C4.2 - Identifying Products of Chemical Reactions Flashcards
How do you detect CO2 (and how does it work)?
- Bubble the gas through limewater (calcium hydroxide solution)
- if it turns cloudy, The gas is CO2
- it works by…limewater + CO2 reacting to product a white precipitate
How do you detect chlorine (and why does it work)?
- hover a dampened piece of blue litmus paper above the substance
- if chlorine present, paper bleaches (turns red then white)
- this works because….chlorine bleaches dyes
Why does the litmus paper have to be damp?
- As when chlorine reacts with water it creates an acidic solution.
- therefore, the water allows the litmus paper and chlorine to react
- and so the paper becomes bleached
What must you do to make sure you are not harmed when smelling substances in a laboratory?
- keep container a few cm away from nose + a cautious sniff
Make sure you do not breathe in a lot of substance
How do you detect for hydrogen?
- place a lit splint (you can see a flame) near the mouth of test tube
- it should ignite with a ‘squeaky pop’ sound
How do you detect for oxygen?
- place a glowing splint (so almost gone), into mouth of test tube
- flame should relight (becomes a roaring flame)
Describe why a flame test works (the science behind it)
- when metal ions are heated, energy is transferred to electrons
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Electrons move to higher electron shells (outwards) - now unstable
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When electrons move back to normal energy shells, energy is transferred to surroundings as radiation (we see as light, or a flame)
Why do different metals produce different colours of light?
As they have different chemical properties or different placed electrons, so the electrons jump different lengths (different wavelength so different colour produced)
What kind of ions do flame tests work on?
Metal ions (or cations - positive ions)
How do you carry out a flame test?
1) clean nichrome wire loop (with handle), by dipping in HCl acid
2) then rinse it in distilled water
3) place into bunsen burner to see if the blue flame changes colour, if it does dip it in HCL acid again and rinse it
4) dip clean loop into test power/solution
5) place loop into blue flame on Bunsen burner
6) record flame colour
What colour is lithium’s flame?
Red
What colour is sodium’s flame?
Yellow
What colour is potassium’s flame?
Lilac
What colour is calcium’s flame?
Orange-red
What colour is copper’s flame?
Green-blue