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MIDLANDS STATE UNIVERSITY
DEPARTMENT OF CHEMICAL TECHNOLOGY
HCT 202: INORGANIC CHEMISTRY PRACTICAL
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EXPERIMENT 1
The Chemistry of Chromium.Preparation of Potassium tris(oxalate)chromate(111)-K3[Cr(C2O4)3].3H2O
Experimental (Adams and Rayner,page 50)
1.Reactions of Chromium
Record all observations and interpret them as far as possible.
(a) Add a drop of sodium hydroxide to a solution of potassium dichromate.
(b) Add a few drops of concentrated sulphuric acid to solid potassium dichromate.Notice the colour
change.Add solid solid sodium chloride and warm gently.
(c) Add hydrogen peroxide dropwise to a solution of potassium dichromate to which has been
added an equal volume of ether.What occurs on shaking? Repeat this using an alkaline solution.
(d) Warm a mixture of 1g potassium dichromate in 1 ml concentrated hydrochloric acid and 1 ml
water. Allow to stand, and recrystallize the product from acetone.
(e) Dissolve in dilute hydrochloric acid formaldehyde.Cool and add graduated zinc.
For the following tests use chrome alum solution:
(a) Reduce with zinc and hydrochloric acid.
(b) Add ammonium or potassium peroxidisulphate and one drop of silver nitrate solution and
warm.
2. Synthesis and spectroscopy of k3[Cr(oxalate)3]3H2O
Preparation
To a solution of 2.0g H2C2O4.2H2O and 0.84g K2C2O4.2H2O in 30 ml of water, is added 0.7g of K2Cr2O7 in
small portions with vigorous stirring.( The reaction mixture might not spontaneously warm, heating
solution might be necessary).When the reaction is ended, the solution is evaporated nearly to dryness
and allowed to crystallize.( A quick recrystallization can be achieved by dissolving the complex in
minimum amounts of water and reprecipitating it with ethanol.This should be done quickly with minimal
heating to minimize equation of the complex.Record the yield.
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Spectral Assignments
1. Prepare a 0.01 M solution of the above complex in water, and run its visible spectrum(350 nm –
750 nm). Interpret the results by assigning λmax(nm and cm-1), the extinction coefficient(Є) and
the transitions (different states) of the various bands which you observe.
2. Record the infrared spectrum of the compound and interpret the spectrum.
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EXPERIMENT 2
Synthesis and Spectral study of Cu(11) Complexes
Purpose
To synthesize some Cu(11) complexes having water, ammonia, ethylenediamine, the acteylacetonate
anion and the glycinate anion as the ligands.This selection gives some variety of oxygen and nitrogen
donors as well as a mixed donor ligand.
Experimental
Preparation of cis-Bis(glycinate)copper(11) Monohydrate
A 1.5g sample (6.0 mmole) of copper(11) sulphate pentahydrate is dissolced in 17 ml of 1M HCl. To this
solution 0.75g(10.0 mmole) of glycine is added and then warmed for about one hour.Sodium
bicarbonate is added until precipitation is complete(avoid a large excess).The precipitate is suction
filtered, recrystallised from hot wter and dried in an oven.
Preparation of Bis(acetylacetonate)Copper (11)
A solution of acetylacetone is prepared by adding 1.25g (12.5 mmol) of acac to 50ml of 0.25M NaOH
solution (12.5 mmol). This solution is added to a solution of 1.55g (6.25 mmole) of CuSO4. 5H2O in 100
ml of water.The precipitate is suction filtered, recrystalised from dioxane and air-dried.
Spectra of Cu(11) Complexes
A) Prepare the following stock solutions:
1) A solution of 0.01M Cu(NO3)2 in 2M NH4NO3.
2) A solution of 0.01M Cu(NO3)2 in 1M KNO3.
3) 0.1M NH3.
4) 0.1M ethylenediamine.
B) Determine the spectra of the following nine solutions in the wavelength range 350-900nm:
1) Cu2+ in water
2) Cu2+-NH3 in 1:1, 1:2, 1:3 and 1:4 mole ratio (use stock solution 1).
3) Cu2+-en in 1:1 and 1:2 mole ratio(use stock solution 2).
4) Cu2+ glycine complex in a 0.01M aqueous solution.
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5) Cu2+aca complex in a 0.01M chloroform or methylene chloride solution.
Lab Report
Your lab report should consist of the following:
(a) The yield of both your glycine and acac complexes.
(b) The spectra of the nine solutions.
(c) λmax of the solutions.
(d) 1/λmax(cm-1) of the solutions.
(e) Literature values for 1/λmax(cm-1)
(f) The absorbing species in the various solutions.
(g) Order of spectrochemical series for the ligands used,i.e. for H2O, NH3, en, glycine, acac.
(h) Discussion.
References
1) Bjerrum etal.,Acta Chem.Scand.,8,1275(1954).
2) Bjerrum etal.,ibid., 2, 297 (1948).
3) Jorgensen, C.K., ibid.,9,1362 (1955).
General References
1. Advanced Inorganic Chemistry, 3rd ed., F.A. Cotton & G.Wilkinson.
2. Inorganic Chemistry,2nd ed., J. Huheey.
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EXPERIMENT 3
Preparation of bis(cyclopentadienly) iron
A 250 cm3 three-necked flask equipped with a magnetic stirring bar and a concentration from one side
to a source of nitrogen is charged in 70 cm3 of 1,2-dimethoxyethane and 25g of KOH powder.While the
mixing is slowly stirred while flushing with a stream of nitrogen, 5.5 cm3 of freshly cracked
cyclopentadiene is added. The other side neck is stoppered and the main neck fitted with a 100 cm3
dropping funnel with stop-cock open. After the air has been flushed out the stop-cock is closed and a
solution of 7.5g of iron(11) chloride tetra hydrate in 25 cm3 of DMF is placed in the dropping funnel. The
mixture is stirred vigorously. After five minutes drop-by-drop addition of the iron(11)chloride solution is
begun.The rate of addition is adjusted so that all the solution is added in 20 minutes.Stirring is continued
for another 15 minutes. The flow of nitrogen is then stopped and the mixture is added to 90 cm3 of 6M
HCl containing about 100g of ice.After stirring for five minutes the precipitate is collected on a coarse
sintered-glass funnel and washed with four 25 cm3 portions of water.Record the yield.
Complementary work
1. Measure the melting point of your compound.
2. Heat a small sample in a test tube and note what happens
3. Note the solubility of the substance in toluene
4. Give the overall reaction equation for the experiment.
5. What is the role of the potassium hydroxide.
6. Record the infrared spectrum of the compound as a Nujol mull and assign the peak.
7. Add 0.2g of your compound to water (10 cm3) followed by concentrated nitric acid (10 cm3).
Shake the tube gently for two minutes and record your obsvervations.
8. What other compounds have a similar structure to ferrocene?
Reference: G. Wilkinson et al J.Amer.Chem.Soc. 1954, 76, 1970.
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EXPERIMENT 4
Synthesis and Chromatography of ferrocene derivetives.
This experiment illustrates the ease with which ferrocene will undergo electrophilic substitution and
many of these reactions resemble those of benzene.However, to effect substitution, milder reaction
conditions are usually employed with ferrocene. It is considered to be more ‘aromatic’ than benezene
but differs from this molecule in that it cannot be directly halogenated or nitrated. In these reactions
electrophilic substitution takes place only with difficulty at a positively charged centre.
Materials required:
Concentrated phosphoric acid
Ferrocene
Acetic Anhydride
Sodium bicarbonate
Alumina for chromatography
Benzene
Petroleum ether(b.p. 40 – 60oC)
Diethyl ether.
Procedure:
Add ferrocene (1.5g, *.05 mmoles) to acetic anhydride 5 ml (5.25g, 87 mmoles) in a small Erlernmeyer
flask and this mixture carefully add 1 ml of 85% phosphoric acid with constant stirring. Fit a calcium
chloride guard tube to the flask and heat on a steam bath for 10 minutes. Pour the hot mixture on to
ice( about 80g ) with stirring and when all has melted neutralize the mixture by adding solid bicarbonate.
Cool the neutralized solution in ice for about 30 minutes and remove the brown solid that is deposited
by filtration, using a Buchner funnel. Dry the orange- brown solid by suction.
Prepare a chromatography column, using alumina in petroleum ether( b.p 40-60oC).Dissolve the orange
product in the minimum quantity of benzene(caution: benzene is a cancer suspecting agent, handle in a
fumehood) and add it to the top of the column with a teat pipette. Allow solvent to run out of the
bottom of the column until level has fallen to the top of the column( do not allow it to run dry).Add
petroleum ether(b.p 40-60oC) to the column, allow the solvent to pass through and collect the yellow
band which is eluted. When all of the first band has been eluted increase the polarity of the eluent by
adding a mixture of ether-petroleum ether(2:1) to the top of the column.Elute the second red-orange
band. Evaporate the solvent on a rotary evaporator from each fraction to leave red-orange crystals.
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Recrystallize the solid from the first band using an ether-petroleum ether mixture and the solid from the
second band from petroleum ether.
Characterization:
(i) Determine the melyting points of each compound.
(ii) Record the infrared spectrum of each compound.
(ii) The NMR of one of the compounds is provided. Use the spectrum to identify the compound in
conjuction with the melting point and infrared.
Your report should include the following:
(i) Percentage yield of the two components and their melting points.
(ii) Infrared spectra of the two compounds isolated. Point out differences and similarities and why?
(iii) NMR spectrum provided and interpretation.
Questions:
(i) Write a complete mechanism for the reaction carried out in this experiment.
(ii) What methods might be used to detect the elution of colourless compounds from a column?
(iii) Which of the two components of the mixture eluted first? Why?
(iv) Briefly describe how choice of solvents in column chromatography is made.
References
1. B. Douglas, D.H. McDaniel and J.J. Alexander, Concepts and Models of Inorganic Chemistry, John
Whiley and Sons. 2nd Edition, P.447.
2. R.E. Bozak, J. Chem. Educ. 1966, 43,73
3. R.J.Grahma, R.V.Lindsey, G.w.Parshall, M.L. Peterson and G.M. Whitman, J.
Amer.Chem.Soc.1957, 79,3416.
4. L.F. Druding and G.B.Kauffaman, Coord. Chem. Rev. 1968, 3,409.
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EXPERIMENT 5
Carbonyl Stretching frequencies in metal carbonyls
Mesitylenetricarbonyl tungsten(O)
[1,3,5-C6H3(CH3)3]W(CO)3
The reaction is carried out using a 100 cm3 two-necked round bottomed flask.Place W(CO)6 0.5g (1.4
m.moles) and 10 cm3 (72 m.moles) mesitylene in the flask then flush out the apparatus with nitrogen
gas for about 5 minutes. Adjust the flow of gas so that it is passing very slowly.(The gas passes out of the
condenser which is fitted with a bubbler). Heat the mixture to reflux for 30 minutes using a heating
mantle. Remove the heating mantle and increase the flow of ether (B.P. 60-80oC ) ( 10 cm3) which helps
to precipitate the product.Collect by filtration the yellow product which contains some tungsten metal,
and wash the product with petroleum ether (6 cm3). Recrystallize the product by dissolving it in the
minimum quantity of dichloromethane (about 12 cm3) and filter this solution through a fluted filter
paper.Add petroleum ether 30 cm3 to the filtrate and when the product has precipitetated collect it by
filtration on a Buchner funnel. Wash the product with petroleum ether (5 cm3) and dry it in a vacuum
desiccators.
Use the bulk of your product to prepare(Ph3P)3W(CO)3, this is used in place of cycloheptatriene W(CO)3
in Abel, Bennett and Wilkinson J.C.S.,(1959), p 2324 (Chemistry Depertment library).
1. Record the I.R. Spectra of W(CO)6 and the two complexes prepared both as KBr discs and as
solutions in CCl4.
Consult Cotton and Wilkinson Second edition, Nicholls and Whiting J.C.S.(1959) p 551
R.D.Fischer Chem. Ber. 93(1960) p 165.
Comment on your results and compare with those of free CO.
Questions
1. If the reaction of Mo(CO)6 with mesitylene were conducted in the presence of air, what would
probably be the decomposition products?
2. How would you expect the C-O stretching frequencies in the compounds (C6H6)Mo(CO)3, [1,3,5C6H3(CH3)3]Mo(CO)3 and [C6(CH3)6]Mo(CO)3 vary and why?
3. How would you determine in an afternoon’s experiment whether or not your isolated [1,3,5C6(CH3)3]Mo(CO)3 (or (C6H6)Cr(CO)3 was pure?
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References
1. E.O.Fischer, K. Ofele, H. Essler, W. Frohlich, J.P. Mortensen and W. Semmelinger, Chem. Ber.
1960, 93,165.
2. B. Nicholls and M.C. Whiting J. Chem .Soc.1959,551
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EXPERIMENT 6
The Chemistry of Nickel: Preparation of Cis-chlorobis(triphenylphosphine) nickel (11) NiCl2(PPh3)2
Experimental
1. Reactions of Nickel
Use a solution of nickel sulphate or chloride.
Record all observations and interpret them as far as possible.
(i) Examine the effect of sodium hydroxide and ammonium hydroxide.
(ii) Investigate the effect of dimethylglyoxine at different pH. Do cobaltous solutions give a
precipitate under similar conditions?
(iii) Add potassium cyanide solution dropwise and divide the solution into two parts:
(a) Add sodium hydroxide solution
(b) Crystallize and isolate any solid formed.
(iv) Record the visible and ultraviolet spectrum of a solution of nickel chloride in water. Now add
ethylenediammine hydrate to the solution and repeat the spectrum.
(a) How many bands are there in the spectrum?
(b) Assign the transitions with reference to a Tanabe-Sugano diagram.
(c) Why is the spectrum shifted to higher frequencies when ethylenediammine is added?
2. Dichlorobis(triphenylphosphine)nickel (11) NiCl2(PPh3)2
Materials required :
nickel chloride hydrate
n-Butanol
Benzene
Nitromethane
Dean and Stark apparatus
Rotary evaporator
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Dissolve nickel chloride hexahydrate (1.5g) in the minimum quantity of warm water (less than 10 cm3)
and add n-butanol (50 cm3), benzene(6 cm3) and triphenylphosphine (3.2g). Distill this mixture
azeotropically using a Dean and Stark apparatus until no more water passes over. Transfer the flask from
the Dean and Stark apparatus to a rotary evaporator and evaporate the solution until crystals are
deposited on cooling the solution.Collect the crystals by filtration on a Buchner funnel and immediately
recystallize from nitromethane.The crystals should be stored in a desicator over calcium chloride.
Exercises
1. Record the infra-red spectrum of the complex as a Nujol (paraffin oil) mull; does the spectrum
confirm the presence of triphenylphosphine in the complex ?
2. Record the ultra-violet and visible spectrum of the complex (0.005g) in nitromethane (10 cm3),
using a 1 cm cell.
Determine the molar extinction coefficients for the bands observed.What do the spectrum and
the values of the extinction coefficients indicate about the stereochemistry of the complex?
3. Explain the observation of coluor changes during the recrystallization procedure and its
significance on the structure of NiCl2(PPh3)2
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EXPERIMENT 7
Complex ion composition by jobs method
Frequently it is possible to detect the interaction of two molecules in solution without being able to isolate a
stable compound. For example, benzene and iodine interact in carbon tetrachloride.
C6H6
+
I2
↔
C6H6I2
to form a highly colored 1:1 adduct which is too unstable for isolation. The presence of an adduct is
demonstrated by the intense color of these solutions, yet its composition is uncertain until it has been
established that only one molecule of benzene react with one molecule of iodine.
The area of coordination chemistry has thrived on studies of complexes which have been identified
in solution without being isolated. The interaction for example, of Ni2+ with NH3 in water produces
complexes of the compositions, Ni(NH3)(OH2)52+, Ni(NH3)2(OH)42+, Ni(NH3)3(OH2)32+,
Ni(NH3)4(OH2)22+ Ni(NH3)5(OH2)2+ and Ni(NH3)62+.Of this series only Ni(NH3)62+ has actually been
isolated yet spectrophotometric and Potentiometric investigations leave little doubt concerning the
existence of the others in solution. Because the complexes have not been isolated does not always imply
that the interactions are weak. Indeed bond formation between transition metal ions and ligands is highly
exothermic. For other reasons, however, it is frequently not possible to crystallize from solution all the
species which may be present in solution. Their composition must then be established by other techniques.
The procedure to be used in determining the solution composition of Ni2+-ethylenediamine complex in this
experiment is known as the method of continuous variations for Job’s method. In the general case, it is
concerned with evaluating n for the equilibrium,
Z
+
nl
↔
zLn…………………………………(1)
is Ni2+ and L the ligand ethylenediamine(en). Both Ni2+ and the product
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In the present experiment, Z
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Ni(en)n2+
have absorptions in the visible region of the light spectrum but their spectra are different.
Experimentally, the intensity of absorption at a given wavelength of a series of solutions containing
varying amounts of Ni2+ and en is measured. This absorbance is related to the concentration of
Ni(en)n2+
in solution. These solutions are prepared with the restriction that the sum of the
concentrations of Ni2+ and en be the same in all solutions. In the case where the equilibrium constant
for reaction (1) is very large, ie., the equilibrium lies far towards the right it is clear that the intensity of
the
Ni(en)n2+
absorption will be greatest when the en concentration in solution is exactly n times
greater than of Ni2+ . As will be shown later, this is also true when the equilibrium does not lie far to
the right. Sufficient concentrations of zLn must, however, be produced so that accurate absorbance
measurements maybe obtained on the solutions. It is therefore possible to determine n and the
composition of Ni(en)n2+ by knowing the ratio of en to
Ni2+in the solution which contains a
maximum absorbance for Ni(en)n2+ .
For the Ni2+-en system, a series of complexes, Ni(en)2+ , Ni(en)22+ , Ni(en)32+ , Ni(en)42+ and
so forth are possible. The purpose of this experiment is to determine which of the species are actually
present in the solution, the possible equilibria involved follow:
K1
Ni2+ +
en
Ni(en)2+
↔
K2
Ni(en)2+
+ en
↔
Ni(en)22+
K3
Ni(en)22+ +
en
↔
Ni(en)32+
K4
Ni(en)32+ +
en
↔
Ni(en)42+
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The values of the equilibrium constants will determine which species will predominate in solution. Thus
if k2 is so much larger than k1 ,that virtually no Ni(en)2+
is present in solution, the Job procedure will
identify Ni(en)22+ without giving any evidence of Ni(en)2+ . Likewise the relative size of K3 to K1and
k2 will determine what species are characterized. One of the limitations of the method of continuous
variations is the requirement that only one equilibrium of the type in equation (1) be present in a
solution of Z and L. That is, it will give nonintegral values of n if addition to Z, L, and ZLn, another
complex,ZLn+1 is also present.For the Ni2+-en reactions, this means that only 2 complexes(Ni2+ and
Ni(en)2+ or Ni(en)2+ and Ni(en)22+, and so forth) can be present in any given solution. This will be true if
K1, K2, and K3 are greatly different. From potentiometric studies of the interactions of Ni2+and en, the
values of K1, K2, and K3 have been evaluated(see Experiment 13), and they in fact are separated by large
factors.Although Job’s method allows the determination of complex compositions in this system,
misleading or erroneous results might be obtained in a system where the K values for successive
equilibria are unknown. For this reason, the method of continous variation is limited to relatively simple
systems.
Theory
The purpose of this section is to prove that the value of n in zLn of equation (1) may be determined
from spectrophotometric absorbance measurements on a series of solutions containing varying
amounts of Z and L yet having the same total concentration of Z plus L. If the absorbance at a given
wavelength of each solution is plotted vs the mole fraction,X, of L in solution, the maximum absorbance
will occur at a mole fraction which corresponds to the composition of
zLn. Hence n is determined.
Assume that substances Z and L react according to equation (1) . Equimolar solutions of Z nad L, each of
M moles per litre concentration, are mixed in varying amounts so that the total concentration (Z & L) is
M. A series of these solutions may be prepared by the addition of X litres of L to (1-X) litres of Z(where
X<1). The concentration of Z , L and zLn at equilibrium in these solutions are designated C1, C2,and C3,
respectively. Thus for any solution the concentrations are expressed as follows:
C1= M(1-x)-C3…………(2)
C2= MX-nC3…………….(3)
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C3 = KC1C2n……………(4)
where K is the equilibrium constant for reaction(1). The condition for a maximum in the curve of C3
plotted against X is that
dC3/dX = 0………………………..(5)
Differentiation of equations (4),(3) and(2) with respect to X and combination of the three resulting
differential equations with equations(2), (3) and(5) gives
n= X/(1-X)…………………(6)
Therefore, from the value of X for which C3 is a maximum n may be calculated from equation (6).Now it
remains to be shown that a maximum in the absorbabnce at a given wavelength of light when X is varied
coincides with the maximum of C3.From the Beer-Lambert Law,
From beer lambert law A= ЄCl………….(7)
Where A=absorbance, Є=molar extinction coefficient,C=molar coefficient,I= length of light path
or thickness of the cell.
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The extinction coefficients of Z,L, ZLn at a given wavelength are designated Є1, Є2, Є3
respectively.Since the absorbance of a solution is the sum of the absorbances at that wavelength of the
contained species , the measured absorbance,Ameas, is
Ameas = (Є1C1 + Є2C2 + Є3C3 )………………….(8)
If there is no interaction between Z and L ie: C3 = 0, the absorbance AZ+L ,would be
AZ+L = [Є1M(1-X) + Є2MX]I………………………(9)
The diff btwn Ameas and AZ+L is designated Y
Y = (Є1C1 + Є2C2 + Є3C3 )- [Є1M(1-X) - Є2MX]I………..(10)
By differentiating equation (10) with respect to X it can be shown that Y is max when C3 is a
maximum if Є3 > Є2 or a minimum when C3 is a maximum if Є3< Є1.
In this experiment
Ni2+
corresponds to Z and ethelendiamine(en) to L. Since en has
no absorptions in the region of the spectrum under study, Є2 will be always zero. The cell to be used in
the measurements has a thickness of 1 cm . Under these conditions equation (10) reduces to
Y = Ameas – (1-X) AZ………………………………(11)
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Where AZ is the absorbance of the pure M molar Ni2+ solution. To evaluate n in Ni(en)22+,a plot of Y
vs X at a given wavelength is made. A max in this plot occurs at a certain mole fraction. From this value
of X n may be calculated from equation (6).Because more than one complex composition will be
examined in this experiment, plots will be constructed from data taken at several wavelengths
corresponding to different Ni(en)2+
complexes.
Procedure
Prepare 100ml of the following solns
. 0.4M nickel sulphate
. 0.4M ethylenediamine
By mixing these solutions, prepare mixtures having a total volume of 10ml in which the mole fraction of
ethylenediamine, X will be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9. Determine the absorbances of each of these
solutions and of the pure 0.4M nickel sulphate at the following wavelengths: 530, 545, 578, 622 and
640цm.If a scanning visible spectrophotometer is available, the most convenient method of determining
the absorbances at the various wavelengths is to record the spectrum of each solution from
approximately 500-600 цm. The spectra of all solutions can be run on the same piece of paper of chart
paper. Calculate Y values (use equation 11) at each wavelength for entire series of solutions and make a
plot of Y vs X for each of the five wavelengths. From the value of X at each of the five maxima the values
of n for the Ni(en)22+ complexes may be calculated from equation (6).
Report
Include the following
1. Spectra or absorbance measurements of the solutions
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2. Plots of Y Versus X for each of the five wavelengths
3. Calculated values of n and formulas of Ni2+ complexes present in solution.
Questions
1. Draw structures of Ni(en)n2+ complexes in solution
2. From the observed changes in the spectra and knowledge of the complexes present in the solutions
what can be said about the relative ligand field strength of en and H2O?
3. Derive equation (6).
4. By differentiating eqn (10), show that Y is a maximum when C3 is a maximum.
5. Give a specific example of a reaction in which jobs method would be useful.
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