All Mixed Up!

What properties
helped you separate
stones, wood, and
salt?
All Mixed
Up!
1. Always wear safety goggles.
How can you
retrieve the
solid salt?
2. Rinse the strainer and beakers in the sink.
3. Put a scoop of Mixture into Beaker 1.
4. Look at the mixture and find the three parts:
small rocks, white salt crystals, and bits of wood.
A Closer Look
5. Add 300 mL of water to the mixture in Beaker 1.
Use the scoop to mix the contents.
Chemists often separate substances by their
different properties or characteristics.
6. Let the beaker sit for a few moments.
• Where are the stones, wood shavings, and salt now?
Wood, water, and stones have different densities.
Substances with a lower density than water, such as
wood, float on water. Objects with a greater density
than water, such as stones, sink.
7. Separate the mixture using the following steps:
• Set the strainer over Beaker 2.
• Carefully pour the wet mixture in Beaker 1 through
the strainer into empty Beaker 2.
• Try to pour so that the stones stay in Beaker 1.
• Take the strainer off Beaker 2.
• Where are the stones, wood shavings, and salt now?
Many substances, like salt, dissolve in water, while
others, like wood and stones, do not. If you heat
salt-water or leave it in the sun, the water
evaporates, leaving solid salt behind. Look at the
examples in the dishes.
8. Scrape the rocks and the wood into the "WASTE" beaker. Rinse
the beakers and the strainer in the sink.
©2010 OMSI
Talking Points: All Mixed Up
Extensions
In-Depth Information
Ask:
1) How could you separate a mixture of sugar, safety pins, and
plastic foam?
Just repeat this experiment. The sugar will dissolve in the
water, the safety pins will sink to the bottom, and the plastic
foam will float.
2) How can you add a step to this experiment and separate a
mixture of salt, pebbles, wood chips and safety pins? What
additional tool would you need?
Follow this procedure. The wood chips and salt will be
separated in the same manner. Then, in an added step, use a
magnet to separate the safety pins from the pebbles.
Density
The fact that water is a liquid makes it possible to separate the solid
materials with greater density from those with lesser density.
Connect Æ See the experiment Density Rainbow for In-Depth
information about density
Applications
Mixtures can be separated by careful use of their physical and
chemical properties. Salt and sugar are soluble in water; pebbles,
wood, and plastic foam are not.
These are among the methods used to separate materials that are
recycled. Some time ago it was necessary to separate all recycled
materials in the home; now many materials can be mixed together
and separated at the recycling center. Magnets can be used to
separate many metals; water can be used to separate materials with
a higher density from those of a lower density. Soluble materials can
be dissolved in water and recovered after evaporating the water.
This makes it possible to reuse many materials we used to throw
away.
Salt in Solution
Connect Æ This information is also relevant to the
experiment Currently Working
Water is an exceptionally good solvent. In fact, even though we
commonly think that oil will not dissolve in water, try separating oil
and water and then tasting the water that has been in contact with
oil. You will taste that some of the oil has been dissolved.
In the water molecule, oxygen holds electrons (with their negative
charge) more tightly than does hydrogen. Because the H2O molecule
is “bent” into a “L” shape, the part of the molecule to the “back” of
the oxygen (the end pointing away from the hydrogens) has a partial
negative charge, while there is a partial positive charge on the end of
the molecule that contains the hydrogens.
In the dissolved salt, the Na+ ions will be surrounded with water
molecules with the negative end pointing towards the cation (ion with
a positive charge), while the Cl- anion (ion with a negative charge)
will be surrounded with positive end of the water molecules pointing
toward it.