Question

In the determination of hardness of water by complexometric, 20 ml of standard hard water containing 0.1g of CaCO3 per 100 ml consumed 15 ml of EDTA solution. 100 ml of hard water sample consumed 12 ml of EDTA solution. After boiling and filtering the same water sample consumed 6ml of EDTA solution. Calculate the temporary and permanent hardness of water.​

Answer 1

Main Answer:

The temporary hardness of water is 240 mg/L, and the permanent hardness is 60 mg/L.

Step-by-step explanation:

In complexometric titration, the consumption of EDTA (Ethylenediaminetetraacetic acid) is used to determine the hardness of water. The difference in the volume of EDTA solution consumed before and after boiling and filtering represents the temporary hardness.

In this case, the initial consumption was 12 ml, and after boiling and filtering, it reduced to 6 ml. The difference (12 ml - 6 ml) is 6 ml, which corresponds to the volume of EDTA solution required to titrate the temporary hardness.

Now, knowing that 1 ml of EDTA solution is equivalent to 1 mg of CaCO₃, the temporary hardness is calculated as 6 mg/L (6 ml * 1 mg/L).

To find the permanent hardness, the volume of EDTA solution consumed by the standard hard water is subtracted from the initial consumption by the water sample. The difference (15 ml - 12 ml) is 3 ml, equivalent to the volume of EDTA solution required to titrate the permanent hardness. Converting this to mg/L (3 ml * 1 mg/L) gives the permanent hardness as 3 mg/L.

Understanding the distinction between temporary and permanent hardness is crucial for water quality assessment. Temporary hardness is due to the presence of bicarbonates, which can be removed by boiling, while permanent hardness remains even after boiling and is often attributed to sulfates and chlorides of calcium and magnesium.