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Hardness

Hardness. CE 370 - Lab. Definition.

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Hardness

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  1. Hardness CE 370 - Lab

  2. Definition Hardness of water is a measure of its capacity to precipitate soap and is caused mainly by the presence of divalent cations of calcium (Ca2+) and magnesium (Mg2+). Other multivalent cations also cause water hardness such as Fe3+, Sr2+, Zn2+, Mn2+.

  3. How does soap precipitate? 2 NaC15H31COO + Ca2+ Ca(C15H31COO)2 + 2 Na+ Fatty Acid Soap Precipitate

  4. Types of Hardness Hardness can be categorized by either of two methods: • calcium versus magnesium hardness • carbonate versus non-carbonate hardness Hardness caused by calcium is called calcium hardness and hardness caused by magnesium is called magnesium hardness. Calcium and magnesium are normally the only significant minerals that cause hardness, so it is generally assumed that: Total harness = Ca2+ hardness + Mg2+ hardness

  5. Carbonate Hardness Carbonate hardness is caused primarily by the bicarbonate salts of calcium and magnesium, which are calcium bicarbonate, Ca(HCO3)2, and magnesium bicarbonate Mg(HCO3)2. Calcium and magnesium combined with carbonate (CO3) also contribute to carbonate hardness.

  6. Non-Carbonate Hardness Non-carbonate hardness is a measure of calcium and magnesium salts other than carbonate and bicarbonate salts. These salts ate calcium sulfate (CaSO4), calcium chloride (CaCl2), magnesium sulfate (MgSO4), and magnesium chloride (MgCl2). Therefore, non-carbonate hardness is hardness exceeding carbonate hardness, or: Non-Carbonate hardness = Total hardness – carbonate hardness.

  7. Environmental and Health Concerns • Hard water is mainly an aesthetic concern because of the unpleasant taste that a high concentration of calcium and other ions give to water. • It also reduces the ability of soap to produce a lather. • Causes scale formation in pipes and on plumbing fixtures. • Soft water can cause pipe corrosion and may increase the solubility of heavy metals such as copper, zinc, lead and cadmium in water. • In some agricultural areas where lime and fertilizers are applied to the land, excessive hardness may indicate the presence of other chemicals such as nitrate.

  8. Purpose To become familiar with the concept of hardness and its measurement in water.

  9. Materials Burette, 25 ml Porcelain dish Magnetic stirrer and rod Pipette Measuring cylinder, 100 ml Ammonia buffer solution Sodium hydroxide solution Eriochrome black T indicator Murexide (Ammonium purpurite) 0.01M EDTA (Ethylene Diamine Tetra Acetate, Sodium Salt) Raw water sample Treated water sample

  10. ProcedureEDTA Titrinmetric Method 1. Analysis for hardness is performed in two stages by estimating Total and Calcium Hardness separately and the Magnesium Hardness is calculated from the difference between the two. 2. Pipette exactly 25 ml of raw water sample into a porcelain dish and drop in a magnetic rod. 3. Mount of 50 ml burette and fill it to the mark with 0.01M EDTA solution. 4 Add 1-2 ml of Ammonia buffer, 0.2 g Eriochrome Black T indicator and add slowly 0.01M EDTA solution until the color of the solution changes from wine red to blue. Record the volume of EDTA solution and calculate Total Hardness. 5 Add 1-2 ml sodium hydroxide buffer and 0.2 g Murexide indicator into 25 ml of raw water sample and add 0.01M EDTA solution slowly till the color of the solution changes from purple to violet. Record the volume of EDTA solution and calculate Calcium Hardness. 6 Repeat titration for the treated water and calculate the hardness.

  11. Calculations Total hardness and calcium hardness are both calculated using the following equation: Hardness (EDTA) as mg/l CaCO3 = • A = ml EDTA solution used • B = mg CaCO3 equivalent to 1 ml EDTA titrant Magnesium Hardness as mg/l CaCO3 = Total Hardness - Calcium Hardness

  12. Report format is very important • Adhere to given formats • Do not copy from others • Solve Problems in Handouts • Quiz next week (all labs)

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