HardnessHardness

CE 370 - LabCE 370 - Lab

DefinitionDefinition

Hardness of water is a measure of its capacity to Hardness of water is a measure of its capacity to precipitate soap and is caused mainly by the precipitate soap and is caused mainly by the presence of divalent cations of calcium (Capresence of divalent cations of calcium (Ca2+2+) ) and magnesium (Mgand magnesium (Mg2+2+). Other multivalent ). Other multivalent cations also cause water hardness such as Fecations also cause water hardness such as Fe3+3+, , SrSr2+2+, Zn, Zn2+2+, Mn, Mn2+2+. .

How does soap precipitate?How does soap precipitate?

2 NaC2 NaC1515HH3131COO + CaCOO + Ca2+2+ Ca(C Ca(C1515HH3131COO)COO)22 + 2 Na + 2 Na++

Fatty Acid Fatty Acid Soap PrecipitateSoap Precipitate

Types of HardnessTypes of Hardness

Hardness can be categorized by either of two methods:Hardness can be categorized by either of two methods: calcium versus magnesium hardnesscalcium versus magnesium hardness carbonate versus non-carbonate hardnesscarbonate versus non-carbonate hardness

Hardness caused by calcium is called calcium hardness Hardness caused by calcium is called calcium hardness and hardness caused by magnesium is called and hardness caused by magnesium is called magnesium hardness. Calcium and magnesium are magnesium hardness. Calcium and magnesium are normally the only significant minerals that cause normally the only significant minerals that cause hardness, so it is generally assumed that:hardness, so it is generally assumed that:

Total harness = CaTotal harness = Ca2+2+ hardness + Mg hardness + Mg2+2+ hardness hardness

Total Hardness

Calcium Hardness

Magnesium Hardness

CarbonateCa(HCO3)2 ,CaCO3

Non-CarbonateMgCl2 , MgSO4

CarbonateMg(HCO3)2 ,MgCO3

Non-CarbonateCaCl2 , CaSO4

Carbonate Hardness

Non-Carbonate Hardness

Carbonate HardnessCarbonate Hardness

Carbonate hardness is caused primarily by the Carbonate hardness is caused primarily by the bicarbonate salts of calcium and magnesium, bicarbonate salts of calcium and magnesium, which are calcium bicarbonate, Ca(HCOwhich are calcium bicarbonate, Ca(HCO33))22, and , and

magnesium bicarbonate Mg(HCOmagnesium bicarbonate Mg(HCO33))22. Calcium . Calcium

and magnesium combined with carbonate (COand magnesium combined with carbonate (CO33) )

also contribute to carbonate hardness.also contribute to carbonate hardness.

Non-Carbonate HardnessNon-Carbonate Hardness

Non-carbonate hardness is a measure of calcium Non-carbonate hardness is a measure of calcium and magnesium salts other than carbonate and and magnesium salts other than carbonate and bicarbonate salts. These salts ate calcium sulfate bicarbonate salts. These salts ate calcium sulfate (CaSO(CaSO44), calcium chloride (CaCl), calcium chloride (CaCl22), magnesium ), magnesium

sulfate (MgSOsulfate (MgSO44), and magnesium chloride ), and magnesium chloride

(MgCl(MgCl22). Therefore, non-carbonate hardness is ). Therefore, non-carbonate hardness is

hardness exceeding carbonate hardness, or:hardness exceeding carbonate hardness, or:

Non-Carbonate hardness = Total hardness – carbonate hardness.Non-Carbonate hardness = Total hardness – carbonate hardness.

Total Hardness (mg/L as CaCO3)

Soft 0-30

Moderately soft 30-60

Moderately hard 60-120

Hard 120-180

Very hard > 180

Environmental and Health ConcernsEnvironmental and Health Concerns

Hard water is mainly an aesthetic concern because of Hard water is mainly an aesthetic concern because of the the unpleasant tasteunpleasant taste that a high concentration of that a high concentration of calcium and other ions give to water. calcium and other ions give to water.

It also It also reduces the ability of soap to produce a lather.reduces the ability of soap to produce a lather. Causes Causes scale formationscale formation in pipes and on plumbing in pipes and on plumbing

fixtures. fixtures. Soft water can cause pipe corrosionSoft water can cause pipe corrosion and may and may

increase the increase the solubility of heavy metalssolubility of heavy metals such as such as copper, zinc, lead and cadmium in water. copper, zinc, lead and cadmium in water.

In some agricultural areas where lime and fertilizers In some agricultural areas where lime and fertilizers are applied to the land, are applied to the land, excessive hardness may excessive hardness may indicate the presence of other chemicals such as indicate the presence of other chemicals such as nitrate.nitrate.

PurposePurpose

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

MaterialsMaterials

Burette, 25 mlBurette, 25 mlPorcelain dishPorcelain dishMagnetic stirrer and rodMagnetic stirrer and rodPipettePipetteMeasuring cylinder, 100 mlMeasuring cylinder, 100 mlAmmonia buffer solutionAmmonia buffer solutionSodium hydroxide solutionSodium hydroxide solutionEriochrome black T indicatorEriochrome black T indicatorMurexide (Ammonium purpurite)Murexide (Ammonium purpurite)0.01M EDTA (Ethylene Diamine Tetra Acetate, Sodium Salt)0.01M EDTA (Ethylene Diamine Tetra Acetate, Sodium Salt)Raw water sampleRaw water sampleTreated water sample Treated water sample

ProcedureProcedureEDTAEDTA Titrinmetric Method Titrinmetric Method

1.1. Analysis for hardness is performed in two stages by estimating Total and Calcium Analysis for hardness is performed in two stages by estimating Total and Calcium Hardness separately and the Magnesium Hardness is calculated from the difference Hardness separately and the Magnesium Hardness is calculated from the difference between the two.between the two.

2.2. Pipette exactly 25 ml of raw water sample into a porcelain dish and drop in a magnetic Pipette exactly 25 ml of raw water sample into a porcelain dish and drop in a magnetic rod.rod.

3.3. Mount of 50 ml burette and fill it to the mark with 0.01M EDTA solution.Mount of 50 ml burette and fill it to the mark with 0.01M EDTA solution.

44 Add 1-2 ml of Ammonia buffer, 0.2 g Eriochrome Black T indicator and add slowly 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. 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.Record the volume of EDTA solution and calculate Total Hardness.

55 Add 1-2 ml sodium hydroxide buffer and 0.2 g Murexide indicator into 25 ml of raw 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 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 from purple to violet. Record the volume of EDTA solution and calculate Calcium Hardness.Hardness.

66 Repeat titration for the treated water and calculate the hardness. Repeat titration for the treated water and calculate the hardness.

CalculationsCalculations

Total hardness and calcium hardness are both Total hardness and calcium hardness are both calculated using the following equation:calculated using the following equation:

Hardness (EDTA) as mg/l CaCOHardness (EDTA) as mg/l CaCO33 = =

A = ml EDTA solution usedA = ml EDTA solution usedB = mg CaCOB = mg CaCO33 equivalent to 1 ml EDTA titrant equivalent to 1 ml EDTA titrant

Magnesium Hardness as mg/l CaCOMagnesium Hardness as mg/l CaCO33 = Total Hardness - Calcium Hardness = Total Hardness - Calcium Hardness

sampleml

1000BA

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