Inorganic Chemistry Practical
Under UGC Syllabus for M.Sc. (Previous) in all India Universities
1. Qualitative and Quantitative Analysis
(a) Qualitative analysis of mixtures containing not more than six radicals including:
(i) Rare-earth elements
(ii) Anions, which have not been done in under graduate practical.
(iii) Insoluble. (4-30)
(b) Quantitative Analysis of mixtures of metal ions involving Volumetric (by complexometric titration using masking and demasking agents) and gravimetric analysis. (38-42)
2. Chromatography
Separation of cations and anions by- Paper Chromatography/ Thin Layer Chromatography (48-60)
3. Preparations (60-76)
Preparation of selected inorganic compounds:
VO (acac)2
TiO(C9H8NO)2.2H2O
cis-K[Cr(C2O4)2(H2O)2]
Na[Cr(NH3)2(SCN)4]
Mn(acac)3
K3[Fe(C2O4)3]
Prussian Blue, Tumbull’s Blue.
Co[(NH3)6][Co(NO2)6]
cis-[Co(trien)(NO2)2]Cl.H2O
Hg[Co(SCN)4]
[Co(Py)2Cl2]
[Ni(NH3)6]Cl2
Ni(dmg)2
[Cu(NH3)4]SO4.H2O
1. Qualitative Analysis
Experiment 1. To identify acidic and basic radical in the given mixture.
Experiment 2. To identify the interfering radicals in the given mixture.
Experiment 3. To identify Borate, Chromate, permanganate in the given inorganic mixture.
Experiment 4. Identify Sulphate in the presence of Sulphite and sulphide.
Experiment 5. Identify interfering radicals in the given inorganic mixture.
Experiment 6. Identify halogens in the given mixture in the presence of each other.
SALT ANALYSIS
• Introduction
• Confirmation tests for Acidic Radicals
• Confirmation tests for Basic Radicals
• Data files used
• Main Program
• Output Verification List
INTRODUCTION TO SALT ANALYSIS
Usually a salt contains at least one Basic Radical and one acidic radical. We must identify the name of the basic radical and acidic radical to name the salt and to use without confusion. We can say that identification of various elements such as acidic radicals and basic radicals that are present in a salt is called as Salt Analysis. In schools and in colleges students use different books and tables to help them in salt analyzing. Most of the students cannot understand them and take decision that is what should be done in next step. This program can help them by giving instructions about next step.
By using this program, we can identify 22 basic radicals and 14 acidic radicals. The basic radicals are as follows,
1. Aluminium 2. Ammonium 3. Antimony
4. Arsenic 5. Barium 6. Bismuth
7. Cadmium 8. Calcium 9 . Chromium
10 . Cobalt 11. Copper 12. Ferric
13. Ferrus 14. Lead 15.Magnesium
16. Manganese 17. Mercury 18.Nickel
19. Strontium 20. Tin 21.Zinc
22. Silver
The acidic radicals are as follows,
1.Arsanide 2.Arsenate 3.Borate
4.Bromide 5.Carbonate 6.Chloride
7.Chromate 8.Flouride 9.Iodide
10.Nitrate 11.Oxalate 12.Phosphate
13.Sulphide 14.sulphate
CONFIRMATION TESTS FOR ACIDIC RADICALS
1.Arsanide 2.Arsenate 3.Borate
4.Bromide 5.Carbonate 6.Chloride
7.Chromate 8.Flouride 9.Iodide
10.Nitrate 11.Oxalate 12.Phosphate
13.Sulphide 14.sulphate
ARSENATE
To 2 ml of extract add dil.HNO3 till there is no effervescence. Add Silver Nitrate Solution. If precipitate is formed filter it. Add ammonium Hydroxide along the walls of test tube.
RESULT: Chocolate brown ring at the neutral zone.
ARSENIDE
To 2 ml of the extract add dil. HNO3 till there is no effervescence. Pass H2S.
RESULT: Yellow precipitate appears.
BORATE
1. Boron Tri Fluoride Test:
Mix a little of the substance with Borax and Conc.H2SO4 in a test tube. Heat and set fire to the vapor.
RESULT: Green flame appears.
2.Ethyl Borate Test:
To a little of the substance in a test tube add about 1 ml of Conc. H2SO4 and 2 ml of Ethyl Alcohol . Heat and set fire to the vapour.
RESULT: Green edged flame.
BROMIDE
Mix the substance with a little MnO2.Add Conc.H2SO4 and warm.
RESULT: Reddish brown gas turning starch iodide paper Blue.
CARBONATE
Add a few ml of diluted HCl to a little substance in a test tube.
RESULT: Brisk effervescence. Colorless, odourless gas turning lime water milky.
CHLORIDE
Chromyl Chloride test:
Heat 0.1 gm of the substance with 0.3 gm of Potassium Chromate and 1 ml of Conc.H2SO4.Pass the red vapour of Chromyl Chloride into a little water. Add NH4OH and acetic acid add lead acetate.
RESULT: Yellow precipitate appears.
CHROMATE
Heat 0.1 gm of the substance with Sodium Chloride 0.3 gm of Potassium dichromate and 1 ml of Conc.H2SO4.Pass the red vapours of Chromyl chloride into water. Add NH4OH and acetic acid and lead acetate.
RESULT: Yellow precipitate appears.
FLOURIDE
Boron Tri Fluoride test:
Mix a little of the substance with Borax and Conc.H2SO4 in a test tube. Heat and set fire to the vapour.
RESULT: Green flame appears.
IODIDE
Mix the substance with a littleMnO2.add Conc. H2SO4 and warm.
RESULT: Violet vapour turning starch paper Blue.
NITRATE
Brown Ring Test:
To 2 ml of the extract add dil.H2SO4 till there is no effervescence. Add FeSO4 along the side of the test tube.
RESULT :Brown ring in the junction of two liquids.
OXALATE
Add dil. H2SO4 to a little of the substance in a test tube. Warm and add a pinch of MnO2.
RESULT: Colourless Gas turning lime water milky.
PHOSPHATE
1.Ammonium Molybdate test:
To a little substance in a test tube add 2 ml of Conc. HNO3 and warm. Cool it under the tap. Add the mixture to 5 ml of Ammonium Molybdate solution taken in another test tube.
RESULT: Yellow precipitate appears.
2.Magnesia Mixture Test:
To 2ml of the extract add dil.H2SO4 till there is no effervescence. Add NH4CL,NH4OH and then MgSO4 solution. Scratch the side of the test tube.
RESULT: White crystalline.
SULPHATE
Add 2 ml of extract with dil H2SO4 till there is no effervescence. Add BaCl2 solution.
RESULT: White precipitate appears.
SULPHIDE
Add few ml of diluted HCl to a little of the substance in a test tube and warm.
RESULT: Colourless gas with the smell of rotten eggs. It turns lead acetate paper shining black.
CONFIRMATION TESTS FOR BASIC RADICALS
1. Aluminium 2. Ammonium 3. Antimony
4. Arsenic 5. Barium 6. Bismuth
7. Cadmium 8. Calcium 9 . Chromium
10 . Cobalt 11 . Copper 12. Ferric
13. Ferrus 14. Lead 15.Magnesium
16. Manganese 17. Mercury 18.Nickel
19. Strontium 20. Tin 21.Zinc
22. Silver
ALUMINIUM
1.Add Nesler's Reagent to salt solution.
RESULT: Purple precipitate appears.
2.Add Sodium Hydroxide solution to salt solution.
RESULT: White precipitate appears. It dissolves in excess Sodium Hydroxide solution.
3.Add 2 ml of Sodium Hydroxide solution to salt solution and add Aluminon reagent.
RESULT: Reddish precipitate appears
AMMONIUM
1.Add salt solution with a few drops of Nesler's solution and excess amount of Sodium Hydroxide.
RESULT: Brown precipitate appears.
2.Add salt with Sodium Hydroxide and heat it.
RESULT: Gas with smell of Ammonia comes. It turns Red litmus into Blue and gives white fume with glass bar, soaked in Conc. Hydrochloric acid.
ANTIMONY
Add 5 ml of diluted HCL to salt. Pass H2S.Precipitate appears. Dissolve it by adding diluted HCL. To it add KOH and Bromine water. Add solid NH4Cl and boil for a few minutes. Filter it and add diluted HCL. Pass H2S.
RESULT: Orange colour precipitate appears.
ARSENIC
Add pure Zinc and diluted H2SO4 to an arsenic compound. Cover the mouth of the test tube with filter paper soaked in AgNO3.
RESULT: The paper first turns Yellow and then black.
BARIUM
1.Add 5 ml of HCl to Salt. Add NH4OH and NH4CL.Add strong solution of Ammonium carbonate. Boil and filter. Precipitate appears. Add hot dil Acetic acid and add K2CRO4 solution.
RESULT: Yellow precipitate appears.
Dissolve it in HCL. Add S2S2 solution.
RESULT: White precipitate appears.
BISMUTH
Add 5 ml of diluted HCl to salt. Pass H2S.Precipitate appears. Boil it with 5 ml of diluted Nitric acid. Add 5ml of Conc. H2SO4.Add Thio Urea.
RESULT: Yellow colour precipitate appears.
CADMIUM
Add 5 ml of diluted HCl. Pass H2S.Precipitate appears. Boil it with 5ml of diluted Nitric acid .Add 5 ml of Conc.H2SO4.Add Ammonium Hydroxide.
RESULT: Yellow precipitate appears.
CALCIUM
1.Add salt solution and 2 ml of Pottassium Chromate solution.
RESULT: No precipitate.
2.Add salt solution and 1 ml of Ammonium chloride and 1 ml of Ammonium Hydroxide and 2 ml of Ammonium oxalate.
RESULT: White precipitate appears. It does not dissolves in Acetic acid.
CARBONATE
Add a few ml of diluted HCL to a little substance in a test tube.
RESULT: Brisk effervescence. Colourless,odourless gas turning lime water milky.
CHROMIUM
Add 5 ml of diluted HCL to salt. Add NH4CL. Precipitate appears. Boil it with Sodium Peroxide. Precipitate dissolves. Add acetic acid and lead acetate.
RESULT: Yellow precipitate appears.
COBALT
1.Add 5ml of dil HCL to salt and boil it. Add 1ml of Amyl alcohol ether and 1 ml of NH4 CNS solution. Shake well.
RESULT: The upper layer is colour edintense blue.
2.Add 5 ml of HCL to salt. Boil it .Add 2 ml of ZNSO4 solution. Soak a roll of filter paper and burn the wet end.
RESULT: The ash will be green.
COPPER
1.Add Ammonium Hydroxide solution .Then light blue precipitate appears. Add excess Ammonium Hydroxide.
RESULT: It will become dark blue.
2.Add 2 ml of Pottassium Fluoride to salt solution.
RESULT: Chocolate brown colour precipitate appears.
FERRIC
1.Add 2 ml of Pottassium Ferro cyanide to salt solution.
RESULT: Blue precipitate appears.
2.Add 2ml of Ammonium Thio cyanide solution to salt solution.
RESULT: Bloddish red appears.
FERRUS
Add Pottassium Ferri cyanide to the salt solution
RESULT: Blue precipitate appears
LEAD
1.Add 2 ml of Pottassium Chromate to salt solution.
RESULT: Yellow precipitate appears.
2.Ass 2 ml of Pottassium Iodide solution.
RESULT: Yellow precipitate appears. This becomes glittering gold particle when hot water is added and cooled.
MANGANESE
Add 5 ml of diluted HCL to salt. Add NH4CL .Precipitate appears. Add Benz dine and acid.
RESULT: The precipitate turns Blue.
MERCURY
1.Add 5 ml of Hydrochloric acid to little substance.
RESULT: Precipitate appears.
Boil the precipitate with water. It does not dissolves. Add Sodium Hydroxide solution. Heat it and filter.
RESULT: Black precipitate appears.
2.Add 5 ml of diluted Hydrochloride acid to salt solution. Pass Hydrogen Sulphide gas. Precipitate appears. Boil it with 5 ml of diluted Nitric acid and the filter. In one portion add SnCl2 .
RESULT: White precipitate turns grey.
To other portion add KI
RESULT: Red precipitate appears.
NICKEL
Add HCL to the salt. Boil it. Add NH4CL,NH4OH and K3FE(CN)4 to a few drops.
RESULT: Yellowish brown precipitate soluble in NH4OH.
SILVER
1.Add 5ml of HCl. to a little substance. Precipitate appears. Boil the precipitate with water. It does not dissolves. Add Ammonium Hydroxide solution to it.
RESULT: The precipitate dissolves.
Add diluted Nitric acid
RESULT: Curdy White precipitate appears.
STRANTIUM
Add 5 ml of Hydrochloric acid to salt. Add Ammonium Hydroxide and Ammonium Chloride. Add strong solution of Ammonium Carbonate. Precipitate appears. Dissolve it in hot acetic acid. Add K2CrO4 solution. Filter it. Boil with Ammonium Sulphate solution.
RESULT: White precipitate appears.
TIN
Add 5 ml of n diluted HCl to salt. Pass H2S. Precipitate appears. Dissolve it by adding diluted HCL. Add KOH and Bromine water until the colour of the liquid remains yellow. Add solid NH4OH and boil for a few minutes.White precipitate appears . Reduce by boiling with iron fillings, Filter and add HgCl.
RESULT: White precipitate appears.
ZINC
1.Add Sodium Hydroxide solution to salt solution.
RESULT: White precipitate appears.
2.Add 2 ml of Potassium Ferro Cyanide solution.
RESULT: White precipitate appears. It dissolves in Sodium Hydroxide solution.
Aluminium:
1. colour : colourless
2 flame test : colourless
3. heat salt : no result
4. ash test : blue
5.HCl+salt : no result
6. HCl+salt+H2S : no result
7. HCl+NH4OH+NH4Cl : precipitate ( white )
Ammonium:
1. colour : colourless
2. flame test : colourless
3. heat salt : smell of NH3
Antimony:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : no result
6. HCl+salt+H2S : precipitate ( yellow )
7. HCl+H2S+precipitate : dissolves
8. KOH +bromine water
+NH4Cl : orange coloured
Arsenic:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl+ salt : no result
6. HCl+salt+H2S : precipitate ( yellow )
7. HCl+H2S+precipitate : not dissolves
Barium:
1. colour : colourless
2. flame test : apple green
Bismuth:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : no result
6. HCl+salt+H2S : precipitate ( brown )
7. precipitate+HNO3+H2SO4 : no result
8. Add NH4OH : precipitate( white )
Cadmium:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : no result
6. HCl+salt+H2S : precipitate ( brown) ( yellow)
7. precipitate+H2SO4+NH4OH
+pass H2S : yellow precipitate
Calcium:
1. colour : colourless
2. flame test : brick red
Chromium:
1. colour : colourless
2. flame test : colourless
3.heat salt : no result
4. ash test : no result
5. HCl +salt : no precipitate
6. HCl+salt+H2S : no precipitate
7. salt+NH4OH+NH4Cl+HCl : precipitate ( green )
8. boil with sodium peroxide : precipitate dissolves
9. HCl+NH4OH : no precipitate
10. acetic acid + lead acetate : precipitate (yellow)
Cobalt:
1. colour : pink
2. HCl +salt : no precipitate
3. HCl+salt+H2S : no precipitate
4. salt+NH4OH+NH4Cl+HCl : precipitate (greeen)
5. salt+HCl+NH4OH+NH4Cl+
pass H2S : precipitate(black)
6. add HCl : ppt not dissolves
7. HCl+KClO3 : blue or bluish green residue
8. add NH4CNS : blue colour turning pink colour
Copper:
1. colour : blue
2. flame test : bluish green
3. HCl +salt : no precipitate
4. HCl+salt+H2S : precipitate (black)
1. colour : bright green colourless
2. flame test : bluish green colourless
3. HCl +salt : no precipitate
6. HCl+salt+H2S : precipitate ( black )
Ferrus:
1. colour : light green
2. HCl +salt : no precipitate
3. HCl+salt+H2S : no precipitate
4. salt+NH4OH+NH4Cl+HCl : precipitate (brown)
5. boil with sodium peroxide : not precipitate dissolves
6. HCl+NH4CNS : deep red
7. salt+Fe3(CN6) : precipitate (blue)
Ferric:
1. colour : brown
2. HCl +salt : no precipitate
3. HCl+salt+H2S : no precipitate
4. salt+NH4OH+NH4Cl+HCl : precipitate (brown)
5. boil with sodium peroxide : not precipitate dissolves
6. HCl+NH4CNS : deep red
7. salt+NH4(CN6) : precipitate (red )
Lead:
1. colour : colourless
2. heat salt : no result
3. HCl +salt : precipitate
4. boil with water : precipitate dissolves
5. add K2CrO4 : precipitate ( yellow )
Magnesium:
1. colour : colourless
2. flame test : no result
3. heat salt : no result
4. ash test : pale red
Manganese:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : no precipitate
6. HCl+salt+H2S : no precipitate
7. salt+NH4OH+NH4Cl+HCl : no precipitate
8 salt+NH4OH+NH4Cl+HCl
+H2S : precipitate ( flesh or buff )
9. add dil HCl : precipitate dissolves
10. boil with NH4OH : brown precipitate
11. acetic acid + lead acetate : precipitate (yellow)
Mercury:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : precipitate
6. boil the precipitate : not dissolves
7. heat with NH4OH : precipitate(white)
Nickel:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl+salt : no precipitate
6. HCl+salt+H2S : no precipitate
7. salt+NH4OH+NH4Cl+HCl : no precipitate
8 salt+NH4OH+NH4Cl+HCl
+H2S : precipitate(black)
9. add KClO3 : yellow residue
10. NH4Cl + dimethyl glyoxime : red precipitate
1. colour : colourless
2. flametest : crimson red
Tin:
1. colour : colourless
2. flame test : colourless
3.heat salt : no result
4.ash test : no result
5. HCl +salt : no precipitate
6. HCl+salt+H2S : precipitate (yellow)
7. add dil HCl and boil : precipitate dissolves
8. add KOH+bromine water : white precipitate
Zinc:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl +salt : no precipitate
6. HCl+salt+H2S : no precipitate
7. salt+NH4OH+NH4Cl+HCl : precipitate(white)
8. add dil HCl : precipitate dissolves
9. add NH4OH : no precipitate
10. pass H2S : precipitate (white)
Silver:
1. colour : colourless
2. flame test : colourless
3. heat salt : no result
4. ash test : no result
5. HCl + salt : precipitate
6. boil precipitate :not dissolves
7. add NH4OH :no precipitate
8. add HNO2 :curdy white precipitate
Arsenite:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. H2SO4+KmnO2 : no result
6. Ammonium Molybdate test : precipitate(yellow)
7. add HCl : precipitate(yellow)
Arsenate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. H2SO4+KmnO2 : no result
6. Ammonium Molybdate test : precipitate (yellow)
7. add HCl : no precipitate
Bromide:
1 flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt +H2SO4 : reddish brown gas ,vapour turns
starch paper blue
6. salt+H2SO4+KmnO4 : decolourisd readily
Borate:
1. flame test : bright green
Chloride:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4 extract colour : no colour
5. salt +H2SO4 : vigorous reaction
6. extract +HNO3 : precipitate(white)
7. salt+MnO2+H2SO4 : yellowish green
Carbonate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt+H2SO4 : no result
6. add HCl : brisk effervescence
Fluoride:
1. flametest : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt+H2SO4 : oily appearance
6. extract +acetic acid+CCl2 : precipitate(white)
7. H2SO4+MnO4 : decolourised
Chromate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : yellow colour
Iodide:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour :no colour
5. salt +H2SO4 : violet vapour
6. extract +HNO3 : yellow precipitate
7. salt+H2SO4+KmnO4 : decolourisd slowly
Nitrate:
1. flame test : colourless
2. ash test : no result
3. heat salt : reddish brown gas
4. extract colour : no colour
5. salt +H2SO4 : reddish brown gas
6. salt+H2SO4+copper turning : reddish brown gas
Oxalate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt +H2SO4 : violet vapour
6. salt+HCl : no result
7.Ammonium molybdate test :no result
8. H2SO4 +MnO2 : brisk effervescence
Phosphate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt +H2SO4 : no result
6. extract +HNO3 : no result
7. salt +HCl : no result
8. ammonium molybdate test : precipitate (bright yellow)
Sulphate:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt +H2SO4 : violet vapour
6. extract+HNO3 : no precipitate
Sulphide:
1. flame test : colourless
2. ash test : no result
3. heat salt : no result
4. extract colour : no colour
5. salt +H2SO4 : no result
7. salt +HCl : rotten egg smell
Quantitative Analysis of mixtures of metal ions involving Volumetric (by complexometric titration using masking and demasking agents) and gravimetric analysis.
Introduction
The technique involves titrating metal ions with a complexing agent or chelating agent (Ligand) and is commonly referred to as complexometric titration. This method represents the analytical application of a complexation reaction. In this method, a simple ion is transformed into a complex ion and the equivalence point is determined by using metal indicators or electrometrically. Various other names such as chilometric titrations, chilometry, chilatometric titrations and EDTA titrations have been used to describe this method. All these terms refer to same analytical method and they have resulted from the use of EDTA (Ethylene diamine tetra acetic acid) and other chilons. These chilons react with metal ions to form a special type of complex known as chelate.
Titration Selectivity, Masking and Demasking Agents
EDTA is a very unselective reagent because it complexes with numerous doubly, triply and quadruply charged cations. When a solution containing two cations which complex with EDTA is titrated without the addition of a complex-forming indicator, and if a titration error of 0.1% is permissible, then the ratio of the stability constants of the EDTA complexes of the two metals M and N must be such that KM/KN ≥ 106 if N is not to interfere with the titration of M. strictly, of course, the constants KM and KN considered in the above expression should be the apparent stability constants of the complexes. If the complex-forming indicators are used, then for a similar titration error KM/KN ≥ 108.
Use of masking and demasking agents:
Masking agents act either by precipitation or by formation of complexes more stable than the interfering ion-EDTA complex.
a) Masking by Precipitation: Many heavy metals e.g.- Co, Cu and Pb, can be separated either in the form of insoluble sulphides using Sodium sulphide, or as insoluble complexes using thioacetamide. These are filtered, decomposed and titrated with disodium EDTA. Other common precipitating agents are sulphate for Pb and Ba, oxalate for Ca and Pb, fluoride for Ca, Mg and Pb, ferrocyanide for Zn and Cu, and 8-hydroxy quinoline for many heavy metals. Thioglycerol (CH2SH.CHOH.CH2OH) is used to mask Cu by precipitation in the assay of lotions containing Cu and Zn.
b) Masking by Complex formation: Masking agents form more stable complexes with the interfering metal ions. The most important aspect is that the masking agent must not form complexes with the metal ion under analysis. The different masking agents used are enlisted below:
Ammonium fluoride will mask aluminium, iron and titanium by complex formation.
Ascorbic acid is a convenient reducing agent for iron(III) which is then masked by complexing as the very stable hexacyanoferrate(II) complex. This latter is more stable and less intensely coloured than the hexacyanoferrate(III) complex.
Dimercaprol (2,3-Dimercaptopropanol); (CH2SH.CHSH.CH2OH). Cations of mercury, cadmium, zinc, arsenic, tin, lead and bismuth react with dimercaprol in weakly acidic solution to form precipitates which are soluble in alkaline solution.
All these complexes are stronger than the corresponding edetate complexes and are almost colourless. Cobalt, copper and nickel form intense yellowish-green complexes with the reagent under the above conditions. Cobalt and copper, but not nickel, are displaced from their edetate complexes by dimercaprol.
Potassium cyanide reacts with silver, copper, mercury, iron, zinc, cadmium, cobalt and nickel ions to form complexes in alkaline solution which are more stable than the corresponding edetate complexes, so that other ions, such as lead, magnesium, manganese and the alkaline earth metals can be determined in their presence. Of the metals in the first group mentioned, zinc and cadmium can be demasked from their cyanide complexes by aldehydes, such as formaldehyde or chloral hydrate (du
selectively titrated.
Potassium iodide is used to mask the mercury(II) ion as (HgI4) and is specific for mercury. It can be used in the assay of mercury(II) chloride
Tiron (disodium catechol-3,5-disulphonate) will mask aluminium and titanium as colourless complexes. Iron forms highly coloured complexes and is best masked as its hexacyanoferrate(II) complex.
Triethanolamine [N (CH2.CH2.OH)3] forms a colourless complex with aluminium, a yellow complex with iron(III), the colour of which is almost discharged by adding sodium hydroxide solution, and a green manganese(III) complex which oxidizes mordant black II. For these reasons, if murexide is used in the presence of iron and manganese.
Demasking
It is the process in which the masked substance regains its ability to enter into a particular reaction. This enables to determine a series of metal ions in one solution containing many cations.
Example of using masking and demasking agents in complexometry is the analysis of 3 metals, Cu, Cd and Ca. the following method of analysis is followed:
1. Direct titration of the mixture with the EDTA gives the sum of the 3 metals.
2. Cu and Cd may be masked with the addition of cyanide to the solution, leaving only Ca ion.
3. When formaldehyde or chloral hydrate is added to the cyanide containing mixture, only Cd is demasked and the EDTA titrates the sum of Ca and Cd. In this manner, the concentration of three ions is determined by 3 individual titrations.
Indicators used in complexometric titrations
Name of the Indicator Colour change pH range Metals detected
Mordant black II Eriochrome blackT Red to Blue 6-7 Ca, Ba, Mg, Zn, Cd, Mn, Pb, Hg
Murexide
or
Ammonium purpurate Violet to Blue 12 Ca, Cu, Co
Catechol-violet Violet to Red 8-10 Mn, Mg, Fe, Co, Pb
Methyl Blue Blue to Yellow 4-5 Pb, Zn, Cd, Hg
Thymol Blue Blue to Grey 10-12 Pb, Zn, Cd, Hg
Alizarin Red to Yellow 4.3 Pb, Zn, Co, Mg, Cu
Sodium Alizarin sulphonate Blue to Red 4 Al, Thorium
Xylenol range Lemon to Yellow 1-3 Bi, Thorium
4-5 Pb, Zn
5-6 Cd, Hg
Type Exercise:
Experiment 1. Masking and demasking for the stepwise complexometric determination of aluminium, lead and zinc from the same solution.
A complexometric method based on selective masking and de-masking has been developed for the rapid determination of aluminium, lead and zinc from the same solution in glass and glass frit samples. The determination is carried out using potassium cyanide to mask zinc, and excess disodium salt of EDTA to mask lead and aluminium. The excess EDTA was titrated with standard Mn(II)SO4 solution using Erichrome Black-T as the indicator. Subsequently selective de-masking agents – triethanolamine, 2,3-dimercaptopropanol and a formaldehyde/acetone mixture – were used to determine quantities of aluminium, lead and zinc in a stepwise and selective manner.
Apparatus
Calibrated pipettes and volumetric flasks supplied by Borosil Glass Works Ltd India were used. The digestion process was carried out on a Laminar flow bench equipped with an appropriate ventilation system.
Reagents
Hydrofluoric acid 40% (m/m), nitric acid (16 N), ammonia solution (NH4OH), triethanolamine 30% (v/v), potassium cyanide solution 20% (m/v), 2,3-dimercaptopropanol, formaldehyde solution, acetic acid, ascorbic acid 98% of AR/GR grade and all other standard chemicals supplied by E. Merck (Germany) were used. De-ionized water (18 mega ohm resistivity) prepared from the Millipore milli-Q water purification system, USA, was used throughout.
Standard solutions
Standard zinc solution, 0.01 M
0.656 g of zinc metal (99.99% purity) was dissolved in hydrochloric acid and diluted to 1 L with distilled water.
Standard EDTA solution, 0.01 M
3.744 g of the disodium salt of EDTA were dissolved in deionized (DI) water and diluted to 1 L. The stock solution was standardised according to the conventional method [6] with standard 0.01 M zinc solution using EBT as the indicator.
Mn(II)SO4 solution 0.01 M and 0.005 M
For the preparation 0.01 M and 0.005 M Mn(II)SO4 solutions, respectively, 1.7 g and 0.85 g of 1-hydrate were dissolved in water and diluted to 1 L with water. The stock solution of 0.01 M Mn(II)SO4 was standardised against standard aluminium according to the conventional method using EBT indicator. Similarly 0.005 M Mn(II)SO4 solution was standardised against standard lead solution according to the conventional method [6] using EBT indicator.
Lead nitrate Solution, 0.01 M
For the 0.01 M stock solution, 3.312 g of lead nitrate were dissolved in water and acidified with a few drops of HNO3, before being diluted to 1 L with DI water.
Standard aluminium solution, 0.025 M
0.6745 g of polished aluminum foil were cleaned with absolute alcohol and then dissolved in 25 mL of hydrochloric acid and 150 mL of DI water, before being further diluted to 500 mL. Erichrome Black-T
This was prepared by dissolving 0.12 g of EBT and 1.2 g hydroxylamine hydrochloride in ethanol.
Preparation of the sample solution
0.5 g of a well ground sample obtained after loss on ignition (100 ± 5°C) was put into a cleaned teflon basin, moistened with a few drops of water, before the addition of 2 mL of HNO3 and 10 mL of 40% HF acid. The Teflon basin containing whole components was evaporated to dryness on a hot plate and the process repeated several times to ensure the total evaporation of silica as SiF4. The residual mass was then dried several times with 10 mL of DI water to remove the acids. Finally the residue was dissolved with 5 mL of HNO3 and diluted to 250 mL with DI water. Subsequently, 25 mL of stock solution were taken in a conical flask and diluted to 100 mL to which was added a known excess amount of 0.01 M EDTA solution and 0.1 g of ascorbic acid, before being boiled on a hot plate for 1 minute. To this solution 25 mL of 20% potassium cyanide solution were added and immediately 10 mL of concentrated ammonium hydroxide were added to prevent the formation of HCN. During work with KCN gloves and masks must be used as a precaution. The total solution was cooled to 10°C in an ice bath, and excess EDTA was titrated against standard 0.01 M manganese solution, with a few drops of a 0.1% alcoholic solution of Erichrome Black T as indicator. At the end point the blue colouration was seen to change to red. The total volume of the EDTA consumed in the reaction corresponded to the sum of all the constituents which complexed with EDTA.
Procedure
Determination of Al
To determine aluminium, 20 mL of triethanolamine and 5 mL of hydroxyl amine 10% (w/v) were added to the solution remaining after the above titration, before being boiled for 1 minute. The liberated EDTA was then titrated with standard 0.01 Mn(II)SO4 solution using Erichrome Black-T as the indicator. At the end point a blue colouration was seen to change to red. The consumed manganese solution was equivalent to the aluminium content of the sample.
Determination of lead
After the titration of aluminium, 5 mL of 20% alcoholic solution of 2,3-dimercaptopropanol were added with slow swirling. The red colouration was seen to change to blue. Again liberated EDTA was titrated with 0.005 M manganese using Erichrome Black-T. At the end point the blue colouration was seen to change to a sharp red wine colour. The consumed manganese solution corresponded to the lead content of the sample.
Determination of zinc
After the titration of lead, zinc was quantitatively de-masked from its cyanide complex by the addition of (3:1) 20 g of 4% formaldehyde:acetone solution. Then the liberated zinc was titrated with a 0.01 M EDTA solution using EBT as the indicator. The end point was indicated by a sharp colour change from red to blue. After titration addition of a formaldehyde:acetone mixture was repeated followed by a second titration, until the solution no longer turned red. The total amount of EDTA consumed corresponded to the zinc content of the sample.
Experiment 2. Determination of Calcium and magnesium ions using Complexometric titration
Complexometric titration is based on the formation of a complex ion. Ethlyenediaminetetraacetic acid (EDTA or H4Y, where Y = C10H12N2O8) is a complexing agent designed to bind metal ions quantitatively, forming stable, water soluble complexes with a 1:1 stoichiometry for most metal ions . EDTA binds to both calcium and magnesium, but binds more tightly to calcium, thus:
Ca2+ + Y4– ----CaY2–
Mg2+ + Y4– -----MgY2–
Ca2+ + MgY2–----CaY2– + Mg2+
PROCEDURE
The EDTA Solution.
You will be using the disodium salt of EDTA (M.W. = 372.24 g/mole). It has been dried for 1 week at 80°C to drive off any superficial moisture. It is in the TA desiccator. Be sure to return it to the desiccator when you are through with it. Weigh carefully about 0.9 g of EDTA (record to the nearest 0.1 mg). Quantitatively transfer this into a 250 mL volumetric flask then add 2-3 mL
of pH 10 ammonia buffer. Fill the flask about halfway to the mark with deionized water and swirl to dissolve. This process can take up to 15 minutes. Once dissolved, dilute to the mark and then cap and invert the flask at least 6 times to get a uniform solution. Keep the solution capped.
The Blank and Titration Procedure.
In order to correct for any error attributable to the deionized water and the indicator color transition, you will be analyzing a blank solution. The volume of EDTA used to titrate the blank will be subtracted from all other titration volumes.
Pipette a 10.00 mL sample of deionized water into a clean 250 mL Erlenmeyer flask. Add about 1mL of ammonia buffer, using a 10mL graduated cylinder. At this point heat the flask on the hot plate until condensation forms on the inside rim of the flask. Immediately add a few drops of indicator. If the solution turns blue, there is no measurable calcium or magnesium in solution and you will not have a blank correction. If the solution stays red or violet, immediately start titrating with the EDTA solution. Titrate until there is no trace of red or violet in your solution.
Be sure to go dropwise as you approach the endpoint. The kinetics of the indicator reaction is low; heating aids in speeding up the transition from red to blue. However, it is necessary to titrate slowly as you approach the endpoint so that it is not overshot.
The color change upon reaching the endpoint for this titration is subtle. Two pieces of advice will help improve your results. First, ask a TA or the instructor to inspect your solution near the endpoint of your first titration to be sure you really are at the endpoint. Second, try to reach the same color for each titration of your unknowns and standards. This consistency in technique will improve the precision of your measurements.
Titrating the Unknown.
Repeat the above procedure, substituting 10.00 mL portions of your unknown sample, in place of the 10.00 mL deionized water sample. Repeat the unknown titration between 3 and 6 times depending upon time constraints. Typically, the more titrations you perform, the better the results.
Chromatography
Chromatography is a family of analytical chemistry techniques for the separation of mixtures. It involves passing the sample, a mixture which contains the analytic, in the "mobile phase", often in a stream of solvent, through the "stationary phase." The stationary phase retards the passage of the components of the sample. When components pass through the system at different rates they become separated in time, like runners in a marathon. Ideally, each component has a characteristic time of passage through the system. This is called its "retention time."
A chromatograph takes a chemical mixture carried by liquid or gas and separates it into its component parts as a result of differential distributions of the solutes as they flow around or over a stationary liquid or solid phase. Various techniques for the separation of complex mixtures rely on the differential affinities of substances for a gas or liquid mobile medium and for a stationary adsorbing medium through which they pass; such as paper, gelatin, or magnesium silicate gel.
Analytical chromatography is used to determine the identity and concentration of molecules in a mixture. Preparative chromatography is used to purify larger quantities of a molecular species. Most of the following refers to analytical chromatography.
Chromatography theory
Chromatography is a separation method that exploits the differences in partitioning behavior between a mobile phase and a stationary phase to separate the components in a mixture. Components of a mixture may be interacting with the stationary phase based on charge, relative solubility or adsorption. There are two theories of chromatography, the plate and rate theories.
Retention
The retention is a measure of the speed at which a substance moves in a chromatographic system. In continuous development systems like HPLC or GC, where the compounds are eluted with the eluent, the retention is usually measured as the retention time Rt or tR, the time between injection and detection. In interrupted development systems like TLC the retention is measured as the retention factor Rf, the run length of the compound divided by the run length of the eluent front:
The retention of a compound often differs considerably between experiments and laboratories due to variations of the eluent, the stationary phase, temperature, and the setup. It is therefore important to compare the retention of the test compound to that of one or more standard compounds under absolutely identical conditions.
Paper chromatography
A small spot of solution containing the sample is applied to a strip of chromatography paper about one centimetre from the base. This sample is adsorbed onto the paper. This means that the sample will contact the paper and may form interactions with it. Any substance that will react with (and thus bond to) the paper cannot be measured using this technique. The paper is then dipped in to a suitable solvent (such as ethanol or water) and placed in a sealed container. As the solvent rises through the paper it meets the sample mixture which starts to travel up the paper with the solvent. Different compounds in the sample mixture travel different distances according to how strongly they interact with the paper. Paper chromatography takes some time and the experiment is usually left to complete for some hours.
The final chromatogram can be compared with other known mixture chromatograms to identify sample mixes. Two-way paper chromatography involves using two solvents and rotating the paper 90o inbetween. This is useful for separating complex mixtures of similar compounds.
Thin layer chromatography (TLC)
In thin layer chromatography or TLC the stationary phase consists of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat carrier like a glass plate, a thick aluminum foil, or a plastic sheet.
The process is similar to paper chromatography with the advantage of faster runs, better separations, and the choice between different adsorbents. TLC is a standard laboratory method in organic chemistry. Because of its simplicity and speed TLC is often used for monitoring chemical reactions and for the qualitative analysis of reaction products.
TLC plates are made by mixing the adsorbent with a small amount of inert binder like calcium sulfate (gypsum) and water, spreading the a thick slurry on the carrier, drying the plate, and activation of the adsorbent by heating in an oven. The thickness of the adsorbent layer is typically around 0.1 - 0.25 mm for analytical purposes and around 1 - 2 mm for preparative TLC.
Several methods exists to make colorless spots visible:
• Often a small amount of a fluorescent dye is added to the adsorbent that allows the visualization of UV absorbing spots under a black light ("UV254").
• Iodine vapors are a general unspecific color reagent.
• Specific color reagents exist into which the TLC plate is dipped or which are sprayed onto the plate.
Once visible, the spots can be quantified by way of calculating their Rf values. These values should be the same regardless of the extent of travel of the solvent, and in theory are independant of a single experimental run. They do depend on the solvent used, and the type of TLC plate.
Thin-Layer Chromatography: Analysis of a Commercial Analgesic
Most non-prescription pain-relieving remedies contain aspirin (o-acetylsalicylic acid) or acetaminophen - and some contain both. Many also have some auxiliary compounds with analgesic properties. In addition, caffeine is included in some preparations. Caffeine is not an analgesic, but aids in the relief of certain types of headaches because of its stimulant effect (CNS and cardiac).
PROCEDURE
Crush the tablet to a powder on a piece of glassine weighing paper. Put half of the powder in a 5 mL plastic beaker and add 2 mL of methanol and 1 mL of dichloromethane.
Stir the mixture with a glass rod for about one minute to allow the solvent to extract the active ingredients. Allow the insoluble matter to settle. Carefully decant the supernatant liquid into a clean, dry 5-mL beaker.
On a TLC strip coated with Silica Gel IB-F, apply a spot of the solution of "unknown" and two of the four known solutions. On a second Silica Gel strip, spot the "unknown" solution and the remaining two known solutions. Be sure to mark the identity of each spot on each strip. Develop each chromatogram in a bottle containing 100% ethyl acetate.
Examine each strip under the ultraviolet light viewer (short wave UV light). Compare the spot positions (the Rf values) of the constituents of the tablet with those of the individual authentic substances. If very little movement of components has occurred on a strip, do not mark any visible spots with a pencil. Replace the strip in the bottle and repeat the development. Make a table recording the distance each substance moved from the origin and the distance the solvent moved.
Lab Report
Title: Thin Layer Chromatography
Name:
Date:
In the following table, enter the distance traveled by each spot, along with its' corresponding Rf
Sample Distance Front
Traveled (cm). Distance Component
Traveled ( cm.) Silica Gel TLC Plate in
100 % Ethyl Acetate Solvent
Aspirin
RfAspirin = __________
Acetaminophen
RfAcetominophen = __________
Caffeine
RfCaffeine = __________
Phenacetin
RfPhenacetin = __________
Unknown
Tablet
1_________
2_________
3_________
4_________
Rf1 = __________
Rf2 = __________
Rf3 = __________
Rf4 = __________
Experiment: Paper Chromatographic separation of Ag(I),Hg2(II) and Pb (II) Ions
Materials required
The following materials are required for the separation of Ag(I) ,Hg(II) and Pb(II) ions
(a) CHROMATOGRAPHY PAPER: What man no.1 filter paper strip of 25cm x 7cm used.
(b) JAR: Paper chromatographic jar is used whose height is 30 cm and diameter 10cm.
(c) Salt solution: aqueous 1% solution of silver nitrate , mercurous nitrate and lend nitrate are prepared .these solution are slightly acidified with dilute nitric acid .
(d) Developing solvents: one can use anyone of the following solvents:
(i) Tertiary butanol (40 ml) + acetone (30 ml)+water (12 ml)+conc.nitric acid (8ml)
(ii) Methyl n-propyl keton (85ml)+10 N HCI (15 ml)
(iii) n – butyl alcohol mixed with 5% (V/V) of glacial acetic acid followed by water to turbidity
(iv) Distilled or deionised water.
(e) Visualising agent :one may use anyone of the following visualising agents
(i) Colourless ammonium sulphide solution is prepared by bubbling H2S in dilute NH4OH.
(ii) 0.5% dithyzone in chloroform solution is used. The paper chromatogram may also be developed by exposure to H2S gas but the results are not satisfactory as with dithizone .
(iii) K2CrO4 and ammonia solution.
Procedure
What man no.1 filter paper strip 25cm x 7cm is cut with a pair of stainless steel scissor .then a line is drawn horizontally across the width of filter paper strip using a lead pencil. This line should be about 2cm from the end of the filter paper. Location of the sports is marked with “x” on this line with pencil so that each “x” is at least 2cm from each other.
Pb (II),Ag (I)and Hg2 (II) salt solutions are applied at spots A,B and C respectively with fine capillary tubes .on the spot D, a mixtuxe of Pb (II),Ag(I) , Hg2(II) salt solution is applied .after drying the spotsthe filter paper strip is fixed vertically by means of a clip attached to the inner cover of the chromatography jar .
After this, the paper is lowered carefully into the chromatographic jar in such a way that the lower 1cm portion dips into the developing solvent which is either a mixture of tertiary butyl alcohol (40ml), aceton (40ml) , water (12ml)and nitric acid or methyl n-butyl ketone (85ml)and 10 N hydrochloric acid or n-butyl alcohol mixed with 5% (V/V) of glacial acetic acid .followed by water to turbidity.
When the solvent has travelled a reasonable distance (say 15 cm), it is taken out and allowed to dry. The spot can be visualised by using the visulising reagent.
1. If the spots are sprayed with ammonium sulphide solution , silver mercury and lead spots become dark brown
2. If the spots are sprayed with dithizene in chloroform the following spots are then obtained:
Pb2+ Orange
Ag2+ Pink
Hg22+ Rose pink
3. At the end of the run paper is removed from jar. Then it is dried and dipped into 0.25 molar K2CrO4 solution then following colour will be seen:
Pb2+ Yellow
Ag2+ Orange-red
Hg22+ Orange
The excess K2CrO4 is removed by washing with water . now the paper held over the top of ammonia bottle, the colour of silver will fade whereas mercurous will turn black.
Record the RF values. For solvent system involving n-butanol, glacial acetic acid and water the following values are obtained.
Cation RF Values Colour
Pb2+ Yellow Rose pink
Ag2+ Orange-red Orange
Hg22+ Orange Pink
Preparation of inorganic compounds
1. Preparation of Tris(2,4-pentanedionato)manganese(III) [Acetylacetonatomanganese(III)]
Introduction
Manganese is a first row transition metal that has a tremendous variety of oxidation states that appear in its compounds. The oxidation numbers range from Mn(–III) in compounds like
Mn(NO)3CO to Mn(VII) in KMnO4. Compounds of manganese range in oxidation number between these two extremes. This experiment involves the preparation of a Mn(III) complex of actylacetone (also named 2,4-pentanedione) which is a useful starting material for the preparation of other Mn(III) compounds. Manganese(III) complexes are relatively stable and can be prepared directly by reactions of the hydrous manganese(III) oxide or by oxidation of the hydrous manganese(II) oxide with air or an oxidizing agent. In aqueous solution Mn(III) is readily hydrolyzed.
Mn3+ + 2 H2O Mn(OH)2 + H+ K = 0.93
and is most stable in acid solutions. Manganese(III) is also slowly reduced by water.
4 Mn3+ + 2 H2O 4 Mn2+ + 4H+ + O2
In this experiment a solution of manganese(II) chloride is oxidized with potassium permanganate in the presence of acetylacetone giving the brown acetylacetonemanganese(III), Mn(acac)3.
Because the ground state for octahedral complexes like that of Mn(acac)3 is a 5Eg (t2g 3eg1) there exists considerable Jahn-Teller distortion. Therefore, the complexes are not “pure” octahedral. Two forms of Mn(acac)3 are known: one with substantial tetrahedral elongation (two Mn-O bonds at 212 pm, and four at 193 pm), the other with moderate tetragonal compression (two Mn-O bonds at 195 pm and four at 200 pm). The electronic spectrum of Mn(acac)3 shows a broad band at approximately 20,000 cm-1 (500 nm).1 The complex forms lustrous crystals which are black to dark brown by reflected light and green by transmitted light. The Mn(acac)3 complex can be reversibly oxidized to Mn(acac)3 + (0.96 V vs SCE), or reduced to Mn(acac)3– (–0.06 V vs SCE) in acetonitrile solution (0.1 M tetraethylamonium perchlorate). It has been shown that many electron transfer reactions like those above are ligandcentered rather than metal-centered.3 This implies that in many transition metal complexes electron transfer reactions are facilitated by stabilization of the ligand-radical product via covalent bond formation with an unpaired d electron of the transition metal center. The covalent bond energy is proportional to the negative shift in the potential for the ligand oxidation relative to that for the free ligands anion.3 The Mn(acac)3 prepared here may be used in a later magnetic susceptibility experiment.
Procedure
In a 250-mL conical flask prepare a solution of 1.00 g (5.05 mmol) manganese (II) chloride tetrahydrate and 2.72 g (17.1 mmol) of sodium actetate trihydrate in 40 mL water. To this solution add by digital pipet 3.79 mL (4.10 g or 40.0 mmol) acetylacetone. Place a small magnetic stirring bar in the solution and place the flask on a magnetic stirrer in the hood. To the stirred mixture add dropwise a solution of 0.21 g (1.3 mmol) of potassium permanganate in 10 mL water. (Note 1: Because of the color intensity of the permanganate solution it is difficult to determine if all the solid has dissolved; therefore, stir thoroughly and check for undissolved solute.) After the addition of the potassium permanganate solution continue stirring for 5 minutes. Prepare a solution containing 2.72 g (17.1 mmol) sodium acetate trihydrate in 10 mL of water and add this in approximately 1-mL portions to the stirred solution of crude Mn(acac)3.
Heat the reaction mixture to near boiling (hot plate) for 10 minutes and cool to room temperature. Filter the dark solid on a small Buchler funnel and wash with three 10-mL portions of water. (Note 2: Do not used sintered glass filters for this step.) Spread out the product on a porcelain dish and dry the product in a drying oven at 60 oC to 70 oC for at least one-half hour.
Weigh the dry product and determine the percent yield. Under the hood dissolve the dried acetylacetonatomanganese(III) in 4.0 mL of benzene contained in a 25-mL conical flask. Filter the solution through a 30-mL medium porosity glass filter. Transfer the filtrate to a 30-mL beaker and cool in an ice bath, being careful not to get any water in the benzene solution. Add 15 mL of petroleum ether to the solution to reprecipitate the product. Collect the recrystallized product on a 30-mL medium porosity filter funnel and place in a drying oven at 60 °C. (Note 3: Place the filtrate in a proper lab waste container, not down the drain.) Weigh the recrystallized product and calculate the percent yield from starting material.
References
1. Cotton, F., A., Wilkinson, G., Murillo, C. A., Bochmann, M., Advanced Inorganic Chemistry, 6th Ed., Wiley and Sons, New York, 1999.
2. Charles, R. G., Inorg. Synth., 1963, 7, 183.
3. Richert, S. A., Tsang, P. K. S., Sawyer, D. T., Inorg. Chem., 1989, 28, 2471.
2. VO(acac)2 Preparation (Five coordinationated)
Most of the complexes prepared in experiments 1 to 6 have been 6-coordinate with octahedral or at least pseudooctahedral inner coordination spheres. These have also been the most studied complexes historically. Nevertheless, there are many examples of coordination chemistry with coordination numbers ranging from 3 to 9, and a variety of structures can be found. (See reference 1.) After 6-coordinate octahedral, the next moststudied geometries have been 4-coordinate systems, which may be tetrahedral or square planar. Considerably effort has gone into elucidating the relationship between these two geometries. Some complexes can easily interconvert between the two geometries, and in fact the halogen complexes of Ni(II) [NiX2{P(CH2C6H5)(C6H5)2}2] can be crystallized in both forms.
Five coordinate complexes are much less common than either four or six-coordinate ones, but have received intensive study in recent years. They are more common for some metals, and often for one oxidation state, than others.There are two principal geometries, trigonal bipyramidal and square pyramidal. It is interesting and highly important that these two structures are similar enough in energy to be easily converted. Consequently, the deformation energy is low, and many complexes exist with some intermediate shape. The interconversion process, called Berry pseudorotation, is used to explain the stereochemical non-rigidity (fluxionality) of many five coordinate complexes.
In this experiment we will prepare a five-coordinate complex of V (IV) using the chelating acetylacetonate ligand, the anion of acetylacetone, or 2,4-pentanedione.Consequently, the IUPAC name for this complex is bis-(2,4- pentanedionato)oxovanadium(IV). Although all five donor atoms to the metal are oxygen atoms, they are of different type. The terminal V=O bond is extremely short (1.55-1.68 Å), and this always remains the axial ligand. In other words, vanadyl acetylacetonate is not subject to Berry pseudo-rotation. On the other hand, this complex does show a common reaction of 5-coordinate compounds, vis à vis the addition of a sixth ligand to achieve a pseudooctahedral geometry. The effect of the coordination change can be monitored by visible spectroscopy (a colour change) as well as by IR spectroscopy.
Vanadium(IV), d1, is paramagnetic with a single unpaired electron. This oxidation state is most commonly found as the vanadyl ion, and the complex prepared in this experiment can be thought of as a derivative of the vanadyl group. Vanadyl has a very characteristic "signature" in the electron paramagnetc resonance (EPR) spectrum. This is due to coupling of the electron spin with the nuclear spin of the metal atom.
Procedure
To 2.5 g of pure vanadium(V) oxide in a large Erlenmeyer flask are added 6 mL distilled water, 4.5 mL concentrated sulfuric acid and 12.5 mL of 95% ethanol. The mixture is heated to boiling on a steam or boiling-water bath and stirred. As the reaction proceeds the initial slurry of vanadium (V) oxide darkens, becomes light green and finally turns dark blue. The reduction of vanadium (V) is completed in 30 minutes. 10 mL of water is addded, and the solution is filtered by gravity and the filtrate is collected in a 600 mL beaker. 6.5 mL of acetylacetone (2,4-pentanedione) is added and the solution is stirred for 10 minutes. The solution is neutralized by adding a solution of 10 g of sodium carbonate dissolved in 60 mL of water slowly with continuous stirring to avoid excessive frothing. The precipitated product is collected by filtration on a Büchner funnel and dried by drawing air through it.
Recrystallize the product by dissolving in the minimum amount of hot chloroform (about 4 mL) in a small Erlenmeyer flask, filtering hot by gravity through fluted filter-paper, cooling to room temperature and adding 10 mL of diethyl ether to complete the precipitation. Filter and allow to dry in air.
References
1. D.E. Shriver, P.W. Atkins and C.H. Langford, Inorganic chemistry, (N.Y.: Freeman, 1990), 192ff.
2. M.C. Browning, J. Chem. Soc. (1962), 693.
3. I.S. Butler and J.F. Harrod, Inorganic Chemistry, (Redwood City, Cf.: Benjamin/Cummings, 1989), p. 221ff. (A simple introduction to ESR spectroscopy.) [QD151.2.B88]
4. G. Wilkinson, R.D. Gillard and J.A. McClevery, Comprehensive coordination chemistry (Oxford: Pergamon Press, 1987). Vol. 1, pp. 47ff; Vol. 2, 365ff and Vol. 3, p. 504. [QD474.C65]
5. G. Wilkinson and F.A. Cotton, Advanced Inorganic Chemistry (N.Y.: Wiley, 1988), 5th ed., p. 671ff. [QD151.2.C68]
6. A.B.P. Lever, Inorganic electronic spectroscopy, 2nd edition (Amsterdam: Elsevier, 1984), p. 389ff. [QD96.E44.L49]
7. K. Nakamoto, Infrared spectra of inorganic and coordination compounds (NY: Wiley, 1970), p. 256. [QC457.N3]
3. Preparation of Ni (DMG)2 Complex
The precipitation reaction of the nickel with the DMG is:
Ni (DMG)2 can be obtained by 1:2 stoichiometry reaction between any nickel salt and DMG.
4. Preparation of Prussian blue - Fe4[Fe(CN)6]3•14H2O
Materials:
Item Amount per student
Iron (III) Chloride (FeCl3) 4 g
Potassium Ferrocyanide (K4[Fe(CN)6]) 1.5 g
Filter paper 1
Equipment:
Item Amount per student Amount for 24 students
Buchner funnel 1
Filter flask 1
Tubing 1
Filter-vac rubber rings (for suction flasks) 1
Fe3+ + 3 [Fe(CN)6]4- → Fe4[Fe(CN)6]3
Procedure: Dissolve iron(III) salt in water in a beaker and K4[Fe(CN)6] in another one.
Slowly add K4[Fe(CN)6] solution to the iron(III) solution, while stirring. Let the blue precipitate settle. Decant the supernatant liquid and wash the precipitate with water. Swirl the mixture and let the precipitate settle, decant and repeat the washing once more. Filter out the product and let it dry by air pulling air through the filter for a few minutes.
1. Prepare a saturated solution of iron (III) chloride by placing 3.7 g FeCl3 in a small beaker with 5 mL distilled water. Use a graduated cylinder to measure the volume of water you used. Stir to dissolve.
2. Separately, prepare a saturated solution of potassium ferrocyanide by placing 1.39 g K4[Fe(CN)6] in another beaker with 5 mL distilled water
3. Make the Prussian Blue by pouring the potassium ferrocyanide solution into the beaker with the ferric chloride solution. Stir with a glass rod.
4. Obtain filter paper that fits the Buchner funnel (so it lays flat in the bottom). Set up the aspirator by connecting a piece of tubing from the little side-arm on the filter flask to the similar arm sticking out from the side of the faucet.
5. Turn on the faucet to create suction. Then pour your reaction mixture into the funnel.
Scrape the entire blue product into the funnel: use a little distilled water to rinse the beaker.
6. Dry to obtain Prussian blue.
5. Preparation of Mn(acac)3
Acetylacetonate (acac) is a common monoanionic bidentate ligand derived from the monodeprotonation of acetylacetone (2,4-pentanedione). The binding of this ligand to a transition metal ion can be thought of as consisting of a covalent bond through one oxygen and a dative bond through the other oxygen. In actuality, the bonding is usually delocalized and is most correctly drawn using the delocalized resonance structure shown on the right.
Mn(acac)3 will synthesize according to the following equation:
5. Synthesis of Turnbull s Blue (iron (II) hexacyanoferrate(III)] )complex.
Prussian blue and Turnbull’s blue are similar kind of dyes, their difference can explained by the different method of preparation as:
Fe2+ + Fe(CN)63- == Turnbull s Blue
Fe3+ + Fe(CN)64- == Prussian Blue
Turnbull s Blue can be prepared by the 1:1 stoichiometry reaction of FeSO4.7H2O and K4Fe(CN)6
6. Preparation of copper ammine sulphate [Cu(NH3)4]SO4.H2O
CuSO4 + 4 NH3(aq) + H2O → [Cu(NH3)4]SO4.H2O
Material: CuSO4.5H2O, NH3(aq), C2H5OH
Procedure: Place 5 g of finely powdered copper sulphate, CuSO4.5H2O, in a small beaker, pour upon it 7.5 ml of concentrated ammonia and 3 ml of water. Shake it for about 1 minute and then heat it gently until all the solid dissolves. Add about 10 ml of ethanol to the solution, let it stand for about one hour and filter off the crystals. Wash them with a mixture of 5 ml of concentrated ammonia and 5 ml of ethanol. Dry them on air in the hood.
[Cu(NH3)4]SO4.H2O – dark blue crystals, soluble in water (18 g in 100 ml of water at
21.5 oC), stable on air.
7. Preparation of μ-hydroxo-bis(pentaamminechromIII) – work in a fume
Hood
2 CrCl2 + 9 NH3 + NH4Cl + ½ O2 → [(NH3)5Cr-OH-Cr(NH3)5]Cl5
Material: K2Cr2O7, HCl, C2H5OH, NH4Cl, NH3(aq)
Procedure: Spread 12 g of K2Cr2O7 and mix it with 7.2 ml of C2H5OH and 28.2 ml of concentrated HCl in a flask. Write equation of this reaction.
Put the calculated amount of Zn (for reduction of Cr3+ to Cr2+ and 50 % excess) into a 250-ml flask and add CrCl3 solution. Close the flask with a stopper with two holes. One is for a separatory funnel with 15 ml of concentrated HCl, the second is for a glass tube. Observe change of colour from green (Cr3+) to blue (Cr2+) after adding HCl. Pour the solution to the flask with a mixture of 250 ml NH3(aq) and 100 g of NH4Cl. Swirl the flask and observe change of colour to red. Red crystals should precipitate in a few minutes. Filter off the crystals and wash them with diluted HCl (1:2). Recrystallize the crude product by dissolving in small volume of water and precipitate with diluted HCl (1:2). Filter off the pure product, wash it with a small amount of ethanol and dry it on air.
[(NH3)5Cr-OH-Cr(NH3)5]Cl5 – red crystals, soluble in water. Creates blue complex
[(NH3)5Cr-O-Cr(NH3)5]Cl4 in NH3 or NaOH solutions
8. Preparation of potassium tris(oxalate)ferrate(III) trihydrate
Fe(OH)3 + 3 KHC2O4 → K3[Fe(C2O4)3] + 3 H2O
Material: FeSO4.7H2O or (NH4)2Fe(SO4)2.4H2O, K2C2O4, H2C2O4, HNO3, ethanol Procedure: Dissolve 35 g of FeSO4.7H2O in 100 ml of warm water and add slowly diluted HNO3 (1:1) to oxidize Fe2+. Add NH3(aq) to the solution until the precipitation of Fe(OH)3 is completed. Let the precipitate settle and decant the liquid. Filter out the precipitate and wash it with hot water. Prepare a hot solution of 44 g of KHC2O4 (calculate it as a mixture of K2C2O4 and H2C2O4) in 100 ml H2O. Add precipitate of Fe(OH)3 in small portions to this solution. Filter the resulting solution and evaporate it on a steam bath to crystallization. Filter out and wash the crystals on the Buchner funnel with ethanol/water 1:1 and finally with acetone. Transfer the product to a dry filter paper and let it dry in air.
K3[Fe(C2O4)3].3H2O – green crystals, photosensitive and decomposes due to influence of light:
2 K3[Fe(C2O4)3] → K2[Fe(C2O4)2] + K2C2O4 + 2 CO2
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Publication Date: 06-13-2010
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