Etiket Arşivleri: EDTA

Experiment 9 – Total Hardness with EDTA Method ( Kenan ÖZ )

Name of Experiment : Total Hardness with EDTA Method

Number of Experiment : 9
Submitted by : Kenan ÖZ


– To determined total hardness of water with EDTA Method.


Water Hardness and Alkalinity

It may be that your water hardness and alkalinity are perfect for discus but unfortunately this is not always the case. It is far easier to adjust hardness and alkalinity upwards as when keeping hard-water fishes, but lowering these values is by no means impossible. It simply involves another step in the water conditioning process. Total hardness (general hardness) is the sum combination of carbonate and noncarbonate hardness of your water. Total hardness is measured as, degrees, dH, or ppm (parts per million). One dH is 17.9 ppm. How total hardness is expressed depends upon the author and his orientation. I prefer dH simply because as a discuskeeper, I like to see smaller
numbers when I am measuring water hardness! If I were keeping African cichlids I might prefer to measure my water's hardness in ppm. Total hardness is usually not a big issue in keeping discus; alkalinity is a far more important factor in the breeding of discus. Alkalinity is sometimes referred to as carbonate hardness(KH)or buffering capacity. Alkalinity is the important factor in breeding discus and controlling the pH of the water. Alkalinity refers to the level of calcium, carbonate and bicarbonate in the water. It is measured in KH or mg/L CaCo3 or parts per million. One milligram per liter (mg/L) is the equivalent of one part per million. Soft water is 3dH and 0 to 50 mg/L CaCo3; medium soft water is 3 to 6 dH and 50 to 100 mg/L CaCo3; slightly hard water is 6 to 12 dH and 100 to 200 mg/L CaCo3; moderately hard water is 12 to 18 dH and 200 to 300 mg/L CaCo3; hard water is over 18 dH and over 300 mg/L CaCo3. The values for general hardness and alkalinity given above
do not always match each other. It is entirely possible to have a higher reading of general hardness and a lower reading of alkalinity. The lower reading for alkalinity is the more desirable for discus water. Discus will do quite well in slightly to moderately hard water. In fact, many breeders routinely keep their fish in these values to ensure proper development of the young fish, but for development of the eggs, soft to moderately soft water, particularly concerning alkalinity is critical. Therefore, it is not necessary to drastically adjust the general hardness or alkalinity when you first start to keep discus unless the values are very high.

EDTA Titrations v2

  • EDTA Titrations

  • Chelation in Biochemistry

  • Metal-Chelate Complexes

  • Metals are Lewis acids that accept electron pairs from donating ligands that act as Lewis bases

–CN- is a common monodentate ligand, binding to a metal ion through one atom (C)

–Metals can bind to multiple ligands (usually 6)

  • A ligand that can attach to a metal by more than one atom is multidentate or a chelating ligand

  • Chelating agents can be used for titration of metals to form complex ions (complexometric titration)

  • Chelating Agents in Analytical Chemistry

  • Ethylenediamenetetraacetic acid (EDTA)

  • Acid/Base Properties of EDTA

  • EDTA is a hexaprotic system (H6Y2+) with 4 carboxylic acids and 2 ammoniums:

  • We usually express the equilibrium for the formation of complex ion in terms of the Y4- form (all six protons dissociated). You should not take this to mean that only the Y4- form reacts

  • Fraction of EDTA in Y4- Form

  • Similar to acids and bases, we can define fractional compositions, α, defined as the fraction of “free” EDTA in a particular form.

–“Free” means uncomplexed EDTA

–So, for Y4-:

  • EDTA Complexes

  • The equilibrium constant for a reaction of metal with EDTA is called the formation constant, Kf, or the stability constant:

  • Again, Kf could have been defined for any form of EDTA, it should not be understood that only the Y4- reacts to form complex ion.

  • pH Dependence of αY4-

  • Formation Constants for M-EDTA Complexes

  • Some Metals Form 7 or 8 Coordinate Complexes

  • Conditional Formation Constant

  • We saw from the fraction plot that most of the EDTA is not in the form of Y4- below a pH ~10.

  • We can derive a more useful equilibrium equation by rearranging the fraction relationship:

  • If we fix the pH of the titration with a buffer, then αY4- is a constant that can be combined with Kf

  • Example

  • Calculate the concentration of free Ca2+ in a solution of 0.10 M CaY2- at pH 10 and pH 6. Kf for CaY2- is 4.9×1010 (Table 13-2)

  • At low pH, the metal-complex is less stable

  • Calcium/EDTA Titration Curve

  • Generic Titration Curve

  • Before the Equivalence Point

  • What’s pCa2+ when we have added 5.0 mL of EDTA?

  • At the Equivalence Point

  • What’s pCa2+ when we have added 25.0 mL of EDTA?

–At the equivalence point almost all the metal is in the form CaY2-

–Free Calcium is small and can be found w/ algebra

  • After the Equivalence Point

  • What’s pCa2+ when we have added 26.0 mL of EDTA?

–We have 1.0 mL excess EDTA

  • Auxiliary Complexing Agents

  • In aqueous solution, metal-hydroxide complexes or precipitates can form, especially at alkaline pH

  • We often have to use an auxiliary complexing agent

–This is a ligand that binds strongly enough to the metal to prevent hydroxide precipitation, but weak enough to be displaced by EDTA

  • Ammonia is a common auxiliary complex for transition metals like zinc

  • Metal Ion Indicators

  • To detect the end point of EDTA titrations, we usually use a metal ion indicator or an ion-selective electrode (Ch. 15)

  • Metal ion indicators change color when the metal ion is bound to EDTA:

–Eriochrome black T is an organic ion

  • The indicator must bind less strongly than EDTA

  • Metal Ion Indicator Compounds

  • EDTA Titration Techniques

  • Direct titration: analyte is titrated with standard EDTA with solution buffered at a pH where Kf is large

  • Back titration: known excess of EDTA is added to analyte. Excess EDTA is titrated with 2nd metal ion.

  • EDTA Titration Techniques (2)

  • Displacement titration: For metals without a good indicator ion, the analyte can be treated with excess Mg(EDTA)2-. The analyte displaces Mg, and than Mg can be titrated with standard EDTA

  • Indirect titration: Anions can be analyzed by precipitation with excess metal ion and then titration of the metal in the dissolved precipitate with EDTA.

  • Example Titration

  • 25.0 mL of an unknown Ni2+ solution was treated with 25.00 mL of 0.05283 M Na2EDTA. The pH of the solution was buffered to 5.5 and than back-titrated with 17.61 mL of 0.02299 M Zn2+. What was the unknown Ni2+ M?

Precipitation Titration

Precipitation titration :

Volumetric methods based upon the formation of slightly soluble precipitate are called ” precipitation titration ” . Because of the precipitating titration based upon utilizing silver nitrate (AgNO3) as a precipitating agent, then it called ” argentimetric processes ” .

Precipitation titration is a very important , because it is a perfect method for determine halogens and some metal ions .

Titration curves for precipitation titrations :

Titration curves are represents :

1) The change in conc. of reactants throughout titration .

2) Titration error that is likely occur when using the indicators .

3) The conditions at equivalent point

End point detection precipitation titration :

1) formation of a second colored precipitate (Mohr method):

2) formation of colored complex ( Volhard method ) :

Complex formation titration

Titration curve for complexation titration :

Composition of EDTA solution as a function of pH :

Complexes of EDTA and metal ions :

Derivation of titration curves for EDTA titration :

Indicators for EDTA titration :

Titration method employing EDTA :

1) Direct titration :

2) Back – titration :

3) Displacement titration :

Solubility of precipitates

Solubility product constant (K.S.P) :

Application of KSP in precipitation :

1) Completments of precipitation :

2) Dissolution of precipitate:

3) Prevention of precipitation :

Factors effecting the solubility of precipitates :

2) Effect of hydronium ion concentration (pH) :

3) Formation of complex ion :

4) Temperature :

Effect of electrolyte concentration on solubility :

Coefficient of activity :

Antioksidanlar, Sekuesteranlar ve Lezzet Verici Maddeler

Gıdalara antimikrobiyel amaçla ilave edilmeyen ancak ilave edildikleri gıdalarda bazı mikroorganizmalar üzerinde antimikrobiyel etki gösteren birçok katkı maddesi mevcuttur.


Oksidatif ransiditeyi önleyen antioksidan maddeler fenolik yapıları nedeniyle antimikrobiyel özelliğe sahiptirler. Gıdalara bu amaçla ilave edilen antioksidan maddeler bütil hidroksianisol (BHA), bütil hidroksitoluen (BHT), tersiyer bütil hidroksikuinon, propil galat ve etoksikuin’dir.

Oksidasyonu azaltmak için:

1. Lipoksigenaz enzimi varsa etkisiz hale getirmek gerekir.

2. Metal bulaşmasının önlenmesi.

3. Ambalajdaki havanın uzaklaştırılması ve tepe boşluğunun az bırakılması.

4. Depolama sıcaklığının düşük tutulması.

5. Işıktan korunarak depolama.

6. En etkili yol olan ANTİOKSİDAN kullanılmalıdır.

Fenolik OH grubu içeren tüm antioksidanlar gıda maddelerinde oksidasyonu önlerler. Antioksidanlar ya oluşan radikallere hidrojen vererek stabil hale getirirler ya kendi radikalleri ile oksi ve peroksi radikalleri bağlayarak ya da direkt oksijeni bağlayarak otooksidasyondaki zincirleme tepkimelerin kırılmasını ve oksidasyonun durması sağlarlar.

1. Serbest radikallere hidrojen verirler

R* + AH RH + A*

RO* + AH ROH + A*


2. Radikallerle kompleks oluştururlar:

R* + A* RA

RO* + A* ROA


3. Oksijeni bağlarlar:

Antioksidan + O2 Okside Antioksidan

Bu amaçla gıdalarda kullanılacak antioksidanlar şu özellikleri taşımalıdırlar:

1. Katıldığı gıdanın renk, tat., kokusunu olumsuz etkilememelidir.

2. Katıldığı ortamda homojen olarak çözünmesi gerekir.

3. Toksit olmamalıdır.

4. Az miktarda kullanıldığında etkili olmalıdır.

5. Pişirme gibi işlemler sırasında etkinliğini yitirmemelidir.

Margarin ve sıvı yağlarda antioksidan olarak BHT, BHA, Galatlar, askorbil palmitat ve stearat gibi antioksidanlar kullanılır.


Etillendiamintetraasetik asit (EDTA) gibi sekuesteranlar gıdalarda mevcut mikroorganizmaların gelişmesini inhibe edici etkiye sahiptir. Bu maddeler özellikle gram negatif bakterilerde hücre çeperinin geçirgenliğini etkileyerek ortamda bulunan diğer inhibitör maddelerin etkinliğini arttırmaktadırlar. Sekuesteranların gram negatif bakterilerin hücre çeperindeki lipid tabakasını kısmen veya tamamen Uzaklaştırdığı ve inhibitör maddelerin sitoplazmik membrana ulaştığı tahmin edilmektedir. E.Coli veya bazı gram negatif bakterilerin EDTA veya diğer şelat oluşturan maddelerle muamele edilmesinin bu mikroorganizmaların değişik antimikrobiyel maddelere karşı duyarlılığını arttırdığı saptanmıştır. Sitrik ve polfosfarik asit gibi diğer şelat oluşturan maddelerde EDTA’ya benzer bir etkiye sahiptir.


Gıdalarda kullanılan birçok aroma ve lezzet maddesi antimikrobiyel etkiye sahiptir. Genel olarak bu maddelerin funguslar üzerindeki antimikrobiyel etkisi bakterilere kıyasla daha yüksektir. Özellikle esansiyel yağlar ve baharatlar üzerinde birçok çalışma mevcuttur. Tereyağına tipik aromayı veren diasetil özellikle gram negatif bakterilere ve funguslar üzerinde antimikrobiyel etki gösterir. Besiyerinde bulunan diasetilin birçok küf, maya ve gram negatif bakteriler üzerinde inhibe edici etkisi olduğu saptanmıştır. Diasetilin gram negatif bakteriler üzerinde inhibitör etkisi diğer mikroorganizmalar üzerindeki etkisine kıyasla daha yüksektir. Tereyağında bulunan 2,3- pentandionun da bazı gram pozitif bakterilerle, küf ve mayalar üzerinde antimikrobiyel etki gösterdiği belirlenmiştir. Vanilin ve etilvanilin özellikle küf ve mayalar üzerinde inhibe edici etkiye sahiptir. Mentolün Staphylococcus aureus’ u ******** ise Escheria coli ve Candida albicans’ı inhibe ettiği bildirilmiştir. Gıdalarda lezzet ve çeşni maddesi olarak kullanılan birçok baharat da gıda zehirlenmesine neden olan patojen bakterilerle bazı mikotoksijenik küfler üzerinde antimikrobiyel etkiye sahiptir. Baharatların antimikrobiyel etkisi yapılarında bulunan bazı kimyasal maddelerden veya esansiyel yağlardan kaynaklanır. Baharatların gıdalardaki antimikrobiyel etkisi besiyerlerindeki antimikrobiyel etkisinden daha düşüktür ve bu nedenle de gıdalardaki antimikrobiyel etkileri gıdanın yapısına ve kullanılan baharat miktarına bağlıdır. Baharatlara karşı en hassas mikroorganizmalar gram pozitif bakterilerdir. Besiyerinde bulunan tarçın ve karanfil yağının Aspergillus parasiticus’un aflatoksin üretimine engel olduğu belirtilmiştir. Karanfilin yapısında bulunan öjenolün besiyerinde Vibrio parahaemolyticus, Salmonella typhimurium ve

Staphylococcus aureus üzerinde inhibitör etki gösterdiği saptanmıştır. Kekik ve mercanköşkün yapısında bulunan timolün ise bu üç mikroorganizmayı da inhibe ettiği bildirilmiştir. Sarımsağın etken maddesi alisinin patojenik küflere karşı antimikrobiyel etkisi olduğu saptanmıştır. Sarımsağın Escherichia coli, Aerobacter aerogenes, Staphylococcus aureus ve Shigella sonnei gibi bakteriler üzerinde antimikrobiyel etkisi olduğu ve besiyerinde %1 sarımsak konsantrasyonunun Escherichia coli, Staphylococcus aureus ve Shigella sonnei’yi inhibe ettiği bildirilmiştir.

Et ve et ürünlerinde kullanılan bazı baharatların patojen mikroorganizmalar üzerinde de antimikrobiyel etkileri söz konusudur. %10 et ve %1 tuz içeren et homojenatında %1 oranıda kırmızı biber kullanıldığında kırmızı biberin Staphlococcus aureus’a karşı bakteriyosidal etkisi olduğu bildirilmiştir.Karabiberle kimyonun inhibe edici etkisi bulunmamaktadır. Türk sucuğunda yapılan bir araştırmada ise sucuğa ilave edilen % 0.8 oranındaki sarımsağın Staphylococcus aureus ve Salmonella typhimurium üzerinde önemli bir etkisi olmadığı bildirilmiştir.

EDTA Titrations

EDTA Titrations

1.) Metal Chelate Complexes
Any reagent which reacts with an analyte in a known ratio and with a large equilibrium constant can potentially be used in a titration.

Complexation Titrations are based on the reaction of a metal ion with a chemical agent to form a metal-ligand complex.
Metal-Ligand Complex
Metal – Lewis Acid or Electron-pair acceptor
Ligand – Lewis Base or Electron-pair donor
Note: multiple atoms from EDTA are binding Mn2+

EDTA Titrations

1.) Metal Chelate Complexes
Complexation Titrations are essentially a Lewis acid-base reaction, in which an electron pair is donated from one chemical to another
The ligands used in complexometric titrations are also known as chelating agents.
Ligand that attaches to a metal ion through more than one ligand atom
Most chelating agents contain N or O
Elements that contain free electron pairs that may be donated to a metal
Fe-DTPA Complex

EDTA Titrations
Metal Chelation in Nature

1.) Potassium Ion Channels in Cell Membranes
Electrical signals are essential for life
Electrical signals are highly controlled by the selective passage of ions across cellular membranes
Ion channels control this function
Potassium ion channels are the largest and most diverse group
Used in brain, heart and nervous system
Current Opinion in Structural Biology 2001, 11:408–414
Opening of potassium channel allows K+ to exit cell and change the electrical potential across membrane
K+ channel spans membrane
channel contains pore that only allows K+ to pass
K+ is chelated by O in channel

EDTA Titrations
Metal –Chelate Complexes

1.) Formation Constant (Kf)
The equilibrium constant for the reaction between a metal ion (M+n) and a chelating agent (L-P) is known as a formation constant or stability constant.

Applying different and specific names to the general equilibrium constant is a common occurrence
Solubility (Ksp), acid-base (Ka, Kb), water dissociation (Kw), etc

Chelate effect: ability of multidentate ligands to form stronger metal complexes compared to monodentate ligands.
Kf = 8×109
Kf = 4×109
2 ethylenediamine molecules binds tighter than 4 methylamine molecules

EDTA Titrations
Metal –Chelate Complexes

2.) Chelate Effect
Usually chelating agents with more than one electron pair to donate will form stronger complexes with metal ions than chelating agents with only one electron pair.
Typically more than one O or N
Larger Kf values

Multidentate ligand: a chelating agent with more than one free electron pair
Stoichiometry is 1:1 regardless of the ion charge

Monodentate ligand: a chelating agent with only one pair of free electrons
Multidentate ligand that binds radioactive metal attached to monoclonal antibody (mAb).

mAb is a protein that binds to a specific feature on a tumor cell delivering toxic dose of radiation.

EDTA Titrations

1.) EDTA (Ethylenediaminetetraacetic acid)
One of the most common chelating agents used for complexometric titrations in analytical chemistry.

EDTA has 6 nitrogens & oxygens in its structure giving it 6 free electron pairs that it can donate to metal ions.
High Kf values
6 acid-base sites in its structure

EDTA Titrations

2.) Acid-Base Forms
EDTA exists in up to 7 different acid-base forms depending on the solution pH.

The most basic form (Y4-) is the one which primarily reacts with metal ions.
EDTA-Mn Complex

EDTA Titrations

2.) Acid-Base Forms
Fraction (α) of the most basic form of EDTA (Y4-) is defined by the H+ concentration and acid-base equilibrium constants
Fraction (α) of EDTA in the form Y4-:
where [EDTA] is the total concentration of all free EDTA species in solution
αY4- is depended on the pH of the solution

EDTA Titrations

3.) EDTA Complexes
The basic form of EDTA (Y4-) reacts with most metal ions to form a 1:1 complex.
Other forms of EDTA will also chelate metal ions

Recall: the concentration of Y4- and the total concentration of EDTA is solution [EDTA] are related as follows:
Note: This reaction only involves Y4-, but not the other forms of EDTA
where αY4-is dependent on pH

EDTA Titrations

3.) EDTA Complexes
The basic form of EDTA (Y4-) reacts with most metal ions to form a 1:1 complex.

EDTA Titrations

3.) EDTA Complexes
Substitute [Y4-] into Kf equation

If pH is fixed by a buffer, then αY4- is a constant that can be combined with Kf
where [EDTA] is the total concentration of EDTA added to the solution not bound to metal ions
Conditional or effective formation constant:
(at a given pH)

EDTA Titrations

3.) EDTA Complexes
Assumes the uncomplexed EDTA were all in one form
at any pH, we can find αY4- and evaluate Kf’

EDTA Titrations

4.) Example:
What is the concentration of free Fe3+ in a solution of 0.10 M Fe(EDTA)- at pH 8.00?

EDTA Titrations

5.) pH Limitation
Note that the metal –EDTA complex becomes less stable as pH decreases
Kf decreases
[Fe3+] = 5.4×10-7 at pH 2.0 -> [Fe3+] = 1.4×10-12 at pH 8.0

In order to get a “complete” titration (Kf ≥106), EDTA requires a certain minimum pH for the titration of each metal ion
End Point becomes less distinct as pH is lowered, limiting the utility of EDTA as a titrant

EDTA Titrations

5.) pH Limitation
By adjusting the pH of an EDTA titration:
one type of metal ion (e.g. Fe3+) can be titrated without interference from others (e.g. Ca2+)
Minimum pH for Effective Titration of Metal Ions

EDTA Titrations
EDTA Titration Curves

1.) Titration Curve
The titration of a metal ion with EDTA is similar to the titration of a strong acid (M+) with a weak base (EDTA)

The Titration Curve has three distinct regions:
Before the equivalence point (excess Mn+)

At the equivalence point ([EDTA]=[Mn+]

After the equivalence point (excess EDTA)

EDTA Titrations
EDTA Titration Curves

2.) Example
What is the value of [Mn+] and pM for 50.0 ml of a 0.0500 M Mg2+ solution buffered at pH 10.00 and titrated with 0.0500 m EDTA when (a) 5.0 mL, (b) 50.0 mL and (c) 51.0 mL EDTA is added?
Kf = 108.79 = 6.2×108
αY4- at pH 10.0 = 0.30
mL EDTA at equivalence point:
mmol of EDTA
mmol of Mg2+

EDTA Titrations
EDTA Titration Curves

2.) Example
(a) Before Equivalence Point ( 5.0 mL of EDTA)
Before the equivalence point, the [Mn+] is equal to the concentration of excess unreacted Mn+. Dissociation of MYn-4 is negligible.
moles of Mg2+
originally present
moles of EDTA added
Original volume
Volume titrant
Dilution effect

EDTA Titrations
EDTA Titration Curves

2.) Example
(b) At Equivalence Point ( 50.0 mL of EDTA)
Virtually all of the metal ion is now in the form MgY2-
Original [Mn+] Original volume of
Mn+ solution
Original volume
Volume titrant
Dilution effect
Moles Mg+ ≡ moles MgY2-

EDTA Titrations
EDTA Titration Curves

2.) Example
(b) At Equivalence Point ( 50.0 mL of EDTA)
The concentration of free Mg2+ is then calculated as follows:
Initial Concentration (M)
Final Concentration (M)
0.0250 – x
Solve for x using the quadratic equation:

EDTA Titrations
EDTA Titration Curves

2.) Example
(c) After the Equivalence Point ( 51.0 mL of EDTA)
Virtually all of the metal ion is now in the form MgY2- and there is excess, unreacted EDTA. A small amount of free Mn+ exists in equilibrium with MgY4- and EDTA.
Original [EDTA] Volume excess
Original volume
Volume titrant
Dilution effect
Excess moles EDTA
Calculate excess [EDTA]:

EDTA Titrations
EDTA Titration Curves

2.) Example
(c) After the Equivalence Point ( 51.0 mL of EDTA)
Calculate [MgY2-]:
Original [Mn+] Original volume of
Mn+ solution
Original volume
Volume titrant
Dilution effect
Moles Mg+ ≡ moles MgY2-
Only Difference

EDTA Titrations
EDTA Titration Curves

2.) Example
(c) After the Equivalence Point ( 51.0 mL of EDTA)
[Mg2+-] is given by the equilibrium expression using [EDTA] and [MgY2-]:

EDTA Titrations
EDTA Titration Curves

2.) Example
Final titration curve for 50.0 ml of 0.0500 M Mg2+ with 0.0500 m EDTA at pH 10.00.
Also shown is the titration of 50.0 mL of 0.0500 M Zn2+
Note: the equivalence point is sharper for Zn2+ vs. Mg2+. This is due to Zn2+ having a larger formation constant.
The completeness of these reactions is dependent on αY4- and correspondingly pH.
pH is an important factor in setting the completeness and selectivity of an EDTA titration

EDTA Titrations
Auxiliary Complexing Agents

1.) Metal Hydroxide
In general, as pH increases a titration of a metal ion with EDTA will have a higher Kf.
Larger change at the equivalence point.

Exception: If Mn+ reacts with OH- to form an insoluble metal hydroxide

Auxiliary Complexing Agents: a ligand can be added that complexes with Mn+ strong enough to prevent hydroxide formation.
Ammonia, tartrate, citrate or triethanolamine
Binds metal weaker than EDTA
Fraction of free metal ion (αM) depends on the equilibrium constants (β) or cumulative formation constants:
Use a new conditional formation constant that incorporates the fraction of free metal:

EDTA Titrations
Auxiliary Complexing Agents

2.) Illustration:
Titration of Cu+2 (CuSO4) with EDTA
Addition of Ammonia Buffer results in a dark blue solution
Cu(II)-ammonia complex is formed
Addition of EDTA displaces ammonia with corresponding color change

EDTA Titrations
Metal Ion Indicators

1.) Determination of EDTA Titration End Point
Four Methods:
Metal ion indicator
Mercury electrode
pH electrode
Ion-selective electrode

Metal Ion Indicator: a compound that changes color when it binds to a metal ion
Similar to pH indicator, which changes color with pH or as the compound binds H+

For an EDTA titration, the indicator must bind the metal ion less strongly than EDTA
Similar in concept to Auxiliary Complexing Agents
Needs to release metal ion to EDTA
Potential Measurements
End Point indicated by a color change from red to blue

EDTA Titrations
Metal Ion Indicators

2.) Illustration
Titration of Mg2+ by EDTA
Eriochrome Black T Indicator
Addition of EDTA
Before Near After
Equivalence point

EDTA Titrations
Metal Ion Indicators

3.) Common Metal Ion Indicators
Most are pH indicators and can only be used over a given pH range

EDTA Titrations
Metal Ion Indicators

3.) Common Metal Ion Indicators
Useful pH ranges

EDTA Titrations
EDTA Titration Techniques

1.) Almost all elements can be determined by EDTA titration
Needs to be present at sufficient concentrations

Extensive Literature where techniques are listed in:
G. Schwarzenbach and H. Flaschka, “Complexometric Titrations”, Methuen:London, 1969.
H.A. Flaschka, “EDTA Titrations”, Pergamon Press:New York, 1959
C.N. Reilley, A.J. Bernard, Jr., and R. Puschel, In: L. Meites (ed.) “Handbook of Analytical Chemistry”, McGraw-Hill:New York, 1963; pp. 3-76 to 3-234.

Some Common Techniques used in these titrations include:
Direct Titrations
Back Titrations
Displacement Titrations
Indirect Titrations
Masking Agents

EDTA Titrations
EDTA Titration Techniques

2.) Direct Titrations
Analyte is buffered to appropriate pH and is titrated directly with EDTA

An auxiliary complexing agent may be required to prevent precipitation of metal hydroxide.

3.) Back Titrations
A known excess of EDTA is added to analyte
Free EDTA left over after all metal ion is bound with EDTA

The remaining excess of EDTA is then titrated with a standard solution of a second metal ion

Approach necessary if analyte:
precipitates in the presence of EDTA
Reacts slowly with EDTA
Blocks the indicator

Second metal ion must not displace analyte from EDTA

EDTA Titrations
EDTA Titration Techniques

4.) Displacement Titration
Used for some analytes that don’t have satisfactory metal ion indicators

Analyte (Mn+) is treated with excess Mg(EDTA)2-, causes release of Mg2+.

Amount of Mg2+ released is then determined by titration with a standard EDTA solution
Concentration of released Mg2+ equals [Mn+]


EDTA Titrations
EDTA Titration Techniques

5.) Indirect Titration
Used to determine anions that precipitate with metal ions

Anion is precipitated from solution by addition of excess metal ion
ex. SO42- + excess Ba2+
Precipitate is filtered & washed

Precipitate is then reacted with excess EDTA to bring the metal ion back into solution

The excess EDTA is titrated with Mg2+ solution

[Total EDTA] = [MYn-4] + [Y4-] complex

EDTA Titrations
EDTA Titration Techniques

6.) Masking Agents
A reagent added to prevent reaction of some metal ion with EDTA

Demasking: refers to the release of a metal ion from a masking agent
Al3+ is not available to bind EDTA because of the complex with F-

Laboratory‎ > ‎Total Hardness With EDTA Method


Experiment No : 9



Submitted by : Mutlu DEMIREL

Group No : 2

Group Members : Sevgi COLAKOGLU





Determine the hardness in a water sample.


The quality of natural waters is important to the health and survival of all living things. A part of water quality deals with the hardness of water. Water hardness is defined as the concentration of dissolved divalent cations such as Ca2+ and Mg2+. The contributing factors to water hardness are municipal and individual waste, chemicals, fertilizers, herbicides, and pesticides that leach into the groundwater supply. Another factor is the fact that water is the universal solvent, which means it dissolves minerals as it percolates through the soil and rocks.1 Different types of rock give up Ca2+ and Mg2+ ions. Sedimentary rocks such as limestone (calcium carbonate CaCO3) are soluble in acidic water. Calcium also comes from the dissolution of igneous rock revealed by the decomposition of anorthite (CaAl2Si2O8), which occurs in the higher acidity of groundwater. An example of magnesium from the dissolution of rock is the decomposition of fosterite (Mg2SiO4) into serpentite (Mg6(OH)8Si4O10).1

There are no national standards for water hardness published by the Environmental Protection Agency (EPA), because the minerals, calcium and magnesium, are not considered health threats. Levels of water hardness are based the amount of calcium carbonate found in the water sample if the water were evaporated. The water is considered soft if it contains 0 to 60 mg/L of hardness, moderately hard from 61 to 120 mg/L, hard between 121 and 180 mg/L, and very hard if it contains if more than 180 mg/L.2 Commonly accepted level range for calcium is 100-300mg/L and the levels for magnesium are lower, based on how the water tastes.

There are various methods to measure water hardness. These include EDTA titration, Atomic Absorption Spectrometry, TDS (total dissolved solids) test, fluorescence fibre-optic sensor, and test strips.

The EDTA titration process uses EDTA (ethylenadiaminetetracetic acid) as the chelating agent.1 The EDTA attaches itself to the minerals with a bond called a chelate. The EDTA molecule forms complexes with nearly all metals. It forms particularly strong complexes, because it has six points of attachment that allow the molecule to wrap itself around the metal ion. Eriochrome black T (EBT) is the indicator dye used in EDTA titration, which is water soluble due to the sulfonate group’s (-SO3-) negative charge and also a pH indicator, so a buffer is added to make the blue form (HD2-) of EBT predominant. EBT forms a colored chelate with Mg2+, but not Ca2+.1 The initial wine red color is caused by the dye attaching itself to the metal ions. The endpoint of the titration is when all of the ions are coated by the EDTA and there are none left to complex with the dye, so the red color is replaced with sky blue.6 The values gained from the EDTA titration after some calulations are moles of Ca2+ and Mg2+, which can be converted into parts per a million (ppm) hardness of CaCO3.

Applications of EDTA chetation of Ca2+ and Mg2+ include bathroom cleaners in the form of tetrasodium salt because it dissolves lime and scum deposites. CaEDTA (calcium chelate) removes iron/copper that would spoil oil so it is used as a preservative in salad dressings.1 The calcium chelate is also effective in medical treatment for lead toxicity and blood vessel disease.5 EDTA is used as a titrant in industry because it is inexpensive; however, the downsides of it are that it is time consuming, requires a certain level of skill, and is subject to operational errors.

Atomic Absorbtion Spectrometry (AAS) is an instrumental technique that is used to determine the amount of trace elements, metals, dissolved in a solution. AAS is used in modern analytical chemistry, biochemistry, and ecology for inorganic trace analysis. It is used because of its high sensitivity, selectivity, broad scope, low cost, and reliability. Atoms have unique electronic energy levels. The light falling on the atom must match the energy separation between two electronic energy levels to be excited. In other words, absorption will occur if the wavelength of the light is the same as the change of energy.1 The atomic absorbtion spectrophotometer is based on the principle of excited atoms. A monochromatic light that has the energy correponding to the delta energy of the atoms is projected through the sample being analyzed.1 The wavelength used for calcium is 422.7 nanometers (nm), 202.5 nm for magnesium.8 The Beer’s law, A=abc, is used to calculate the metal concentration in the sample because absorbance is proportional to the concentration of the atoms in the sample.1

There are three main chambers of the atomic absorption spectrophotometer. The first chamber is where the source of the light is contained in cathode lamps.1 The fuels / oxidents used for analyzing calcium and magnesium are C2H2 and air.8 The monochromatic light is produced when the atoms relax, which is the opposite of absorption. The light is then absorbed by the Mg or Ca in the water sample in the second chamber. The second chamber is where the water sample enters the process by being aspirated into the sample chamber where it is converted into an aerosol, only about 10% of which is introduced to the flame from the burner. The 2300°C flame is capable of atomizing all of the components of the water sample.1 The light is absorbed by only the Mg or Ca atoms which produces a rich yellow flame.8 The third chamber of the atomic absorption spectrophotometer contains a monochrometer, a detector, and an internal computing system. Only the wavelength of the light corresponding to delta energy, which was produced from the excited metal emissions can pass through the narrow slit for the monochrometer. The detector is a photomultiplier tube (PMT), which detects a decrease in the initial signal from the lamp. The intensity transmitted (It) from the lamp through the flame is regulated by the Beer-Lambert law : It= I0(10-abc). The value given by the internal computing system is the light absorbance, which can be converted to concentration of the metal ion in ppm by the use of a linear regression graph produced from the calibration curve.1

The dissolved total solids test is a visual observation that compares the amount of total dissolved solids in a water sample to that in distilled water. It compares the ring of residue left on aluminium foil when the water is evaporated. The disadvantages of this are that it is only an observation and includes all of the dissolved minerals, not just Mg and Ca.


Water sample, conical flask, , Erioch,


1. We took 100 mL of sample into conical flask and add tree drops of phenol phatalein when the color is pink titrate the solution with 0.04 M and the recorded the used amount of acid.

2. Into same sample added three drops of methyl orange when the yellow titrate the sample with same acid until the color turns to red.


1. Total Hardness : The combined concentration of earth-alkali metals, predominantly magnesium (Mg 2+ ) and calcium (Ca 2+ ), and some strontium (Sr 2+ ). Most natural waters have a more or less high level of hardness. The source of this hardness is limestone dissolved by water rich in carbon dioxide. Total Hardness is expressed in mg/L of calcium carbonate (CaCO 3 ), though calcium carbonate is not water soluble, but calcium bicarbonate is. Hardness levels range from <50 mg/L (soft) to >500 mg/L (very hard).

Calcium Hardness : The calcium portion of total hardness expressed as calcium carbonate. Typically 65-75% of total hardness. Low calcium hardness can cause damage to pool surface and components.

Carbonate Hardness : The part of the total hardness that is formed by the ions of carbonates(Co3) and hydrogen carbonate(HCo3). It is symbolized by dCH. It is important to know the dCH of your water, as it affects both the ph. and Carbon Dioxide amounts in your water. It is also commonly called “buffering capability”. a dCH of 4 to 8 is fine for most fish.

Temporary Hardness : Hardness is produced by calcium and magnesium in water. These ions cause a precipitate with soap. Temporary hardness is caused by bicarbonate and can be removed by boiling which converts the bicarbonate to carbon dioxide and calcium carbonate.

Permanent Hardness : Permanent hardness can be removed by

· the addition of washing soda (sodium carbonate)

· ion exchange

· the use of polyphosphate water softeners

All the methods that remove permanent hardness also remove temporary hardness at the same time.

Alkalimetric Titer: the term can reflect the nature of the titrant, such as acidimetric, alkalimetric, iodimetric titrations as well as coulometric titrations, in which the titrant is generated electrolytically rather than being added as a standard solution.

German hardness: 1 °DH = 10 mg/L CaO = 0.178 mmole/L Ca (M(CaO) = 56 g/mole)

English hardness: 1 °EH = 1 grain/UK gallon CaCO3 = 0.142 mmole/L Ca (1 grain = 64.79891 mg; 1 UK gallon = 4.54596 L)

French hardness: 1 °FH = 10 mg/L CaCO3 = 0.1 mmole/L Ca (M(CaCO3) = 100 g/mole)

American hardness: 1 °AH = 1 ppm CaCO3 = 1mg/L CaCO3 = 0.01 mmole/L Ca

2. The following hardness classes can be distinguished

0-4 °DH (0-0.7 mmole/L Ca): very soft water

4-8 °DH (0.7-1.4 mmole/L Ca): soft water

8-12 °DH (1.4- 2.1 mmole/L Ca): normal water

12-18 °DH (2.1-3.2 mmole/L Ca): hard water

>18 °DH (>3.2 mmole/L Ca): very hard water

In The Netherlands the hardness of drinking water should be in the range of 1-2.5 mmole/L Ca.

Hard water is not unhealthy. Calcium en magnesium are essential minerals for our bones.

3. Water is used a lot of process in food industry. So water is very importatnt for food industry.

Effects of hard water :

a) cause the heat loses ( energy loses )

b) reduce the cleaning ability of soap

c) reduce the foaming ability of soap

d) changes the water boiling scala

4. 1. We took 100 mL of sample into conical flask and add tree drops of phenol phatalein when the color is pink titrate the solution with 0.04 M and the recorded the used amount of acid.

2. Into same sample added three drops of methyl orange when the yellow titrate the sample with same acid until the color turns to red.



Water is referred to as the “universal solvent” because, over the course of time, water will dissolve or erode almost any material that it is in contact with. It is this natural occurrence that contributes to the hardness of water.

Water hardness is normally referred to as a measure of the soap or detergent consuming power of water. Technically, hard water is water having a high concentration of calcium and magnesium ions. These, along with other minerals, are commonly present in all natural water.

Water is used a lot of process in food industry. So water is very importatnt for food industry.

Effects of hard water :

a) cause the heat loses ( energy loses )

b) reduce the cleaning ability of soap

c) reduce the foaming ability of soap

d) changes the water boiling scala

e) unhealty