Lab Report Chemistry I - Flame test

Chemistry I

Activity 3.4: Lab Report – Flame tests.

The elements are a rainbow when they burn Purpose The purpose of this experiment is observe different substances being exposed to high temperatures and see how they react. Then, make a chart identifying the color emissions of the ten different compounds previously observed in the laboratory. Try to identify the unknown substances by the flame color. In this case, our hypothesis will be: The different salts exposed to fire will produce flames of different colors according to their chemical composition and the energy received.

Introduction The flame test is an experiment that we realized to get the knowledge of the colors that different elements can make when they get burned. First we need to have special care about this experiment, because of the fire and the alcohol, and also if some elements that were in the salts we used, when they get burned, they leave toxic gas or something that can be dangerous for us. We burned the different element salts with alcohol on 70% and we observed the colors emitted. Emission spectra are the light emitted by an element and the element can emit it in different colors, our experiment was about what colors they were in each case. Because each element has an exactly defined emission spectrum, scientists are able to know what elements are the workings in by the color of the flame. Some typical colors are blue (in Copper), red (in Lithium and Strontium) or orange (in Calcium). The energy of the flame excites the electrons of the salt ion to higher energy orbital (valence electrons), those electrons eventually relax back they normally occupy in the ground state and release photons whose energy is equal to the gap between the orbital the electrons fall from and fall to. That energy can be related to a frequency of light and it can be related to the color of the light.

Materials Bunsen burner Watch glasses Laboratory tweezers 70% ethanol Copper(II) chloride Sodium chloride Calcium chloride

Potassium nitrate Lithium chloride Iron(III) nitrate Barium chloride Unknown substance A Unknown substance B Unknown substance C

Methods 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Place all the substances on watch glasses (one substance per glass). Put alcohol at 70% in the watch glasses of the liquids (CaCl2, LiCl, CaCl 2, unknown substance C). Light the Bunsen burner. Approach the burner to the substances in the following order: First, the copper chloride (CuCl2). It will burn in an emerald green flame. Then the Lithium chloride (LiCl). Its flame will be carmine red. After that, the Calcium chloride (CaCl 2). It will have an orange color. Do the same with the solids. First, approach the burner to the Iron nitrate, which is Fe(NO 3)3. It produces golden sparkles. Then the Potassium nitrate (KNO3). The flame will be lilac. After, the Sodium chloride or common salt (NaCl). It will have an intense yellow tonality. After that, the Barium chloride (BaCl2). It acquires a yellowish green. Apply the same procedure to the unknown substances. Start approaching the fire to the unknown substance A, which is a solid. It will burn in a lemon green flame. Then to the unknown substance B, which is toxic, fine, and is a solid, too. Its flame will be sky-blue. Finally, approach the burner to the unknown substance C, which is a liquid. It will produce a soft red.

Results Compound tested 1. Copper (II) chloride 2. Sodium chloride 3. Calcium chloride 4. Potassium nitrate 5. Lithium chloride 6. Iron (III) nitrate 7. Barium chloride

Chemical formula

Ion

Color observed

CuCl2

Cu+2

Emerald green

NaCl

Na+1

Bright yellow

CaCl2

Ca+2

Bright orange

KNO3

K+1

Lilac

LiCl2

Li+1

Carmine red

Fe(NO3)3

Fe+3

Golden sparkles

BaCl2

Ba+2

Yellowish green

1 2 3 5 4

67

Flame color observed

Metallic element present

Chemical symbol of the element

Unknown substance A

Lime green

Boron

B+3

Unknown substance B

Sky blue

Lead

Pb+2

Unknown substance C

Sr+2 Red

Strontium

Name and chemical formula of the unknown compound Sodium borate - Borax Na2B4O7·10H2O Lead (II) nitrate Pb(NO3)2 Lead (II) chloride PbCl2 Strontium nitrate Sr(NO3)2 Strontium chloride SrCl2

C B A

Discussion or Analysis In the experiment we saw that the entire compounds had different colors when they got in contact with the energy (the fire). This happened because the electrons of the atoms received a lot of energy, and when that happened, they get excited and they jump from one orbital to the next one. So when they cool down they release all the energy they received. This is what produces the light, and the color depends on the emission spectrum. So, with all these data, we concluded that our hypothesis was accepted. Our probably mistakes may be some wrong information, but we were very careful to chose our references.

Conclusions The experiment consisted in heat with fire ten different substances to see the color of the light. Every compound had a different flame color; some of them were really alike. After the investigation and the

analysis we concluded that our hypothesis was accepted, this means that each element have a different flame color because the energy of the fire makes that the electrons jump to the next orbital and when they return to their original orbital, they release energy and this produces the light.

Complementary tasks: 1) Were the observed colors from the metal or the non-metal? How do you know? It depends only on the metal in the compound. Because when you heat the salt it splits into the metallic and non-metallic ions. Due to the change of temperature metallic ion changes state, and when returns it the electromagnetic radiation given off has a particular color. For a salt, it is always the metallic element that is involved in projected the color that is present, the non-metal atoms doesn’t have influence on the presented color. For example you will find the color red given off when all strontium compounds are used, all sodium compounds give yellow and all potassium compounds give a purple radiation. 2) What particles are found in the chemicals that may be responsible for the production of colored light? Electrons, because the excitement caused by heating makes the electrons jump from their ground state into a higher energy level. The absorbed energy from there is released as a photon of light when returning to its original place. 3) Why do different chemicals emit different colors of light? The color of the light emitted depends on the energies of the photons (particles of light) emitted, which are in turn are determined by the energies required to move electrons from one orbital to another. A flame has lots of different energies existing within it all the time, and every so often, it gets lucky and has the right quantity present to push an electron from one orbital to another. When the electron drops back, it must release the same exact amount energy that it absorbed. Depending on the element you put in the flame, various different energies of photons (colors) will appear. Those colors are as distinctive to each element as fingerprints are to people. 4) Why do you think the chemicals had to be heated in the flame first before the colored light is emitted? When a chemical that can be made to emit light is held over a burner, the energy of the burner spreads quickly through the chemical as heat. The atoms begin moving faster and faster as more energy is given to their electrons. Eventually the electrons gain so much energy that they bump up an energy level. The electrons are unable to continue operating at their higher energy levels and drop down to their original starting levels. But as the electrons move down, they lose some of their energy. This energy escapes the atoms, and in some atoms it escapes as photons that are emitted from the chemical as light. 5) Colorful lights emissions are applicable to everyday life. Where else have you observed colorful light emissions? Are these lights emission applications related? Explain why you think they are or are not. I think these emissions are applicable in our life because we can identify the elements in this way; burning them, just imagine if we are cooking and we saw some green fire, of course we’ll have caution, we know copper burns green. I have seen those colorful light emissions in the neon lights at parties or when someone is repairing electricity and he needs to burn wires. I think those applications in the light emissions are related because elements are everywhere in our world! Everything is made of atoms and with the heat we can know which they are.

Final reflections

“We can identify a compound or an element, even if we don’t know the name, because of the color when it burns. We can apply the element’s light emissions to objects that we use every day, according to the color of light. For example, the lampposts produce an intense yellow color, because it is made of sodium. Some phosphorescent ads are made of Neon, and so on. Depending of the purpose, it is possible to use different elements to generate different colors of light.”

References  (2009, November 18). Retrieved October 11, 2014, from Flame Test Lab: http://melissaschroth.wikispaces.com/Flame+Test+Lab  Scientific American. (1999, March 29). Retrieved October 12, 2014, from Why do certain elements change color over a flame?: http://www.scientificamerican.com/article/why-docertain-elements-c/  Chemistry and light. (2010, April 29). Retrieved October 12, 2014, from Science in School : http://www.scienceinschool.org/2010/issue14/chemlight  Lacoma, T. (2014, September 01). Why Do Chemicals Have to Be Heated in the Flame First Before the Colored Light Is Emitted? Retrieved October 12, 2014, from eHow: http://www.ehow.com/about_6389214_do-before-colored-light-emitted_.html  Bleshenski, D. (n.d.). Flame Test Lab - David's Digital Portfolio. Retrieved October 12, 2014, from https://sites.google.com/a/hightechhigh.org/davidbleshenski/10th-grade-2/mathchemistry/flame-test-lab  Flame tests. (n.d.). Retrieved October 12, 2014, from http://www.chemguide.co.uk/inorganic/group1/flametests.html  Qualitative Reasoning Group Northwestern University. (n.d.). Temperature System. Retrieved October 12, 2014, from http://www.qrg.northwestern.edu/projects/vss/docs/thermal/3-whatmakes-em-radiation.html  Brightstorm. (s.f.). Retrieved October 12, 2014, from http://www.brightstorm.com/science/chemistry/the-atom/atomic-emission-spectra/  Chemskills. (s.f.). Retrieved October 12, 2014, from http://chemskills.com/?q=flame_test

 Webexhibits. (s.f.). Retrieved October 12, 2014, from Flame Tests: http://www.webexhibits.org/causesofcolor/3BA.html