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Flame tests

Teacher : Claudia De CandidoTutor: Elena MontiITC “O.Mattiussi” 2005/06

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Menu

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

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ObjectivesObjectives

In this unit the students will:

identify some elements from the flame tests;

explain the results by the model of energy levels.

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Time

3 class periods 50 min. each.

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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.

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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.

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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.

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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.

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Suggestions

What the students need to do:Ask, ask, ask if you don’t understand.During the experiments follow instructions carefully.Take notes and take part in the lessons.Practice and revise even when we don’t tell you.

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

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

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Apparatus and materials

Bunsen burner

Watch glass dish

Platinum wire

Beaker

Salts

Hydrochloric acid solution, (dilute)

Be careful!

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ProcedureProcedureDip the wire in a acid solutionHold the wire in Bunsen flame (to check if wire is clean)Place some of the salt on the wireHold the salt in the flameNote the colour imparted to the flame.Repeat for other salts.Record your results in flame test chart (first table) , using different coloursUse the first table to fill in the blanks of the second table.

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SafetySafety

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

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Record your results during the experiment in the table below.

barium calcium copper potassium sodium strontium

Use the first table to work out the metals in the new samples and than fill in thebottom row.

Sample KNO3 CuSO4 CaCl2 NaNO3

Flame colourmetal

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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.

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Useful modelUseful 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.

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ShelvesShelves

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.

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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."

Energy levelsEnergy levels

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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 ofthis 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.

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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.

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Ne

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Energy levels

The normal electron configuration of atoms of an element is known as the "groundstate." In this most stable energy state, all electrons are in the lowest energy 1_________available. When atoms in the 2_______state are heated to high temperatures, someelectrons may absorb enough energy to allow them to "jump" to higher 3______levels.The element is then said to be in the "excited state.".This 4__________configuration is unstable, and the electrons "fall" back to their normalpositions of 5_______energy. As the electrons return to their normal levels, the energythat was absorbed is emitted in the form of electromagnetic energy. Some of this energymay be in the 6________of visible light. The colour of this light can be used as a meanof 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 Bunsen7______ . Thus, flame tests are useful in the 8_________of atoms. Many metallicelements exhibit characteristic 9___________ when vaporised in the burner flame. Ifthe light emitted is carefully analyzed for its characteristic frequencies, it can be shownthat each element has a characteristic fingerprint, because ofdifferent___________structure.

Bank words

burner colours energy electronic electronic excited form ground identification levels lower

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Energy levels

The normal electron configuration of atoms of an element is known as the "groundstate." In this most stable energy state, all electrons are in the lowest energy levelsavailable. When atoms in the ground state are heated to high temperatures, someelectrons may absorb enough energy to allow them to "jump" to higher energy levels.The element is then said to be in the "excited state.".This electronic configuration is unstable, and the electrons "fall" back to their normalpositions of lower energy. As the electrons return to their normal levels, the energy thatwas absorbed is emitted in the form of electromagnetic energy. Some of this energy maybe given off in the form of visible light. The colour of this light can be used as a mean ofidentifying 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 Bunsenburner. Thus, the flame tests are useful in the identification of atoms. Many metallicelements exhibit characteristic colours when vaporised in the burner flame. If the lightemitted is carefully analyzed for its frequencies, it can be shown that each element has acharacteristic fingerprint, because of different electronic structure.

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Multiple choiceCheck the correct answer

1) The carrier for the salt in this demonstration was

a- water b-potassium c-acid solution d- sodium e-calcium

2) Which of the following flame colours is matched correctly with its metal ?

a- strontium- violet flame b- potassium –lilac c- sodium – green flame

d – copper- red e – calcium- yellow

3) Electrons of an atom reside in concentric spheres known as:

A – nuclei b- cations c- molecules d- energy levels e- ions

4) When energy is supplied to an atom, the electron

a- does not react to the energyb- moves from its energy shell to a lower energy shellc- moves from its energy shell to a higher energy shell and stays thered- moves from its energy shell to a higher energy shell then back againe- none of the above

5) The excited state of an electron

a- put it in an energy shell with a higher valueb- put it in a more stable energy statec- put it in a higher energy leveld- put it in a less stable energy statee- put it in a lower energy level

6) When electrons move from the ground state to the excited state we say they have been

a- assistedb- excitedc- promotedd- demotede- discharged

7) The metal in a salt exist as

a- a neutral particleb- a positivec- a negative particled- a catione- an anion

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Assisted helpedBunsen the scientist who gave his name to a particular burnerCarrier the person or thing transporting or moving somethingDemote reduce to a lower rank (position)Discharged releasedExcited state the unstable energy stateFingerprint used for identificationGround state the most stable energy stateLoosely in the loose way, not fixed in placePattern modelPromoted raised to the higher rankShell the electronic level