Flame tests

1
Flame tests

• Teacher Claudia De Candido
• Tutor Elena Monti
• ITC O.Mattiussi 2005/06

2
Menu

• Demonstration flame tests.
• Giving reasons for the behaviour of the salts.
• Energy levels.
• Flame chart, multiple choice ,fill in the gaps.

3
Objectives

• In this unit the students will
• identify some elements from the flame
  tests
• explain the results by the model of energy
  levels.

4
Time

• 3 class periods 50 min. each.

5
Skills

• Knowledge of the new words and the new concepts.
• Accurate explanation of the behaviour of the
  salts in the flame.
• Prediction of behaviour through the acquainted
  knowledge.
• Grade Level second classes - secondary school.

6
Evaluation

• During the lessons the students can evaluate
  their understanding and their improvements
  through activities single or in group.
• Assessment
• flame chart,
• fill in the blanks,
• multiple choice.

7
Procedures

• Show the students the procedure in the flame
  tests .
• Give instructions about safety.
• The students will record the colour imparted to
  the flame in the flame test chart.
• They will use the first table to work out the
  metals in the unknown samples.
• They will learn that the colour of flame is
  emitted by the metal in the salt and that
  different metals produce different coloured
  light. Every coloured light has a specific
  energy, wavelength and frequency.
• We will do a kinaesthetic exercise to introduce
  the levels of energy.
• Show the slides about the electrons levels and
  explain it
• Review the content by a multiple choice exercises
  and filling in the blanks.

8
Resources required

• Platinum wire, salts of various metals, acid
  solution , Bunsen burner (special burner),
  beakers, gloves and goggles.
• Every material and apparatus is labeled with its
  name.

9
Suggestions

• What the students need to do
• Ask, ask, ask if you dont understand.
• During the experiments follow instructions
  carefully.
• Take notes and take part in the lessons.
• Practice and revise even when we dont tell you.

10
What do the street lamps , salt and fireworks
have in common ?
?
11

• They all contain SODIUM which gives off a unique
  yellow flame when it is heated.

12
Flame tests
13
Flame tests
14
Apparatus and materials

• Bunsen burner
• Watch glass dish
• Platinum wire
• Beaker
• Salts
• Hydrochloric acid solution, (dilute)
• Be careful!

15
Procedure

• Dip the wire in a acid solution
• Hold the wire in Bunsen flame (to check if wire
  is clean)
• Place some of the salt on the wire
• Hold the salt in the flame
• Note the colour imparted to the flame.
• Repeat for other salts.
• Record your results in flame test chart (first
  table) , using different colours
• Use the first table to fill in the blanks of the
  second table.

16
Safety

• Take the necessary precautions before beginning
  this experiment. Wear goggles and gloves.

17
(No Transcript)
18
Kinaesthetic exercise

• Stand up and close your eyes
• Imagine a book on a shelf , a lower shelf, next
  to the ground.
• Now get the book and put it on a higher shelf,
  on top.
• It is heavy.It is a big book.
• The book now is in an higher shelf, it has more
  energy because of your work.
• Unfortunately the book is unstable and suddenly
  falls to the ground, on your foot. Ouch!The book
  has given off the energy of your work!
• Open your eyes.
• Imagine the electron in the atom, which occupy
  only certain positions or levels of energy, like
  shelves or steps.

19
Useful model

• The diagram shows some steps leading up from
  horizontal ground. It is a useful model to
  explain the energy levels of electrons in the
  atoms.
• The energy levels can be occupied or vacant. In
  the example three energy levels 1,2, 4 are
  occupied and one energy level (3 ) is vacant.

20
(No Transcript)
21
Shelves

• Raising an electron to a higher energy level
  takes work. Similarly an electron falling to a
  lower step releases energy. This energy appears
  as radiation. The lowest electron is on the
  ground and cannot fail lower. An other useful
  model is shelves.

22
(No Transcript)
23
Energy levels
The normal electron configuration of atoms of an
element is known as the "ground state." In this
most stable energy state, all electrons are in
the lowest energy levels available. When atoms in
the ground state are heated to high temperatures,
some electrons may absorb enough energy to allow
them to "jump" to higher energy levels. The
element is then said to be in the "excited state."
24
This excited configuration is unstable, and the
electrons "fall" back to their normal positions
of lower energy. As the electrons return to their
normal levels, the energy that was absorbed is
emitted in the form of electromagnetic energy.
Some of this energy may be in the form of visible
light. The colour of this light can be used as a
means of identifying the elements involved. Such
crude analyses are known as flame tests. Only
metals, with their loosely held electrons, are
excited in the flame of a laboratory burner.
25
Thus, flame tests are useful in the
identification of atoms. Many metallic elements
exhibit characteristic colours when they are
vaporised in the burner flame. If the light
emitted is carefully analysed for its
characteristic frequencies, it can be shown that
each element has a characteristic pattern or
fingerprint.
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)