Chapter 9: Dangerous Techniques
Some common laboratory techniques are actually quite dangerous. Identify practices in your school that seem likely to cause harm and devise safer alternatives. Below are some examples of techniques often performed in the laboratory that can easily bring harm and alternative methods to do the same thing more safely.
9.1 Mouth Pipetting
Many schools use pipettes for titrations. Many students use their mouths to fill these pipettes. We strongly discourage this practice.
The solutions used in ordinary acid-base titrations are not particularly dangerous. A little 0.1M NaOH in the mouth does not merit a trip to the hospital. Nevertheless, there are two pressing safety issues.
First, there are often other solutions present on the same benches – the qualitative analysis test reagents for example – that can kill if consumed. It seems like it would be a rare event for a student to mix up the bottles, but in the panic of the exam anything is possible.
The second safety issue applies to the best students, those that continue on to more advanced levels. High level secondary and university students must measure volumes of the size fit for pipettes for chemicals that under no circumstances should be mouth pipetted. If a student is trained in mouth pipetting, she will continue with this habit in advanced level, especially in a moment of frustration when a pipette filling bulb seems defective, or if the school has not taught her how to use them, or if they are not supplied. Students have died in many countries from mouth pipetting toxins.
Fortunately, there is no reason to ever use a pipette in secondary school, even if rubber-filling bulbs are present. Disposable plastic syringes are in every way superior to pipettes for the needs of students.
- They have no risk of chemical ingestion.
- They are more accurate. Plastic is much easier to make standard size than glass; the pipettes available generally vary from their true volume, but all the syringes of the same model and maker are exactly the same volume.
- Plastic syringes are easier to use
- They are faster to use
- They are much more durable
- When they do break they make no dangerous shards
- They are much less expensive, by about an order of magnitude
Schools all over are already substituting plastic syringes for glass pipettes. For information on how to use these plastic syringes, please see Laboratory Techniques: Use of a Plastic Syringe to Measure Volume (p. 58).
9.2 Shaking Separatory Funnels
Separatory funnels are useful for separating immiscible liquids. They are also made of glass, very smooth, and prone to slipping out of students’ hands. The liquids often used in these funnels can be quite harmful and no one wants them splashed along with glass shards on the floor.
Much better is to add the mixture to a plastic water bottle, cap it tightly, and shake. After shaking, transfer the contents of the bottle into a narrow beaker. Either layer can be efficiently removed with a plastic syringe.
There are some cases where a separatory funnel remains essential. For secondary school, however, simply design experiments that use other equipment - and less harmful chemicals.
9.3 Looking Down into Test Tubes