Chemical Testing Flashcards
How to test for hydrogen
Dip lit splint into test tube filled with gas
Positive result: squeaky pop sound
How to test for oxygen
Dip glowing splint into test tube filled with gas
Positive result: splint reignites
How to test for carbon dioxide
Bubble gas through limewater
Positive result: limewater turns from clear to cloudy
How to test for ammonia
Dip damp red litmus paper into gas
Positive result: paper turns from red to blue
How to test for chlorine
Dip damp blue litmus paper into the gas
Positive result: paper turns from blue to white
How to carry out a flame test
- Clean the wire: dip the end into the acid and burn in flame 3 times
- Dip wire end into acid and then into solid sample
- Burn sample in flame
- Note colour observed and compare to known colours
What are flame tests used for?
They can identify if the following cations are present in a compound:
Li+, Na+, K+, Ca2+, Cu2+, Ba2+
What colour flame does a Li+ cation form?
Red
What colour flame does a Na+ cation form?
Yellow
What colour flame does a K+ cation form?
Lilac
What colour flame does a Ca 2+ cation form?
Orange-red
What colour flame does a Cu 2+ cation form?
Blue-green
What colour flame does a Ba 2+ cation form?
Green
How to test for NH4 + cation
- Add a few cm3 of sodium hydroxide solution to solid ammonium chloride.
- Heat gently using a bunsen burner
- Test gas produced using damp red litmus paper
Positive result: ammonia gas produced, turn litmus paper red to blue
How to test for Cu 2+, Fe 2+ and Fe 3+ cations
- Add a few drops of sodium hydroxide solution until in excess
- Observe result
What colour precipitate does Cu 2+ form?
Blue
What colour precipitate does Fe 2+ form?
Green
What colour precipitate does Fe 3+ form?
Brown
How to test for Cl-, Br- and I- anions
- Put 2cm3 of the solution to be tested into a test tube
- Add a few drops of dilute nitric acid
- Add a small amount of silver nitrate solution
- Record observations
What colour precipitate does Cl- form?
White
What colour precipitate does Br- form?
Cream
What colour precipitate does I- form?
Yellow
How to test for SO4 2- anions
- Put 1 small spatula of test sample into test tube and add 10cm3 of water to dissolve it.
- Add barium chloride solution drowse until you see s result.
Positive result: white precipitate forms
How to test for CO3 2- anions
- Put a few marble chips into a test tube.
- Put 5cm3 limewater into another test tube.
- Add approx 5cm3 dilute hydrochloric acid to the carbonate
- Quickly put the bung of the delivery tube in the test tube with the other end in the limewater.
Positive result: effervescence, limewater turns cloudy (due to carbon dioxide being produced)
How to test for water:
Add anhydrous copper sulphate
Positive result: mixture turns from white to blue
Dip in cobalt chloride paper
Positive result: paper turns from blue to pink
