1 Chemistry Lab Getting to know your Bunsen burner Part I The Bunsen or Tirrell burner is commonly used in laboratory heating operations. While the details of construction vary among burners, each has a gas inlet located in the base, a vertical tube or barrel in which the gas is mixed with air, and an adjustable opening or ports in the base of the barrel to introduce air into the gas stream. The burner may have an adjustable needle valve to regulate the supply of gas, or adjusting the valve on the supply line may regulate the gas supply simply. The burner is always turned off at the gas valve, never at the needle valve. Take your burner apart and examine it. Compare the parts with the drawing in Fig. 1-1. Put the parts together again and note particularly how you can control the amount of air admitted near the base of the burner. In lighting the burner, partially close the ports at the base of the barrel, turn the gas full on, and hold the lighted match about 5 cm above the top of the burner. If you are using a torch lighter place the torch lighter next to and slightly above the burner, apply a downward pressure of the flint towards the plate and strike the lighter. The gas may then be regulated until the flame has the desired height. If a very low flame is needed, the ports should be kept partly closed when the gas pressure is reduced. Otherwise the flame may "strike back" and burn inside the base of the barrel. If this happens, turn off the gas, decrease the amount of air admitted, and re-light. Part II LUMINOUS FLAME Relight the Bunsen burner. Close the airports or inlets as completely as possible and note the color and shape of the flame which is now luminous. A Pass your hand quickly through the flame, which can be done without discomfort. B Using crucible tongs, hold a dry porcelain-evaporating dish in the flame for a few seconds. Examine the dish and record your observations. After the dish cools, clean and dry the evaporating dish. C Sketch the luminous flame and show its structure as far as you can see. D. 2 Using a test tube holder, hold one end of a glass tube about 15 cm long and inclined at a 45 degree angle just inside the barrel and attempt to light the gas which escapes from the other end of the glass tube. If unsuccessful with lighting the gas at the end of the glass tube, then increase the flow of gas slightly and try again. Record your observations. F Extinguish the burner flame. Part III NON LUMINOUS FLAME For laboratory work, you should adjust the burner so that the flame will be free of yellow color, and also free from the "roaring" sound caused by admitting too much air. Regulate the flow of gas to give a flame extending roughly 8 cm above the barrel. Slowly open the airports and notice that the flame loses its luminosity and two well-defined regions appear in the flame. The two distinct regions of the flame are called the oxidizing and reducing regions. This is the so-called Bunsen flame, and it should always be used for heating purposes. You may have to adjust the amount of air admitted and the amount of gas mixing with the air. A yellow flame yields much light but little heat. Such a flame is the mark of an amateur. Obtain a flame which is quiet, steady, and does not go out. A Insert a wooden splint in the reducing region across the flame near the base of the blue inner region, resting on the top of the barrel for a few seconds. Remove from the flame, extinguish, examine and record observations. B Repeat the process, but place the splint one cm above the oxidizing region. C Using tongs, hold a cool, dry porcelain-evaporating dish above the top of the reducing region for about ten seconds. Do not permit the evaporating dish to incandesce. Remove from the flame, place on a wire gauze, and allow the dish to cool. Then examine and record your observations. D Repeat the above process, but place the dish above the top of the oxidizing flame. E. Diagram the non-luminous flame and show its structure. F Hold one end of a glass tube inclined at a 45-degree angle in the inner cone of the Bunsen flame, just above the barrel opening, and attempt to ignite any gas escaping from the other end of the glass tube. Record observations. 3 Part IV TEMPERATURE OF PARTS OF THE BUNSEN FLAME The approximate temperatures at different parts of the flame can be determined by observing the color of a copper wire held in the flame. If the color is faint red the temperature is about 500 degrees Celsius; if the color of the wire is dark red its temperature is about 650 degrees Celsius; and if the color is orangeyellow the temperature is about 900 degrees Celsius. A Obtain a 10 cm piece of copper wire and hold it using crucible tongs. Place the tip of the wire in the flame for two seconds and estimate the temperature at the corresponding point on your diagram of a Bunsen flame. Repeat this process at five to 10 widely separated points of the flame. B Obtain another piece of copper wire, place in the reducing cone, (use forceps;), and lift it slowly up into the oxidizing cone. Keep it in this cone for a few minutes. According to the "Handbook of Chemistry and Physics" the melting point of copper is 1083 °C. C Turn off your burner. Obtain a match and a piece of wire, at the mid-point of the wire make a loop and place the match in the loop. Place the match into the barrel supported by the wire. Relight the burner and record observations. D Using tongs, slowly lower a piece of wire gauze which is held horizontally into the flame of a Bunsen burner until the gauze rests on the top of the barrel. Raise the gauze slowly. Allow the gauze to cool and repeat, lowering the gauze quickly. Try to 'pick up' the flame by slipping a cool gauze under the flame at the top of the barrel. Record observations. Lab Report Format Title Introduction Procedure Equipment List Table of Observations Conclusions and Answer Questions Lab Report Questions: 1 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. How would you describe the flame in Part II? Draw a picture of the flame. How would you describe the flame in Part III? Draw a picture of the flame. The flame in Part II is seldom used in the laboratory. Why? What happened to the bottom of the evaporating dish? What do you think the substance is on the bottom of the porcelain? What are the three requirements for combustion. Under what conditions do we have complete combustion and incomplete combustion? Is there a minimum temperature at which a fuel will burn? What is this temperature called? What is the difference, if any, between flash point and kindling point? Why is your hand not burned in the luminous flame? Write an equation to account for the formation of the deposit. Where is the hottest part of the Bunsen flame? Why is this particular region the hottest? Where is the coolest part of the Bunsen flame? Why is this particular region the coolest? Write a short paragraph on the history of the Bunsen Burner or any other type of laboratory burner.