To determine if chalk of unknown composition is appropriate for use in the Activity, break off a small piece and drop it into a container with a few mL of vinegar. If bubbles form, the chalk can be used in the Activity. If there are no bubbles, the chalk does not contain calcium carbonate and will not neutralize acid in the model lake. You may wish to include calcium sulfate chalk in the Activity in addition to calcium carbonate chalk, as one of the additional solids. This could be used to begin a discussion with students about composition of chalk. Students might be interested in comparing other properties of the different chalks and attempting to discover reasons why all chalk is not the same.

Low-dust chalk can usually be purchased at stores that sell educational or instructional supplies or office supplies, but is not usually available at discount stores or grocery stores.

The JCE Classroom Activity Editors thank Don Lewis, a retired teacher from Texas, for bringing this to our attention. The corrected PDF is available at JCE Online.