Analysis + gases in the atmosphere
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What are the three steps to identify positive ions in substances?
• flame test • add sodium hydroxide to produce precipitate • warm solution in hot water baths and test gas produced with damp litmus paper
Describe how to carry out a flame test
• clean a platinum wire by dipping it into concentrated acid to remove any impurities that may change colour of flame • then dip wire into substance being tested and hold it above a blue Bunsen flame until a recognisable colour change is visible
Why is platinum wire used?
• inert (unreactive) and so doesn’t colour the flame • high melting point so can withstand heat from blue flame
Lithium flame test
Red
Sodium flame test
Yellow
Postassium flame test
Lilac
Calcium flame test
Orange-red
Copper(II) flame test
Blue-green
Name the four ways to collect gases
• gas syringe • over water • upward delivery • downward delivery
What can we use gas syringe method for?
• any gas • most accurate measuring
What can we use over water method for?
• only works for gasses that are not soluble in water as they’d bubble through it and collect at top • works for gases in similar density to air
What can we use the upward delivery method for?
• gases thta are less dense than air so they would rise over it can collect at top • solubility in water is irrelevant
What can we use downward delivery for?
• gasses that are more dense than air air as they would sink beneath it • solubility is irrelevant
Test for chlorine gas
• damp red litmus paper • positive result = litmus paper bleaches
Test for ammonia
• damp red litmus paper • positive result = red litmus paper tunes blue (gas was alkaline)
Test for hydrogen
• lit splint in tube of hydrogen • squeaky pop will be heard
CO2 test
• bubble through limewater • positive result = limewater turns cloudy
Test for oxygen
• use a glowing splint into tube if oxygen • positive result = splint will relight
Test for presence of water
• anhydrous white copper(II) sulfate • turns from white to blue
Test for purity of water
• heat water and measure boiling point • positive result = pure water boils at 100 degrees C
Test for copper(II) ions
• add sodium hydroxide to copper(II) sulfate • positive result = clear blue solution becomes a cloudy blue one ( blue precipitate forms)
test for iron(II)
• add sodium hydroxide to iron(II) sulfate • positive result = colourless solution becomes green due to formation of green precipitate
Test for Iron(III)
• add sodium hydroxide to iron (III) sulfate • positive result. = yellow solution to red-brown precipitate forms
Test for ammonium
• add sodium hydroxide to ammonium chloride • put test tube containing this into hot water bath • positive result = gas evolved turned red damp litmus paper blue a