Question

Hardness of water is commonly expressed in the parts of (1) Calcium chloride (2) Calcium bicarbonate (3) Calcium hydroxide (4) Calcium carbonate

Short answer

Option (4) Calcium carbonate

Step-by-step solution

Identify the Common Expression

The hardness of water is typically expressed in terms of the concentration of calcium carbonate (CaCO3) equivalents because it is a standard and makes it easier to compare and calculate the hardness imparted by different compounds.

Evaluate Each Option

Consider each compound in the options: Calcium chloride (CaCl2), Calcium bicarbonate (Ca(HCO3)2), Calcium hydroxide (Ca(OH)2), and Calcium carbonate (CaCO3).

Select the Correct Option

Given that hardness is usually expressed in the parts of calcium carbonate (CaCO3), we select option (4) as the correct answer.

Key concepts

calcium carbonate

Calcium carbonate (CaCO3) is a common compound found in rocks, and it is the main component of shells of marine organisms, snails, and eggs. In water chemistry, it plays a crucial role. Hardness in water is commonly expressed in terms of calcium carbonate equivalents. This is because calcium carbonate is a standard compound, making calculations and comparisons more straightforward. When various compounds like calcium chloride or calcium bicarbonate are present in water, their hardness is converted into calcium carbonate equivalents. This means that even if the actual compound isn't calcium carbonate, we use it to express the 'hardness' to keep things simple and standardized. This expression helps in ensuring uniformity in water quality assessments across different regions and applications.

water hardness measurement

Water hardness is an important parameter to measure for both domestic and industrial purposes. Hard water contains high levels of dissolved minerals, primarily calcium and magnesium. The measurement of water hardness typically uses the concentration of calcium carbonate (CaCO3) as a reference. This is measured in parts per million (ppm) or milligrams per liter (mg/L). There are a few common methods to measure water hardness:

• Titration with a chelating agent such as EDTA (Ethylenediaminetetraacetic acid).
• Using a water hardness test strip which changes color based on the hardness level.
• Complexometric titration, which involves forming a stable complex between the metal ions and a reagent.

Measuring water hardness helps in understanding the scaling potential of water, which is crucial for maintaining plumbing, appliances, and in manufacturing processes.

chemical compounds in water

Water in nature contains various dissolved chemical compounds, some of which contribute to its hardness. These can include:

• Calcium Chloride (CaCl2).
• Calcium Bicarbonate (Ca(HCO3)2).
• Calcium Hydroxide (Ca(OH)2).
• Magnesium Salts, which also contribute to hardness.

Each of these compounds, when present in water, increases the hardness level because they release calcium and magnesium ions. However, for simplicity and standardization, the hardness contributed by these different compounds is usually converted into the equivalent amount of calcium carbonate (CaCO3). This helps in comparing the hardness levels and understanding the potential impacts on water use. For example, high hardness water can cause scaling in boilers and hot water pipes, which is why it's essential to measure and manage it.