Hard water contains dissolved salts of calcium and magnesium. When soap, which is a sodium or potassium salt of a long-chain fatty acid, is added to hard water, the calcium and magnesium ions react with the soap molecules to form insoluble salts. These insoluble salts are called scum. Scum appears as a white, sticky substance that floats on the surface of the water.
The formation of scum reduces the effectiveness of soap. This is because soap molecules are needed to form micelles, which are tiny spheres that surround and trap dirt and grease. When soap molecules react with calcium and magnesium ions to form scum, fewer soap molecules are available to form micelles. As a result, less dirt and grease can be removed from surfaces, and more soap is needed to achieve the same level of cleaning.
The chemical reaction that occurs between soap and hard water can be represented as follows:
2RCOONa + Ca2+ → (RCOO)2Ca + 2Na+
2RCOONa + Mg2+ → (RCOO)2Mg + 2Na+
In these equations, R represents the long-chain hydrocarbon part of the soap molecule. The calcium and magnesium ions in hard water displace the sodium ions in the soap molecules, forming insoluble calcium and magnesium salts of fatty acids. These salts are the scum that we see.
FAQ‘s
What is hard water?
Hard water is water that contains dissolved minerals, primarily calcium and magnesium ions. These minerals come from the ground as water flows over rocks and soil.
What are the disadvantages of using hard water?
Hard water can cause many problems, including:
- It can leave a white, chalky residue on surfaces.
- It can make soap less effective, requiring more soap to be used.
- It can cause hair to become dry and brittle.
- It can leave spots on dishes and glassware.
How can hard water be softened?
There are several ways to soften hard water, including:
- Using a water softener
- Adding a water softener to your washing machine
- Using a water filter
- Boiling water
What are the benefits of using soft water?
Soft water can help to:
- Improve the effectiveness of soap
- Protect plumbing fixtures from mineral buildup
- Make hair and skin softer
How can I tell if my water is hard?
There are a number of ways to test your water for hardness, including:
- Using a home water test kit
- Having your water tested by a professional
- Observing whether your soap lathers well and whether you see a buildup of scale on your fixtures