concentrated HCl
Dip into solid sample
Put into hot part of blue roaring flame
Observe colour
Colours of ions in flame test
Li+
Na+
K+
Ca2+
Cu2+
Li+ is red
Na+ is yellow
K+ is lilac
Ca2+ is orange-red
Cu2+ is blue-green.
Test for NH4+
Add sodium hydroxide
Gently warm and test gas evolved with damp red litmus paper.
Ammonia gas produced = blue
How to identify cations (Cu2+, Fe2+ and Fe3+) using sodium hydroxide
Add sodium hydroxide solution to a sample solution.
Precipitation reaction: Cu2+
Blue precipitate
Precipitation reaction: Fe2+
green precipitate, brown on standing
Precipitation reaction: Fe3+
brown precipitate
How to identify anions: Test for SO4 2-
Add few drops of dilute HCl
Add barium chloride solution
Positive result: White precipitate
