Expt:Making a reaction tube

From Learn Chemistry Wiki

Introduction

Many reactions between gases and solids are suitable for demonstrations and class practicals. Making reaction tubes is an excellent lesson in physical chemistry in its own right as well as being cheaper than buying in expensive material.

There are many reactions between gases and solids which illustrate chemical principles. Heating a solid in an atmosphere of the required gas can be carried out in a modified boiling tube or test tube. Heating a Pyrex test tube or boiling tube fitted with a bung, causes the pressure to rise inside and the glass to soften. Eventually the tube fails and a hole is made.

Although this practical is not part of any Awarding Body specification, and although the purpose of making reaction tubes is for the reaction they will contain, the overall experience is so beneficial to students that most teachers say it is a practical worth doing in its own right.

Apparatus and chemicals

• Pyrex test tube (or boiling tube) (must be a borosilicate tube, such as Pyrex)
• Bung to fit (see note 1)
• Bunsen burner
• Heat resistant mat
• Sharps bin required for broken glass.
• Dust pan and brush

Technical notes

1. The bung needs to be clean and undamaged and make a gas-tight seal on the tube
2. In step d of the procedure, if the glass balloons out into a large fragile globe this could pose a hazard. Students should be told to call over a teacher if this happens.
3. You must make sure there is no broken glass on the benches to harm the pupils coming in for the next lesson.

Procedure

HEALTH & SAFETY: Wear eye protection

a The bung is pushed very firmly into the tube.

b Place the Bunsen burner on the mat , light it and adjust it to a roaring blue flame.

c Hold the tube by hand around the top of the tube and hold the tube in the hottest part of the flame as shown in the diagram. Heat a single spot. Do not rotate the tube.

d The glass will start to glow red and will begin to deform and then ‘pop’. It frequently blows the Bunsen burner flame out. Depending on the Bunsen burner, this usually takes between 30 seconds and two minutes.

e Relight the Bunsen if necessary and heat the glass around the hole for a few seconds. The sharp glass will retract to form a neat edged hole.

f Put the tube down on the mat to cool.

Reference

This experiment was written by Mike Thompson on behalf of the RSC.

Health & Safety checked, December 2009