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"ard water can be softened by many techni6ues we will be studying. Water treatmentcan lower the concentration of hard ions to an acceptable level. 'on e2change cansubstitute softer sodium ions for the hard ions, making the water soft but also corrosive.

Once an acceptable level of hardness has been achieved, scale formation can be

controlled by various additives

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Once scales are formed they can be removed slowly by changing the water chemistry andactually dissolving the formed scale. cales can be mechanically removed by reaming, atype of mechanical machining inside the pipes. cales can also be removed by acidi8ingwith strong mineral acids, such as "Cl, containing inhibitors that will prevent the pipesfrom being dissolved.

'f the scale contains e , ferrous sulphide, which is a black colored band of precipitate,then e2treme care has to be followed since deadly " 1 , hydrogen sulphide, gas isliberated on acidi8ing.

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To determine the hardness of a water sample, technologists use the EDTA(ethylenediaminetetraacetic acid) titration. &/T disodium salt is a soluble salt thatreacts readily with all 91 ions, namely Ca+2, Mg+2, Fe+2 and Ba+2. The &/T anionreacts 6uickly with any 91 metal to form a soluble metal &/T comple2. &/T is calleda chelating or sequestering agent since it will react with and tie up heavy metal ions andrender them harmless to humans and water systems.

ll metal#&/T salts are colourless and re6uire an indicator to tell us when the reactionis over. 7arious hardness indicators have been developed. They all tell the operator

when the titration is complete. "ardness indicators are large comple2 organic dyes thatreact with &/T to form coloured comple2es. &/T reacts preferentially with highlymobile metal ions, but once they are all tied up, the &/T will react with the slowmoving, massive dye molecules to give an endpoint. s a conse6uence, endpoints arechallenging.

We will use &riochrome :lack T for the total hardness endpoint, which includes the sumof calcium and magnesium ions. !ure2ide indicator gives us the calcium endpoint.

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PROCEDURE

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0. ill a 4@ m) burette with @.@0 ! &/T solution, making sure the tip is full andfree of air bubbles. et tart volume.

1. dd 4@.@@ m) of an unknown hard water solution into a 0@@ m) beaker.

3. Obtain !agnetic tirrer from &6uipment menu. ?lace beaker on stirrer. 'ncreasetir from the conte2t menu.

. dd m) of 0.@ ! odium "ydro2ide.

4. dd 0@@ mg of !ure2ide indicator.

5. Titrate with the @.@0 ! &/T until the colour changes from salmon pink toorchid purple. *ecord all pertinent data on data sheet. *ead burette to 9A# @.0@m).

%. *epeat the titration until the final volumes agree to 9A# @.1@ m).

TOT) " */+& /&T&*!'+ T'O+

0. ill a 4@ m) burette with O.0 ! &/T solution, making sure the tip is full and free of air bubbles. et tart volume.

1. dd 4@.@@ m) of an unknown hard water solution into a 0@@ m) beaker.

3. Obtain !agnetic tirrer from &6uipment menu. ?lace beaker on stirrer. 'ncrease tirfrom the conte2t menu.

. dd 0@ m) of mmonia to the beaker.

4. dd 0@@ mg of &riochrome :lack T indicator.

. Titrate with the @.@0 ! &/T until the colour changes from wine red to pure blue.*ecord all pertinent data on data sheet. *ead burette to 9A# @.0@ m).

5. *epeat the titration until the final volumes agree to 9A# @.1@ m).

'ncidentally, &/T is a common food additive that is used in salad dressing and otherspicy condiments. 't is totally safe for sink disposal.

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BE CAREFUL WITH CALCIUM AND TOTAL HARDNESS BUFFERS

Spills on your skin or !" #loor $r" %orrosi&" $n' s!oul' (" )$s!"' o## )i ! so$p $n')$ "r i**"'i$ "ly+ B" sur" o )"$r your s$#" y ,l$ss"s $ $ll i*"s $s p"r*$n"n

(lin'n"ss %$n "$sily r"sul #ro* s ron, ($s"s spl$s!"' in o your "y"s+ DO NOT )"$r%on $% l"ns"s+ Ask your ins ru% or #or #ur !"r in#or*$ ion+

REPORT -+ PLEASE SHOW DETAILED CALCULATIONS FOR THE FOLLOWING.

!olarity of calcium in unknown- ppm calcium in unknown- ppm calcium carbonate in unknown-

7olume of &/T for magnesium portion- ppm magnesium in unknown

Questions

0. corrosion technologist pipetted a 0@@.@@ m) hard water sample and titrated itwith 3%.5 m) of @.@0 ! &/T solution for a total hardness endpoint, and 1B.31m) of @.@0 ! &/T solution for a calcium endpoint. Calculate the concentrationof magnesium and calcium in ppm. *ecord your answers as ppm Mg2+, and Ca2+ espectively. or each answer indicate the ppm as CaCO3 also.

1. Write and balance the reaction between the magnesium ion, the bicarbonate ionand heat.

3. Write and balance the scale removal reaction involving the scale generated in6uestion 1 with HCl.

. 'n a sour water system (H2 ) there is an opportunity for ferrous sulphide to formalong with the calcium and magnesium carbonate scales. 'f acidi8ing is used toclean away scales, what danger e2istsD 'ndicate this by using a balanced reaction.

4. 'n the field, where the scale in 6uestion is removed by acidi8ing, what precautions should be takenD

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CALCIUM CONTENT OF A HARD WATER

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CALCIUM AND MAGNESIUM CONTENT OF A HARD WATER

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