Microscale Chemistry - What and Why?
Microscale chemistry really began in the 1980s with two main strands:
1. aimed at introducing practical work for schools in poorer countries where there might not be laboratories and chemicals/equipment are in short supply.
2. used in a few universities in the USA where significant educational advantages were found in working at this scale.
However, in Europe and America at least it remained a niche activity. Then, in the mid 2000s, green chemistry came on the scene in a big way and the green credentials of microscale gave it a new lease of life. It seems to us that while there will always be a place for large scale chemical work, microscale chemistry for schools in the UK is an idea whose time has come.
Microscale chemistry has many advantages.
Microscale procedures are safer than the original demonstrations because of their size.
• The classic reduction of copper oxide by hydrogen had resulted in many serious accidents: the microscale version is safer because an explosive mixture of hydrogen and air cannot be made.
• Electrolysis reactions often produce toxic gases which affect asthmatics but dealing with volumes of less than 10 cm3 cause no serious issues.
• The cracking of alkanes can lead to explosions caused by the suck back of cold water into a hot glass test tube. With the microscale version, this cannot occur.
Microscale equipment is mostly plastic and inexpensive. Balances weighing to 2 decimal places can be found for less than £10 and even 3 decimal places for not much more); and they are accurate. A full size Hofmann voltameter would cost over £150 the glass, the taps and the electrodes are easily broken: a microscale one can be made for less than £20. In addition, working on a micro scale means using smaller quantities of sometimes expensive chemicals.
Dealing with waste is of great concern to all countries now. Using smaller amounts produces smaller amounts of waste. This in turn reduces time in preparation, clearing up and disposing of waste. The UK is lucky in having technicians do a lot of this work but if there is less of this to do then more time can be devoted to more constructive activities.
A laboratory is not always required
This is not always a desirable advantage but it can very useful at times for instance:
• when, due to timetabling, some chemistry lessons are scheduled in an oprdinary classroom
• carrying out procedures quoted in text books but said to be impossible to perform in the laboratory eg The Haber process for making ammonia from nitrogen and hydrogen and the Ostwald process for making nitric acid from ammonia and oxygen can be demonstrated in a few minutes. Even the hydrogenation of propene is possible.
Reduces practical times
If demonstrations and practical procedures take too long and have to shelved to the next lesson, continuity is lost and the subject can become disconnected, not understood and in the end boring. Also, less time spent on the mechanics of the experiment allows for more discussion and questioning
Better classroom control
Much of the time wasted in lessons is caused by students moving around the room to find sinks and balances and collecting chemicals and equipment. This can lead to poor behaviour but microscale activities can be carried out in a small area of the room. Another revolution is that as the quantity of liquid used is in the most 2 cm3, with practiced techniques, students can sit down to carry out the activity.
Easier for students to manage
Recent observations are that the use of microscale are easier to manage by the students.
Quantitative results and data manipulation are possible
Despite the small scale and the generally inexpensive equipment, a lot of good results can be achieved by these methods, comparable in many cases with the full-scale approach. The combustion of magnesium to illustrate an increase in mass of combustion is traditionally carried out in a crucible but with often poor results. Using magnesium sandwiched between 2 bottle tops, held with nichrome wire produces excellent quantitative results in the space of 15 minutes for students.
Are there any problems?
The fact that it is on a very small scale does mean that there are issues with using this technique for demonstrations. It is possible to get around this though. Images can be projected onto a white board using a webcam or video microscope.
Another problem is that using very small quantities can raise problems with dexterity for some pupils. Like any other skill, however, this is one that can be improved with practice.