This class practical introduces concepts of chemistry and smell. A number of common chemicals with distinctive smells have been chosen to help students get their nose around different functionalities in chemistry. This is done via a series of solutions, which can be smelled using smelling sticks.

Class practical

This class practical introduces concepts of chemistry and smell. A number of common chemicals with distinctive smells have been chosen to help students get their nose around different functionalities in chemistry. This is done via a series of solutions, which can be smelled using smelling sticks. Participants can smell each of the solutions, discussing ‘good’ smells and ‘bad’ smells. This leads nicely into a comparison of structures, trying to identify similarities and differences. A spectroscopic discussion of functional groups (eg IR) could then be entered into if appropriate.

Lesson organisation

The chemical solutions can be prepared in advance of the lesson. This practical activity takes 20 minutes for student groups to complete.

Apparatus Chemicals

Eye protection

Balance

Small glass vials or conical flasks (25 cm3), 10

Rubber stoppers or lids for the vials/flasks

Measuring cylinders (25 cm3)

Dropping pipettes, 10

Smelling sticks (either cut filter paper, cut rigid card or wooden splints)

The quantities listed below are sufficient for multiple class practicals:

R-(-)-Carvone (HARMFUL, LOW HAZARD), 293 mg

S-(+)-Carvone (LOW HAZARD), 293 mg

Vanillin (IRRITANT, LOW HAZARD), 91 mg

R-(+)-Limonene and  S-(-)-Limonene  (FLAMMABLE, IRRITANT, MAY CAUSE ALLERGIC SKIN REACTION), 470 mg

Ammonium sulphide (FLAMMABLE, TOXIC, LOW HAZARD), 10 mg

Ammonium thioglycolate (TOXIC, IRRITANT, MAY CAUSE ALLERGIC SKIN REACTION), 475 mg

Butanoic acid (IRRITANT, LOW HAZARD), 238 mg

Indole (HARMFUL, TOXIC, LOW HAZARD), 18 mg

Menthol (IRRITANT, LOW HAZARD), crude solid used

Purified (distilled or deionised) water, 15 cm3
for each sample solution

Surfactant such as Tween20 15 cm3 for each Limonene sample used

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Preparing the solutions

The table below gives concentrations which produce an easily detectable, but not overpowering smell. The mass given is the mass required to make a 15 cm3 solution at the stipulated concentration. Most of the solutions can be made up in water, but in the case of limonene a surfactant such as Tween20 will be required.

Compound Solution volume / cm3 Concentration / M Mr Mass required / g
R-(-)-Carvone 15 0.13 150.22 0.293
S-(-)-Carvone 15 0.13 150.22 0.293
Vanillin 15 0.04 152.15 0.091
R-(+)-Limonene 15 0.23 136.23 0.470
S-(-)-Limonene 15 0.23 136.23 0.470
Ammonium sulfide 15 0.01 68.14 0.010
Ammonium thioglycolate 15 0.29 109.15 0.475
Butanoic acid 15 0.18 88.11 0.238
Indole 15 0.01 117.15 0.018
Menthol neat solid 156.27 n/a

The solutions can then be stored in airtight vials, ready for use.

CLEAPSS guidance for disposal of corrosive or irritant chemical solids stipulates that their concentrations must be below 1 % (w/w). All the sample solutions in this practical are therefore safe for disposal.

Procedure

The recommended steps for smelling the solutions are as follows:

1. Check if there is a likelihood of allergic responses; if so the pupil/s should not participate. All participants should wear safety spectacles.

2. Drop 2-3 drops of the aqueous solutions onto the smelling strips (non-labelled end) and distribute over the end of strips using the dropper.

3. Once the stick has dried such that no liquid is likely to flick off, pupils can pass the sticks around by the labelled end and smell the strips by positioning them near their noses and inhaling (it should be emphasised that when smelling concentrated or bulk chemicals the odour should be wafted towards the nose rather than sniffed directly).

4. Collect the strips, wrap in paper, and dispose in the normal waste.

Health & Safety checked, October 2013

Page last updated June 2015

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Additional information

The Royal Society of Chemistry would like to thank Dr Jacob Cox, Dr Simon Rees, Rebecca Edwards and Kate Madden as part of the Educational Techniques Group (ETG) for their involvement in the development of this resource.