FLAME TEST PRACTICAL TASK (DCP) Background Knowledge (Refer to task sheet) Aim To identify each of the unknown samples presented as a specific salt through the observation of flame colours. Hypothesis N/A Apparatus Bunsen burner Gauze mat Rubber tube Matches HCl solution Salt samples Small beaker (with water) Nichrome wire Watch glasses Spatula Safety In order to conduct a safe experiment, certain precautions must be taken into account. These are: Wearing a lab coat, important to avoid damage to skin and clothes if acid is split Tying long hair back, important to lower the risk of hair catching fire while using the Bunsen burner Placing the Bunsen burner on a gauze mat, important to avoid burning the desk Firmly push the rubber tube (from the Bunsen burner) into the gas outlet, important to avoid gas leaks and fire risk Ensure that the air port is closed when lighting the Bunsen burner, important to ensure that the flame is a ‘safe flame’ and is clearly visible (lower fire risk) Place the Bunsen burner flat in the centre of the bench (on the gauze mat), important to ensure that the Bunsen burner does not slide off the edge of the bench Clear the area of any books, papers or other objects that aren’t needed for the experiment, this is important to avoid fire risks Ensure that neither the Bunsen burner or the rubber tube have any cracks or holes, important to lower the fire hazard Do not leave open flames unattended, important to lower the risk of an accident and a fire Turn off the gas when the experiment is complete, important to avoid gas leaks and fire risk Allow the Bunsen burner to cool down before handling, important to avoid burns Wear safety glasses, important to avoid contact between the acid and the experimenter’s eyes Light the match before turning on the gas, important as to avoid a large flame because of excessive gas Method Independent Variable: Salt being tested Dependent Variable: Flame colour Controlled Variables: N/A Control Sample: N/A 1. Clean a nichrome wire by dipping into HCl solution. Heat the wire in the heating flame of a Bunsen until no more colour is produced. 2. Mix a little of the salt to be tested with the acid solution on a watch glass and dip the end of the clean wire in the solution. 3. Hold this end of the wire in the outer blue part of the flame and note any flashes of colour that may appear and the intensity. Note that these may fade quickly. 4. Test subsequent salts in the same manner, cleaning the wire between each test as described in #1. 5. Tabulate your results making sure to include qualitative and quantitative data. 6. Use the information you have collected to identify the cations in each of the unknown samples provided to you. Results Sample Name Colour Produced Intensity NaCl Bright orange Very intense CuCl₂ Strong blue and green, sharp stream of white in centre Bright white Very intense MgCl₂ White sparks at beginning, then blue and green Moderately Intense KCl Pink/ Orange/ Purple Blood Orange Moderately Intense Very Intense Predominantly pink, some red Very Intense FeCl₃ CaCl LiCl Very intense Time the colour lasted for Lasted for a very long time (2 minutes+) All colours lasted a short amount of time (15 seconds) Other Notes/ Observations Cloudy texture Lasted a short amount of time (10 seconds) Lasted a short amount of time (10 seconds) Harsh sparks Lasted a long time (2 minutes+) Lasted a long time (2 minutes+) Lasted a long time (2 minutes+) Began green and blue, white stream appeared Formed white powder/ salt on wire, sparks not very intense A little cloudy BaCl₂ Green Not very intense Strontium Cl Predominantly red, some pink Very Intense Unknown A Yellow/ Orange Very Intense Unknown B Green Not very intense Lasted a very short amount of time (2 seconds) Lasted a short amount of time (5 seconds) Lasted a long time (2 minutes+) Lasted a very short amount of time (2 seconds) Formed a solid grey salt on the wire Formed a solid grey salt on the wire From the observations, it looks as though unknown A is NaCl and unknown B is BaCl2. Discussion There were no obvious trends in my results. Each of the different salts had a different reaction and the colours were all quite evenly varied, each appearing two to three times. The intensity of the flame produced was just as varied as the colours, and so with the amount of time that the flames lasted for. Unknown A and NaCl produced very similar results, as with unknown B and BaCl2. These trends (or lack of trends) are due to the fact that apart from the unknowns, all of the samples were different, and so produced different results. Evaluation My data is moderately reliable. On one hand, all of my data was taken from observation, judgement and estimation. I observed the flame colours (and in some cases the texture of the flame or the aftermath), judged whether the flames produced were intense or not, and estimated the amount of time that each of the colours lasted for. This could make my data somewhat unreliable since it is personal judgement and may be subjected to human error or bias (random error). On the other hand, I worked closely with another student (Celene) since we were working next to each other, and we frequently compared results. Having another opinion and a second set of observations and judgements significantly reduced the chance of random error. This was because if Celene and I produced obvious differences in our observations of the same substance, we would repeat the test and record the results that were constant for both of us. One strength of my design was the table I created before completing the experiment. Having an in depth and clear table allowed me to come out of the experiment with thorough observations. This was very useful when it came to identifying the two unknown substances, since I had recorded observations for more than just the colour produced. If I had only recorded the colour, I may have found it more difficult since some of the substances produced the same colour. A second strength of my design was the safety section. Having not used a Bunsen burner for a while, I found it very helpful to review the method of using Bunsen burners and safety precautions before I began the practical. This way, not only did I avoid accidents, but I was able to set up and complete my practical quickly and thoroughly because I didn’t have to spend any time figuring out how to use the equipment. One improvement that could be made to this experimental design would be to use a stopwatch to time how long the flame colours produced last for. This would allow for more precise results and help to identify the unknowns. A second improvement that could be made to this experimental design would be to repeat the tests. Some groups had trouble recording accurate results because some of the salt samples had fallen inside of the Bunsen burner and had therefore had an impact on some of the flame colours produced with subsequent salt samples. If the Bunsen burners were cleaned and the tests repeated twice more, this would eliminate the problem. This method was valid, as it allowed me to collect all the data I needed in order to identify unknown A and B. As mentioned before, timing the flames with a stopwatch could be an improvement, however, it is not essential, as the observational techniques I used were sufficient. Having completed this experiment, I am inspired to further investigate how the different flame colours are produced and if flame colours are produced with other salts (if so, what colours). Conclusion A hypothesis was not applicable for this particular experiment. However, through the observation of flame colours in different salts, I have come to the conclusion that unknown A is NaCl and that unknown B is BaCl2. ATOMIC SPECTRA PRACTICAL TASK (DCP) Background Knowledge (Refer to task sheet) Aim To calculate frequency and energy values of specific wavelengths by observing and recording the line spectra of hydrogen gas. Hypothesis N/A Apparatus Spectrometer White light source Hydrogen gas discharge tube (set up prior to the experiment) Safety In order to conduct a safe experiment, certain precautions must be taken into account. These are: Not touching the hydrogen gas tube, in order to prevent injury or damage to the materials (There are no more safety requirements for this experiment) Method Independent Variable: Type of light being tested Dependent Variable: Wavelengths produced Controlled Variables: Spectrometer used Control Sample: N/A 1. Go to the station where a hydrogen gas discharge tube is set up. Here, an induction coil is being used to provide energy to “exite” the gas atoms. 2. Using the spectrometer, look at one of the fluorescent light in the room. You will see coloured lines corresponding to specific wavelengths emitted by the white light. 3. Record the values for the violet and green lines. These should be 4360 Å and 5460 Å respectively. Note any error in these readings so that adjustments can be made in subsequent readings. 4. Turn on the electricity to the hydrogen gas tube (for no more than 30 sec at one time to prevent burn out). 5. Look through the spectrometer and observe/record the coloured lines that are produced. 6. Tabulate your results, including qualitative and quantitative data. 7. Process your data thoroughly, providing as much information as possible about each line found including error and uncertainty. Results White Light Hydrogen Gas Tube Colour of Line Wavelength (Å ±50) Dark Purple Violet Dark Green Light Green Orange Red Purple Green Yellow Red 4200 4400 4900 5500 5900 6100 4400 5500 5800 6500 Wavelength (m± 50 x 1010 ) 4200 x 10-10 4400 x 10-10 4900 x 10-10 5500 x 10-10 5900 x 10-10 6100 x 10-10 4400 x 10-10 5500 x 10-10 5800 x 10-10 6500 x 10-10 (Qualitative): The lines produced by white light were a lot thicker than those produced by the hydrogen gas tube, which were sharp and thin. Calculations: E = energy (J or kJ) h = Planck’s constant = 4.00 x 10-13 kJ.s.mol-1 v = frequency (Hz or s-1) c = speed of light = 3.00 x 108 m.s-1 λ = wavelength (nm, cm, Å) Frequency ÷λ c = λv -> v = c Energy E = hv White light Dark Purple: E = (4.00 x 10-13 kJ.s.mol-1) x (7.14 x 10-14 s-1) E = 2.86 x 10-26 kJ Violet: E = (4.00 x 10-13 kJ.s.mol-1) x (6.82 x 10-14 s-1) E = 2.73 x 10-26 kJ Dark Green: E = (4.00 x 10-13 kJ.s.mol-1) x (6.12 x 10-14 s-1) E = 2.45 x 10-26 kJ Light Green: E = (4.00 x 10-13 kJ.s.mol-1) x (5.45 x 10-14 s-1) E = 2.18 x 10=26 kJ Orange: E = (4.00 x 10-13 kJ.s.mol-1) x (5.08 x 10-14 s-1) E = 2.03 x 10-26 kJ Red: E = (4.00 x 10-13 kJ.s.mol-1) x (4.92 x 10-14 s-1) E = 1.98 x 10-26 kJ Hydrogen Gas Tube Purple: E = (4.00 x 10-13 kJ.s.mol-1) x (6.82 x 10-14 s-1) E = 2.73 x 10-26 kJ Green: E = (4.00 x 10-13 kJ.s.mol-1) x (5.45 x 1014 s-1) E = 2.18 x 10=26 kJ Yellow: E = (4.00 x 10-13 kJ.s.mol-1) x (5.17 x 10-14 s-1) E = 2.07 x 10-26 kJ Red: E = (4.00 x 10-13 kJ.s.mol-1) x (4.62 x 10-14 s-1) E = 1.85 x 10-26 kJ Wavelength (m± 50 x 10-10) Frequency (s-1) Energy (kJ) White light Dark Purple: v = (3.00 x 108 m.s-1) ÷ (4200 x 10-10m) v = 7.14 x 10-14 s-1 Violet: v = (3.00 x 108 m.s-1) ÷ (4400 x 1010 m) v = 6.82 x 10-14 s-1 Dark Green: v = (3.00 x 108 m.s-1) ÷ (4900 x 10-10m) v = 6.12 x 10-14 s-1 Light Green: v = (3.00 x 108 m.s-1) ÷ (5500 x 10-10m) v = 5.45 x 10-14 s-1 Orange: v = (3.00 x 108 m.s-1) ÷ (5900 x 1010 m) v = 5.08 x 10-14 s-1 Red: v = (3.00 x 108 m.s-1) ÷ (6100 x 10-10m) v = 4.92 x 10-14 s-1 Hydrogen Gas Tube Purple: v = (3.00 x 108 m.s-1) ÷ (4400 x 1010 m) v = 6.82 x 10-14 s-1 Green: v = (3.00 x 108 m.s-1) ÷ (5500 x 10-10m) v = 5.45 x 10-14 s-1 Yellow: v = (3.00 x 108 m.s-1) ÷ (5800 x 1010 m) v = 5.17 x 10-14 s-1 Red: v = (3.00 x 108 m.s-1) ÷ (6500 x 10-10m) v = 4.62 x 10-14 s-1 White Light Hydrogen Gas Tube Colour of line Dark Purple Violet Dark Green Light Green Orange Red Purple Green Yellow Red 4200 4400 4900 5500 5900 6100 4400 5500 5800 6500 x x x x x x x x x x 10-10 10-10 10-10 10-10 10-10 10-10 10-10 10-10 10-10 10-10 Absolute uncertainty = ±50 Percentage uncertainty White Light: Dark Purple (50 ÷ 4200) Violet (50 ÷ 4400) Dark Green (50 ÷ 4900) Light Green (50 ÷ 5500) Orange (50 ÷ 5900) Red (50 ÷ 6100) Hydrogen G.T: Purple (50 ÷ 4400) x x x x x x x 100% 100% 100% 100% 100% 100% 100% 7.14 6.82 6.12 5.45 5.08 4.92 6.82 5.45 5.17 4.62 = = = = = = = x x x x x x x x x x 10-14 10-14 10-14 10-14 10-14 10-14 10-14 10-14 10-14 10-14 2.86 2.73 2.45 2.18 2.03 1.98 2.73 2.18 2.07 1.85 x x x x x x x x x x 10-26 10-26 10-26 10=26 10-26 10-26 10-26 10=26 10-26 10-26 1.19% 1.14% 1.02% 0.91% Percentage Error 0.85% White Light: Violet (4200 – 4000) ÷4000 x 100% = 0.82% 5.00% 1.14% Red (6100 – 7000) ÷7000 x 100% = 12.86% Green Yellow Red (50 ÷ 5500) x 100% = 0.91% (50 ÷ 5800) x 100% = 0.86% (50 ÷ 6500) x 100% = 0.77% [A graph is not relevant or necessary for this particular set of data] Discussion A trend that I noticed in my results was that the shorter the wavelength of a certain colour, the greater the amount of energy. This is the same with frequency, shorter wavelengths produced higher frequencies. These are both evidence of Planck’s conclusion that the amount of energy is inversely related to the wavelength of light (the same goes for frequency). Evaluation My data may is moderately reliable. On one hand, it followed the general trends that are suggested by Planck and the results are fairly logical. On the other hand, however, there may have been a fault at the data collection stage. This is because although the values I collected make sense, they are quite far from the accepted values. A strength of my design was the table. Having this already prepared before my prac made it quick and easy for me to record the measurements while I was doing the prac. An improvement that I could make would be to familiarise myself with the formulas and conversion a bit more thoroughly before completing the prac because it would have deepened my knowledge and also cut down the calculation time. Having done this experiment, I am inspired to investigate the wavelength, frequency and energy of light in other ways and using other types of equipment. Conclusion A hypothesis was not applicable for this particular experiment. However, I was able to calculate frequency and energy values of specific wavelengths by observing and recording the line spectra of hydrogen gas (see calculations above).