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All Mixed

Up! 1. Always wear safety goggles.

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.

5. Add 300 mL of water to the mixture in Beaker 1.

Use the scoop to mix the contents.

6. Let the beaker sit for a few moments.

• Where are the stones, wood shavings, and salt now?

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?

8. Scrape the rocks and the wood into the "WASTE" beaker. Rinse

the beakers and the strainer in the sink.

A Closer Look Chemists often separate substances by their

different properties or characteristics.

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.

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.

What properties

helped you separate

stones, wood, and

salt?

How can you

retrieve the

solid salt?

Talking Points: All Mixed Up Extensions 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.

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.

In-Depth Information

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 See the experiment Density Rainbow for In-Depth information about density

Salt in Solution

Connect 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.