The correct answer is option 2. Calcium and Magnesium ions.
The hardness of water is primarily caused by the presence of dissolved calcium \((Ca^{2+})\) and magnesium \((Mg^{2+})\) ions. Here's an explanation of why calcium and magnesium ions contribute to water hardness:
1. Presence of Calcium and Magnesium: Calcium and magnesium ions are commonly found in natural water sources such as rivers, lakes, and groundwater. These ions originate from the dissolution of minerals and rocks in the Earth's crust, particularly calcium carbonate \((CaCO_3)\) and magnesium carbonate \((MgCO_3)\).
2. Calcium and Magnesium Salts: Calcium and magnesium ions can also be present in water as salts, such as calcium sulfate \((CaSO_4)\) and magnesium sulfate \((MgSO_4)\), or as bicarbonates, such as calcium bicarbonate \((Ca(HCO_3)_2)\) and magnesium bicarbonate \((Mg(HCO_3)_2)\).
3. Formation of Hard Water: When water containing calcium and magnesium ions evaporates or comes into contact with carbon dioxide \((CO_2)\) from the atmosphere, chemical reactions occur that lead to the precipitation of calcium carbonate \((CaCO_3)\) and magnesium carbonate \((MgCO_3)\) minerals. These minerals can form scale deposits on surfaces such as pipes, plumbing fixtures, and appliances, causing problems such as reduced water flow and decreased efficiency of heating systems.
4. Effects of Hard Water: Hard water can cause various issues in domestic and industrial settings. For example, it can interfere with the lathering of soap, resulting in reduced cleaning effectiveness and leaving soap scum on surfaces. Additionally, the formation of scale deposits in pipes and appliances can lead to decreased water flow, reduced heat transfer efficiency, and increased energy consumption.
5. Measurement of Hardness: Water hardness is typically measured in terms of the concentration of calcium and magnesium ions, expressed in units such as parts per million (ppm) or milligrams per liter (mg/L) of calcium carbonate equivalents \((CaCO_3)\).
In summary, the presence of dissolved calcium and magnesium ions, primarily originating from minerals and rocks, is responsible for the hardness of water. These ions can lead to various issues in domestic and industrial applications, making water-softening treatments necessary in some cases to mitigate the effects of hardness. |
