gravimetric methods of analysis [compatibility mode]

75
Dr. Jehad M Diab Faculty of pharmacy Damascus University Gravimetric Analysis اﻟﺗﺣﻠﯾل اﻟوزﻧﻲPharma.analytical chemistry II

Upload: lujain-al-ashqar

Post on 22-Nov-2014

2.244 views

Category:

Documents


11 download

DESCRIPTION

 

TRANSCRIPT

Page 1: Gravimetric methods of analysis [compatibility mode]

Dr. Jehad M DiabFaculty of pharmacyDamascus University

Gravimetric Analysisالتحلیل الوزني

Pharma.analytical chemistry II

Page 2: Gravimetric methods of analysis [compatibility mode]

Gravimetric Analysis

Gravimetry is the Quantitative measurement of theanalyte by weighing a pure solid form of theprecipitate.

Gravimetric Analysis is one of the most accurateand precise methods of macro-quantitative analysis.

Often required for high precision

Obtaining pure solids from solutions containingan unknown amount of a metal ion is done byprecipitation. Dr.Jehad Diab

Page 3: Gravimetric methods of analysis [compatibility mode]

Electrogravimetric methods. analyte isprecipitated on cathode as metal or on anodeas metal oxide Dr.Jehad Diab

طرائق الترسیب

طرائق التطایر

طرائق التحلیل الوزني الكھربائي

Page 4: Gravimetric methods of analysis [compatibility mode]

and wash

and calculateDry and ignite

precipitating

Precipitation steps in gravimetry

Dr.Jehad Diab

مراحل التحلیل الوزني

Page 5: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

خواص الرواسب

Page 6: Gravimetric methods of analysis [compatibility mode]

Mechanisms of precipitation1.Saturation: the amount of salt dissolved ismaximum under certain condition of pressure andtemperature

2.Supersaturation: the amount of salt is larger than atsaturation step, turbid solution

3.nucleation: when a small number of ions ,atoms,molecules initially unite either spontaneous orinduced resulting in very small aggregates of asolid during precipitation.

4.Particle growth: the three dimensional growth ofparticle nucleus converted into a larger crystal

Dr.Jehad Diab آلیات الترسیب

اإلشباع

فوق اإلشباع

التنوي

النمو الجزیئ

Page 7: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 8: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 9: Gravimetric methods of analysis [compatibility mode]

Particle size and filterabilityVon Weimarn described an equation that can control

the particle size of ppt; named Von Weimarn ratio• RSS= Q-S/S (Rss = Relative supersaturation, Q is

concentration of the solute at any instant. S is itsequilibrium solubility)

Dr.Jehad Diab

Page 10: Gravimetric methods of analysis [compatibility mode]

Proportional to RSS

Inversely Proportional to RSS

Dr.Jehad Diab

Page 11: Gravimetric methods of analysis [compatibility mode]

pH control of precipitation

Ca2+ + C2O42- CaC2O4 (s)

H2C2O4 2 H+ + C2O42-

Feeder Reaction:

Dr.Jehad Diab

Weak basic medium

Page 12: Gravimetric methods of analysis [compatibility mode]

10-6 - 10-4 mm

10-1 – 10 mm

Dr.Jehad Diab

Page 13: Gravimetric methods of analysis [compatibility mode]

Primary adsorbed layer

AgNO3 + NaCl →AgCl↓ + NaNO3

reagent analyte

(Secondaryadsorbedlayer)

Dr.Jehad Diab

Page 14: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

------------------------

------------------------------------------------------------------------------------------------

-------------------------------------------------

Page 15: Gravimetric methods of analysis [compatibility mode]

coagulationpeptization

Dr.Jehad Diab

Page 16: Gravimetric methods of analysis [compatibility mode]

adsorbed

adsorbed

The result is coagulation of colloidal precipitate

of adsorbed

Dr.Jehad Diab

Colloids particles must collide with one another tocoalesce. However ,the negatively charged ionicatmospheres of particles repel one another. the particles,therefore ,must have enough kinetics energy to overcomeelectrostatic repulsion before the can coalesce. Heatpromotes coalescence by increasing the kinetic energy .

And coagulation of colloidal precipitate is resulted in.

Page 17: Gravimetric methods of analysis [compatibility mode]

And coagulation of colloidal precipitate is resulted in.Dr.Jehad Diab

increasing electrolyte concentration (HNO3 for AgCl) decreasesthe volume of the ionic atmosphere and allows particles tocome closer together before electrostatic repulsion becomesignificant. For this reason .most gravimetric precipitations aredone in the presence of an electrolyte.

Page 18: Gravimetric methods of analysis [compatibility mode]

High Electrolyte Concentrationto Aid Precipitation

Excess charge on colloid creates ionicatmosphere around particle

D.C. Harris, Quantitative Chemical Analysis, 6th Ed., p686

Page 19: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Washing a colloid with water to remove excess counterion or trapped impurities can result in peptization.

معالجة الببتزة او التشبغر

Page 20: Gravimetric methods of analysis [compatibility mode]

Use a volatile electrolyte

Dr.Jehad Diab

Page 21: Gravimetric methods of analysis [compatibility mode]

Digestion and aging

,to reduce impurities present and largerparticles obtained

Or more

Dr.Jehad Diab

التھضیم والتعتیق

Page 22: Gravimetric methods of analysis [compatibility mode]

Fig. 10.1. Ostwald ripening.

During digestion at elevated temperature:

Small particles tend to dissolve and reprecipitate on larger ones.

Individual particles agglomerate.

Adsorbed impurities tend to go into solution.

During digestion at elevated temperature:

Small particles tend to dissolve and reprecipitate on larger ones.

Individual particles agglomerate.

Adsorbed impurities tend to go into solution.

©Gary Christian,Analytical Chemistry,

6th Ed. (Wiley)التھضیم أو نضوج استوالد

Page 23: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

الرواسب البلوریة

-----------------------------

-----------------------------------------------------------------------

--------------------------------------------------

Page 24: Gravimetric methods of analysis [compatibility mode]

(inclusion)

Sources of Coprecipitation

(trapped impurities)

adsorption

(interferences)

Post precipitation الترسیب التالي: Sometimes a precipitate standingin contact with the mother liquor becomes contaminated by theprecipitation of an impurity on top of the desired precipitate.

Dr.Jehad Diab

الترسیب المشترك

اإلمتزاز السطحياإلحتباس

اإلحتواء

Page 25: Gravimetric methods of analysis [compatibility mode]

adsorbed

Dr.Jehad Diab

اإلمتزاز السطحي

()l

silver and nitrate ions, soAgNO3 is coprecipitated with the AgCl.

Page 26: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

------------------------------------------------ --------------

---------------------------------------------------------------------------------------------------------------------

Coprecipitation error: negative or positive errorsEx: (a). in Cl analysis, colloidal AgCl + AgNO3 → (+) error(b). in Ba2+ → BaSO4 analysisif Ba(NO3)2 (larger FW than BaSO4) → (+) errorif BaCl2 ( FW: BaCl2 < BaSO4) → (-) error

Page 27: Gravimetric methods of analysis [compatibility mode]

Dealing with surface adsorption

Dr.Jehad Diab

Page 28: Gravimetric methods of analysis [compatibility mode]

Dealing with surface adsorption

Dr.Jehad Diab

-------------------------------------------------------------------

Page 29: Gravimetric methods of analysis [compatibility mode]

Occlusion

Dr.Jehad Diab

اإلحتباس

Page 30: Gravimetric methods of analysis [compatibility mode]

Occlusion

Dr.Jehad Diab

Page 31: Gravimetric methods of analysis [compatibility mode]

Occlusion

Dr.Jehad Diab

--------------------------------------------------------------------------------------

--------------------------------------------------------------------------------

Page 32: Gravimetric methods of analysis [compatibility mode]

dDetermination of NH4+ as NH4MgPO4 , K+ will cause a mixed

crystal containing KMgPO4

(inclusion اإلحتواء)

Dr.Jehad Diab

Page 33: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

-------------------------------------------------------------------------------------------

------------

---------------------------------------------------------------------------------------------

-------------------------------

Page 34: Gravimetric methods of analysis [compatibility mode]

Homogeneous precipitation. The best precipitates are obtained withhomogeneous precipitation, in which theprecipitating reagent is gradually generated in thesample solution, through a slow chemical reaction.

In this way there is never a large excess ofreagent, so that nucleation is slow, giving allexisting nuclei plenty of time to grow.

The precipitating reagent is usually formed bythe slow hydrolysis of an organic compound atelevated temperature, but even synthesis ispossible, as in the generation of dimethylglyoxime

Dr.Jehad Diab

الترسیب المتجانس

Page 35: Gravimetric methods of analysis [compatibility mode]

Methods have been worked out to generate avariety of precipitants, such as hydroxide, sulfide,sulfate, phosphate, oxalate, 8-hydroxyquinoline,and chromate.

Both the temperature and the pH must becontrolled, because both usually affect the rates ofthe hydrolysis reaction. Moreover, as we saw in thepH is often crucial in the formation of theprecipitate.

Homogeneous precipitation

Dr.Jehad Diab

Solid formed by homogeneous precipitation are generally purer and moreeasily filtered than precipitate generated by direct addition of a reagent tothe analyte solution.

Page 36: Gravimetric methods of analysis [compatibility mode]

3

Preparation of NH4OH as precipitant by hydrolysis of urea

Al(OH)3,Fe(OH)3,Sn(OH)4,Bi(OH)3,Th(OH)4

Dr.Jehad Diab

Page 37: Gravimetric methods of analysis [compatibility mode]

thioacetamide CH2·CS.NH2 + H20 → CH2·CO.NH2 + H2S Cd, Cu, Mo, Sb

urea (NH2)2CO + 3H20 → CO2 + 2NH4+ + 20H- AI, Bi, Ga, Fe, Sn, Th

Sulfamic acid NH2S03H + H20 → NH4+ + H + + SO4

2+ Ba, Ca, Pb, Sr

Trimethyle phosphate (CH30)3PO + 3H20 → 3CH30H + 3H+ + PO43- Zr

Dimethyl oxalate CH30.CO.CO.OCH3 + 2H20 → 2CH30H + 2H + + C2042- Ca, Mg, Zn

8-acetoxyquinoline + H20 → CH3C02H + 8-hydroxyquinoline AI, Mg, U, Zn

2Cr3+ + BrO3- + 5H20 → Br- + l0H+ + 2CrO42- Pb

Biacetyl plus hydroxylamine CH3·CO.CO.CH3 + NH20H → dimethylglyoxime + 2H20 Ni

Table. Some common reactions for homogeneous precipitationreagent generating reaction used to precipitate

Dr.Jehad Diab

Page 38: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

تجفیف الراسب

--------------------------------------------------------

Page 39: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 40: Gravimetric methods of analysis [compatibility mode]

250 oC 600 oC

Dr.Jehad Diab

Page 41: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

الحسابات في التحلیل الوزني

----------------

---------------------------------------

Page 42: Gravimetric methods of analysis [compatibility mode]
Page 43: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 44: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 45: Gravimetric methods of analysis [compatibility mode]

Gravimetric calculations

f.wt analyte(g/mol) a (mol analyte)

gf = ------------------------- × ------------------------

f.wt ppt(g/mol) b(mol ppt)

gf = g analyte / g ppt

g analyte = g ppt × gf

% analyte =( g analyte / g sample) × 100

% analyte = (g ppt × GF) / g sample) ×100% analyte = (g ppt × GF) / g sample) ×100

Dr.Jehad Diab

Page 46: Gravimetric methods of analysis [compatibility mode]

Cl2 → AgCl(s)

GF=1/2 × Cl2 /AgCl = Cl2 / 2AgCl=35.5*2/2(108+35.5)= 0.25

AlCl3 → AgCl(s)

GF=1/3 × AlCl3 / AgCl = AlCl3 / 3AgCl I → Hg5(IO6)2

GF=2I/ Hg5(IO6)2

Determine GF:

Dr.Jehad Diab

Page 47: Gravimetric methods of analysis [compatibility mode]

Problems: Calculate the mass of analyte interm of grams to each gram of ppt for the

following analytes:

Analyte ppt

P(31g) → Ag3po4 (711g )

K2HPO4(136g) → Ag3po4 (711g )

Bi2S3 (514 g) → BaSO4 (233 g)

g analyte = g ppt × gf

g p =g Ag3PO4 ×GF= 1 ×31 / 711=0.044 g p/1g ppt

Dr.Jehad Diab

Page 48: Gravimetric methods of analysis [compatibility mode]

Problem : Determine the gravimetricfactors in term of symbols for thedetermination of:

AnalyteAnalyte pptppt G.F.G.F.CaCaOO CaCaCOCO33 CaOCaO/CaCO/CaCO33

FeFeSS BaBaSSOO44 FeSFeS/BaSO/BaSO44

UUOO22(NO(NO33))22 UU33OO88 33UOUO22(NO(NO33))22/U/U33OO88

CrCr22OO33 AgAg22CrCrOO44 CrCr22OO33//22AgAg22CrOCrO44

Dr.Jehad Diab

Page 49: Gravimetric methods of analysis [compatibility mode]

Problem : Determine the gravimetric factors interm of symbols for the determination of:

(a) Aluminum as its hydroxyquinolate,AI(C9H60N)3 (Al AI(C9H60N)3)

(b) Phosphorus as phosphomolybdic anhydride,P2Mo24078 (P P2Mo24078 )

(c) Potassium as its chloroplatinate

K → K2PtCl6(d) Sulfur as barium sulfate,( S → BaS04)

(e) Nickel as nickel dimethylglyoxime,

( Ni → Ni(C4H702N2)2Dr.Jehad Diab

Page 50: Gravimetric methods of analysis [compatibility mode]

Problem : Determine the gravimetric factors for thedetermination of:

1. In -> In2O3 GF

2. HgO -> Hg5(IO6)2 GF

3. K3PO4 -> K2PtCl6 GF

4. K3PO4 -> Mg2P2O7 GF

5. AgIO3 -> Ba(IO3)2 GF

6. AgNO3 -> AgIO3 GF

7. (NH4)2SO4 -> BaSO4 GF

8. Mn3O4 -> MnO2 GF

9. Cu2HgI4 -> Cu GF

Cr -> Cr203 GFDr.Jehad Diab

10.

Page 51: Gravimetric methods of analysis [compatibility mode]

Example: in an organic sample (0.352g) phosphorouswas dissolved and converted to Mg2P2O7 precipitate(0.223 g). Calculate the percentage %P in the original

sample.

Dr.Jehad Diab

2P(gfw 31 g) → Mg2P2O7 (gfw 222.6)GF=2× 31 /222.6 =0.2783% analyte =(g ppt × GF / g sample) × 100

%P =( 0.223 × 0.2783 / 0.352) ×100 = 17.1 %

Page 52: Gravimetric methods of analysis [compatibility mode]

Example: When an sample of impure potassiumchloride (0.4500g) was dissolved in water andtreated with an excess of silver nitrate, 0.8402 g ofsilver chloride was precipitated. Calculate thepercentage KCl in the original sample.

Answer:KCl ( gfw =74.50) => AgCl ( gfw =143.50)GF= 74.50/143.50=0.519%KCl = (mass of AgCl *GF/mass of KCl) *100=

=( 0.8402*0.519/0.4500 )*100 = 96.90%

Dr.Jehad Diab

Page 53: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 54: Gravimetric methods of analysis [compatibility mode]

Mainly Al and Mg

Dr.Jehad Diab

Page 55: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Organic reagents

Page 56: Gravimetric methods of analysis [compatibility mode]

Table: some of inorganic precipitating agentsprecipitants analyte and (formed precipitate, weighed)*

NH3(aq) Be (BeO),Al (Al2O3),Cr(Cr2O3), Fe(Fe2O3)

(NH4OH) Sn (SnO2),Zr (ZrO2)

H2S Zn (ZnS→ZnO),As (As2S3 →As2O3 Or

As2O5),Bi (Bi2S3

(NH4)2HPO4 Mg(Mg2P2o7),Zn(Zn2P2O7),Cd(Cd2P2O7)

H2SO4 Sr,Cd,Pb,Ba (all as sulphate)

H2PtCl6 K (K2PtCl6)

HCl Ag (AgCl), Hg(Hg2Cl2)

AgNO3 C l(AgCl), Br (AgBr), I (AgI)Dr.Jehad Diab

Page 57: Gravimetric methods of analysis [compatibility mode]

Table: some of inorganic precipitating agentsprecipitants analyte ( formed precipitate, weighed)* BaCl2 SO4

2- (BaSO4)( NH4)2S Hg (HgS) HNO3 Sn4+ (SnO2) H5IO6 Hg (Hg5(IO6)2 NaCl, Pb(NO3)2 F (PbClF) MgCl2,NH4Cl PO4

3- (Mg2P2O7)Ca2+ H2C2O4 CaCO3 or CaO

Dr.Jehad Diab

-------------------------------------------------------------------------------------------------------* After drying or ignitionFe3+ + OH-→Fe(OH)3 → Fe2O3

weighed formppt

Page 58: Gravimetric methods of analysis [compatibility mode]

Mainly Mg and AL

بعض عوامل الترسیب : جدولالعضویة

Cs+

Mn+ +nHR→ MRn + nH+

M2+ +2HR →MR2 + 2H+

2 , Ag+ , Cu+

M+ +NaR →MR + Na+

Dr.Jehad Diab

interfere

Page 59: Gravimetric methods of analysis [compatibility mode]

Mn+ +nNH4R -> MRn + nNH4+

M2+ +H2R →MR + 2H+

An- + nRCl -> RnA + nClDr.Jehad Diab

Page 60: Gravimetric methods of analysis [compatibility mode]

Ca2+→ CaC2O4 → CaO

Page 61: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 62: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 63: Gravimetric methods of analysis [compatibility mode]
Page 64: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

القیاس الوزني الكھربائي

•used for electroplating, extraction and purification ofof the analyte

Page 65: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 66: Gravimetric methods of analysis [compatibility mode]
Page 67: Gravimetric methods of analysis [compatibility mode]

كمون التفكك

current-voltage relation for electrolysis .

Page 68: Gravimetric methods of analysis [compatibility mode]

Cu2+ +2e => Cu

Ag(CN)2- + e => Ag +2CN-

Pb2+ +2H2O => PbO2 + 4H+ +2e

Dr.Jehad Diab

Page 69: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diabفاراداي ویقدر بالكولوم1= 96500

Page 70: Gravimetric methods of analysis [compatibility mode]

CU2+Determine the number of grams of Cu2+ thatcould be deposited on cathode as Cu,if currentof 6 amperes is applied for 5 minutes

Dr.Jehad Diab

Page 71: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 72: Gravimetric methods of analysis [compatibility mode]

Dr.Jehad Diab

Page 73: Gravimetric methods of analysis [compatibility mode]

RevisionDiminishing importance of gravimetry, as a resultof the development of much faster (though usuallyless precise) instrumental methods.

Consequently, gravimetry is used only when itssuperior precision is really needed. In that case,great care must be exercised to avoidcoprecipitation of other sample components,occlusion of solvent in the precipitate, andadsorption of excess reagent, otherwise the extraeffort is negated by an impure or otherwise poorlydefined precipitate

Dr.Jehad Diab

Page 74: Gravimetric methods of analysis [compatibility mode]

We have emphasized the factors that facilitate theformation of coarse, pure, easily filterableprecipitates, explained why precipitates arepreferably generated homogeneously, and why theyare usually washed with electrolyte solutions ratherthan with water.

Ammonium salts are often used for this purpose,because they will readily volatilize upon subsequentheating of the precipitate.

Dr.Jehad Diab

Page 75: Gravimetric methods of analysis [compatibility mode]

The End

Dr.Jehad Diab