German version
| Supermarket product: |
| curd soap |
Chemicals:
| CaCl2 · 6 H20 | |
Glass wares:
| gas collecting cylinder h = 20 cm, d = 5 cm
| beaker 100 mL
| Pasteur pipette with rubber bulb | |
Experimental procedure:
Using a Pasteur pipette, some drops of aqueous calcium chloride solution are added to a cylinder containing an aqueous solution of curd soap.
| Result:
A white precipitate is formed. |
 Video clip (Download RealPlayer .rm-Datei)
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Discussion and background:
Calcium ions react with soap anions (e.g. stearate anions) to form sparingly soluble "calcium soaps" (e.g. calcium stearate)
Hard water contains a greater quantity of Ca 2+ and Mg 2+ ions. The reaction of the earth alkali ions with soap produces precipates which create an insoluble residue on fabrics and can also discolor the fabric. White fabrics may become grayed or yellowish and dingy. Hard water can also leave a film on hair and glasswares. Hardness of the water is very important in industrial uses, because it forms scale in heat exchange equipment, boilers, and pipe lines.
