Chemical tests
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tests for anions and cations produce 5 gases
• ammonia • carbon dioxide • oxygen • chlorine • hydrogen
ammonia turns damp red litmus paper what colour
blue
how to test for ammonia
have a test tube with the solution over a bunsen burner hold litmus paper at the tip of the test tube but don’t touch the sides the red litmus paper should turn blue
what is the reaction for the test for carbon dioxide
bubble the gas through limewater, it turns cloudy
test for carbon dioxide
The test for carbon dioxide involves bubbling the gas through an aqueous solution of limewater
test for chlorine gas
• handle in a fume cupboard as it is toxic • put some damp blue litmus paper to the test tube and it should turn red and then bleach white
why does damp blue litmus paper turn red at the beginning for chlorine
as acids are produced when chlorine comes into contact with water
chlorine has a sharp characteristic, what is it
the smell
colour change for chlorine
from damp blue litmus paper to red and then to white
Test for hydrogen gas
consists of holding a burning splint at the open end of a test tube of gas If the gas is hydrogen it burns with a loud “squeaky pop” Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn
why is there a squeaky pop for hydrogen
its the result of the rapid combustion of hydrogen with oxygen to produce water
test for oxygen
place a glowing splint inside a test tube of gas If the gas is oxygen, the splint will relight
how do you tell the test for hydrogen and oxygen apart
Try to remember that a ligHted splint has an H for Hydrogen, while a glOwing splint has an O for Oxygen.
how do you carry out a flame test
• dip the loop of a wire in dilute hydrochloric acid • then place it into a blue flame which decontaminates it • then place it in a solid sample containing metal ions • place it back into a blue flame a colour change should appear
lithium ions produce what colour flame
RED
Potassium ions produce what colour flame
LILAC
Sodium ions produce what colour flame
YELLOW
Copper ions produce what colour flame
Blue- green
Calcium ions produce what colour flames
orange- red
Metal cations in aqueous solution can be identified by what
the colour of the precipitate they form on addition of sodium hydroxide
the metal ion copper forms what precipitate when adding Sodium hydroxide
light blue precipitate formed
the metal ion Iron II forms what precipitate when adding Sodium hydroxide
Green precipitate formed
the metal ion Iron III forms what precipitate when adding Sodium hydroxide
brown precipitate formed
effect of adding sodium hydroxide to ammonium
Ammonia gas is produced which turns damp red litmus paper blue