REED COLLEGE SCIENCE OUTREACH PROPERTIES OF MATTER

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Lesson Six- Exploring Solubility
Objectives
o Students will learn that different types of matter have different solubility.
Lesson Background- Solubility
Today students will learn about another chemical property of matter. Students will
learn that different types of solids react differently when mixed with a liquid. Each type
of matter has a different solubility, or ability to dissolve into a liquid. When a solid
dissolves, all the molecules in a solid separate and are surrounded by the molecules of a
liquid. The molecules of the liquid will then hold each of the solid molecules in a
solution.
All solids are able to dissolve into
certain types of liquid. However, some
types of matter will dissolve into water
and others will only dissolve into other
types of liquids like alcohol. This is
because there are two types of
molecules: polar and non-polar. Polar
molecules act like a magnet. One side
of the molecule has a slight negative
charge and the other side has a slight
positive charge. Just like a magnet,
opposite poles of polar molecules
attract. Water is a polar molecule, so
when a polar molecule (such as sugar) is mixed into water, the water molecules’
negative poles are attracted to sugar molecule’s possible poles (and viscera). As a result,
water will only be attracted to (and dissolve) polar molecules. Similarly, non-polar
liquids (such as alcohol), will only dissolve non-polar molecules (such as CO2).
Activity overview- Paper Chromatography
This week, students will work together to identify different types of ink by separating
the ink’s molecules using paper chromatography. Ink is made up of a mix of different
types of chemicals, each with different chemical properties. Some of the chemicals are
water-soluble and others are only soluble in non-polar liquids such as alcohol. Paper
chromatography uses a process called capillary action, to draw liquid up a piece of paper
on which there is a sample of ink. As the liquid moves up the paper it will begin to
dissolve some of the chemicals in the ink and move them up the paper. Smaller
molecules will be drawn up the paper faster than larger chemical, so each type of ink
will create its own unique pattern. In addition each type of ink will produce a different
pattern when dissolved in water or alcohol, since not all chemicals can be dissolved by
water/alcohol. Using this process, the students will separate the different chemicals
using their unique chemical properties, and identify a mystery ink by its unique pattern.