Lesson 3: Flame Tests/ Instrumental Methods

Question 1

What are flame tests used for?

Answer 1

• Flame tests are used for identifying some metal ions (cations.)

Question 2

What colour flame do lithium compounds result in in flame tests?

Answer 2

• Lithium compounds result in a crimson flame

Question 3

What colour flame do sodium compounds result in in flame tests?

Answer 3

• Sodium compounds result in a yellow flame

Question 4

What colour flame do potassium compounds result in in flame tests?

Answer 4

• Potassium compounds result in a lilac flame.

Question 5

What colour flame do calcium compounds result in in flame tests?

Answer 5

• Calcium compounds result in an orange-red flame

Question 6

What colour flame do copper compounds result in in flame tests?

Answer 6

• Copper compounds result in a green flame.

Question 7

Why can’t flame tests be used to test for numerous cations in a sample containing a mixture of ions?

Answer 7

• If a sample containing a mixture of ions is used some flame colours
  can be masked.

Question 8

What is meant by the term: “instrumental methods?”

Answer 8

• Carried out by a machine.

Question 9

What are the 3 main of advantages of instrumental methods in comparison to chemical methods?

Answer 9

1.) More rapid.
2.) More sensitive (ie. flame emission spectroscopy will work on even a tiny sample of compound.)
3.) More accurate (flame emission spectroscopy more likely to idenify an ion than flame tests.)

Question 10

Give an example of an instrumental method and its use

Answer 10

• Flame emission spectroscopy.
• To analyse metal ions in solutions.

Question 11

How does flame emission spectroscopy work?

Answer 11

1.) The sample is put through a flame and the light given out is passed through a spectroscope.
2.) The output (from the spectroscope) is a line spectrum.

Question 12

What are line spectrums from flame emission spectroscopy used for?

Answer 12

• You can analyse to identify the metal ions in the solution.
• Measure the concentrations of each ion (based on the intensity of the line drawn on spectrum.)

Question 13

What is the image formed from flame emission spectroscopy known as?

Answer 13

• The image formed is known as a “line spectrum.”

Question 14

How do you carry out a flame test?

Answer 14

1.) Dip nichrome wire into hydrochloric acid.
2.) Hold the tip of the wire in a blue, roaring flame (Bunsen Burner) until there’s no colour seen.
3.) Place nicrhome wire into solution/ Bunsen Burner and record the colour the solution causes the flame to turn.