What is drawing out a glass jet and how is it done in the laboratory
Glass is a material that softens when heated and can be formed into the desired shape. Glass is used to make laboratory equipment, marbles, paperweights, mirrors, decorative items, windows, and television screens. Glass is a transparent material that takes on different colours when electrically charged ions are evenly distributed. Let's see how the glass is formed into a jet shape.
Aim of the Experiment
To learn the fundamentals of drawing a glass jet and glass rods with a simple process.
Materials Required for Drawing Glass Jet and Rod
15 cm long soda-glass tube
15 cm long soda-glass rod
Triangular file
Bunsen Burner
20-25 cm long glass tube
Triangular file
Bunsen Burner
Sandpaper
How To Draw A Jet?
Choose a glass tube with the appropriate diameter for drawing a jet.
Using a triangular file, cut the glass tube to the desired length.
Heat the tube by holding it at both ends in the hottest part of the Bunsen burner flame.
Rotate the tube gently until the portion in contact with the flame becomes red hot and softens.
Remove the glass tube from the flame and slowly and smoothly pull the ends apart until it becomes narrow in the middle and then stretches into a fine jet.
Cut the tube in the middle, then sandpaper and fire polish the ends until they are smooth.
Procedure for Glass Rod Drawing
Place the rod or glass tube on the table.
Mark the glass tube or rod with triangular file keeping.
Keep the triangular file perpendicular to the rod or tube and pull it towards you so that a single deep scratch is made.
Hold the glass rod or tube with the help of your thumbs.
Now apply pressure in the direction away from you and try breaking the glass rod or tube.
If the glass rod or tube does not break, use the triangular file to make a deeper scratch on the previous mark.
Trim any jagged edges with a wire gauge if you see them.
To get a good finish, gently hold the cut edge of the glass rod or tube in the flame.
Hold the edge of the glass rod or tube in the bunsen burner and rotate it back and forth until both ends have a good finish (smooth and round).
Precautions to be Taken While Drawing Glass Rod and Glass Jet
Pull the softened part of the glass tube gently until it is evenly thin.
Touching the red hot portion of the tube will be too hot and may cause injury.
In a single stroke/attempt, try to make a single deep scratch of the required length.
Be cautious during the filing process and when breaking the glass tube/rod.
To achieve optimal balance, keep your face away from the glass tube/rod and hold it away with a piece of cloth.
Important Questions
1. Why is a Glass Tube Rotated While Heating in a Burner?
Ans: To make a single deep scratch at the desired length, rotate the glass tube with one stroke of the file. This is done to ensure that all sides are properly heated due to uneven thermal expansion, which prevents cracking. It should be rotated in this order to ensure even heating. Never forcefully bend the glass tube. You risk breaking the tubing if you do so. Finally, do not heat the end for an extended period of time. Because it may seal the end or narrow it, the glass tube is rotated while heating in a burner.
2. What is the temperature that makes a glass break?
Ans: A glass is unaffected by cold or warm temperatures. When the temperature rises above 300 degrees Fahrenheit, the excessive thermal variation causes the glass to shatter. Because glass is a poor conductor of heat, rapid temperature changes cause stress and fractures on the glass, resulting in shattering or breaking. When placed at an overheated temperature of 500 degrees, the glass transforms from a solid to a plastic state.
Conclusion
At room temperature, glass tubes are very brittle and easily break. However, one can conclude that an amorphous crystalline solid, such as glass, has special properties that allow it to bend when subjected to intense heat. The bending of a glass tube experiment shows that materials like glass have a wide range of applications, owing to their malleability and ability to be shaped to the desired orientation when properly heated.
Multiple Choice Questions
1. Jet propulsion works on the principle of:
a) Newton’s first law
b) Newton’s second law
c) Newton’s third law
d) Thermodynamic properties
Answer: (c)
2. A jet strikes a curved plate at its
a) Sides
b) Surface
c) Centre
d) Does not strike
Answer: (c)
3. Jet propulsion of ship is less efficient than screw propeller due to
a) Pressure
b) Temperature
c) Frictional losses
d) Wear and tear
Answer: (c)
FAQs on Drawing Out a Glass Jet in Chemistry Practical
1. What is drawing out a glass jet in chemistry?
Drawing out a glass jet is a laboratory technique used to form a narrow, tapered tube from a glass tube by heating and pulling it. It is commonly performed using a Bunsen burner to soften the glass and then gently pulling both ends to produce a fine tip. This method is used in preparing delivery tubes, droppers, and gas jets in chemistry experiments.
2. Why is drawing out a glass jet important in laboratory experiments?
Drawing out a glass jet is important because it allows controlled passage of liquids or gases through a narrow opening. In practical chemistry, a fine jet is required for experiments such as gas delivery, titration setups, and preparing wash bottles. A properly drawn jet ensures accurate flow rate and prevents leakage during chemical reactions.
3. How do you draw out a glass jet step by step?
To draw out a glass jet, heat the glass tube uniformly and pull it apart gently to form a thin, tapered end.
- Hold a clean, dry glass tube horizontally with both hands.
- Rotate the tube in the non-luminous (blue) flame of a Bunsen burner until the glass softens and glows red.
- Remove it from the flame and gently pull both ends in opposite directions.
- Allow it to cool and cut at the thinnest point to obtain two glass jets.
4. Which type of flame is used for drawing out a glass jet?
A non-luminous (blue) flame of a Bunsen burner is used for drawing out a glass jet. The blue flame provides:
- Higher temperature
- Smokeless and clean heating
- Uniform softening of glass
5. What precautions should be taken while drawing out a glass jet?
The key precaution while drawing out a glass jet is to ensure uniform heating and safe handling of hot glass.
- Wear safety goggles to protect your eyes.
- Heat the glass evenly by rotating it continuously.
- Do not overheat, as the glass may collapse.
- Allow the jet to cool before touching it directly.
- Fire-polish sharp edges to prevent cuts.
6. Why must the glass tube be rotated while heating?
The glass tube must be rotated to ensure uniform heating and prevent uneven softening. Continuous rotation:
- Distributes heat evenly around the tube.
- Prevents bending or flattening.
- Produces a symmetrical, smooth jet.
7. What are the common uses of a glass jet in chemistry?
A glass jet is commonly used for controlled delivery of gases or liquids in laboratory setups.
- As a delivery tube in gas preparation experiments
- In wash bottles for directing water flow
- In droppers or pipette tips
- For connecting apparatus in chemical reactions
8. How do you cut and finish a drawn glass jet safely?
A drawn glass jet is cut at the thinnest point and then fire-polished to smooth sharp edges.
- Allow the drawn portion to cool.
- Use a glass cutter or file to scratch at the narrowest point.
- Gently snap the tube apart.
- Briefly heat the cut edge in the blue flame to fire-polish it.
9. What happens if the glass is overheated while drawing a jet?
If the glass is overheated, it may collapse, bubble, or lose its cylindrical shape. Excessive heating can:
- Cause thinning at unintended points
- Create weak structural spots
- Block the inner bore of the tube
10. Can a glass jet be used in gas preparation experiments?
Yes, a glass jet is widely used in gas preparation experiments to deliver gases safely and precisely. For example, in the laboratory preparation of carbon dioxide:
- CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
