Water Technology: Hardness of Water

Water containing soluble salts of calcium, magnesium, iron, and manganese that react with soap to form a scum, making it difficult to lather.

The amount of calcium and magnesium salts in water. It's measured by how much soap is needed to form a lather.

Hardness caused by dissolved calcium and magnesium bicarbonates. It can be removed by boiling the water.

Hardness caused by dissolved salts like chlorides, nitrates, and sulfates. Boiling won't remove this type of hardness.

The total amount of hardness in water. It's the sum of temporary and permanent hardness.

A unit to measure water hardness. It represents the number of parts of calcium carbonate equivalents per million parts of water.

The formation of a hard, crust-like deposit inside boilers due to the deposition of salts from hard water.

A measure of the calcium and magnesium salts dissolved in water, typically expressed in ppm (parts per million) of calcium carbonate equivalents.

Hardness caused by dissolved calcium and magnesium bicarbonates, which can be removed by boiling.

Hardness caused by dissolved calcium and magnesium chlorides, nitrates, and sulfates. Boiling does not remove it.

The sum of temporary and permanent hardness in water.

The process of adding EDTA (ethylenediaminetetraacetic acid) to a water sample until the color changes from pink to blue. This is used to measure permanent hardness.

The amount of EDTA consumed during titration, which directly relates to the concentration of calcium and magnesium in the water sample.

The amount of dissolved oxygen in water, essential for aquatic life but can cause corrosion in industrial settings.

A method to indirectly measure dissolved oxygen in water. It involves reacting dissolved oxygen with MnSO4 to form MnO(OH)2, which then oxidizes KI to I2. The liberated iodine is titrated with standard Na2S2O3.

A chemical used in Winkler's method to react with dissolved oxygen, forming a compound that can be used to oxidize potassium iodide. It's a divalent manganese salt.

A strong alkaline solution of potassium iodide used in Winkler's method. It reacts with MnSO4 to produce a compound that can oxidize potassium iodide.

A measure of water hardness expressed as parts per million (ppm) of calcium carbonate (CaCO3) equivalent hardness. For example, 1 ppm means 1 part of CaCO3 equivalent hardness is present in 1 million parts of water.

A measure of water hardness expressed as milligrams of calcium carbonate (CaCO3) equivalent hardness per liter of water.

A unit of hardness, equivalent to 10 mg/L of calcium oxide (CaO) or 17.848 ppm. Essentially, it measures the amount of hardness in water based on the calcium oxide content.

A method used to determine the total hardness of water using the chelating agent EDTA. The process relies on the complexation of calcium and magnesium ions with the indicator Eriochrome Black-T, followed by titration with EDTA.

The chemical compound disodium salt of Ethylene diamine tetra acetic acid. It is used as a chelating agent in the EDTA method for hardness determination, forming stable complexes with calcium and magnesium ions.

A chemical indicator used in the EDTA Method. It forms a wine-red complex with calcium and magnesium ions in the water sample, which changes to blue when all the hardness ions are chelated by EDTA.

A solution containing a known concentration of EDTA used to titrate the water sample in the EDTA method. The volume of EDTA required to cause a color change from pink to blue indicates the amount of hardness in the sample.

The amount of oxygen required in milligrams for the biological oxidation of organic matter present in one liter of wastewater over a 5-day incubation period at 20°C.

The amount of oxygen dissolved in a water sample.

A chemical used to titrate against iodine, which is liberated during DO measurement.

It's a technique used to measure DO in a water sample. MnSO4 and alkaline KI react with the DO, oxidizing Mn2+ to Mn4+, which is then titrated with Na2S2O3.

This step involves finding the DO in the water sample immediately, before any incubation. This is done by adding MnSO4 and alkaline KI to a known volume of the water sample and titrating with standardized Na2S2O3.

This step involves incubating a water sample for 5 days at 20°C, then following the same process as the blank titration to find the remaining DO.

The difference between the initial DO (from blank titration) and the final DO (from back titration) after incubation.

It's a measure of the amount of organic matter in the water that can be oxidized by microorganisms. A higher BOD indicates more organic matter present.

The amount of dissolved oxygen required to oxidize organic matter in a water sample over a 5-day incubation period at 20°C.

The amount of dissolved oxygen consumed during the oxidation of organic matter in a water sample. It's typically measured over a 5-day incubation period at 20°C.

A chemical reaction where silver sulfate (Ag2SO4) reacts with chloride ions (Cl-) present in wastewater, forming insoluble silver chloride precipitates (AgCl).

A process to determine the Chemical Oxygen Demand (COD) of wastewater samples. It involves oxidizing organic compounds using potassium dichromate (K2Cr2O7) in the presence of sulfuric acid (H2SO4) under reflux conditions. The amount of oxidizable organic matter is measured by titrating the remaining dichromate with a standard solution of ferrous ammonium sulfate (FAS).

A substance that speeds up a chemical reaction without being consumed itself. In COD determination, silver sulfate acts as a catalyst to oxidize organic compounds effectively.

A chemical compound used to prevent interference from chloride ions (Cl-) in the COD analysis. Mercuric sulfate forms a complex with chloride ions, preventing them from reacting with the oxidizing agent (dichromate) in the COD test.

A standard solution of ferrous ammonium sulfate (FAS) used for titrating the remaining dichromate (K2Cr2O7) in the COD determination. The volume of FAS solution used is directly proportional to the amount of organic matter present in the wastewater sample.