Hardness Of Water In Chemistry
In chemistry, the hardness of water refers to the concentration of dissolved mineral ions, mainly calcium and magnesium ions, in the water.
In chemistry, the hardness of water refers to the concentration of dissolved mineral ions, mainly calcium and magnesium ions, in the water.
Hard water is characterized by high concentrations of these ions, which can interfere with the lathering of soaps and detergents, and cause mineral buildup in plumbing and appliances.
The hardness of water can be expressed in terms of two types of hardness: temporary and permanent hardness.
Temporary hardness is caused by the presence of dissolved bicarbonate ions, which can be removed by boiling the water, causing the bicarbonate ions to decompose into carbonate and water.
Permanent hardness, on the other hand, is caused by the presence of dissolved calcium and magnesium ions in the water, which cannot be removed by boiling alone.
The total hardness of water is usually expressed in terms of the concentration of calcium carbonate (CaCO3) in the water, in units of milligrams per liter (mg/L) or parts per million (ppm).
Water with a hardness of less than 60 mg/L is considered soft, while water with a hardness of more than 120 mg/L is considered hard.
Water with a hardness between these values is considered moderately hard.
The chemical formula for water hardness refers to the concentration of dissolved calcium and magnesium ions in water.
The general formula for the reaction of calcium or magnesium ions with soap can be expressed as:
Ca2+ (aq) + 2RO- (aq) → (RO)2Ca (s)
Mg2+ (aq) + 2RO- (aq) → (RO)2Mg (s)
where Ca2+ and Mg2+ are the dissolved calcium and magnesium ions, RO- represents the anion of the soap, and (RO)2Ca and (RO)2Mg are the precipitates formed when the calcium and magnesium ions react with the soap anions.
The total water hardness is usually expressed as the concentration of calcium carbonate (CaCO3) in the water, which is calculated based on the concentration of calcium and magnesium ions.
The formula for the calculation of water hardness in terms of CaCO3 is:
Water hardness (mg/L as CaCO3) = 2.5 x Ca2+ + 4.1 x Mg2+
where [Ca2+] and [Mg2+] are the concentrations of calcium and magnesium ions, respectively, in units of milligrams per liter (mg/L) or parts per million (ppm).
