Tests for common compounds

Sulfur dioxide

Pass the gas over a piece of filter paper soaked in acidified Na₂Cr₂O₇. The paper goes from an orange colour for the Cr⁶⁺ to a green colour for Cr³⁺

Water

Cobalt chloride paper turns from blue to pink in the presence of water.

Acid

Blue litmus paper turns red in the presence of an acid.

OR

Testing using universal indicator shows a pH of less than 7

Carbon dioxide

Passing Carbon dioxide through limewater (calcium hydroxide solution) turns the clear solution milky.

Oxygen

Oxygen gas will relight a glowing splint

Hydrogen

A test tube of hydrogen gas gives off a squeaky pop when lit (do not try to test large volumes of hydrogen gas!)

Ammonia Gas

Damp litmus paper is turned blue

Bring an open bottle of concentrated Hydrochloric Acid near, a dense white gas can be seen.