Use a thermometer strip to examine temperature changes when drops of different liquids evaporate

In this practical, students will take three liquids, ethoxyethane, dionised water and ethanol, and discover the rate of evaporation for each in relation to temperature. 

This experiment should take 10 minutes.

Equipment

Apparatus

  • Student worksheet
  • Temperature strip
  • Pipettes

Chemicals

  • Ethoxyethane (diethyl ether)
  • Deionised water
  • Ethanol

(NB Do not use propanone for this experiment – it attacks the temperature strip)

Health, safety and technical notes

  • Read our standard health and safety guidance.
  • Students must wear eye protection.
  • Ethoxyethane (diethyl ether) and ethanol are both highly FLAMMABLE (see CLEAPSS Hazcard HC042, HC040a).
  • Ethoxyethane is also a respiratory irritant and harmful if swallowed.

Procedure

  1. Put a row of drops of water along the strip. Note the shape of the drops and note whether there are any temperature changes over the next few minutes.
  2. Repeat using ethanol.
  3. Repeat using ethoxyethane.
  4. Record your observations in a table and try to give explanations. Bear in mind what you know about intermolecular forces when you interpret your findings.

Observations

Water, which forms well-defined droplets, produces very little, if any, change in temperature since the rate of evaporation is slow due to the high degree of hydrogen bonding.

With ethanol, the drops spread out and a fall in temperature will be noted due to the higher rate of evaporation. With ethoxyethane the drops evaporate very quickly and a marked drop in temperature is observed.

This is consistent with the low boiling point and absence of hydrogen bonding between the molecules. The energy changes accompanying changes of state are an important concept in science. One example is the addition of ice to cool drinks. Here it is the melting of ice that cools the drink rather than the contact of ice with the liquid.

Student questions

  1. If you have been swimming, and you do not dry yourself quickly after you get out of the water, you often start to feel cold. Why do you think this is?

Downloads

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References

S. W. Breuer, Microscale practical organic chemistry. Lancaster: Lancaster University, 1991.

Additional information

This resource is part of our Microscale chemistry collection, which brings together smaller-scale experiments to engage your students and explore key chemical ideas. The resources originally appeared in the book Microscale chemistry: experiments in miniature, published by the Royal Society of Chemistry in 1998.

© Royal Society of Chemistry

Health and safety checked, 2018