prof Viktor Kanický, Analytická chemie I
1
GRAVIMETRY

prof Viktor Kanický, Analytická chemie I
2
Gravimetry
nBasic method, classical
nConstituent to be determined is transferred from a given, precise amount of a sample into a
defined chemical individuum, whose mass determined by weighing is a measure of a content of the
constituent in the sample
nAnalytical weighing  balances (scales) in principle isosceles lever + pendulum
qsensitivity
qaccuracy
rovnoramenne vahy.JPG

prof Viktor Kanický, Analytická chemie I
3
Weighing
q1) accuracy – the same length of both scale beams
q (Gauss method of double weighing)
nBuoyancy force (reduction of weighing at vacuum)
n mx – real mass
n z – weight of the weight
n sx, sz – specific mass of mx , z
n σ – specific mass of air
nΣ = 0,0012 g.cm-3, sz = 8,4 g.cm-3 (brass) → for z = 1
n 0,5 g of subst. ≈ buoyancy 0,08 mg

prof Viktor Kanický, Analytická chemie I
4
Weighing
nOther influencing factors:
qair humidity: adsorption of H2O, time factor
qfinger prints: tweezers, laboratory tongs
qhygroscopic substances: ground-glass weighing bottles
qelectric charge: powdered non-conductive substances on dry glass
qweights (relative calibration – calbration standards)
qweighing procedure: to lock balances, opening… no overloding !!!

prof Viktor Kanický, Analytická chemie I
5
Weighing
q2) sensitivity l – scale beam
§ G – beam weight
§ d -  distance
qAnalytical balances
q Capacity: The larges weight the balance is capable of weighing       Accuracy: the extent to
which a given measurement agrees with the standard value for the measurement. (i.e. given weight is
100.000 g, weighed 100.002 g, accuracy is 2 mg.
qCalibration: to determine, check or rectify the graduations of balance. It is the comparison
between the output of a scale or balance against a standard value.
qReproducibility: ability of scales to return to the same numeric result with repeated application
of the same weight. (hysteresis)
q
q
q
n
gravimetrie1

Weighing
nHysteresis: property of load cells, and other weighing systems dependant on elastic materials,
such as spring balances, resulting in different indication at the same load, depending upon the
direction of approach to that load, i.e. whether it is approached by increasing the load or
decreasing the load. Hysteresis error refers to the condition of repeatedly weighing the same
object, but obtaining different readings on the numeric readout.
nDrift: is a progressive (continuously upward or continuously downward) change in the number
displayed on the digital readout.  The weight readings does not stabilize, or unstable readings
with no weight applied.  All analytical balances show some uncertainty.
prof Viktor Kanický, Analytická chemie I
6

Weighing
nPrecision: The extent to which a given set of measurements of the same sample agree with their
mean. Amount of agreement between repeated measurements of the same quantity.  Also know as
repeatability.  A scale can be extremely precise, but not necessarily be accurate.
nRepeatability: refers to an instrument’s ability to consistently deliver the same weight reading
for a given object, and to return to a zero reading after each weighing cycle.  Test this by
repeatedly weighing the same object.
nCount (digit): The smallest increment of weight which the digital display resolves.  Also called
"division.”
nDivisions: The amount of increments a scale offers.
n
prof Viktor Kanický, Analytická chemie I
7

Weighing
prof Viktor Kanický, Analytická chemie I
8
forcemotor.gif
Mechanically the sensor is a simple lever & fulcrum.  One end of the lever holds the weighing pan
where an unknown weight is placed.  On the opposite end of the lever is a FORCE COIL suspended in a
magnetic field (much in the same way a speaker operates).  The displacement detector, and power
amplifier produce an appropriate current to hold the lever balanced in the null position for any
weight placed on the pan.  The amount of current required to do this is proportional to the weight
on the pan.
The MICROPROCESSOR monitors the current produced in response to the applied load to determine the
magnitude of the weight.  Software contained in memory allows the user through the front panel,
keybord or one of the optional interfaces to perform such tasks as converting units of weight and
parts counting.  In addition the user can change filter parameters to suit most environments or
gather statistical data form groups of weights.  Calibration coefficients and user developed
constants are stored in a non volatile memory.

prof Viktor Kanický, Analytická chemie I
9
Precipitation
nclassical separation technique for gravimetry
npreparation of pure compounds
qinsolubility of precipitate x loss (< 0,1 mg)
qsolubility of precipitate ≈ concentration of saturated solution above the precipitate
qLow soluble salts ≈ strong electrolytes ≈ complete dissociation
q
q
q         ← unit activity of the solid phase is included in the constant
q
q      = solubility product (thermodynamic value)

prof Viktor Kanický, Analytická chemie I
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Calculation of solubility of pure compounds
nuni-univalent electrolyte
n
qIt is valid in distilled water in the absence of other ions

prof Viktor Kanický, Analytická chemie I
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Calculation of solubility of pure compounds
nexample: How many grams of  AgCl is contained in 1 l of saturated solution of AgCl, M (AgCl) =
143,32 g.mol-1
n
n
n
nexample: What is the solubility of Ag2CrO4 in H2O?

prof Viktor Kanický, Analytická chemie I
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Solubility
nFactors influencing solubility
qown ions
qpH
qcomplexation
qtemperature
qsolvent
qparticle size
qionic strength
}  side reactions

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
n1) influence of own ions – excess of precipitatnt
qM+B-  a) precipitant excess:
q b) precipitant excess:
qgenerally
n
nexample:
n by precipitating of Ag+ by excess of
n
n → washing the precipitate by diluted solution of precipitant, no water
n x large excess → (soluble) complexes formation → dissolution

prof Viktor Kanický, Analytická chemie I
14
Factors influencing solubility
nexample: calculate concentration of SO42- necessary for quantitative precipitation of
BaSO4                                     (M (BaSO4) = 233,43g.mol-1; Ks = 1,08 . 10-10)
nCondition: m (BaSO4) in solution < 10-4 g; V = 300 cm3
n

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
n2) pH and complex formation
qside equilibria → soluble complexes (hydroxocomplexes of  cations, protonization of  anions)
q
qsolid phase dissolution
q
qacids and bases increase solubility of precipitate
q

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
qconditional solubility product
q     c (M)  c (B)
q
qα – side reaction coefficient

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nexample: diprotic acid:

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nexample: what is solubility of CaF2 in 0,01 M – HCl?
n

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nexample: calculate solubility of AgI v 0,01 M NH3
n
n
n
n
n
n
n
n
n
n Solubility increases 40x.
n

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nexample: calculate molar solubility of BaCO3 at pH = 6 and I = 0,1 (pKs = 8,09; pK1 = 6,15; pK2 =
9,99)

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
qDissolution of BaCO3 in H2O, influenced pH, iteration
n1) hydrolysis neglected →
n
n2) we find pH at hydrolysis of CO32-
n a)
n
n hydrolytic constant
n
n
n
n
n b)
nwe neglect for calculation of pH, because

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
n c) pH of weak acid:
n
n
n
n
n3) we find cond. solub. product. Ks´ and  c (BaCO3)
n
n
n
n
n
n4) we repeat calc. pH according 2c) with c (CO32-) = 1,48.10-4
n we get pH = 9,90, Ks´ = 10-7,74, c (BaCO3) = 1,35.10-4 M
n further approximation yields c (BaCO3) = 1,32.10-4 M
n

prof Viktor Kanický, Analytická chemie I
23
Factors influencing solubility
qdependence of  solubility of sulfides on pH – principle of „sulfane“ separation of cations
qsulfide MS:
qboundary condition: pH ≤ 6 – simplification → x (S)
q comprises only 1 term:
q K1, K2 – dissoc. const. H2S a HS-, hydrolysis of M is neglected

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
graf_1

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
qInfluence of formation of complexes with own ions
q M – cation; B – anion, ligand; MB – weak soluble comp.
q
q             soluble complexes
q (MB)r – soluble, non-dissociated portion of MB
q
q βMB – stability constant
q
q
q
q
q
q calculation of solubility MB in excess of  precipitant

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nexample: AgCl, solub. compl. [AgCl2]-, [AgCl3]2-, [AgCl4]3-
n       Ks, β1      β2 β3        β4
graf_2

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
qDependence of solubility of hydroxides on pH

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
nHydroxides of  trivalent cations are less soluble than hydroxides of divalent ones.
nAt pH 4,5 to 6: Fe(OH)3 ↓, Al(OH)3 ↓ quantitatively
nSeparate from Zn2+, Mn2+, Co3+, Ni2+,Ca2+ and Mg2+
graf_3

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
n3) ionic strength (influence of third ions)
qindifferent electrolyte
q 1)
q
q 2)
q
q 3)
q
q
q
qsolubility increases with increasing concentration of third ions
n
n
n

prof Viktor Kanický, Analytická chemie I
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Factors influencing solubility
n4) particle size of precipitate
n influence of surface of crystals
n
n
n
n
n
n
n
n colloid dispersion – charge of adsorbed ions decreases solubility
q
n
qfor > 10-3 mm is valid
q
qsolubility increases – crystal edges – weaker attractive forces
qsmall crystals dissolve – bigger grow
aging of the precipitate
OSTWALD - FREUNDLICH

prof Viktor Kanický, Analytická chemie I
31
Factors influencing solubility
n5) influence of solvent
qOrganic solvents decrease solubility of inorangic substances
qexample: CaSO4 in 50% EtOH quantitatively precipitates
q          LiCl soluble in amylalcohol,
q             neither KCl a NaCl
qInfluence increases with charge of ions
q
q
n

prof Viktor Kanický, Analytická chemie I
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Properties of precipitates
ndepend on : - chemical composition
n - properties and composition of   medium in which precipitation occurs
n - method of precipitating
nprecipitate types: - colloidal (sulfur)
n - gel-like (Fe(OH)3)
n - lumpy (AgCl)
n - crystalline (convenient, better filterable,          more pure than amorphous):
§fine (BaSO4)
§coarse(PbCl2)
nrequirements: filterability, easy drying, ignition, defined composition

prof Viktor Kanický, Analytická chemie I
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Properties of precipitates
nmechanism: 1) formation of oversaturated solution     (metastable)
q 2) formation of crystallization centers      (cores, primary)
q 3) growth of paticles (aging)
nbig particles grow at the expense of small
n
qa) rate of formation of precipitate (Weimarn)
q c´ - instantaneous concentration of       oversaturated solution c - solubility

prof Viktor Kanický, Analytická chemie I
34
Properties of precipitates
qb) mean particle size depends on original concentration of solution (Weimarn)
q
q
q
q
nMore soluble substances – bigger particles
nt – time – aging
n
qc) mean particle size increases
q with time of contact of precipitate
q    with original solution.
n
graf_5 graf_6

prof Viktor Kanický, Analytická chemie I
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Properties of precipitates
naging:
nless perferct → more perfect crystals
nMetastable modifications→ stable (aragonit → kalcit)
nchange of number of crystal water moleules
n
ndehydratation (hydrat. oxidy Fe, Ti, Sn, Al, Zr, Th)
npolymeration (CoS, NiS)
graf_7

prof Viktor Kanický, Analytická chemie I
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Properties of precipitates
qColloidal dispersions (10-5 – 10-7 cm): Brown motion
q      Tyndall effect
qRTG → crystalline character
nlarge specific surface (S/V)
nadsorption ability
qexistence of colloidal dispersions: repulsive elastic forces
qelectric double layer → micelles
qexample:
q         change of sign of charge in
q           isoelectric point x point of           equivalence
graf_8

prof Viktor Kanický, Analytická chemie I
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Properties of precipitates
ncoagulation
qcharges of the same sign on micelles x coagulation
qelectrolyte excess disturbs a double-layer→ micelles coagulate
qcoagulation increases with discharge of salt in washing solution (AlCl3 >> NH4Cl, 1000 x)
q x ammonia salts preferred–removable at heating
q dispersion stability – H2O molecules binding →
nlyophobic colloids – unstable (As2S3, S, Au, AgX)
nlyophilic cololoid   – stable (starch, gels, proteins, Al2O3.xH2O,        SiO2.xH2O)
npeptization – the opposite of coagulation
qat filtration and washing with water – removing of electrolyte – unwanted effect! – therefore we
wash with electrolyte soloution

prof Viktor Kanický, Analytická chemie I
38
Contamination of precipitates
qco-precipitation
qpost-precippitation (induced preciptation)
q
ncoprecipitation adsorption
n occlusion
n inclusion
n mixed crystals
n a) adsorption: depends on – conc. of adsorbed substances
n            - properties of adsorbed substances
n            - properties of precipitate
nPaneth-Fajans: most adsorbed own ions and forming low soluble substances

prof Viktor Kanický, Analytická chemie I
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Coprecipitation
qexample: BaSO4 in excess of Ba2+: Br- < Cl- < ClO3- < NO3-
q             BaSO4 in excess of SO42-: Na+ < K+ < Ca2+ < Pb2+
qeasier adsorbed ions with higher charge
qFreundlich adsorption isotherm
q         (T=const.); k, n – const.; x – amount /1 g precip.
qrelatively highest adsorption of impurities occurs at lowest conc. of impurities
qcontamination of precipitate is proportional to surface → coagulated colloidal dispersion x coarse
crystalline precipitate
graf_9

prof Viktor Kanický, Analytická chemie I
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Coprecipitation
n b) occlusion: mechanical stripping of extraneous components of solution at precipitating and
growth of crystals around the impurity ≈ concentration of solution and ≈ rate of precipitation
n
n c) inclusion: mechanical closure of parent solution at crystal growth

prof Viktor Kanický, Analytická chemie I
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Coprecipitation
n d) mixed crystals: isomorphic substitution of ions at ∆rion < 10-15 % and at the same crystal
group = solid solutions
n preferred ions with the same electric charge numbers
n
n
n
n D – partition koef.; c1,c2 – koncentration of isomorphic const.; t – precip.; r-solution
n
n it is not possible to purify by repeated precipitating with the same precipitant!!!
n D less depends on T(K), precip. rate, conc.
n

prof Viktor Kanický, Analytická chemie I
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Coprecipitation
qtypes of contamination
q
q
graf_10

prof Viktor Kanický, Analytická chemie I
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Postprecipitation
npostprecipitation– induced
1)originally pure precipitate:
2)after some time from oversaturated solution of MgOx  precipitates MgOx
n it is therefore advisable to keep concentration ratios, and CaOx soon be filtered off, dtto
sulfides
nKlathrates:                              inside benzen

prof Viktor Kanický, Analytická chemie I
44
Amorphous precipitates
nAmorphous precipitates – by coagulating of colloids → gels
qlarge specific surface → significant sorption
qcoagulation by excess of electrolyte – source of contamination
qfiltration – immediately after precip.
qto wash with electrolyte solution (peptization!!!)
nMinimizing of coprecipitation – by a suitable procedure

prof Viktor Kanický, Analytická chemie I
45
Principles of precipitation
nprecipitation from hot solutions – better formation of crystal lattice without third ions –
contaminating ions; to cool before filtration in case of more soluble precipitates (MgNH4PO4)
nprecipitation from sufficiently diluted solutions; repeated  precipitation (2x) (hydroxides);
diminuition of coprecipitation   of cations on precip. A+B- by precipitating with B- and vice versa
nprecipitating agent is added slowly at agitation x local  increase of concentration; formation of
coarse precipitate with small surface
nallow to settle before filtration– less occlusion x less postprecipitation!
nthorough washing (hot water, electrolyte), colloids!! Too  much soluble substances by alcohol
n

prof Viktor Kanický, Analytická chemie I
46
Precipitation procedure
n1) solution of substance to be precipiated is adjusted according to instruction (pH, temperature)
and precipiptated with clear solution of preciptitating reagent
1.
n2) precipitation is carried out in 250-400 ml beakers, sample volume is adjusted to ca 100-200 ml
1.
n3) precipitation solution is added slowly from burette  or pipette + stirring with glass rod
1.
n4) after the precipitate is settled the test for complete precipitation is performed
n

prof Viktor Kanický, Analytická chemie I
47
Precipitation procedure
nPrecipitating from homogeneous medium:
qprecipitatin reagent occurs gradually and continuously by chemical reaction
qdecomposition, hydrolysis
qexample: precipitation of sulfides by thioacetamide (at hot, hydrolysis)
q
q
q
q sulfide precipitates better coagulate and less adsorb
reakce1

prof Viktor Kanický, Analytická chemie I
48
Precipitation procedure
qexample: precipitation of hydroxides (M3+, M4+) separation from M2+
q       binding H+

prof Viktor Kanický, Analytická chemie I
49
Filtration
nrate of filtration
n
n
n P –    filtration area
n r  –    pore radius
n p1-p2 hydrostatic pressure differecnce between both sides of            filtration medium
n l  –    effective length of capillaries
n η –    dynamic viskosity
n V –    capillary volume
n t  –     time
qfiltration acceleration:
nincrease P (folded filter,frit) p1-p2 (exhausting, longer filer funnel stem)
ndecreased η (by warming)

prof Viktor Kanický, Analytická chemie I
50
Filtration
nbesides mechanical effect influenced by:
nhydration
nadhesion
nadsorption
nelektrokinetic effect
ncharacter of filtered substance
n
qhydration – swelling of lyophilic filtration material → filtration retardation (retained even
smaller particles)
qadhesion – liquid in capillaries  flows slower along capillary walls

prof Viktor Kanický, Analytická chemie I
51
Filtration
qadsorption – precipitate particles adhere on capillary walls
qelektrokinetic effekct – potential difference between capillary wall and liquid →
nnegative charge of fitr. paper retains cations and positively charged particles of the precipitate
npaper retains negative particles after washing with HCl
qcharacter of filtered substance – it creates another filtration layer – different capillarity
nGels – filter clogging, therefore larger filter porosity is required and  filtration with
exhausting is necessary (p1-p2)

prof Viktor Kanický, Analytická chemie I
52
Filtration
nquantitative paper filters (ash-free) pure cellulose, 0,01 mg of ash
nDifferent colour codes
n„red ribbon“ – medium fast filtration (amorphous Fe2O3)
n„yellow ribbon“ (colloides, sulfides)
n„green ribbon“ – slow filtration, fine precipitates
n„blue ribbon“ – slow filtration, very fine crystalline  precipitate, BaSO4
n„black ribbon“ - fast filtration, coarse precipitates
n„white ribbon“ – medium fast filtration, standard filter for many applications

prof Viktor Kanický, Analytická chemie I
53
Filtration
n> 10% solutions of acids or bases damages paper filters
npaper filters can not be used for filtration of substances that are reduced at ashing
n
nfiltration crucibles
qcrystalline  precipitates
qglass crucibles – only drying (to 200°C)
qporcelain crucibles – ignition (to 1200°C)

prof Viktor Kanický, Analytická chemie I
54
Washing of precipitate
nremoval of residues of parent solution –decantation is efficient – washing in beaker after
precipitation
nusing smaller volumes more times
n
n
n
n V1 – filtrate volume retained by precipitate
n V2 – washing volume
n cn – concentration of third ions after n-times washing

prof Viktor Kanický, Analytická chemie I
55
Washing of precipitate
nprecipitate – ionex – it is necessary to substitute third ions by adsorption of ions of a washing
solution electrolyte
n
ncrystalline precipitates – washing by solution of salt with common ion with precipitate
n
ncolloidal precipitates – washing by solution of electrolyte protecting from peptisation
n
nammonium salts – easily removable by ignition
n
nwater at last, alcohol for more soluble precipitates

prof Viktor Kanický, Analytická chemie I
56
Drying
na) drying in open atmosphere
nremoval of excess moisture until equilibrium with the pressure of water vapor in the air at a
given temperature
qFreundlich adsorption isotherm y = a.xb – monomolecular layer of water
q     a) non-hygroscopic substances
q      b) hygroscopic substance
q           (more layers of H2O)
q
q ad b) can not be dried in open atmosphere → it is necessary to decrease ambient pressure and
increase temp.; vacuum drying
qWater vapor pressure of surface bound water is lower nižší, therefore 105-110°C is needed
graf_11

prof Viktor Kanický, Analytická chemie I
57
Drying
nb) in dessicator – dessicants
nchemically (P2O5)
nBy adsorption (silik.)
n mg/l H2O in vapor
n P2O5 2 . 10-5
n Mg(ClO4)2 5 . 10-4 (anhydron) – for elemental analysis
n BaO 7 . 10-4
n KOH 2 . 10-3
n silica gel 3 . 10-2 – retains water vapor up to 40 % of its mass
n addition of CoCl2 – anhydrous blue → wet pink, regeneration 180-200°C

prof Viktor Kanický, Analytická chemie I
58
Drying
qmolecular sieves – silicates Al, Ca, K, Na
q
qgas adsorption
nacid (CO2, SO2) ≈ CaO, KOH, NaOH
nalkaline (NH3) ≈ P2O5, H2SO4
n
qalcohol vapors ≈ CaCl2
q
qbenzine, chloroform, ether ≈ paraffin

prof Viktor Kanický, Analytická chemie I
59
Drying
nc) at elevated temperature
qdryer oven to180°C, ± 5°C control, 105-110°C, also: loss of crystallization water
q
q
q
qvolatilization: NH3, CO2, SO2, ammonium salts at 150°C, volatile chlorides
qfiltration paper can withstand 150°C
qdrying to constant wight– if a precipitate is dried directly to the form suitable for weighing –
repeat the drying and weighing until the weight change (0,2 mg)
q
n

prof Viktor Kanický, Analytická chemie I
60
Ignition
ntransfer of precipitate to ignited state
nporcelain crucible + triangle with ceramic rollers (Pt- crucible)
n temperatures:
n Bunsen burner - porcel. 700-800°C
n    - Pt 850-1000°C
n Teclu + 100°C x Buns.
n Mecker + 200°C x Buns.
kahan

prof Viktor Kanický, Analytická chemie I
61
Principles and procedures of ignition
1)drying and  ignition of empty crucible to constant weight slowly (non-luminous flame), tongs
2)filter into the crucible:
a)to dry at 70°C in drying oven or over burner
b)to incinerate (charring, air, no fire!!!)
n
3)ignition (500-1000°C) – burner, muffle furnace; after cooling down to 100-200°C → into
dessicator; to constant weight (± 0,2 mg)

prof Viktor Kanický, Analytická chemie I
62
Types of gravimetric determinations
a)without  precipitation reagent – salts ignition, heavy metal salts with anions of volatile acids
(NO3-, CO32-, SO42-) → CuO, ZnO, Fe2O3, Al2O3, Cr2O3, Bi2O3, Sb2O3, SnO2, TiO2, ZrO2)
b)
b)addition of precip. reagent : H2S, HCl, H2SO4, NH4OH, Na2HPO4, AgNO3, BaCl2  oragnic reagents :
8-hydroxyquinoline, anthranilic acid, oxalic acid

prof Viktor Kanický, Analytická chemie I
63
Types of gravimetric determinations
c)precipitation from homogeneous solution
n for precipitation of hydroxides (urea, carbonyldiamide, carbamide, diaminmethanal):
n
n for precipitation of oxalates, phosphates and sulphates – hydrolysis of esters:
n
n for precipitation of sulphides:
n
n       thioacetamide              acetamide
n
n

prof Viktor Kanický, Analytická chemie I
64
Overview of gravimetric methods
ion
precipitating reagent
form: precipitated/weighted
temperature dry./ign. °C
Ag+
HCl
AgCl
130
Al3+
NH4OH
8-quinolinol
Al(OH)3 / Al2O3
Al(C9H6ON)3
1000
130
Ba2+
H2SO4
(NH4)2CrO4
BaSO4
BaCrO4
700
550
Bi3+
(NH4)2HPO4
8-quinolinol
BiPO4
Bi(C9H6ON)3.H2O / Bi(C9H6ON)3
800
130
Ca2+
(NH4)2C2O4
Ca C2O4.H2O
105
Cu2+
benzoin oxime
Cu(C14H11O2N)
110
Fe3+
NH4OH
8-quinolinol
Fe(OH)3
Fe(C9H6ON)3
1000
120
Hg2+
H2S
HgS
110

prof Viktor Kanický, Analytická chemie I
65
Overview of gravimetric methods
ion
precipitating reagent
form: precipitated/weighted
temperature dry./ign. °C
Mg2+
(NH4)2HPO4
NH4MgPO4.6H2O/Mg2P2O7
1100
Ni2+
2,3-butandion-dioxim
Ni(C4H7O2N2)2
120
Pb2+
K2Cr2O7
anthranilic acid
PbCrO4
Pb(C7H6O2N)2
140
110
Zn2+
(NH4)2HPO4
8-quinolinol
NH4ZnPO4 / Zn2P2O7
Zn(C9H6ON)2.2H2O/Zn(C9H6ON)2
900
130
AsO43-
MgCl2, NH4Cl
NH4MgAsO4.6H2O/Mg2As2O7
900
Br-, Cl-, I-
AgNO3
AgCl, AgBr, AgI
130

prof Viktor Kanický, Analytická chemie I
66
Overview of gravimetric methods
ion
precipitating reagent
form: precipitated/weighted
temperature dry./ign. °C
CrO42-
BaCl2
BaCrO4
500
PO43-
MgCl2, NH4Cl
NH4MgPO4.6H2O/Mg2P2O7
1100
SO42-
BaCl2
BaSO4
700

prof Viktor Kanický, Analytická chemie I
67
Calculation of gravimetric analysis
ngravimetric factor– what is < 1, the error is smaller
qex. a (g) sample → b (g) AgCl, chlorides content is

prof Viktor Kanický, Analytická chemie I
68
Calculation of gravimetric analysis
nindirect determination of K+ and Na+ - mixture of chlorides