##### Calcium Compounds

Calcium Carbonate

1. Calcium is a reactive metal. Therefore, it does not exist in its pure form in nature.

2. Calcium tends to combine with other elements to form compounds.

3. Calcium carbonate is one of the many useful calcium compounds.

4. Calcium carbonate is a compound of calcium, oxygen and carbon.

5. Calcium carbonate occurs in several forms in nature.

6. Limestone and marble are examples of natural calcium compounds.

7. Limestone is a sedimentary rock which is formed from the remains of sea creatures and fragments of shells settles at the bottom of the sea.

8. The stalagmites and stalactites built up in caves are examples of calcium carbonate too.

9. Seashell, eggshell, coral reefs amd bones are largely calcium carbonate.

The Properties Of Calcium Carbonate

1. Calcium carbonate is a fairly stable compound.

2. It does not dissolve in water. However, it does if the water is slightly acidic.

3. Calcium carbonate reacts with acid to form salt, carbon dioxide and water.

4. Below is the equation in words for the reaction of calcium carbonate with acid.

5. When calcium carbonate is heated strongly, it decomposes and changes into calcium oxide (quicklime) and carbon dioxide.

6. The decomposition of calcium carbonate by heat:

$$Calcium\quad carbonate\quad \underrightarrow { heated\quad strongly } \quad calcium\quad oxide\quad (quicklime)\quad +\quad carbon\quad ioxide$$

7. Calcium oxide (quicklime) reacts with water to form calcium hydroxide, which is called slaked lime. Heat is produced in the process.

$$Calcium\quad oxide\quad (quicklime)\quad +\quad water\quad \rightarrow \quad calcium\quad hydroxide\quad (slaked\quad lime)\quad +\quad heat\quad$$

8. Calcium hydroxide is an alkali. It dissolves in water to become lime water which is used to test for the presence of carbon dioxide gas.

$$Calcium\quad hydroxide\quad solution\quad (lime\quad water)\quad +\quad carbon\quad dioxide\quad \rightarrow \quad calcium\quad carbonate\quad (white\quad precipitate)\quad +\quad water$$

The Uses Of Calcium Compounds

1. The uses of calcium compounds related to their properties are shown in Table 6.2.

Table 6.2  The properties of calcium compounds and their uses

 Calcium compound Properties Uses Calcium carbonate - Reacts with acid - To treat acidic soil and water - Used as antacid to reduce stomach    discomfort Limestone - Easy to shape into blocks    and can be split in any    direction. - As building material (cement, concrete,    glass) Calcium oxide - Forms alkali when dissolved    in water. - To treat acidic soil - Make mortar and plaster in building    industry Calcium hydroxide - Alkaline - To treat acidic soil - As lime water to test for the presence    of carbon dioxide