Chemistry Lab 2 - Flame Tests - Emission Spectros PDF Emission Spectrum Energy Level 2
Chemistry Lab 2 - Flame Tests - Emission Spectros PDF Emission Spectrum Energy Level 2
Chemistry Lab 2 - Flame Tests - Emission Spectros PDF Emission Spectrum Energy Level 2
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INTRODUCTION
+ + + 2+ 2+ 2+
AIM: 1. To investigate and predict the identity of metal ions, Li , Na , K , Ca , Ba , Cu
BACKGROUND:
+ + + 2+ 2+ 2+
A number of common metal ions, (Li , Na , K , Ca , Ba , and Cu ) give a distinct colour in
the presence of a flame. Therefore, a flame test is often used as a confirmatory test in identifying
an unknown metal. Compounds of these ions provide the beautiful colours in a fireworks display.
When glass is melted in a Bunsen burner flame, sodium ions colour the flame bright yellow. A
copper wire inserted into the flame often results in a striking deep blue or green colour.
THEORY:
According to the Bohr Theory of the atom, electrons may occupy only specific energy levels.
When an atom absorbs sufficient energy, an electron can “jump” to a higher energy level. Higher
energy levels tend to be less stable, however, and if a lower energy level is available, the electron
will “fall” back, giving off energy in the process. The difference in energies between the two
levels is emitted in the form of a photon of electromagnetic radiation. The energy of each photon
is described by the equation E = hv, where h is Planck‟s constant and v is the frequency of the
radiation. If the wavelength of the released photon is between 400 and 700 nm, the energy is
emitted as visible light. The colour of the light depends on the specific energy change that is
taking place. White light is a continuous spectrum in which all wavelengths of visible light are
present. An excited atom, however, produces one or more specific lines in its spectrum,
corresponding to the specific changes in energy levels of its electrons. Because each element has
Flame tests are a quick method of producing the characteristics colours of metallic ions. The
loosely-held electrons of a metal are easily excited in the flame of a lab burner. The emission of
energy in the visible portion of the spectrum as those electrons return to lower energy levels
produces a coloured flame. The colour is a combination of the wavelengths of each transition,
and may be used to determine the identity of the ion. If two metals are present in a mixture, the
colour of one flame may obscure or hide that of the other. However, if cobalt glass is used, it is
possible to absorb one of the colours and not the other. Therefore we will also look at a flame
produced from a mixture of compounds. From the data, we will then be able to identify which
metals are in the unknown substance based on what colour flame it produces upon heating.
METHOD:
Each test tube (not the test tube containing the 7.0M HCl) was filled to a depth of 1cm with their
respective stock solutions. The Bunsen burner was then ignited and the flame was adjusted to
produce a non-luminous (smokeless blue flame with a pale blue inner core) flame. The nichrome
wire was then cleaned by dipping it into the test tube containing the 7.0M HCl and then held in
the hottest part of the flame. This was repeated until the wire imparted no colour to the flame.
The loop of the clean nichrome wire was then inserted into the test tube containing the solution
and held in the hottest part of the flame. The wire was then cleaned as instructed before and the
flame test was repeated for each solution. The colour of the flame for each of the cation was then
recorded in a Data Table. The flame test was then repeated for Na + ions using a little dry sodium
The nichrome wire was cleaned and the flame test was done on the two unknown solutions. The
solutions were also retested to ensure accuracy when identifying them. The results were then
The nichrome wire was cleaned again and the flame test was carried out on the solution
containing the mixture of the KNO 3 and NaNO3. The results were then recorded in the Data
Table.
PRECAUTIONS:
Safety:
1) Proper care was taken when handling the HCl to prevent injury as it is caustic and
corrosive.
2) Proper care was taken when rinsing out the test tubes containing the acid, as adding water
to acid will result in an explosion.
Efficiency:
RESULTS:
The following data table shows the results that were obtained in this experiment:
Table 1: Colours Emitted from the Various Cations in the Presence of a Flame
LIMITATIONS:
2) The brightness of the signal varies from one sample to another. For example, the yellow
emission from sodium is much brighter than the red emission from the same amount of
lithium.
3) Impurities or contaminants affect the test results. Sodium, in particular, is present in most
4) The test cannot differentiate between all elements. Several metals produce the same
flame colour. Some compounds do not change the colour of the flame at all.
OR
5) The HCl became saturated butUnlock this page a"er
was replaced withanfresh
ad HCl.
SOURCES OF ERROR: 10
1) The position of the wire in the flame. If the nichrome wire was held too low of too high,
4) How long the wire was kept in the fire and how strong the fire was as well.
5) The HCl became saturated but was replaced with fresh HCl.
DISCUSSION:
1) The position of the wire in the flame. If the nichrome wire was held too low of too high,
according to the
3) Traces ofamount of energy
impurities absorbed.
from the It was seen
last substance that some elements produced similar
tested.
flame
4) colour as well.
How long the In thewas
wire experiment, it was
kept in the noted
fire and thatstrong
how impurities canwas
the fire mask the flame colour,
as well.
DISCUSSION
for example, sodium, with
AND its CONCLUSION
intense yellow flame, was capable of masking the colour produced
by other elements if it is present as an impurity. It was seen that the flame test is used to visually
determine the identity of an unknown metal or metalloid ion based on the characteristic color the
DISCUSSION:
salt turns in the presence of a bunsen burner flame. The heat of the flame converted the metal
according
that flame to theare
tests amount of energy
an example of aabsorbed. It test,
qualitative was that
seenis,
that some
they canelements
detect theproduced
presencesimilar
of certain
flame colour
elements, as well.it In
however, the experiment,
cannot tell us how itofwas
the noted thatisimpurities
element present in can mask the flame colour,
the sample.
for example, sodium, with its intense yellow flame, was capable of masking the colour produced
by other elements if it is present as an impurity. It was seen that the flame test is used to visually
determine the identity of an unknown metal or metalloid ion based on the characteristic color the
ions into atoms which became excited and emitted visible light. The characteristic emission
spectra was also used to differentiate between some unknown elements. Therefore, it can be said
that flame tests are an example of a qualitative test, that is, they can detect the presence of certain
elements, however, it cannot tell us how of the element is present in the sample.
OR
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10
In conclusion, we were capable of observing and evaluating the colours produced by certain
metal ions when they are vaporized in a flame. The results of this lab were obvious, other than
finding out the unknown element. The obvious part was that every element has a unique
spectrum as no two elements have the same number of electrons, or electron configuration.
When elements are exposed to energy, their electrons may enter an excited state. The energy
added may be in the form of electricity or in this case heat. In this excited state, electrons move
from their normal position around the nucleus to higher energy levels. When the excited
CONCLUSION:
electrons return to their ground sate or normal position, they give off energy in the form of light.
In
Theconclusion, we light
colour of the werewe
capable of observing
see when andisevaluating
this occurs the coloursof
really a combination produced by certain
several colours of light
metal
in the ions whenof
spectrum they
thatare vaporized
element. in aelement
Each flame. or
The results ofemits
compound this lab were obvious,
a unique other than
set of wavelengths,
finding outwavelengths
only those the unknownthat
element. The obvious
correspond part was
to the quanta of that every
energy elementfor
necessary hasthat
a unique
element‟s
spectrum
electrons as no twofrom
to jump elements
groundhave thetosame
state numberstof
the excited ate.electrons, or electron
The uniqueness configuration.
of each substance‟s
When elements
spectrum allowsare exposed
scientists to to energy,
use their
them as electrons
a tool may enter
in identifying an excited
unknown state. The
chemicals. Oneenergy
method
added
used tomay be in the the
demonstrate form of electricity
emission spectraorof
inchemicals
this case heat.
is theIn this excited
flame state,this
test. Using electrons
method,move
a
from
small their normal
amount of a position
substancearound the in
is heated nucleus to higher
a Bunsen burnerenergy
flamelevels.
and theWhen
flame the excited
colour is observed.
electrons return to their ground sate or normal position, they give off energy in the form of light.
The arrangement of electrons in an atom determines the sizes of the quantum jumps, and thus the
The colour of the light we see when this occurs is really a combination of several colours of light
energy and colours of the collection of photons emitted, known as an emission spectrum. In this
in the spectrum of that element. Each element or compound emits a unique set of wavelengths,
way the emission spectrum serves as a „fingerprint‟ of the element to which the atoms
only those wavelengths that correspond to the quanta of energy necessary for that element‟s
belong. We can view the emission spectrum of colours all at once with the naked eye. It will
electrons to jump from ground state to the excited state. The uniqueness of each substance‟s
appear to be one colour, which we will carefully describe. It is also possible to view the separate
spectrum allows scientists to use them as a tool in identifying unknown chemicals. One method
colours of the emission spectrum by using a spectroscope, which bends light of different energies
used to demonstrate the emission spectra of chemicals is the flame test. Using this method, a
small amount of a substance is heated in a Bunsen burner flame and the flame colour is observed.
The arrangement of electrons in an atom determines the sizes of the quantum jumps, and thus the
energy and colours of the collection of photons emitted, known as an emission spectrum. In this
way the emission spectrum serves as a „fingerprint‟ of the element to which the atoms
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belong. We canRead
view
andthe emission
download spectrum of colours all at once with the naked eye. It will
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appear to be one colour, which we will carefully describe. It is also possible to view the separate
differently. Low energy red light is bent thethis
Unlock mostpageand
a"erhigh
an adenergy violet the least. This allows
colours of the emission spectrum by using a spectroscope, which bends light of different energies
us to see the various distinct colours of the emission spectrum of a sample.
10
1) Flame coloration is a test for the Metallic ion because, the metallic ions will enter an
excited state and release photons energy, in the form of light, as they return to their
ground state. Nitrate contains nitrogen and oxygen, and these atoms do not have energy
2) Dry sodium
differently. chloride
Low energy red and
lightthe solutions
is bent of sodium
the most nitrate
and high andviolet
energy sodiumthechloride all impart
least. This allows
us to seethe
thesame colour
various because:
distinct By placing
colours atoms ofspectrum
of the emission a metal into
of a asample.
flame, electrons can be
induced to absorb energy and jump to an excited energy state, a quantum jump. They
POST LAB QUESTIONS:
then return to their ground state by emitting a photon of light (the law of conservation of
1) Flame
energy coloration is a the
indicates that testphoton
for the emitted
Metallicwill
ioncontain
because,the
thesame
metallic
amountionsofwill enterasanthat
energy
excited
absorbedstate andquantum
in the release photons energy,
jump). The in theofform
amount of light,
energy in theas they return
photon to their
determines its
ground state.
color; red for Nitrate contains
the lowest energynitrogen
visible and oxygen,
light, and energy
increasing these atoms do not
through the have energy
rainbow of
levels
orangethat would
yellow giveblue
green a color to aand
indigo, flame.
finally violet for the highest energy visible
2) Dry
light.sodium chloride
Photons outsideand
thethe solutions
visible of sodium
spectrum nitrate
may also and sodium
be emitted, but chloride
we cannotallsee
impart
them.
3) the
Thesame colour
test for because:
sodium By placing
and potassium atoms
ions of both
when a metal
are into a flame,
present electronsFirst,
is as follows: can beget a
induced
wire andto absorb
bend energy
it into and
a ring jump
and put atofew
an excited
crystalsenergy
of yourstate,
solidaon
quantum
it. Do ajump.
flame They
test
then
usingreturn to their
a bunsen ground
burner or a state
match.byThe
emitting
coloura photon
emitted of light
will (thethat
show lawPotassium
of conservation of
will give
energy
a violetindicates
flame andthat the photon
Sodium emitted
will give will contain
a yellow flame. the same amount of energy as that
4) absorbed
If recalledincorrectly
the quantum
fromjump).
the lab,The
notamount
much ofofthe
energy in the
solution wasphoton determines
needed to identifyitseach
orange
numberyellow green blue indigo, and finally violet for the highest energy visible
of atoms.
light. Photons outside the visible spectrum may also be emitted, but we cannot see them.
3) The test for sodium and potassium ions when both are present is as follows: First, get a
wire and bend it into a ring and put a few crystals of your solid on it. Do a flame test
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using a bunsen burner or a match. The colour emitted will show that Potassium will give
4) If recalled correctly from the lab, not much of the solution was needed to identify each
compound. It is very sensitive, because you can see light emitted by a "relativel y" small
number of atoms.