Apparatus and techniques for microscale chemistry

Microscale experiments give students the opportunity to develop their observational and investigative skills using simple equipment and smaller quantities of chemicals.

This practical guide is designed to accompany our Microscale chemistry resources, supporting you to use microscale experiments in your classroom. Find out about required apparatus, and discover guidance on techniques such as filtration and titration.

You can also learn how to prepare solutions using compounds of a variety of elements, from calcium to tungsten.

1. Common microscale apparatus

1.1. Transparent plastic sheet (OHP sheet)

These sheets are widely used in schools and colleges and are used to overlie the student worksheets in several experiments. Students add drops of solutions onto the sheets to do the reactions. The sheets are reasonably resilient and may be wiped clean with household tissues and re-used many times. However, they could be attacked by strong acids and they are stained by iodine solution if left in contact for more than a few minutes.

Alternatively, clear plastic wallets (A4 size) can be used or the student worksheets could be laminated. Again the wallets or laminated sheets can be wiped clean after use.

Whichever type is used, aqueous solutions form nicely-defined drops on the surface which enable chemical reactions to be conveniently carried out. A discussion of the shape of the drops can provide students with interesting insights into the effects of hydrogen bonding on surface tension.

1.2. Plastic pipettes

These very versatile pieces of plastic apparatus may be used for storing solutions and dispensing drops of solution during experiments. By cutting and reshaping them it is possible to make scoops and spatulas, filter funnels, mini reaction vessels and electrolysis apparatus. The two most useful forms of pipette are shown below.

These plastic pipettes have many uses. Two of the most useful are preparing a shortened pipette for storing solutions and making a scoop.

Preparing a shortened pipette

The diagram below shows how to make a shortened pipette from a fine-tip pipette using the edge of a bench and some scissors.

Making a scoop

You can make a scoop from a plastic pipette by cutting the bulb of the pipette at an angle, as in the diagram below.

1.3. Plastic Petri dishes

These are used as containers in which test gases can be generated. Examples are the 4.5 cm and 9 cm diameter Petri dishes supplied by Philip Harris (ref: B8H64838).

1.4. Well-plates

Clear plastic well-plates are sometimes listed in catalogues under culture apparatus. The most useful version is the 24-well plate which consists of an arrangement of 6 × 4 cylindrical wells each well having a capacity of approximately 3 cm³.

These well-plates are used for organic chemistry experiments, equilibria, rates of reaction and colorimetry experiments. They are compatible with many organic liquids.

1.5. Other apparatus

Other useful pieces of equipment are audio-cassette boxes for storing shortened plastic pipettes, plastic boxes for 35 mm film, plastic display boxes for pens, temperature strips and screw-top sample bottles.

2. Microscale techniques

2.1. Filtration

The diagram below illustrates a simple but effective method for constructing a filter funnel from a plastic pipette.

Your filter funnel is now ready to use. The efficiency of the filter funnel depends mainly on how compact the cotton wool is in the funnel. For coarse particles the cotton wool need not be packed very tightly. However, if very fine particles are to be separated from the liquid tight packing is essential for effective separation.

2.2. Sampling a bottle of hydroxybenzene (phenol)

Hydroxybenzene is a hazardous substance and sampling a bottle of hydroxybenzene using a spatula is usually difficult. The need to ensure that crystals of hydroxybenzene do not come into contact with the skin, the wearing of gloves and the fact that hydroxybenzene is hygroscopic, causing the crystals to stick together, all add to the difficulties. The following procedure reduces safety hazards and allows students to gain in confidence and practical skills. Students must still wear eye protection and gloves.

This technique illustrates the use of two plastic pipettes for obtaining small samples of hydroxybenzene crystals suitable for use in microscale chemistry experiments.

Procedure

1. Take a standard form plastic pipette and cut off the ends as indicated.

2. Cut the tip off the end of a fine-tip pipette as shown below.

3. Taking the modified standard pipette, press it gently down into the crystals in the hydroxybenzene bottle and withdraw. A small column of solid hydroxybenzene should be held on the inside of the bevelled end.
4. Place the pipette over the petri dish and insert the fine-tipped pipette to press out a small quantity of hydroxybenzene crystals. (Repeat if necessary at other locations in the petri dish for example if you are investigating the reactions of hydroxybenzene.)
5. Place the ends of both pipettes into a 100 cm³ beaker about half full with 1 mol dm⁻³ sodium hydroxide solution. This dissolves any solid hydroxybenzene remaining on the pipettes.
6. The pipettes may then be washed with deionised water, dried on tissue paper and stored ready for reuse.

2.3. Titration

Titrations are widely used in post-16 chemistry courses. The traditional apparatus comprises 50 cm³ burettes and 25 cm³ pipettes. For a whole class, experiments with this size of apparatus consume large quantities of solutions and students often take a long time to do the titrations. They are frequently very messy with spillages from pouring solutions and leaking taps on burettes!

In microscale titrations like those in our Microscale chemistry collection, the 50 cm³ burette is replaced by a 2 cm³ graduated pipette and the 25 cm³ pipette by a 1 cm³ pipette. A diagram of the apparatus is shown below.

To do the titration the plunger is gently pressed down. The volume of the drops produced is approximately 0.02 cm³ – without the fine tip the drop volume is approximately 0.04 cm³. The apparatus can be read to 0.01 cm³ (compared with 0.05 cm³ with a conventional burette) although the volume of solution delivered (less than 2 cm³) is far less.

The main advantages of this technique are:

• The greatly reduced volumes of solutions required (with the associated reductions in cost)
• The removal of the need for pouring solutions
• Increased speed of titration
• The smaller quantities of solutions to dispose of at the end of the experiment

The apparatus can be used for the following experiments:

• Measuring an equilibrium constant
• Finding out how much salt there is in seawater
• Measuring the amount of vitamin C in fruit drinks

Apparatus

• Clamp stand with two bosses and clamps
• Graduated pipette, 2 cm³
• Plastic pipette (fine-tip form)
• Plastic syringe, 10 cm³
• Rubber tubing (for connectors)
• Adaptor (made from a 1 cm³ plastic syringe)
• Beaker, 10 cm³

Constructing the burette

1. Place the 2 cm³ pipette in a clamp. This is your ‘burette’ during the titration.
2. Cut the end off a fine-tip plastic pipette and push it carefully onto the end of the ‘burette’.
3. Attach the 10 cm³ plastic syringe to a clamp above the ‘burette’.
4. Cut the end off a 1 cm³ plastic syringe to make an adaptor.
5. Cut two short pieces of rubber tubing and use them to attach the syringe to the top of the ‘burette’ via the adaptor.

Filling the burette

1. Take a 10 cm³ beaker and using a plastic pipette half-fill it with the solution for the ‘burette’.
2. Place the tip of the ‘burette’ in the solution and slowly raise the plunger. The solution is drawn up into the ‘burette’. (If air bubbles are drawn up raise and lower the plunger slowly a few times to expel them). When the desired level is reached release the plunger and the liquid level in the ‘burette’ should remain stationary. If the level falls, adjust the connections on the apparatus to ensure that the system is air-tight and repeat the filling process.

2.4. Constructing a conductivity meter

The diagram below illustrates a conductivity meter that can be used for testing conductivity of solutions or solids. It is possible for students to make the apparatus themselves. Alternatively students could be given the instruments ready-made.

Apparatus

• Light-emitting diode (LED)
• Resistor, 1000 Ω
• Battery, 9 V
• Battery connector
• Piece of thin wood or plastic, approximately 150 × 25 mm
• Solder wire or tape
• Soldering iron
• Sticking tape
• Thick rubber band

2.5. Hoffman apparatus

Students can make their own microscale Hoffman apparatus from plastic pipettes, using it to investigate aspects of electrolysis.

Apparatus

• Four plastic pipettes (standard form, eg Aldrich ref’ Z13,500-3)
• Scissors
• A pin
• Pencil leads (HB 0.9 mm)
• Adhesive, eg polystyrene glue

Procedure

1. Using the scissors cut two holes in two of the pipettes as indicated in the diagram below.
2. Cut off the stem from a third pipette and insert it in the first two pipettes to join them.
3. Cut off the tip and end of the bulb of the fourth pipette and insert the tip end into a hole in the middle of the stem joining the first two pipettes.
4. With the pin make a hole in the bottom of the two bulbs and carefully insert a pencil lead into each.
5. Apply adhesive to each joint and leave to dry.

3. Preparing solutions

Download our solutions guide to find out how to prepare a variety of solutions for use in microscale experiments. The guide features compounds of a range of common elements, with instructions detailing the chemicals and quantities required, as well as hazard information relating to each solution.