Expert: George Maxwell - 2/10/2008

Question
i am in sixth grade and i chose my science fair project this week i want to measure and see why 4 different types of liquids evaporete such as oil, water, nailpolish remover, and wine i cant find any info in science books so what is the main reason that a iquid with a different consistancy evaporate slower? is it because of the mass of the liquid?

Answer
Hi, and thanks for your question.

There are a few key factors that you might want to think about in completing your project.

Evaporation can be thought of as the process where molecules of a liquid get enough energy to escape from the surface, and float away from the bulk liquid as a vapor.

In a thick (or "viscous" liquid, the forces between molecules of the liquid are stronger - this means it take more energy to remove molecules from the liquid surface, so the liquid will evaporate slower.

In experimenting in this area, you need to be sure that:

a) The temperature is constant - a higher temperature means a faster rate of evaporation for all liquids, so it's important that the surrounding temperature for different experiments is the same.

b) The surface area is constant - evaporation happens quicker over larger areas, so it's important that the container used to hold each liquid while it is evaporating is the same shape and size.

c) The only effect that mass has is that a larger mass takes longer to evaporate. For example, if water evaporates at the rate of 1cm3 per minute, it will take 10 minutes to evaporate 10cm3 and 20 minutes to evaporate 20cm3. You might want to think about using identical volumes of liquid instead of identical masses.

d) Another important factor in evaporation is air-flow - if there is a strong breeze flowing over a liquid surface, evaporation happens quicker. You can demonstrate this at a science fair by putting a drop of nail-polish remover (acetone) on the skin, and blowing on the drop. This will result in fast evaporation, and the energy removed from the surface of the skin by the evaporating fluid will make it feel cold.

Hope this helps - best of luck with the project!