4.6 - Chemical analysis Flashcards
Test for hydrogen
- Collect sample of gas in test tube
- Ignite using lit splint
- Result = squeaky pop
Test for oxygen
- Collect a sample of gas in test tube
- Place glowing splint in test tube
- Result = splint relights
Chemical test for water
- Add anhydrous copper sulfate
- Result = Changes from white to blue
Physical test for water
- Measure BP
- Result = BP is 100 degrees
Test for carbon dioxide
- Bubble a sample of the gas through limewater.
- Result = solution turns cloudy
Test for chlorine
- Place damp blue litmus paper in a sample of gas.
- Result = it turns white (bleaches).
Test for ammonia
- Place damp red litmus paper in a sample of gas.
- Result = it turns blue
How to conduct a flame test.
- Dip a piece of nichrome / platinum wire into hydrochloric acid. These wires don’t colour the flame, and the acid cleans the wire.
- Dip the wire into a sample of solid or solution. This causes some of the sample to stick onto the wire.
- Place the tip of the wire into a non-luminous Bunsen flame.
What does a flame test test for?
What type of metal cation is in a substance
Flame colour of lithium (Li) ?
Red
Flame colour of sodium (Na) ?
Yellow
Flame colour of potassium (K) ?
Lilac
Flame colour of calcium (Ca) ?
Orange-red
Flame colour of copper (Cu) ?
Blue-green
How do you conduct a sodium hydroxide (NaOH) test?
- Dissolve the sample in water.
- Add a few drops of NaOH(aq).
What is a sodium hydroxide test testing for?
To see in Cu, Fe(II) or Fe (III) is present
What colour precipitate is formed with Cu?
Blue
What colour precipitate is formed with Fe(II) ?
Green
What colour precipitate is formed with Fe(III) ?
Brown
How to conduct an ammonium test
- Dissolve the sample in water.
- Add some NaOH(aq) and warm it.
- Test the gas evolved with damp red litmus paper
What happens if ammonium ions are present?
Litmus will turn blue.
How to conduct a halide test?
- Dissolve the sample in water.
- Add nitric acid (HNO3).
- Add silver nitrate (AgNO3) solution.
What are we testing for with a halide test?
If Cl−, Br− or I− ions are present
What colour precipitate does Cl form?
White
What colour precipitate does Br form?
Cream
What colour precipitate does I form?
Yellow
Why do we add HNO3 in the halide test?
- Ag ions also form precipitates with OH and CO3.
- The HNO3 reacts with those anions and prevents false positives
How to conduct a test for carbonates?
- Add hydrochloric acid (HCl), look for effervescence.
- If there is effervescence, bubble the gas through limewater
If carbonate ions are present what colour does the limewater go?
Cloudy
Why do we check the gas is CO2 in the carbonate test?
To prevent false positives
How to conduct a test for sulfates?
- Add hydrochloric acid (HCl), look for effervescence.
- If there’s no effervescence, add barium chloride (BaCl2) solution.
What happens if sulfate ions are present?
White precipitate will be formed
Why do we add HCl is the sulfate test?
Because carbonate atoms also form a white precipitate white Ba ions. So we prevent false positives.
