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الرئيسية / Labs and Analysis for Water Quality / تحاليل المياه – تجارب المعايرة

تحاليل المياه – تجارب المعايرة

Alkalinity1     القلوية

توجد  قلوية المياة نتيجة لوجود أملاح الكربونات والبيكربونات والهيدروكسيد وهي تساعد في عملية التجميع للشبة  (coagulation)  وذلك لان الشبة حامضية والقلوية هامة لتحرير أيون الهيدروكسيد اللازم لعملية

التي تتم علي أيون الهيدروكسيد ولكن وجود القلوية يجب ألا يزيد عن مدي معين حيث أن وجود الهيدروكسيد في المياه ضار بأغشية الحلق وقد يسبب التهاب عند الشرب وكذلك عند وجود الكربونات بكميات ظاهرة أ البيكربوناتما فلا ضرر منها وهي من المكونات الطبيعية للمياه ونجد أن المياة الغازية تحتوي علي صودا ومع ذلك فهي محببة وفي معظم القياسات  تتواجد البورات والفوسفات والسيليكات وبعض القواعد الاخري ولكن بنسبة قليلة جدا

هذه الطريقة تطبق لتعيين القلوية ومعايرتها فى جميع  عينات الماء حتى فى عينات الصرف الصحى

Principle

Alkalinity is a measure of water’s ability to neutralize acids. In most types of water, alkalinity is the result of bicarbonates (HCO3), carbonates (CO32-(, and hydroxides (OH) of the metals calcium, magnesium, and sodium.

Hydroxyl ions present in a sample as a result of dissociation or hydrolysis of solutes react with additions of standard acid. Alkalinity thus depends on the end-point pH used. For methods of determining inflection points from titration curves and the rationale for titrating to fixed pH end points.

Interference

Soaps, oily matter, suspended solids, or precipitates

Equipments ,Reagent and Reference material 

  • Equipments

Burette 25 ml. -Pipette 10 ml- Measuring flask 50 ml -Erlenmeyer Flask 250 ml

.Reagent

  • H2SO4 (0.02 N)

Add 0.54 ml of conc. H2SO4 in 1L of dis.Water.

  • O indicator

Dissolve 0.5 gm M.O powder in 1L of dis. Water.

  • Bromcresol green indicator solution, pH 4.5 indicator

Dissolve 100 mg bromcresol green, sodium salt, in 100 mL distilled water.

  • Mixed Bromcresol Green-Methyl Red indicator solution:
  1. Use either the aqueous or the alcoholic solution.
  2. Dissolve 100 mg Bromcresol Green sodium salt and 20 mg methyl red sodium salt in 100mL distilled water.
  3. Dissolve 100 mg Bromcresol Green and 20 mg methyl red in 100 ml 95% ethyl alcohol or isopropyl alcohol.
  • Phenolphthalein

Dissolve 0.5 gram of phenolphthalein  in 50 ml of ethyl alcohol 95% then complete volume to 100 ml with distilled water which was previously boiled and cooled, then add drops of sodium Hydroxide solution (0.02 N) until the onset of a very light pink color.

  • Standard Na2CO3 soln (0.02 N).

Dissolve 1g anhydrous Na2CO3 in 1L dis.Water.( 1ml of Na2CO3 = 1mg CO3 )=1000 mg/l (dry Na2CO3 powder in oven at 250 0c for two hours) stable for 1 week.

  • Standard soln
  • Take 10 ml of St. Na2CO3 in100ml dis. water, 100 mg/l Standard is Prepared.

Procedures

Standardization of standard

  • Fill burette with Sulphuric acid solution.
  • Take 10 ml of Standard Na2CO3 soln (0.02 N)
  • in flask and add 0.1 ml Bromcresol green indicator or Methyl orange indicator or Mixed Bromcresol Green-Methyl Red indicator solution.
  • Start titration against H2SO4 solution, till reach pale blue end point.
  • Record the volume taken from burette in data presentation sheet.

A = g Na2CO3 weighed into 1-L flask, B = ml Na2CO3 solution taken for titration, and     C = ml acid used.

           Sample measurement

  • Fill burette with Sulphuric acid solution.
  • Take 50 ml of sample in flask and add 0.1 ml Bromcresol green indicator or Methyl orange indicator Mixed Bromcresol Green-Methyl Red indicator solution.
  • Start titration against H2SO4 solution, till reach pale blue end point.
  • Record the volume taken from burette in data presentation sheet.

Calculation

Calculate Alkalinity in the samples by

Where:

A = mL standard acid used &  N= Normality of standard acid used

.

Other Calculation:

Alkalinity = volume of H2SO4 solution taken*eq.wt of CaCO3*Normality of H2SO4*(50/1000)

               = volume of H2SO4 solution taken*50*0.02*20= volume of H2SO4 solution taken*20

Quality Control

The laboratory applies the quality control program as follow:

Laboratory-Fortified Blank.

A laboratory-fortified blank is a reagent water sample to which a known concentration of the analytes of interest has been added. it is used to evaluate laboratory performance and analyte recovery in a blank matrix. As a minimum, include one LFB with each sample set (batch) .

Laboratory Fortified matrix (LFM):

The analytical chemist conduct spiked recovery each use to measure the accuracy of the analytical process.

 

 قياس القلوية بالنسبة لمعالجة المياه تتم بصفة يومية وذلك لان القلوية تعتبر من اكثر البراهين علي اضافة الشبة حيث أنها تقلل القلوية بنسبة  0.45 / جم شبة للمياه العكرة, زيادة القلوية فى عملية التنديف بصورة جيدة وذلك نتيجة لزيادة ايون الهيدروكسيد

Reactions of different kind:-                                                                  

1- Bicarbonate

2NaHCO3 + 2H2SO4 → Na2SO4 + 2H2O +CO2

2-Carbonate

2Na2CO3  + H2SO4 → 2NaHCO3 + Na2SO4

3-Hydroxide                                                                                                                   

2NaOH + H2SO4 → Na2SO4 + 2H2O

الاحتياطات والشروط المطلوبة عند وجود كلور بالعينة

  • يجب تجنب الرج والهز
  • يجب ان يزال الكلور الحر بالعينة( اذا كان اكثر من 1.8 ) باستخدام نقطة من محلول ثيوسلفات الصوديوم(0.1M) لان وجوده يجعل لون الميثيل يختفى بمجرد اضافته للعينة .

جمع وحفظ العينة :-

تجمع العينة فى اوعية نظيفة ويتم تقدير القلوية فى خلال فترة وجيزة لتجنب التغيرات البيولوجية والفيزيقية التى قد تنتج عن التخزين.

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Total Hardness2 العسر الكلى

                                                                                                                                                   Scope

  • This test procedure is applied to all types of water samples either Raw, treated, Ground

Principle

  • The ethylene diaminetetraacetic acid (EDTA) titrimetric method can be used to determine total hardness or calcium hardness. This method is designed for the routine determination of hardness in drinking water.
  • Ethylene Diamine Tetra Acetic acid and its sodium salts (EDTA) form a chelated soluble complex when added to a solution of certain metal cations. If small amount of dye such as Eriochrome black T is added to an aqueous solution containing calcium and magnesium ions at ph of 10.0 ±0.1, the solution becomes wine red. If EDTA is added as titrant, the calcium and magnesium will be complexes and the solution turns from wine red to blue, marking the end point of the titrant. Magnesium ion must be present to yield a satisfactory end point. To insure this a small amount of complex metrically neutral magnesium salt of EDTA is added to the buffer. This automatically introduces sufficient magnesium and eliminates the need for blank correction.
  • when hardness numerically is greater than the sum of carbonate and bicarbonate alkalinity, that amount of hardness equivalent to the total alkalinity is called “Carbonate hardness”, the amount of hardness in excess of this is called ‘ Non carbonate hardness’
  • When the hardness numerically is equal to or less than the sum of carbonate and bicarbonate alkalinity, all hardness is carbonate hardness and non-carbonate hardness is absent.
  • Calcium and magnesium in water cause hardness. Total hardness is defined as the sum of calcium and magnesium concentrations, both expressed as calcium carbonate in mg/L.

Definition

Water hardness  was understood to be  ameasure  of the capacity of water to precipitate Soap, by calcium                                                                                       and magnesium ions present

  • Total hardness: is defined as the sum of calcium and magnesium concentrations, both expressed as calcium carbonate, in milligrams per liter.

تحتوي المياة علي أملاح  االكالسيوم والماغنسيوم في صورة البيكربونات أو الكلوريدات أو الكبريتات وتبعا لتركيز هذه الاملاح  تقسم المياه الي :-

  • مياه يسرة :- وتحتوي علي املاح الكالسيوم والماغنسيوم بتركيز اقل من 75 مجم/لتر
  • مياه متوسطة العسر :- تركيز املاح العسر بين 75 – 100 مجم / لتر
  • مياه عسرة :- تركيز املاح العسر بين 150 – 300 مجم / لتر
  • مياه شديدة العسر :- تركيز املاح العسر اكبر من 300 مجم / لتر

 

  • انواع عسر المياه:-

1- العسر الكربوني (الغير دائم او المؤقت )carbonate hardness

ويرجع الي ذوبان املاح البيكربونات او الكربونات Ca(HCO3)(CaCO3)

وكربونات الكالسيوم شحيحة الذوبان إلا عند درجات الحرارة العادية.

Non – carbonate hardness           2 – العسر غير الكربوني ( الدائم )

ينشا عن ذوبان املاح الكلوريدات والكبريتات للكالسيوم والماغنسيوم وهذه الاملاح تتاثر بارتفاع درجة  الحرارة حيث يقل ذوبان الاملاح الى درجة كبيرة ولكنها لاتتحل

          التداخلات  Interference

  • Suspended or colloidal organic matter may interfere with the end point. Eliminate this interference by evaporating the sample to dryness on a steam bath and heating in a muffle furnace at 5500 until the organic matter is completely oxidized. Dissolve the residue in 20 mL in HCL, neutralize to pH 7 with NaOH and make up to 50 ml with distilled water. Cool to room temperature and continue according to the general procedure.

Equipment

  • Digital Balance (Mettler Tolido)
  • Cylinder 100ml.
  • Measuring flasks(1000ml, 2000ml )capacity.
  • Conical flasks 250ml capacity
  • Pipettes: 10ml graduated: 50ml bulped.
  • Digital Burette

          Chemicals and reagents

Buffer Solution

  • Dissolve 9 g ammonium chloride (NH4Cl) in 143 mL concentrated ammonium hydroxide (NH4OH). Add 1.25 g magnesium salt of EDTA (available commercially) and dilute to 250 ml with distilled water.

Indicator

Eriochrome black T: dissolve 0.5 g dye in 100 g 2,2′,2”-nitrilotriethanol(also called triethanolamine) or 2-methoxymethanol (also called ethylene glycol monomethyl ether).

Standard EDTA titrant 0.01M

  • Dissolve 723 gm of EDTA (Ethylene diamine tetra acetic acid disodium salt) in distilled water and complete to 1000 ml. Store in polyethylene or borosilicate glass bottle. Use grade EDTA

Standard Calcium Solution

  • Weigh 0 gm anhydrous CaCO3 powder into 500 ml Erlenmeyer flask, add a little at a time 1: 1 HCl until all CaCO3 has dissolved. Add 200 ml distilled or milliQ water and boil for a few minutes to expel Co2 .
  • Add a few drops of methyl red indicator then adjust to the intermediate orange color by adding 3 N NH4OH  or 1:1 HCl as required
  • Dilute to 1000 ml. (1ml= 1mg CaCO3)

          Procedure

Standardization of 0.01M EDTA:-

  • Make Standardization for 0.01 EDTA by CaCO3 solution (1ml= 1 mg CaCO3) and make adjustment for 01 M. EDTA. Calculate the correction factor (CF)of EDTA standard.

Analytical Procedure:-

  • Select a sample volume that requires less than 15 ml EDTA titrant and complete titration within 5 minutes, measured from time of buffer addition.
  • to 50 ml sample add 1-2 ml buffer solution to give pH ( 10 to 10.1)
  • add an appropriate amount of indicator powder.
  • Make titration with continues stirring until the last reddish tinge disappears. Add the last few drops at 3-5s intervals; at the end point the solution normally is blue.

          Calculation

  • Hardness (EDTA) as mg CaCO3 /L =

               where ;  A= ml titration for sample & B= mg CaCO3 equvilent to 1 ml EDTA titrant

   Or     Total Hardness = ml of EDTA x 20xCF

       ( if 50ml of sample is used(

Quality control

 Laboratory Fortified matrix (LFM):

  • One sample is select from each batch to be fortified with known concentration, the fortified sample is analyze and the sample is analyze without fortification.

      Duplicate sample:

  • at least 10% of each sample batch shall be analyze in duplicate.

                            Relative percent difference (RPD)

    Laboratory-Fortified Blank or  lab. control sample (LCS)

  • A laboratory-fortified blank is a reagent water sample to which a known concentration of the analytes of interest has been added. A LFB is used to evaluate laboratory performance and analyte recovery in a blank matrix. As a minimum, include one LFB with each sample set (batch)

 

طرق ازالة العسر:-

باستخدام الصودا  (Ca(OH)3  Soda – lime process

Ca(HCO3)2 + Ca(OH)2  → 2CaCO3↓ + 2H2O

MgSO4 + Ca(OH)2 → Mg(OH)2↓ + CaSO4

استعمال المبادلات الايونية :-

المبادلات الايونية الكاتيونية لها القدرة علي الاحتفاظ بالكالسيوم والماغنسيوم عند مرور المياه بها بينما ينطلق في المياه كمية مكافئة من املاح الصوديوم .

{Na2R+Ca&Mg{HCO3-SO4–Cl}→ R{Ca–Mg} + Na{HCO3–SO4-Cl}

وعند تشبع المبادلات باملاح العسر يعاد تنشيطه بامرار محلول 10% من كلوريد الصوديوم حيث تزال املاح الكالسيوم والماغنسيوم ويعود المبادل الي صورته الاصلية التي تحتوي علي الصوديوم ويتكرر استخدام المبادلات بعد تنشيطها

Ca Mg)R  + NaCl→Na2R + (Ca Mg)Cl

العلاقة بين العسر الكلي والقلوية في المياه :-

الاملاح المسببة للعسر والقلوية : –

Cations Anions
Ca++

Mg++

Na+

K+

Al+++

OH

CO3 – –

HCO3

Cl

SO4 – –

أولا :-

OH & CO3 – – &  HCO3  مثل   Anions ترجع القلوية إلي وجود.

ثانيا :-

Ca++ & Mg++غالبا            Cations    يرجع العسر الي وجود

الحالات الناتجة :-

  1. في حالة زيادة العسر الكلي عن القلوية :-

يعني ذلك وجود كاتيونات الكالسيوم والماغنسيوم متحدة مع انيونات أخري غير مسببة للقلوية مثل الكبريتات والكلوريدات وهذا أدي الي زيادة العسر ويكون عبارة عن عسر دائم

قيمة العسر الدائم =  العسر الكلي –  القلوية

قيمةالعسر المؤقت = القلوية

2 – في حالة زيادة القلوية عن العسر الكلي :-

Na+ & K متحدة مع كاتيونات   OH & CO3 -2&  HCO3    يعني ذلك وجود انيونات

وهذا أدي الي زيادة القلوية عن العسر ويكون العسر الكلى هو العسر المؤقت ولا يوجد عسر دائم.  (الحد المسموح به 500 ملجم/ لتر  للعسر الكلى  و 350ملجم /لتر لعسر الكالسيوم  و 150 ملجم /ل لعسر الماغنسيوم )

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Chloride 3  الكلوريدات

          Scope

This test procedure is applied to all types of water samples either Raw, treated, Ground

.Principle

·                 All natural water contains chloride derived from the atmosphere, soluble salts, Chloride can cause a salty taste in water and contribute to corrosion problems in pipes, valves and pumps. The usual method for the determination of chloride in water employs a titration with standard silver nitrate solution.

  • In a neutral or slightly alkaline solution, potassium chromate can indicate the end point of the silver nitrate titration of chloride. Silver chloride is precipitated quantitatively before red silver chromate is formed.

          Interference

  • Substances in amounts normally found in potable waters will not interfere. Bromide, Iodide and cyanide register as equivalent chloride concentrations. Sulfide, thiosulfate and sulfite ions interfere but can be removed by treatment with hydrogen peroxide. Orthophosphate in excess of 25 mg/L interferes by precipitating as silver phosphate. Iron in excess of 10 mg/L interferes by masking the end point.

Equipment

Glassware

  • Pipettes: 10ml graduated,50ml, 100ml measuring pipettes are required for the method, Conical flask 250ml, Digital burette 50ml and Digital balance

 

 

          Chemical and reagents

Standard Silver nitrate titrant N/35.5 (0.0141N)

  • Dissolve 2.395 gm of AgNO3 In 1liter of distilled water. Standardize against NaCl 0.0141 N solution.

Standard Sodium chloride-0.0141 N

  • Dissolve 824 mg of NaCl (dried in an air oven at 140°C for one hour) in 1 liter of distilled water.1ml=0.5mg Cl.

Solution of potassium chromate indicator.

  • Dissolve 50gm K2CrO4 in a little distilled water and add AgNO3 until a definite red precipitate is formed. Let stand overnight, filter and dilute to 1 liter with distilled water.

          Procedure

Silver nitrate standardization

      Standardize silver nitrate standard using sodium chloride NaCl (0.0141N) using

      K2CrO4 indicator and then calculate the correction factor (CF)

                   (N XV) AgNO3 = (NXV)NaCl

Titration

    • Fill the buret with standard silver nitrate titrant.
    • Place 50ml of sample in a suitable Erlenmeyer flask
    • Add 1.0 ml K2CrO4 indicator solution to the sample.
    • Titrate against AgNO3 (0.0141N) until the appearance of a pinkish yellow color.
    • Read the burette and record the volume of silver nitrate titrant used.

   Calculation

mg Cl/L = (A-B) x CF x 10

where, A = ml titration for sample,   B = ml titration for blank, and  CF = correction factor of silver nitrate standardization

           Laboratory Fortified matrix (LFM):

  • One sample is select from each batch to be fortified with known concentration of chloride standard, the fortified sample is analyze and the sample is analyze without fortification.

Duplicate sample:

  • at least 10% of each sample batch shall be analyze in duplicate.
  • Relative percent difference (RPD)

     Laboratory-Fortified Blank (LFB)

  • A laboratory-fortified blank is a reagent water sample to which a known concentration of the analytes of interest has been added. A LFB is used to evaluate laboratory performance and analyte recovery in a blank matrix. As a minimum, include one LFB with each sample set (batch).

                                            الحد المسموح به:-          250  ملجم/ل

 

بقلم / ممتاز السيد محمد بخيت 

باحث دكتوراه كيمياء عضوية – جامعه سوهاج

Reference

1-Standard Methods for the Examination of Water and Wastewater 20st Edition (Method  2320- B)

     2- SMWW Standard Methods for the Examination of Water and Wastewater 21th Edition (EDTA titration method No. (2340C)).

    3-SMWW Standard Methods for the Examination of Water and Wastewater 21st, Edition (Argentometric method No.(4500-Cl B)).

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