Flame Test Lab Report

OBJECTIVE The experiment conducted aimed to give students the opportunity to determine different metal ions in liquid and solid compounds by observing the color of the flames they give off when subjected to open flame using a gas burner. INTRODUCTION Every atom has specific orbital energy levels around the nucleus where electrons can be found. Electrons of an atom normally reside in a specific low energy level which is called their ground state. But, when an atom is bombarded with a form of energy, such as flame, the electrons become excited and will jump to a higher energy level. However, electrons that are excited in a higher energy level are not stable and they tend to go back to their original state. In order for these electrons to go back to their ground state, they need to release energy (electromagnetic radiation) in a very specific wavelength in the visible spectrum which can be seen as specific colors of light. Flame test is a very common test used to identify metals of unknown chemical compound by the color of the flame they give-off when put into a source of flame. Since the energy required (being released) by the electrons to go back to their most stable state is specific and unique for every atom, one can easily determine what kind of metal is present in the compound under study. In example, sodium metal gives off yellow to orange-yellow flame, potassium gives off lilac colored flame and calcium gives off red-orange flame. All alkaline earth metals except beryllium and magnesium impart colored flames. MATERIALS AND METHODS Control Negative control was used in order to determine whether or not the experiment proceeded as expected and that there are no contaminations that might affect the result of the experiment. A plain cotton swab which did not give-off a different colored flame from the flame itself was used as a negative control for this experiment. Ionic compounds used for flame test There were nine ionic compounds which were subjected to direct flame using a gas burner and the color of the flame that these substances give off were observed and recorded. The compounds were CaCO3, CaCl2, KC4H5O6, MgSO4, CaSO4, NaCl, KCl, NaPO4, NaCO3. Procedure 1. A 100 mL beaker was filled half-way with water. 2. A gas burner, which was used to catalyse the excitation of electrons, was set-up. 3. The first flame test was conducted on a negative control by putting a cotton swab over the hottest part of the burner. The color of the flame it gives-off was recorded. Then the burning cotton swab was extinguished by dipping it in a beaker that contains water. 4. To determine the flame color of liquid compounds, the cotton swab was dipped in hydrochloric acid solution and then dipped into the liquid compound. The swab was then put over the hottest portion of the flame and the color of the flame observed was recorded. 5. To determine the flame color of solid compounds, it was first made sure that all solid compounds were pulverized and then dissolved in small amount of water. Then, the cotton swab was dipped in hydrochloric acid solution and then dipped into the compound. Excess compounds were shaken off the swab. The swab was then put over the hottest portion of the flame and the color of the flame was recorded. SUMMARY OF RESULTS Table 1. Flame colors observed from the ionic compounds tested. Compounds Tested CaCO3 CaCl2 KC4H5O6 MgSO4 CaSO4 NaCl KCl NaPO4 NaCO3 Cation Component Ca2+ Ca2+ K+ Mg2+ Ca2+ Na+ K+ Na+ Na+ Anion Component CO32ClC4H5O6SO42SO42ClClPO43CO32- Flame Color Red-orange Red-orange Lilac No color Red-orange Orange-yellow Lilac Orange-yellow Orange-yellow DISCUSSIONS and DATA ANALYSIS The initial flame test was conducted using only a cotton swab to ensure that the cotton swabs were not contaminated with other compounds that might affect the result of the experiment. For safety purposes, all swabs were dipped into a beaker containing water in order to extinguish the flame. It was made sure that a separate cotton swab was used in every compound tested to get an accurate flame color for each compound. Based on the table above, compounds that have similar metal cations give-off similar flame color as explained by unique electromagnetic radiation released when excited electrons go back to their ground state. Magnesium did not impart any color change in the flame. This is because the size of magnesium atom is very small that it holds its electrons more strongly which consequently requires much more energy for its electrons to be excited. QUESTIONS AND ANSWERS 1. Several compounds contain the Cl- anion. a. Do these compounds have the same flame color? b. What about compounds containing the SO42- anion? c. The CO32- anion? d. So, is the anion responsible for flame color? Chemical compounds which contain similar anions such as Cl -, SO42- and CO32- do not have similar flame colors. Hence, it can be concluded that the non-metallic anions are not the ones responsible for the color of the flames observed. 2. Several compounds contain the Na+ cation. a. Do these compounds have the same flame color? b. What about compounds containing the K+ cation? c. The Ca2+ cation? d. So, is the cation responsible for flame color? All compounds containing Na+ cation give off similar flame color which is orangeyellow, compounds that contain K+ cation give off lilac colored flames and compounds that contain Ca2+ cations give off the same flame color which is red-orange. With these observations, it can be concluded that the cations are the ones responsible for the unique flame color of the compounds. CONCLUSIONS Based on the results of the flame test, it was evident that the main ions responsible for the color intensity of the flames are the metal cation. Since a specific energy is needed to radiate specific light color for every cation, all compounds containing similar metal cations have the same flame colors observed. POST LABORATORY QUESTIONS 1. Why did we test the flame color of the cotton swab? The cotton swab used was subjected to the flame test procedure in order to ensure that the swabs were not contaminated and that the experiment will proceed as expected. The cotton swab served as a negative control. 2. Why did we test the flame color of the water and the hydrochloric acid? Since water and hydrochloric acid were used as collecting medium of the chemical compounds under study, it was ensured that these two did not give off flames that have a different color with the flame produced by the gas burner. This is to make sure that the color change observed is due to the color produced by the compounds being studied. 3. Which of the ionic compounds in this experiment would be good for making purple and red fireworks? The compounds KC4H5O6 and KCl would be good for making purple fireworks. Compounds such as CaCO3, CaCl2, and CaSO4 can be good materials to use to make red fireworks. 4. Potassium gluconate KC 6H11O7 produces a light purple flame. Copper(II) sulphate CuSO4 produces a green flame. What flame color would you expect for copper(II) gluconate CuC6H11O7? Explain your reasoning. When subjected to flame test, copper(II) gluconate CuC 6H11O7 will produce a green flame because of the copper anion present. It was already known and observed that metal cations are the ones responsible for the color of the flames produced by the compounds. 5. How could you tell the following three white artificial sweetener powders apart using flame test? You have: Equal (C 14H18N2O5, a non-ionic compound), Ace-K (K + (C3H4NO4S-)) and Sweet ‘N Low (Ca2+[C7H4NO3S-]2 Although the aforementioned artificial sweeteners have similar white and powdery texture, they can be easily distinguished using a flame test. Since C 14H18N2O5 is a non-ionic compound, it does not produce a unique flame color. Ace-K KC 3H4NO4S contains K+ cation which gives off lilac or light purple flame. On the other hand, Sweet ‘N Low Ca(C 7H4NO3S)2 contains Ca2+ cation which gives off red-orange flame color.