Introduction to Chemistry: Bunsen burner

1.0 Introduction to Chemistry

1.9 Bunsen burner

What are the main parts of a Bunsen burner?

Materials and substances required

1. Bunsen burner
2. Gas supply and match box

1. Study the following photograph of a Bunsen burner.
   

   Bunsen burner

   

   Labelled drawing of a Bunsen burner
   
   
   1. How many parts of a Bunsen burner can you see?
   2. Study the labelled drawing of a Bunsen burner to learn its parts. Why should the base be wide?
   3. Open the video below how to light a Bunsen burner
      
      
      (courtesy Youtube - steps to light a Bunsen burner by SASS Chem) and learn the procedure for lighting a Bunsen burner.

Questions 1.9(a)

Explain why, when lighting a Bunsen burner, it is necessary to:

1. Check gas taps to be sure none of them had been left open
2. Open all the windows and allow a few minutes to elapse before lighting a Bunsen burner.
3. Close the air hole (using the collar) before opening the gas tap
4. Hold a burning splint (or match stick) at the mouth of the chimney and open the gas tap at almost the same time.
5. Open the air hole after lighting the gas.

Answers to Questions 1.9(a)

The main parts of a Bunsen burner are the base, gas inlet, gas jet, collar and chimney.

Base: Supports the burner to stand upright

Gas inlet: Allows gas into the Bunsen burner

Gas jet: Sucks air into the Bunsen burner

Collar: Controls amount of air entering the Bunsen burner

Chimney: Space for the gas to mix with air before it (gas) burns

Luminous flame

What are the parts and characteristics of a luminous flame?

Open the video on luminous flame below.

(courtesy of Youtube ‐ Comparing different Bunsen burner flames by Science Web SciWeb Project). Study Part 1 keenly.

Note that a luminous flame is produced when the air hole of a Bunsen burner is closed.

Questions 1.9(b)

1. What is the major colour of this flame?
2. Why do you think it is described as luminous?
3. 1. How many parts of this flame can you see?
   2. Name the parts of this flame according to their colours.
   3. Draw and label the diagram of a luminous flame as seen in the video.
4. Why should the collar be closed for this flame to occur?
5. In what ways is this flame similar to a candle flame?
6. From your knowledge of a candle flame or this demonstration, is luminous flame hot?
7. What is the black substance that readily deposits on the test tube?
8. What is responsible for the major colour identified in Question 1?
9. Is luminous flame suitable for heating? Give a reason.

Answers to Questions 1.9(b)

Do all parts of a luminous flame have the same temperature?

Observe the video, hotness of a candle flame and answer the questions that follow.

Questions 1.9(c)

1. Draw and label a diagram to represent the observation.
2. From what is observed, is the paper burnt uniformly?
3. What does the observation or diagram show about hotness of parts of a luminous flame?

Notice that in all cases, we cannot see what is burning. Even in a candle, burning and flame occur around the wick and not on the wax or its melt. What burns is invisible. It is a gas. We therefore define a flame as a mass of burning gases.

Answers to Questions 1.9(c)

A luminous flame:

1. Is produced when the air hole is closed.
2. Is bright and mainly yellow.
3. Produces soot because of incomplete combustion (burning) of carbon.
4. Is relatively cool and therefore not suitable for heating.
5. Is quiet, unsteady and easily swayed by wind.
6. Has three (3) parts: a small blue zone at the base, colorless zone at the mouth of the chimney, and bright (luminous) yellow as the main colour).

Non-luminous flame

What are the parts and characteristics of a non-luminous flame?

Non-luminous flame is produced when the air hole is fully open, by turning the collar. Watch the video of a non-luminous flame

(courtesy Youtube-Comparing different Bunsen burner flames by Science Web SciWeb Project) and note its effect on the test tube and content being heated. Compare the flame with the picture that follows.

Non-luminous flame: https://o.quizlet.com/9Mo4AC1dJ1IbmsGIsZ3iNQ.jpg

Questions 1.9(d)

1. What is the major colour of a non-luminous flame?
2. Luminous means has the ability to produce light. Why do you think the flame is described as non-luminous?
3. 1. How many parts of this flame can you see?
   2. Describe them.
   3. Draw and label the diagram of a non-luminous flame as seen in the picture.
4. Why should the collar be fully open for this flame to occur?
5. In what ways is this flame similar to the flame of a gas cooker or stove?
6. From your knowledge of a cooker or stove flame, is non-luminous flame hot?
7. State five differences between non-luminous and luminous flame.
8. When turning off a non-luminous Bunsen flame, it is important to screw the collar and cover the air hole first. Give a reason for this.
9. State two similarities between a luminous flame and non-luminous flame.

Answers to Questions 1.9(d)

Labelled drawings of luminous and non-luminous flames

At home

Firewood and charcoal burners produce mixed luminous and non-luminous flames. The luminous part has less heat and produces unburnt carbon (soot) that soils cooking utensils, coating them black. Also it pollutes the environment. A good heating burner produces a blue or pale blue (non-luminous) flame, which is hot.

Use of Bunsen burner (non-luminous flame)

Questions 1.9(e)

1. Laboratory experiments normally use non-luminous flame, and not luminous flame. Explain.
2. Study the picture of a wire gauze, tripod stand and clay triangle which are normally used with a Bunsen flame when heating a substance.






The wire gauze is a wire net made of hardened steel, with ceramic or asbestos cover (the white substance) around the centre. A beaker is not heated directly but through the ceramic, which spreads the heat uniformly across the base. What is the risk of non-uniform heating of a glass beaker or any glass vessel?



3. The arrangements for heating are typically as follows.



(a) Heating in a beaker


(b) Heating in a test tube

(c) Heating in a crucible



What property of hardened steel wire gauze do you think makes it suitable for use with hot flames as indicated in (a)?

4. Study diagram (b) showing the heating of a test tube in a Bunsen flame.



Watch the video, heating substances in a test tube, to learn how to heat the contents of a test tube.




(courtesy Youtube - Heating substances in a test tube by David Read)
1. How would you protect yourself and neighbors when heating a liquid in a test tube (or boiling tube)?
2. Overheating one part of a test tube can cause it to crack, especially when heating a solid. How would you protect the test tube when heating a solid in it?
3. Suggest two reasons why a wire gauze is not used in the set-up in (c).

Answers to Questions 1.9(e)

To simplify diagrams, we normally use a single upward arrow to represent heating (and Bunsen burner) and two such arrows to indicate strong heating. Besides, all other diagrams are two-dimensional. For example, a beaker is represented simply as a rectangle with an open top.

At home

A candle flame is sometimes used for lighting, because it is bright, but not for heating. Heating vessels are held at the hottest parts of the non-luminous flames-neither too low nor too high above the cooker.