Academic journal article The Science Teacher

Try This Tops Idea! in Between: ... Adapted from Solutions #12

Academic journal article The Science Teacher

Try This Tops Idea! in Between: ... Adapted from Solutions #12

Article excerpt

1. Fill a test tube 1/4 full of salt, then 1/4 full of rice. Mark the volume with tape.

[ILLUSTRATION OMITTED]

2. Cap with your thumb and shake well. Does the volume change? Why?

[ILLUSTRATION OMITTED]

3. Empty the tube, and fill V6 full of salt. Trickle water down the side until brim full, then cap tightly with your thumb.

[ILLUSTRATION OMITTED]

4. Rotate the tube slowly to mix. What pressure change do you notice?

[ILLUSTRATION OMITTED]

5. Explain the pressure change in terms of the rice/salt model.

[ILLUSTRATION OMITTED]

OBJECTIVE

To understand why salt and water lose volume when mixed together.

LAB NOTES

BACKGROUND: Solid crystals of table salt break apart into positively and negatively charged atoms called ions as they dissolve in water. Alcohol molecules, by contrast, intermix with water molecules in the process of dissolving (and they negligably break apart into charged ions. Step 3. Gently adding water prevents the salt from dissolving too soon. Filling the tube brim full expels all air from the tube before capping its mouth.

MATERIALS

* A small, dry test tube.

* Rice and fine-grained table salt.

* Masking tape and scissors.

* Water source and paper towels.

* A metric ruler (optional). …

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