Questions and Answers
Explain the difference between temporary hardness and permanent hardness of water.
Temporary hardness is due to bicarbonates of calcium and magnesium, which can be removed by boiling the water. On boiling, the bicarbonates are converted into insoluble carbonates of calcium and magnesium. Permanent hardness, on the other hand, is due to the presence of other soluble salts of calcium, magnesium, and other metals, which can be removed only by chemical treatments.
What is the method used to determine the hardness of water?
The hardness of water is determined by titrating a known volume of water sample with EDTA, using Eriochrome Black T (EBT) as an indicator, in the presence of ammonium hydroxide ammonium chloride buffer (pH 10).
Why does hard water not give lather easily with soap?
Hard water does not give lather easily with soap because the hardness causing ions react with soap to form insoluble soap, which precipitates in the form of a scum.
How is the hardness of water expressed?
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What are the salts responsible for the hardness of water?
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Study Notes
Hardness of Water
- Temporary hardness is a type of water hardness that can be removed through boiling, whereas permanent hardness cannot be removed through boiling.
- The method used to determine the hardness of water is through titration with a standard solution of EDTA (ethylene diamine tetraacetic acid).
Effects of Hard Water
- Hard water does not give lather easily with soap because the calcium and magnesium ions in the water react with the soap to form an insoluble precipitate, known as scum, which consumes the soap.
Expression of Hardness
- The hardness of water is expressed in terms of milligrams per liter (mg/L) or parts per million (ppm) of calcium carbonate (CaCO₃).
Causes of Hardness
- The salts responsible for the hardness of water are primarily calcium and magnesium salts, such as calcium carbonate (CaCO₃), calcium bicarbonate (Ca(HCO₃)₂), magnesium carbonate (MgCO₃), and magnesium bicarbonate (Mg(HCO₃)₂).
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