Heating the carbonates

Magnesium carbonate label

Watch the following video which shows the effect of heating the Group 2 carbonates from magnesium carbonate to barium carbonate. You may have seen the effect of heat on zinc carbonate. We expect similar reactions here, with decomposition producing carbon dioxide gas. I have shown a fairly simple experiment in which any gases are passed through lime-water to detect any carbon dioxide gas.

The principle behind this experiment is to see if there is any trend in the ease of decomposition of these carbonates as we go down the group. In each case I have used 0.025 moles of the carbonate, and heated it with the same Bunsen burner on the same setting and at the same position. Make a note of the time taken for the cloudiness of the lime-water to first appear. This is a rough measure of the ease of decomposition - the shorter it takes the less stable is the carbonate. Also the degree of cloudiness gives an indication of the stability. More cloudiness means more carbon dioxide and so quicker decomposition. Try to explain any trend that you observe and check your answer in the theory link below. You will see that the method I have used is rather destructive on test tubes. If you do your own experiment an alternative approach may be cheaper!

Video - the effect of heat on the group 2 carbonates

Theory - the effect of heat on the group 2 carbonates