Chapter 25: Tests for Gases, Anions and Cations
The test for carbon dioxide involves bubbling the gas through an aqueous solution of calcium hydroxide (limewater)
If the gas is carbon dioxide, the limewater turns milky or cloudy
The test for hydrogen is often referred to as the 'squeaky pop' test
The test for hydrogen consists of holding a burning splint held at the open end of a test tube of gas
If the gas is hydrogen it burns with a loud “pop” sound which is the result of the rapid combustion of hydrogen with oxygen to produce water
Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn
The test for oxygen consists of placing a glowing splint inside a test tube of gas
If the gas is oxygen the splint will relight
The test for chlorine makes use of litmus paper
If chlorine gas is present, damp blue litmus paper will be bleached white
It may turn red briefly before bleaching, as acids are produced when chlorine comes into contact with water
Chlorine should always be handled in a fume cupboard due to its toxicity
dissolve a small sample of the solid salt you are testing in water.
place approximately 10cm3 of the solution into a test tube.
add four drops of nitric acid.
add silver nitrate solution, dropwise.
if a precipitate is produced, observe the colour.
Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide and ammonia
If only a small amount of NaOH is used then normally the metal hydroxide precipitates
If a precipitate is formed from NaOH then the hydroxide is insoluble in water
Add a few drops of dilute sodium hydroxide (NaOH()aq) into an unknown solution and observe any changes.
We can test further by adding excess NaOH()aq and recording any changes.
Add a few drops of dilute ammonium hydroxide (NHOH()4aq) into an unknown solution and observe any changes.
We can test further by adding excess NHOH()4aq and recording any changes
Gas present if there’s a pop sound?
Oxygen
Gas present if when a glowing splint is put inside a test tube of gas it relight?
Hydrogen
Gas present if it turns milky/cloudy?
Carbon dioxide
Gas present is damp, blue litmus paper turns bleached
Chlorine
The test for carbon dioxide involves bubbling the gas through an aqueous solution of calcium hydroxide (limewater)
If the gas is carbon dioxide, the limewater turns milky or cloudy
The test for hydrogen is often referred to as the 'squeaky pop' test
The test for hydrogen consists of holding a burning splint held at the open end of a test tube of gas
If the gas is hydrogen it burns with a loud “pop” sound which is the result of the rapid combustion of hydrogen with oxygen to produce water
Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn
The test for oxygen consists of placing a glowing splint inside a test tube of gas
If the gas is oxygen the splint will relight
The test for chlorine makes use of litmus paper
If chlorine gas is present, damp blue litmus paper will be bleached white
It may turn red briefly before bleaching, as acids are produced when chlorine comes into contact with water
Chlorine should always be handled in a fume cupboard due to its toxicity
dissolve a small sample of the solid salt you are testing in water.
place approximately 10cm3 of the solution into a test tube.
add four drops of nitric acid.
add silver nitrate solution, dropwise.
if a precipitate is produced, observe the colour.
Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide and ammonia
If only a small amount of NaOH is used then normally the metal hydroxide precipitates
If a precipitate is formed from NaOH then the hydroxide is insoluble in water
Add a few drops of dilute sodium hydroxide (NaOH()aq) into an unknown solution and observe any changes.
We can test further by adding excess NaOH()aq and recording any changes.
Add a few drops of dilute ammonium hydroxide (NHOH()4aq) into an unknown solution and observe any changes.
We can test further by adding excess NHOH()4aq and recording any changes
Gas present if there’s a pop sound?
Oxygen
Gas present if when a glowing splint is put inside a test tube of gas it relight?
Hydrogen
Gas present if it turns milky/cloudy?
Carbon dioxide
Gas present is damp, blue litmus paper turns bleached
Chlorine
