SC25a - What colour do Lithium (Li+) ions turn in a flame test?
[Lith-le red riding hood]
SC25a - What colour do Sodium (Na+) ions turn in a flame test?
SC25a - What colour do Potassium (K+) ions turn in a flame test?
P̶u̶r̶p̶l̶e̶.̶ ̶A̶H̶H̶H̶H̶H̶ ̶I̶'̶M̶ ̶S̶O̶R̶R̶Y̶ ̶O̶K̶ ̶O̶K̶ ̶I̶T̶S̶ ̶N̶O̶T̶ ̶P̶U̶R̶P̶L̶E̶
SC25a - What colour do Calcium (Ca2+) ions turn in a flame test?
SC25a - What colour do Copper (Cu+) ions turn in a flame test?
SC25a - What are the 3 main steps in conducting a flame test?
- Light a Bunsen burner to a strong blue flame
- Pick up a sample of the substance with a small wire loop
- Hold the sample into the edge of the flame and observe the colour
SC25a - Why may the flame test loop be a platinum one?
- It has a high melting point and so won't melt
- It is inert and so won't react It doesn't produce/affect a flame colour
SC25a - Why may a nichrome alloy be used as a wire loop for a flame test?
- It is cheaper
- However, it produces a light orange flame that could affect the results
SC25a - What is flame photometry?
- When a solution containing the metal ions creates a flame and the light intensity is measured by a computer.
- This allows it to have quantitative and comparable data
SC25a - What are the main three advantages of photometry over flame tests?
- Sensitivity: Much smaller sample sizes can be used
- Accuracy: They give results closer to the true value
- Speed: They occur with more quickness [look at me defining speed like a pro]
SC25a - What is a callibration curve?
- It shows the light intensity produced by metal ions in different concentrations of solutions
- It is created by using standard solutions of known concentrations
- This allows data comparison to be accurate
SC25a - What can flame photometers do to the light emitted by a flame?
They can separate the light produced into a spectrum of different colours (wavelengths) of light
SC25a - What is an emission spectrum?
- Metal ions each produce their own unique combination of different wavelengths of light
- This different colours are the emission spectrum of an ion and can be used to identify ions
- Together, these different colours will produce the one colour seen in the flame test
SC25b - How do you conduct a precipitate reaction to identify metal ions?
- A few drops of sodium hydroxide are added to a solution containing metal ions
- The metal and the hydroxide will react to form metal hydroxide
- This will be insoluble and form a precipitate of a colour that can be used to identify the metal
SC25b - What colour precipitate do Iron(II) (Fe2+) ions form?
SC25b - What colour precipitate do Iron(III) (Fe3+) ions form?
SC25b - What colour precipitate do Copper (Cu2+) ions form?
SC25b - What colour precipitate do Calcium (Ca2+) ions form?
SC25b - What colour precipitate do Aluminium (Al3+) ions form?
SC25b - What is the problem with the precipitate test for calcium and aluminium and how is this overcome?
- Both calcium and aluminium ions will produce a whit precipitate when reacted with sodium hydroxide.
- Thus, a distinguishing test is required In this case, excess sodium hydroxide is added
- For aluminium ions, this causes the precipitate to eventually turn colourless
SC25b - What is the test for ammonium ions?
- Dilute sodium hydroxide solution is added which produces ammonia gas
- Ammonia gas has a characteristic sharp smell but a confirmatory test is needed to be sure
- Ammonia gas turns damp red litmus paper blue
SC25c - How do you test for carbonate ions?
- Add dilute hydrochloric acid to the sample If it does contain a carbonate, this will cause carbon dioxide to be produced
- This will cause effervesence
- To make sure this is carbon dioxide, bubble the gas produced through limewater
- If carbon dioxide is present, limewater will turn colourless to cloudy.milky
SC25c - How do you test for sulfate ions?
- Add some dilute hydrochloric acid to the solution
- Then add barium chloride If sulfate ions are present, this will produce a white precipitate of (insoluble) barium sulfate
SC25c - Why is hydrochloric acid added when testing for sulfate ions?
To remove any carbonate ions and therefore eliminate the chance of a false positive result
SC25c - How do you test for halide ions?
- Add some dilute nitric acid to your sample
- Add some silver nitrate solution
- Observe the colour of the precipitate formed and compare to check what ion was present
SC25c - What colour precipitate do Chloride (Cl-) ions form?
SC25c - What colour precipitate do Bromide (Br-) ions form?
SC25c - What colour precipitate do Iodide (I-) ions form?