KIDS PAGES - Dissolution Experiment

Dissolution Experiment: Grades K-4

MATERIALS

27 or more sugar cubestoothpicks
A clear fish tank with straight sides
1 spray bottle with water
2 lbs. modeling clay

PROCEDURE

Stack the sugar cubes against the inside of the fish tank. Make the structure at least four cubes high and wide, and three deep. For a more realistic look, a few columns may have one or two more cubes. The sugar cubes represent large areas of limestone and the spaces between the cubes represent the natural cracks and fissures in the limestone through which water travels.

Cover the sugar structure with approximately 1/8-inch of clay. Make sure there are no gaps. The clay represents the surface dirt.

Using the toothpick, poke several holes through the clay into the sugar. This will allow water to seep through. Your experiment will show how limestone is dissolved to make a cave.

Dissolvability can also be demonstrated by dissolving salt or sugar in a glass of warm water.

Dissolution Experiment: Grades 5-8

MATERIALS

White vinegar
Shallow pan
Eye droppers
Samples of rocks, one of which is limestone.

PROCEDURE

Place the rock samples in the shallow pan. Using the eye dropper, start coating the rocks with the vinegar. This is known as the "Bubble Test." The limestone piece will bubble as it dissolves while the other rock(s) will not.

It is sometimes possible to tell what minerals rocks are composed of by their physical properties such as appearance, grain size, hardness, texture, color, and whether they can be dissolved.

Vinegar is a stronger acid than carbonic acid, so it works faster than the acids actually present in a cave. However, this demonstration does show how dissolution works to create a cave.

Could you tell which rock was limestone?

Dissolution Experiment: ADVANCED

Note: appropriate laboratory safety procedures should be followed when working with hydrochloric acid.

MATERIALS

2 beakers
20% solution of hydrochloric acid (also known as muriatic acid)
A sample of limestone
A sample of non-carbonate rock

PROCEDURE

Partially fill two beakers with the acid.

Weigh and measure each rock.

Place them in separate beakers and watch what happens. The limestone will fizz and the non-carbonate rock will not react.

Check the beakers every 15 minutes. (The dissolving action will stop if either the acid or the calcite is no longer available to react. If this happens, either add more acid or break the limestone to expose more calcite.) In about one hour the limestone sample will be noticeably smaller.

After drying, the samples can be weighed and measured again to determine the changes.


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