SC25 - Qualitative Analysis: Test for Ions ✓ Flashcards Preview

Edexcel GCSE Chemistry COPY > SC25 - Qualitative Analysis: Test for Ions ✓ > Flashcards

Flashcards in SC25 - Qualitative Analysis: Test for Ions ✓ Deck (28)
Loading flashcards...
1

SC25a - What colour do Lithium (Li+) ions turn in a flame test?

(Bright) Red

[Lith-le red riding hood]

2

SC25a - What colour do Sodium (Na+) ions turn in a flame test?

Yellow

3

SC25a - What colour do Potassium (K+) ions turn in a flame test?

Lilac

P̶u̶r̶p̶l̶e̶.̶ ̶A̶H̶H̶H̶H̶H̶ ̶I̶'̶M̶ ̶S̶O̶R̶R̶Y̶ ̶O̶K̶ ̶O̶K̶ ̶I̶T̶S̶ ̶N̶O̶T̶ ̶P̶U̶R̶P̶L̶E̶

4

SC25a - What colour do Calcium (Ca2+) ions turn in a flame test?

Orange-red

5

SC25a - What colour do Copper (Cu+) ions turn in a flame test?

Blue-Green

6

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

7

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

8

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

9

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

10

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]

11

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

12

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

13

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

14

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

15

SC25b - What colour precipitate do Iron(II) (Fe2+) ions form?

Green

16

SC25b - What colour precipitate do Iron(III) (Fe3+) ions form?

Brown

17

SC25b - What colour precipitate do Copper (Cu2+) ions form?

Blue

18

SC25b - What colour precipitate do Calcium (Ca2+) ions form?

White

19

SC25b - What colour precipitate do Aluminium (Al3+) ions form?

White

20

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

21

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

22

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

23

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

24

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

25

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

26

SC25c - What colour precipitate do Chloride (Cl-) ions form?

White

27

SC25c - What colour precipitate do Bromide (Br-) ions form?

Cream

28

SC25c - What colour precipitate do Iodide (I-) ions form?

Yellow