B. Sc. CBZ with Biotech 2nd Year
(Chemistry Practical)

1. Qualitative Analysis of Organic Compounds (2-33)
2. Inorganic Quantitative Analysis (33-45)
3. Inorganic Synthesis (46-54)


Qualitative Analysis of Organic Compounds.
The analysis and identification of unknown organic compounds constitutes a very important aspect of experimental organic chemistry. There is no definite set procedure that can be generally applied to organic qualitative analysis. Various books have different approaches, but a systematic approach based on the scheme given below will give good results.
Practical Notes
Before outlining the general scheme, one or two points of practical importance should be noted.
(a) Quantities of substance for tests. For most tests about 0.1 g solid or 0.1 - 0.2 mL (2 - 3 drops) of liquid material (NOT MORE) should be used.
(b) Reagents likely to be met within organic analysis are on the reagent shelves. Students are advised to develop a general knowledge of the physical characteristics of common organic compounds. If in doubt about the expected result of a test between a certain compound and a reagent, carry out a trial test with a known compound and compare with the unknown.
(c) Quantities of substance derivatives. Students have wasted much time and material in the past by taking too large a quantity of substance for preparation of a derivative. In general, 0.5 - 1 g (or 0.5 - 1 mL) of substance gives the most satisfactory results.
General Scheme of Analysis
A. Preliminary Tests
(a) Note physical characteristics - solid, liquid, colour and odour.
(b) Ignition test (heat small amount on metal spatula) to determine whether the compound is aliphatic or aromatic (i.e. luminous flame - aliphatic; sooty flame - aromatic).
B. Physical Constants
Determine the boiling point or melting point. Distillation is recommended in the case of liquids (see Appendix 3). It serves the dual purpose of determining the b.p., as well as purification of the liquid for subsequent tests.
C. Analysis for elements present (Lassaigne's Test)
In organic compounds the elements commonly occurring along with carbon and hydrogen, are oxygen, nitrogen, sulphur, chlorine, bromine and iodine. The detection of these elements depends upon converting them to water-soluble ionic compounds and the application of specific tests.
Theory
It is a general test for the detection of halogens, nitrogen & sulphur in an organic compound. These elements are bonded covalently in the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal. The ionic compounds formed during the fusion are extracted in aqueous solution, and can be detected by simple chemical tests. The extract is called sodium fusion extract or Lassaigne's extract.
PROCEDURE
Place a piece of clean sodium metal, about the size of a pea into a fusion tube. Add a little of the compound (50 mg or 2 - 3 drops).* Heat the tube gently at first, allowing any distillate formed to drop back onto the molten sodium. When charring begins, heat the bottom of the tube to dull redness for about three minutes and finally plunge the tube, while still hot, into a clean dish containing cold distilled water (6 mL) and cover immediately with a clean wire gauze.**
Test for Nitrogen
The carbon and nitrogen present in the organic compound on fusion with sodium metal give sodium cyanide (NaCN) soluble in water. This is converted in to sodium ferrocyanide by the addition of sufficient quantity of ferrous sulphate .Ferric ions generated during the process reacts with ferrocyanide to form blue precipitate of ferric ferrocyanide.


Test for chlorine
Chlorine present in the organic compound forms sodium chloride on fusion with sodium metal. Sodium chloride, extracted with water, can be easily identified by adding silver nitrate solution after acidifying with dil. Nitric acid.


Test for sulphur
If sulphur is present in the organic compound, sodium fusion will convert it into sodium sulphide. Sulphide ions are readily identified by sodium nirtoprusside.

The 'fusion' filtrate which should be clear and colourless, is used for the SPECIFIC TESTS DESCRIBED BELOW:
1. To a portion (2 mL) of the 'fusion' filtrate add 0.2 g of powdered ferrous sulphate crystals. Boil the mixture for a half a minute, cool and acidify by adding dilute sulphuric acid dropwise. Formation of a bluish-green precipitate (Prussian blue) or a blue solution indicates that the original substance contains nitrogen. If no precipitate appears, allow to stand for 15 minutes, filter and inspect filter paper.
2. SULPHUR (SULPHIDE)
To the cold 'fusion' filtrate (1 mL) add a few drops of cold, freshly prepared, dilute solution of sodium nitroprusside. The latter may be prepared by adding a small crystal of the solid to 2 mL of water. Production of a rich purple colour indicates that the original substance contains sulphur. This test is very sensitive. Only strong positive results are significant.
3. HALOGENS (HALIDES)
Acidify a portion (1 mL) of the 'fusion' filtrate with 2N nitric acid, and if nitrogen and/or sulphur are present, boil for 1 - 2 minutes.* Cool and add aqueous silver nitrate (1 mL), compare with a blank. Formation of a heavy, white or yellow precipitate of silver halide indicates halogen. If a positive result is obtained: acidify the remaining portion of the 'fusion' filtrate with dilute sulphuric acid, boil and cool. Add carbon tetrachloride (1 mL) and a few drops of freshly prepared chlorine water. Shake the mixture.
(a) If the carbon tetrachloride layer remains colourless - indicates chlorine.
(b) If the carbon tetrachloride layer is brown - indicates bromine.
(c) If the carbon tetrachloride layer is violet - indicates iodine.
*If nitrogen and/or sulphur are also present, the addition of silver nitrate to the acidified 'fusion' solution will precipitate silver cyanide and/or silver sulphide in addition to the silver halides. The removal of hydrogen cyanide and/or hydrogen sulphide is effected by boiling the 'fusion' solution. GROUP CLASSIFICATION TESTS

D. Solubility tests
The solubility of the unknown in the following reagents provides very useful information. In general, about 3 mL of the solvent is used with 0.1 g or 0.2 mL (2 - 3 drops) of the substance. The class of compound may be indicated from the following table:


SOLUBILITY TABLE
REAGENT AND TEST CLASS GROUP OF COMPOUNDS
Soluble in cold or hot water. (If the unknown is soluble do NOT perform solubility tests below) Neutral, acidic or basic. (Test with litmus or universal indicator paper) Lower members of series. Neutral, e.g. alcohols; Acidic, e.g. acids, phenols; Basic, e.g. amines
Soluble in dil. HCl Basic Most amines (except III amines with only aromatic groups
Soluble in dil. NaOH Acidic Most acids, most phenols.
Soluble in NaHCO3 Strongly acidic Most carboxylic acids.
Insoluble in water, acid and alkali Neutral Hydrocarbons, nitrohydro-carbons, alkyl or aryl halides, esters and ethers. Higher molecular weight alcohols, aldehydes and ketones


E. Group Classification Tests
From the previous tests it is often possible to deduce the functional groups present in the unknown compound. Consult i.r. spectra when available.
Individual tests are then performed to identify and confirm the functional groups present.
NOTE:
1. Students are strongly advised against carrying out unnecessary tests, since not only are they a waste of time but also increase the possibility of error. Thus it is pointless to first test for alcohol or ketone in a basic compound containing nitrogen! Instead tests for amines, etc. should be done on such a compound.
2. A systematic approach cannot be overemphasised in group classification tests to avoid confusion and error.
Once the functional group has been identified, reference is made to tables in a book on organic analysis, for assessing possibilities and for the preparation of suitable solid derivatives.
It should be noted that whilst two substances with the same functional group may sometimes have very similar b.p. or m.p., solid derivatives canusually be chosen from the literature, with m.p. differences of about 10 (or more), which distinguish between the two possibilities.

Example:
COMPOUND B.P. DERIVATIVES (M.P.)
2,4-DNPH SEMICARBAZONE
Diethyl ketone 102 156 139
Methyl n-propyl ketone 102 144 112

G. Preparation of derivatives
The final characterisation of the unknown is made by the preparation of suitable solid derivatives. The derivative should be carefully selected and its m.p. should preferably be between 90 - 150 for ease of crystallisation and m.p. determination.
Preparation of one derivative should be attempted. The derivative should be purified by recrystallisation, dried and the m.p. determined. Derivatives should be submitted correctly labelled for assessment together with the record.


Recording of Results
The results should be recorded in a systematic manner. Results should be recorded in the practical book at the time (not written up afterwards).
A record should be made of every test carried out, no matter whether a NEGATIVE RESULT HAS BEEN OBTAINED.
Tests for unsaturation
1. Cold dilute potassium permanganate solution.
2. Solution of bromine in carbon tetrachloride.
Tests for compounds containing nitrogen
1. Amines
(a) Nitrous acid.
(b) Confirmatory tests.
2. Compounds which give amines or ammonia on acid or alkaline hydrolysis:
Amides, substituted amides, anilides, nitriles.
3. Compounds which give amines on reduction:
Nitro, nitroso, azo, hydrazo, nitriles.
Tests for compounds containing C, H and possibly oxygen
1. Carboxylic acids
Na2CO3 or NaHCO3 solution liberate carbon dioxide.
2. Phenols
(a) Sodium hydroxide solution (soluble). Insoluble in and no CO2 from NaHCO3 (except when electron attracting groups present, e.g. 2,4-dinitrophenol).
(b) Ferric chloride solution.
(c) Bromine water.
3. Aldehydes and Ketones
(a) 2,4-dinitrophenylhydrazine (as Brady's reagent) for C=O.
(b) Iodoform test for CH3CO-.
4. Aldehydes only (reducing properties)
(a) Fehling's solution.
(b) Tollen's reagent (ammoniacal AgNO3 solution).
(c) Jones reagent.
5. Alcohols
(a) Lucas' reagent to distinguish I, II and III alcohols.
(b) Jones reagent.
(c) Metallic sodium (use dry liquid and dry tube).
6. Sugars
(a) Molisch's test.
7. Esters
(a) Hydroxamic acid test.
(b) Hydrolysis.


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Write up of the identification of an unknown organic compound

Compound containing C, H ,N, Halogens, S

Physical characteristics ...................... (solid, liquid, gas, colour, odour, etc.)

Ignition test .............................. (aromatic or aliphatic)

Physical constant ........................ (boiling point or melting point)

Solubility tests (in tabular form)

Group classification tests (in tabular form)
Test Observation Inference

From the above tests and observations the given compound is probably a
.........................(acid, phenol, aldehyde, etc.)

Consultation of literature (Possibilities) M.P. of derivative
(a)

(b)

(c)

Preparation of derivative (method of preparation)

Observed m.p. of derivative
Lit. m.p. of derivative

Result
Compound No. ........................ is ............................
(give formula)


TESTS FOR FUNCTIONAL GROUPS
I. UNSATURATED COMPOUNDS
Two common types of unsaturated compounds are alkenes and alkynes characterised by the carbon-carbon double and triple bond, respectively, as the functional group. The two common qualitative tests for unsaturation are the reactions of the compounds with (a) bromine in carbon tetrachloride and (b) potassium permanganate.
(a) 2% Bromine in carbon tetrachloride
Dissolve 0.2 g (or 0.2 mL) of the compound in 2 mL of carbon tetrachloride or another suitable solvent and add the solution dropwise to 2 ml of 2% bromine solution in carbon tetrachloride and shake. e. g.

Rapid disappearance of the bromine colour to give a colourless solution is a positive test for unsaturation.
NOTE: The reagent is potentially dangerous. Keep it off your skin and clothes; protect your eyes and nose.
(b) 2% Aqueous potassium permanganate
Dissolve 0.2 g (or 0.2 mL) of the substance in 2 mL of water (acetone may also be used as solvent). Add the potassium permanganate solution dropwise and observe the result.
e.g.

For a blank determination, count the number of drops added to 2 mL of acetone before the colour persists. A significant difference in the number of drops required in the two cases is a positive test for unsaturation.
II. COMPOUNDS CONTAINING NITROGEN
1. Amines
(a) Reaction with nitrous acid Dissolve the amine (0.5 mL) in concentrated acid (2.0 mL) and water (3 mL) and cool the solution to 0 - 5 in an ice-bath for 5 minutes. Add a cold solution (ice-bath) of sodium nitrite (0.5 g) in water (2.0 mL) from a dropper, with swirling of the test tube, still keeping the mixture in the ice-bath.

AMINE REACTION

Aliphatic N2 evolved.
RNH2 + HNO2 -> ROH + N2 + H2O
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Aromatic Diazonium salt is formed.
ArNH2 + HNO2 -> ArN=N+
Add the cold diazonium solution and with swirling
to a cold solution of 2-naphthol (0.2 g) in 5% NaOH
solution (2 mL). An orange-red azo dye is formed.
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aliphatic and Yellow oily nitrosamines are generally formed.
aromatic R2NH + HNO2 -> R2N-NO
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(b) Reaction with benzenesulphonyl chloride
Benzenesulphonyl chloride reacts with primary and secondary but not with tertiary amines to yield substituted sulphonamides.
e.g. (a) C6H5SO2Cl + H-NHR + NaOH -> C6H5SO2NHR + NaCl + H2O
(b) C6H5SO2Cl + H-NR2 + NaOH -> C6H5SO2NR2 + NaCl + H2O
The substituted sulphonamide formed from a primary amine dissolves in the alkali medium whilst that produced from a secondary amine is insoluble in alkali.
Place 0.5 mL (or 0.5 g) of the compound, 15 - 10 mL of 5% NaOH and 1 mL of benzenesulphonyl chloride in a test tube, stopper the tube and shake until the odour of the sulphonyl chloride has disappeared. The solution must be kept alkaline (if no reaction has occurred, the substance is probably a tertiary amine).
If a precipitate appears in the alkaline solution, dilute with about 10 mL of water and shake; if the precipitate does not dissolve, a secondary amine is indicated.
If there is no precipitate, acidify it cautiously to congo red with concentrated hydrochloric acid (added dropwise): a precipitate is indicative of a primary amine.
2. Amides R-CO-NH2
Simple primary amides can be decomposed by boiling with alkali and thereby evolving ammonia.
e.g. CH3-CO-NH2 + NaOH -> CH3-CO2- Na+ + NH3 ¬
Boil 0.5 g of the compound with 5 mL of 10% sodium hydroxide solution and observe whether ammonia is evolved.
III. COMPOUNDS CONTAINING C, H AND POSSIBLY OXYGEN
1. Carboxylic acids - test with 5% aq. NaHCO3
R-CO2H + NaHCO3 -> R-CO2- Na+ + CO2 ¬ + H2O
Sodium hydrogen carbonate reacts with carboxylic acids to give the sodium salt of the acid and liberates carbon dioxide. If the acid is insoluble in water and the reaction is sluggish dissolve the acid in methanol and add carefully to a saturated sodium hydrogen carbonate solution, when a vigorous effervescence will be observed.
2. Phenols [Soluble in NaOH and produce no CO2 from NaHCO3]
(a) Bromine water
Phenols are generally highly reactive towards electrophilic reagents and are readily brominated by bromine water. e.g.

Dissolve or suspend about 0.05 g of the compound in 2 mL of dilute hydrochloric acid and add bromine water dropwise until the bromine colour remains. A white precipitate of the bromophenol may form. Solid bromophenol derivatives can be used for the confirmation of the structure of a phenol (cf the preparation of derivatives).
(b) Ferric chloride test
Most phenols react with iron (III) chloride to form coloured complexes. The colours vary - red, purple, blue or green - depending on various factors, e.g. the phenolic compound used, the solvent, concentration. Since some phenols do not give colours, a negative test must not be taken as significant without supporting information.
Dissolve 0.05 g of the compound in 2 mL water (or a mixture of water and ethanol if the compound is not water-soluble) and add an aqueous solution of ferric chloride dropwise. Observe any colour changes which may occur.
3. Aldehydes and ketones
(a) 2,4-Dinitrophenylhydrazine (as Brady's reagent)
A test for the carbonyl group (C=O) in aldehydes and ketones. 2,4- Dinitrophenylhydrazine gives sparingly soluble yellow or red 2,4-dinitrophenylhydrazones with aldehydes and ketones.

Add 3 mL of the reagent to 2 drops of the compound in a test tube and shake. If no precipitate forms immediately, warm and allow to stand for 5 - 10 minutes. A crystalline precipitate indicates the presence of a carbonyl compound.
The bench reagent is very dilute and is intended for qualitative tests only and should not be used in the preparation of a derivative for identification purposes.
(b) Iodoform test for CH3CO-
Dissolve 0.1 g (or 5 drops) of the compound in 2 mL of water; if it is insoluble in water add sufficient dioxan to produce a homogeneous solution. Add 2 mL of 5% NaOH solution and then introduce the potassium iodide - iodine reagent dropwise with shaking until a definite dark colour of iodine persists. Allow to stand for 2 - 3 minutes; if no iodoform separates at room temperature, warm the test tube in a beaker of water at 60 . Add a few more drops of the iodine reagent if the faint iodine colour disappears. Continue the addition of the reagent until a dark colour is not discharged after 2 minutes heating at 60 . Remove the excess of iodine by the addition of a few drops of dilute sodium hydroxide solution with shaking, dilute with an equal volume of water, and allow to stand for 10 minutes. The test is positive if a yellow precipitate of iodoform is deposited. Filter off the yellow precipitate, dry upon pads of filter paper and determine the m.p. Iodoform melts at 120 (it can be recrystallised from methanol- water).
The reaction is given by acetaldehyde and simple methyl ketones. Alcohols containing the CH3CHROH group will be oxidised under the reaction conditions and also give a positive test.
4. Aldehydes only (reducing properties).
(a) Fehling's solution
Aldehydes reduce Fehling's solution to yellow or red copper (I) oxide.
Preparation of the reagent: Mix equal volumes of Fehling's solution solution I (aqueous alkaline potassium tartrate) and Fehling's solution II (copper sulphate solution).
Add 2 drops (or 0.05 g) of the compound and 2 - 3 drops of the reagent and heat on a boiling water bath for 3 - 4 minutes.
The test is positive for aliphatic aldehydes, but is often indecisive for aromatic aldehydes where Jones' Reagent is often useful (see 5).
(b) Tollen's reagent (Ammonical silver nitrate solution)
Aldehydes are readily oxidised to carboxylic acids and will reduce Tollen's reagent to produce a silver mirror on the inside of a clean test tube.
FIRST clean up a test tube with a little hot nitric acid (fume cupboard) and rinse with distilled water.
Preparation of the reagent: To 1 mL of silver nitrate solution add a few drops of sodium hydroxide. Then add dilute ammonium hydroxide dropwise until the precipitate just dissolves.
Add 2 - 3 drops of the compound in methanol to 2 - 3 mL of Tollen's solution contained in a very clean test tube. If no reaction takes place in the cold, warm gently in a water bath.
CAUTION: After the test, pour the contents of the test tube into the sink and wash the test tube with dilute nitric acid. Any silver fulminate present, which is highly explosive when dry, will be destroyed.
(c) Jones Reagent (See section under alcohols).
5. Alcohols
The tests for the hydroxyl group not only detect the presence of the group, but may also indicate whether it is primary, secondary or tertiary.
(a) Jones Reagent (CrO3-H2SO4 in H2O)
This reagent distinguishes primary and secondary alcohols from tertiary alcohols; the test is based on the much greater resistance to oxidation of tertiary alcohols compared to the other two types. Aldehydes also give a positive test.
Place 1 mL of acetone in a test tube and dissolve one drop of a liquid or ca 10 mg of a solid alcohol or aldehyde in it. Add one drop of the reagent to the acetone solution and shake the tube to mix the contents. Primary and secondary alcohols react within two seconds as indicated by the disappearance of the orange colour of the reagent and the formation of a green or blue-green precipitate or emulsion.
Tertiary alcohols do not react even after 3 minutes.
(I) RCH2OH -> RCHO -> RCO2H

(II) R2CHOH -> R2C=O

(III) R3COH -> no visible reaction.
(b) Lucas' Reagent [ZnCl2 - conc. HCl]
This reagent converts alcohols into the corresponding alkyl chlorides. Zinc chloride (a Lewis acid) increases the reactivity of alcohols towards acid. The test depends on the rate of reaction of primary, secondary, and tertiary alcohols with the reagent at room temperature.
(I) RCH2OH -> no reaction at room temperature.

(II) R2CHOH -> R2CHCl + H2O (1 hour or maybe longer)

(III) R3COH -> R3CCl + H2O (immediately)
To 1 mL of the alcohol in a small test tube add 6 mL of Lucas' reagent at room temperature. Close the tube with a cork, shake and allow to stand.
(i) Primary alcohols - the aqueous phase remains clear (except allyl alcohol - droplets after 7 minutes).
(ii) Secondary alcohols - very slow reaction (~ 1 hour or maybe longer) when droplets of alkyl chloride may be seen.
(iii) Tertiary alcohols - very fast reaction and droplets of the alkyl chloride formed almost immediately.
6. Sugars, Carbohydrates
Molisch's Test
This is a general test for carbohydrates. Dissolve 20 - 30 mg of the compound in 2 mL water and add 0.5 mL of the reagent (a 20% solution of 2-naphthol in ethanol). Pour 2 mL of concentrated sulphuric acid from a dropper carefully down the side of the tube so that the acid forms a layer beneath the aqueous solution without mixing with it. A red colouration, changing to dark purple forms at the interface. Carry out a second test on a blank solution.
7. Esters
Hydroxamic acid test
R-CO-OR' + H2N-OH -> R-CO-NH-OH + R'-OH
Esters react with hydroxylamine in the presence of sodium hydroxide to form the sodium salt of the corresponding hydroxamic acid. On acidification and addition of ferric chloride the magenta-coloured iron (III) complex of the hydroxamic acid is formed.
It is always advisable to ensure that an unknown compound does not give a colour with iron (III) chloride before carrying out the hydroxamic acid test.
Procedure for hydroxamic acid test
(a) Ferric chloride test
Dissolve a drop or a few small crystals of the compound in 1 mL of 95% ethanol (rectified spirit) and add 1 mL of M hydrochloric acid. Note the colour produced when 1 drop of 5% iron (III) chloride is added to the solution. If a pronounced violet, blue, red or orange colour is produced, the hydroxamic acid test described below is NOT APPLICABLE.
(b) Hydroxamic acid test
Mix 1 drop or several small crystals (ca 0.05 g) of the compound with 1 mL of 0.5 M hydroxylamine hydrochloride in 95% ethanol and add 0.2 mL of 6 M aqueous sodium hydroxide. Heat the mixture to boiling and after the solution has cooled slightly add 2 mL of M hydrochloric acid. If the solution is cloudy, add 2 mL of 95% ethanol. Observe the colour produced when 1 drop of 5% iron (III) chloride solution is added. If the resulting colour does not persist, continue to add the reagent dropwise until the observed colour pervades the entire solution. Usually only 1 drop of the iron (III) chloride solution is necessary. Compare the colour with that produced in test (a). A positive test will be a distinct burgundy or magenta colour as compared with the yellow colour observed when the original compound is tested with iron (III) chloride solution in the presence of acid. It is often advisable to conduct in parallel the test with, say, ethyl acetate, to ensure that the conditions for this test are correct.
THE PREPARATION OF DERIVATIVES OF ORGANIC COMPOUNDS
The preliminary examination and group classification tests indicate the particular class (functional group) to which an unknown organic compound may belong. Further characterisation and identification depends on the selection and preparation of a suitable solid derivative and accurate determination of its melting point (best, between 90 - 150 ).
The following table lists some of the classes of organic compounds and a selection of derivatives that may be prepared to characterise them. Check with the tables of melting points in Vogel which derivatives are most suitable for the characterisation of your particular compound.


CLASS OF COMPOUND DERIVATIVES
1. ALCOHOLS 3,5-dinitrobenzoate
2. PHENOLS benzoate, acetate, bromo-derivative
3.ALDEHYDES AND KETONES semicarbazone, 2,4-dinitrophenyl-hydrazone, oxime
4. ACIDS anilide, amide, p-toluidide.
5. AMINES benzoyl, acetyl and sulphonamide derivatives

METHODS FOR THE PREPARATION OF DERIVATIVES
ALCOHOLS
(i) 3,5-Dinitrobenzoates
3,5-Dinitrobenzoyl chloride is usually partially hydrolysed and should be prepared in the pure state by heating gently a mixture of 3,5-dinitrobenzoic acid (1 g) and phosphorus pentachloride (1.5 g) in a dry test tube, until it liquifies (5 min).* The liquid is poured on a dry watch glass and allowed to solidify. The phosphoryl chlorides are removed by pressing the solid with a spatula on a wad of filter paper. The residual acid chloride is suitable for immediate use in the preparation of the derivatives.
*Work under fume hood. Fumes are irritating to the eyes and nose.
The 3,5-dinitrobenzoyl chloride is mixed with the alcohol (0.5 - 1 mL) in a loosely corked dry test tube and heated on a steam bath for about 10 min. Secondary and tertiary alcohols require up to 30 min. On cooling add 10 mL sodium hydrogen carbonate solution, stir until the ester crystallises out, and filter at the pump. Wash with a little carbonate solution, water and suck dry. Recrystallise from the minimum hot ethanol or light petroleum. Cool slowly to avoid the formation of oily droplets of your ester.
PHENOLS
(i) Benzoates (Schötten-Baumann method).
To the phenol (0.5 g) is added 5% sodium hydroxide (10 mL) in a well-corked boiling tube or a small conical flask. Benzoyl chloride (2 mL) is added in small quantities at a time, and the mixture shaken vigorously with occasional cooling under the tap or in ice-water. After 15 min the solid benzoate separates out: the solution should be alkaline at the end of the reaction; if not alkaline, or if the product is oily, add a solid pellet of sodium hydroxide and shake again. Collect the benzoate, wash thoroughly with cold water, and recrystallise from alcohol or light petroleum.
(ii) Acetates
Acetates of many simple phenols are liquids; however, this is a suitable derivative for polyhydric and substituted phenols. The phenol (0.5 g) is dissolved in 10% sodium hydroxide solution and an equal quantity of crushed ice is added, followed by acetic anhydride (2 mL). The mixture is vigorously shaken in a stoppered test tube until the acetate separates. The product is filtered and recrystallised from alcohol.
(iii) Bromo derivatives
The phenol (0.3 g) is suspended in dilute hydrochloric (10 mL) and bromine water added dropwise until no more decolourisation occurs. The bromo derivative which precipitates out is filtered off and recrystallised from alcohol.
ALDEHYDES AND KETONES
(i) Semicarbazones
Dissolve semicarbazide hydrochloride (1 g) and sodium acetate (1.5 g) in water (8 - 10 mL), add the aldehyde or ketone (0.3 mL) and shake. Shake the mixture for a few minutes and then cool in ice-water. Filter off the crystals, wash with a little cold water and recrystallise from methanol or ethanol.
(ii) 2,4-Dinitrophenylhydrazones
Suspend 0.25 g of 2,4-dinitrophenylhydrazine in 5 mL of methanol and add 0.5 mL of concentrated sulphuric acid cautiously. Filter the warm solution and add a solution of 0.2 g of the carbonyl compound in 1 mL of methanol. Recrystallise the derivative from methanol, ethanol or ethyl acetate.
(iii) Oximes
Hydroxylamine hydrochloride (0.5 g) is dissolved in water (2 mL). 10% sodium hydroxide (2 mL) and the carbonyl compound (0.2 - 0.3 g) dissolved in alcohol (1 - 2 mL) are added, the mixture warmed on a steam bath for 10 min and then cooled in ice. Crystallisation is induced by scratching the sides of the test tube with a glass rod. The oximes may be crystallised from alcohol.
ACIDS
(i) Amides, anilides and p-toluidides
The acid (0.5 g) is refluxed with thionyl chloride (2 - 3 mL) in a fume cupboard for about 30 mins.* It is advisable to place a plug of cotton wool in the top of the reflux condenser to exclude moisture. The condenser is removed and the excess of thionyl chloride is distilled off (b.p. 78 ). The acid chloride thus produced is treated with concentrated ammonia solution (5 mL) or aniline (0.5 - 1 mL) or p-toluidine (0.5 - 1 g), when the solid derivative separates out. It is collected and recrystallised from alcohol adding decolourising charcoal if found necessary.
*Alternately use PCl5 to form the acid chloride.
AMINES
(i) Acetyl derivatives (acetamides)
Reflux gently in a small dry flask under a dry condenser the amine (1 g) with acetic anhydride (3 mL) for 15 min. Cool the reaction mixture and pour into 20 mL cold water. Boil to decompose the excess acetic anhydride. Cool and filter by suction the insoluble derivative. Recrystallise from ethanol.
(ii) Benzoyl derivatives (benzamides)
Suspend 1 g of the amine in 20 mL of 5% aqueous sodium hydroxide in a well-corked flask, and add 2 mL benzoyl chloride (fume hood!), about 0.5 mL at a time, with constant shaking. Shake vigorously for 5 - 10 min until the odour of the benzoyl chloride has disappeared. Ensure that the mixture remains alkaline. Filter off the solid derivative, wash with a little cold water and recrystallise from ethanol.
(iii) Benzenesulphonamides
To 1 g of the amine in 20 mL of 5% sodium hydroxide solution in a well-corked flask add 1 mL benzenesulphonyl chloride (fume hood!). Shake the mixture until the odour of the sulphonyl chloride disappears. Check that the solution is alkaline. Acidify if necessary to obtain the precipitated derivative. Concentrated hydrochloric acid added dropwise should be used. Filter the product, wash with a little cold water and suck dry. Recrystallise from ethanol.


Inorganic Quantitative Analysis
Gravimetric Estimation of Ba2+, Fe2+, Zn2+ and Cu2+
All Gravimetric analyses rely on some final determination of weight as a means of quantifying an analyte. Since weight can be measured with greater accuracy than almost any other fundamental property, gravimetric analysis is potentially one of the most accurate classes of analytical methods available. These methods are among the oldest of analytical techniques, and they may be lengthy and tedious. Samples may have to be extensively treated to remove interfering substances. As a result, only a very few gravimetric methods are currently used in environmental analysis.
There are four fundamental types of gravimetric analysis: physical gravimetry, thermogravimetry, precipitative gravimetric analysis, and electrodeposition. These differ in the preparation of the sample before weighing of the analyte. Physical gravimetry is the most common type used in environmental engineering. It involves the physical separation and classification of matter in environmental samples based on volatility and particle size (e.g., total suspended solids). With thermogravimetry, samples are heated and changes in sample mass are recorded. Volatile solids analysis is an important example of this type of gravimetric analysis. As the name implies, precipitative gravimetry relies on the chemical precipitation of an analyte. Its most important application in the environmental field is with the analysis of sulfite. Electrodeposition involves the electrochemical reduction of metal ions at a cathode, and simultaneous deposition of the ions on the cathode.
Common Procedures in Gravimetric Analysis
a. Drying to a Constant Weight
All solids have a certain affinity for water, and may absorb moisture from the laboratory air. Reagents that readily pick up water are termed hygroscopic. Those that absorb so much water that they will dissolve in it and form a concentrated solution are called deliquescent (e.g., sodium hydroxide, trichloroacetic acid). These types of substances will continually increase in weight while exposed to the air. For this reason, many types of laboratory procedures require that a sample be dried to a constant, reproducible weight (i.e., absorbed moisture removed to some standard, low level). This is especially important for the gravimetric methods. Generally, the sample is dried in a 103 C to 110 C oven for about 1 hour and allowed to cool to room temperature in a desiccator. It is then weighed, and heated again for about 30 minutes. The sample is cooled and weighed a second time. The procedure is repeated until successive weighings agree to within 0.3 mg.
b. Description and Use of the Analytical Balance
The analytical balance is the most accurate and precise instrument in an environmental laboratory. Objects of up to 100 grams may be weighed to 6 significant figures. Volumetric glassware is accurate to no more than 4 significant figures, and the accuracy of complex analytical methods rarely justifies more than 2 significant figures. Analytical balances are generally used for gravimetric analyses, and for the preparation of standard solutions.
Summary of Gravimetric Methods for Environmental Analysis
Some gravimetric methods are in generally using for the analysis of waters and wastewaters.
Type Analyte Pretreatment
Physical Total Solids Evaporation
Suspended Solids Filtration
Dissolved Solids Filtration + Evaporation
Oil & Grease extraction with C2Cl3F3 + distillation of solvent
Surfactants extraction into ethylacetate + evaporation
Thermal Volatile Solids Evaporation + 550`C for 15 min
Volatile Suspended Solids Filtration + 550`C for 15 min
Precipitative Mg with Diammonium hydrogen phosphate and final pyrolysis
Na with zinc uranyl acetate
Silica precipitation/ ignition/ volatilization (with HF)
SO4 with Ba

PHYSICAL GRAVIMETRY
1. Total, Dissolved and Suspended Solids
a. Definitions
Total solids (TS) is generally defined as all matter in a water or wastewater sample that is not water. Because solids are not a specific chemical compound, but rather a diverse collection of dissolved and particulate matter, their concentration cannot be determined in an unambiguous way. Instead, they must be defined by the procedure used to estimated their concentration. Total solids may be differentiated according to size into total dissolved solids (TDS) and total suspended solids (TSS). Once again, this is an operational distinction, whereby all solids passing through filter paper of a certain pore size (e.g., 1.5 microns, Whatman #934AH) are called dissolved, and those retained are termed suspended.
b. Significance to Environmental Engineering
Most of the impurities in potable waters are in the dissolved state, principally as inorganic salts. Thus, the parameters, "total solids" and especially "total dissolved solids" are of primary importance here. Waters containing high concentrations of inorganic salts are not suitable as sources of drinking water, because such materials are often difficult to remove during treatment. Finished drinking waters containing more than 1000 mg/L TDS are generally considered unacceptable. Waters of this type may also be unsuitable for agricultural purposes due to the harmful effects of high ionic concentrations on plants. In most natural waters, the TDS (total dissolved solids) concentration correlates well with total hardness (i.e., [Ca] + [Mg]). This is useful in assessing the corrosivity of a water and the need for softening.
The total suspended solids (TSS) content of natural waters is of interest for the purpose of assessing particle bed load and transport. High concentrations of suspended matter may be detrimental to aquatic life. In theory, TSS could be used for assessing particle removals during water treatment. However, nearly always the concentration of colloidal particles in water is measured as turbidity since this latter technique is faster and more precise.
Some Typical Solids Concentrations
Source Concentration (mg/L)
Low Avg High
NATURAL WATERS
Fresh TDS 20 120 1,000
Brines TDS 5,000 300,000
DOMESTIC WASTEWATER
Raw TDS 350 600 900
VDS 165 285 600
TSS 100 200 350
VSS 75 135 215
Secondary Effluent TSS 10 30 60
Activated Sludge Mixed
Liquor (conventional) TSS 1,500 3,000
Activated Sludge Mixed
Liquor (extended aeration) TSS 3,000 6,000
Primary Sludge TSS 20,000 70,000
Secondary Sludge TSS 5,000 12,000
STORM WATER TSS 5 300 3,000

Procedures
Total Solids (Total Residue). Total solids is determined by the final weight of a dried sample (minus tare) divided by the original sample volume. Evaporating dishes of platinum, vycor or porcelain may be used. Platinum is preferred, because it is more inert than the other two, and can be heated to a constant weight more easily. However, platinum is very expensive, so porcelain is often used. Porcelain is difficult to bring to a constant weight, and its use should be avoided. Space permitting, evaporating dishes should be stored in a desiccator so as to avoid the collection of dust and absorption of moisture while not in use. The precision of this method has been estimated to be  4 mg or 5%. However, settled wastewater may give better precision, on the order of  1 mg.
1. Preheat a 100 mL evaporating dish at 550 50 C for 1 hour, cool in a in a drying oven or in the open air (protected from dust) for 15-20 minutes, bring to room temperature in a desiccator, and weigh. Repeat until a constant weight is achieved.
2. Measure 75 mL of sample or a volume sufficient to yield 200 mg TS, whichever is less. Add this to the preweighed dish and evaporate to dryness in a drying oven set at 98 C. Alternatively, a steam bath may be used.
3. Dry for an additional hour at 103-105 C.
4. Cool in a desiccator and weigh.
Dissolved Solids (Filtrable Residue). Dissolved solids may be determined directly by analysis of the filtered sample for total solids, or indirectly by determining the suspended solids and subtracting this value from the total solids. When using the direct method, final drying may be conducted at one of two temperatures.

1. Analyze the filtrate in accordance with the total solids procedure.
2. Final drying (1 hour period) may be conducted at either 103-105 C or 180 2 C.
Suspended Solids (Non-filtrable Residue). Suspended solids is measured directly by drying and weighing the solids retained during filtration.
1. Dry this filter at 103-105 C for 1 hour, and cool in a desiccator.
2. Weigh the filter, then pass a water sample of sufficient volume to yield 50-200 mg suspended solids through it. Smaller volumes will result in reduced accuracy.
3. Dry for at least one hour at 103-105 C.
4. Cool in a desiccator and weigh.
C. THERMOGRAVIMETRY AND COMBUSTION ANALYSIS
Thermogravimetry and combustion analysis involve the heating of a sample to 500 C or more with the oxidation and/or volatilization of some of the sample constituents. Either the change of sample weight is determined (thermogravimetry), or the combustion gases are trapped and weighed (combustion analysis). With thermogravimetric methods, it is especially important to return the sample to room temperature before weighing. Otherwise the differences in temperature will create convection currents around the balance pan, which will severely disrupt method accuracy. A steady increase in apparent weight while the sample is on the pan indicates a problem of this type. Large vessels and samples will require longer cooling times to dissipate their excess heat.
Volatile Solids and Fixed Solids
Fixed solids are those that remain as residue after ignition at 550 C for 15 minutes. The weight of material lost is called the volatile solids. Thus the total operational definition for volatile solids would be: all matter lost upon ignition at 550 C for 15 minutes, but not lost upon drying at 103-105 C for 1 hour. The portion lost upon ignition is generally assumed to be equivalent to the organic fraction. The portion remaining is considered the inorganic fraction. For waters of moderate to high hardness, most of this is calcium carbonate which decomposes only at temperatures exceeding 800 C. When igniting a filter with suspended matter, one must be especially careful of the temperature; above 600 C glass fiber filters begin to melt and can loose a significant amount of weight in 15 minutes.
Combining the fractionations resulting from ignition and filtration, one arrives at a total of 9 separate categories: total solids (TS), fixed solids, volatile solids, total dissolved solids (TDS), fixed dissolved solids, volatile dissolved solids, total suspended solids (TSS), fixed suspended solids, and volatile suspended solids (VSS). In practice, only four of these (TS, TDS, TSS, and VSS) are commonly used. When comparing fixed solids with inorganic content, one would expect positive bias from incomplete oxidation of organic matter, and negative bias from decomposition of certain inorganics. Ammonium salts may be lost during low temperature drying or upon ignition. Most others are stable under the conditions used for volatile solids determination with the exception of magnesium carbonate. Volatile solids may be effected by these as well as loss of recalcitrant waters of crystallation (positive bias), and previous losses of organic matter to volatilization during low-temperature drying (negative bias). A modest interlaboratory study found an average standard deviation of 11 mg/L on a sample of 170 mg/L volatile solids.
MgCO3 ------------> MgO + CO2 ¬
Ammonium compounds (often present in sludge in the form of ammonium bicarbonate) may be lost during low temperature drying and therefore should not introduce a bias in volatile solids
NH4HCO3 ---------> NH3 ¬ + H2O ¬ + CO2 ¬
1. Dry and weigh a vessel containing the solids to be analyzed. For volatile and fixed suspended solids analysis, the filter (with residue) prepared for suspended solids analysis and dried to a constant weight may be used. For volatile and fixed total (or dissolved) solids, the evaporating dish (with residue) prepared for total (or dissolved) solids analysis dried to a constant weight should be used.
2. Ignite the sample and vessel in a preheated muffle furnace set at 550 50 C for 15-20 min (water & wastewater) or 1 hour (sludge, sediment & soil).
3. Cool for 15 minutes in the open air in an area protected from dust.
4. Place vessel in a desiccator for final cooling to room temperature and weigh. Due to the approximate nature of this test samples are not generally re-heated and dried to a constant weight.
D. PRECIPITATIVE GRAVIMETRIC ANALYSIS
Precipitative gravimetric analysis requires that the substance to be weighed be readily removed by filtration. In order for a non-filtrable precipitate to form, it must be supersaturated with respect to its solubility product constant. However, if it is too far above the saturation limit, crystal nucleation may occur at a rate faster than crystal growth (the addition of molecules to a crystal nucleus, eventually forming a non-filtrable crystal). When this occurs, numerous tiny micro-crystals are formed rather than a few large ones. In the extreme case, micro-crystals may behave as colloids and pass through a fibrous filter. To avoid this, precipitating solutions may be heated. Because the solubility of most salts increases with increasing temperature, this treatment will lower the relative degree of supersaturation and slow the rate of nucleation. Also, one might add the precipitant slowly with rapid mixing to avoid the occurrence of locally high concentrations.
It is very important that the precipitate be pure and have the correct stoichiometry. Coprecipitation occurs when an unwanted ion or molecule becomes trapped in the precipitate. This may be due to inclusion or occlusion. Inclusion is the term used of a single subsitution in the crystal lattice by an ion of similar size. Occlusion refers to the physical trapping of a large pocket of impurities within the crystal. One technique for minimizing these problems is to remove the mother liquor, re-dissolve the precipitate and then re-precipitate. The second time the mother liquor will contain fewer unwanted ions capable of coprecipitation.
Sulfate Determination
The method of choice for sulfate in waters and wastewaters is the precipitative gravimetric procedure using barium. If Ba(+II) is added in excess under acidic conditions, BaSO4 is precipitated quantitatively. The reaction is allowed to continue for 2 hours or more at 80-90oC. This is to encourage the formation of BaSO4 crystals (non-filtrable) from the initially formed colloidal precipitate (partially filtrable). The precipitate is washed, and then dried at 800`C for 1 hour. Low pH is needed to avoid the precipitation of BaCO3 and Ba3(PO4)
Ba+2 + SO4-2 = BaSO4(ppt.)
Chloride Determination
Chloride may be determined by precipitation with silver. Interfering ions likely to form insoluble silver salts are the other halogens (bromide, iodide), cyanide, and reduced sulfur species (sulfite, sulfide, and thiosulfate). Fortunately, the reduced sulfur compounds can be pre-oxidized with hydrogen peroxide, and the others are rarely present at high concentrations. Although AgCl can be determined gravimetrically, the recommended procedure for water and wastewater is to use a volumetric procedure with chromate as an indicator.

3. Inorganic Synthesis
(i) Synthesis of Cuprous Chloride (work in a fume hood)
(a) Cu2+ + Cu + 2 Cl- → 2 CuCl
Material: CuSO4.5H2O, Cu, NaCl, HCl, Na2SO3, CH3COOH
Procedure: Prepare a solution of 10 g of powdered CuSO4.5H2O and 15 ml of
concentrated HCl in a 250-ml round-bottom flask, add 4 g of NaCl and heat to boiling.
Cover the flask with a little funnel. Add copper to hot solution in small portions. The
green colour of the solution will turn to yellow. Filter off the remaining Cu. Pour the
solution to one litre of cold water with 2 g of Na2SO3.
Wash the precipitated cuprous chloride 2 – 3 times with a solution of 1.5 g of
Na2SO3, 6 ml of HCl and 300 ml of H2O by decantation. Filter out the precipitate and wash it with concentrated acetic acid. Dry it in a drying oven at 100 oC.
( b) 2 Cu2+ + SO2 + 2 Cl- + 2 H2O → 2 CuCl + SO42- + 4 H+

Material: CuSO4.5H2O, NaCl, HCl, SO2, CH3COOH
Procedure: Add 5 g of NaCl to the warm solution (70 oC) of 10 g CuSO4.5H2O and
bubble SO2 through the mixture. CuCl precipitates. Filter out the precipitate and wash
it with a solution of SO2 in water and then with concentrated acetic acid.
CuCl – white crystals, insoluble in water, on air turns to green alkali copper chloride


(ii) Preparation of chrome alum - KCr(SO4)2.12H2O
a) K2Cr2O7 + 3 SO2 + H2SO4 → KCr(SO4)2 + H2O
Material: K2Cr2O7, SO2, H2SO4
Procedure: Blow the SO2 gas through a gas washing bottle with K2Cr2O7 solution acidified with H2SO4. Do not permit the temperature to rise above 60 oC. Above this temperature complexes of chromium (III) sulphate are formed. These complexes contain sulphate in a non-ionisable form and are difficult to crystallise.
Bubble the unreacted gas through a washing bottle with 10 % NaOH solution. Test for the end of the reaction – to the sample of reduced solution in a test tube add small amount of Na2CO3 crystals and heat the mixture just below the boiling point. Let the precipitate settle, the solution over the precipitate has to be colourless. Set the solution aside to crystallise after the end of reduction.When the crystallization is complete, filter off the crystals and wash them with a small amount of water.
Transfer the product to a dry filter paper and let them dry in air.
b) K2Cr2O7 + 3 C2H5OH + 4 H2SO4 → KCr(SO4)2 + 3 CH3CHO + 7 H2O
Material: K2Cr2O7, C2H5OH, H2SO4
Procedure: Dissolve crushed K2Cr2O7 in diluted H2SO4 (1:3) and add, in small portions with stirring, calculated volume (+ 10 % excess) of C2H5OH. Do not permit the temperature to rise above 60°C. Continue like in procedure a).
KCr(SO4)2.12H2O – dark violet crystals, crystallize in regular octahedra, soluble in
water.
(ii) 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


(iv) Preparation of iron alum (Ferrous ammoninium sulphate)
2 FeSO4 + H2O2 +H2SO4 → Fe2(SO4)3
Fe2(SO4)3 + (NH4)2SO4 → 2 NH4Fe(SO4)2
Material: FeSO4.7H2O, H2O2, H2SO4, (NH4)2SO4
Procedure: Dissolve FeSO4.7H2O in water to a solution with w(FeSO4) = 0.15. Filter
this solution if necessary and carefully add concentrated H2SO4 in 10 % excess to the
stoichiometry. Then slowly add H2O2 (double amount compared to stoichiometry),
while stirring the mixture continuously. Heat the mixture to the boiling. Make sure that
Fe2+ was oxidized to Fe3+ by a reaction of sample with K3[Fe(CN)6]. Add further H2O2
if necessary.
Evaporate the solution on a steam bath to half the volume and add warm saturated
(by 60 oC) solution of calculated amount of (NH4)2SO4. Let the solution crystallize.
Put the crystals on a dry filter paper and let them dry in air.
NH4Fe(SO4)2.12H2O – colourless or light violet crystals, turn brown on air.


(v) Preparation of lead carbonate
Pb(CH3COO)2 + (NH4)2CO3 → PbCO3 + 2 CH3COONH4
Pb(NO3)2 + 2 NaHCO3 → PbCO3 + 2 NaNO3 + CO2 + H2O
Material: Pb(CH3COO)2 or Pb(NO3)2, (NH4)2CO3 or NaHCO3
Procedure: Add saturated (NH4)2CO3 or NaHCO3 solution (10 % excess to stoichiometry) to saturated Pb2+ salt solution while continuously stirring. Decant the precipitated product with water, filter it and dry at laboratory temperature.
PbCO3 – white powder, insoluble in water, easy soluble in acids and hydroxides,
decomposes by on heating. If Na2CO3 is used for precipitation, the alkali carbonate
2PbCO3.Pb(OH)2 creates.


(vi) Preparation of lead dioxide
a) Pb(NO3)2 + 2 NaOH → Pb(OH)2 + 2 NaNO3
Pb(OH)2 + 2 NaOH → Na2[Pb(OH)4]
Na2[Pb(OH)4] + CaOCl2 → PbO2 + CaCl2 + 2 NaOH + H2O
Material: Pb(NO3)2 or Pb(CH3COO)2, NaOH, CaOCl2 or NaClO, HNO3
Procedure: Dissolve 0.1 mol of Pb2+ salt in 300 ml of hot water and cool the solution.
If a small amount of substance remains undissolved, it will not affect the result. Add a solution of 20 g NaOH in 180 ml of water. First white precipitate of Pb(OH)2 appears, which dissolves in excess of NaOH to Na2[Pb(OH)4].
Mix 40 g of CaOCl2 with 50 ml of water and the necessary amount of Na2CO3 for
reaction with Ca2+. Add 200 ml of water to the mixture and filter it.
Add the filtrate to the boiling solution of Na2[Pb(OH)4] until the test for presence of
Pb2+ in the final solution is negative.
Test for presence of Pb2+: add one drop of Na2S solution to one drop of the
reaction mixture on filter paper. Black precipitate (PbS) indicates presence of Pb2+.
Pour the mixture into 500 ml of water and decant it. Add 100 ml of diluted HNO3
(1:3) to the precipitate, stir and decant it until pH is neutral. Filter off the lead dioxide,
wash it with boiling water and dry.
b) Pb(NO3)2 + 2NaOH → Pb(OH)2 + 2NaNO3
Pb(OH)2 + 2NaOH + Cl2 → PbO2 + 2NaCl + 2H2O
Material: Pb(NO3)2 or Pb(CH3COO)2, NaOH, Cl2
Procedure: Dissolve 10.0 g of Pb(NO3)2 in 80 ml of water acidified with a drop of
concentrated nitric acid and add solution of 2.4 g of sodium hydroxide dissolved in
50 ml of water slightly with constant stirring. Heat the precipitated lead(II) hydroxide
suspension to 70 - 80 oC and bubble chlorine through it at the same time (do not heat
it over 80 oC or PbO will be obtained!). Decant the precipitated brown-black product
with diluted nitric acid (1:3) and then with water. Dry it at 100 oC.
PbO2 – brown powder, insoluble in water, decomposes on heating to Pb3O4 or PbO and oxygen. Good oxidizer.


Preparation of Potash alum K2(SO4).Al(SO4)3•12H2O)
It is white crystalline solid, soluble in water, used for the purification of water, leather industry paper industry and as fire extinguisher.
Melting point is 92oC
Potash alum is commonly known as "PHITKARI"
Potash alum is prepared by mixing equi-molecular masses of potassium sulphate and aluminum sulphate in water followed by evaporation
K2SO4 + Al2(SO4)3 + 24H2O-- K2SO4.Al2(SO4)3.24H2O


(vii) Preparation of copper ammine sulphate - perform this experiment in a fume hood
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.


(viii) Preparation of cuprous chloride – work in a fume hood
a) Cu2+ + Cu + 2 Cl- → 2 CuCl
Material: CuSO4.5H2O, Cu, NaCl, HCl, Na2SO3, CH3COOH
Procedure: Prepare a solution of 10 g of powdered CuSO4.5H2O and 15 ml of concentrated HCl in a 250-ml round-bottom flask, add 4 g of NaCl and heat to boiling.
Cover the flask with a little funnel. Add copper to hot solution in small portions. The green colour of the solution will turn to yellow. Filter off the remaining Cu. Pour the solution to one litre of cold water with 2 g of Na2SO3.
Wash the precipitated cuprous chloride 2 – 3 times with a solution of 1.5 g of Na2SO3, 6 ml of HCl and 300 ml of H2O by decantation. Filter out the precipitate and wash it with concentrated acetic acid. Dry it in a drying oven at 100 oC.
b) 2 Cu2+ + SO2 + 2 Cl- + 2 H2O → 2 CuCl + SO4
2- + 4 H+
Material: CuSO4.5H2O, NaCl, HCl, SO2, CH3COOH
Procedure: Add 5 g of NaCl to the warm solution (70 oC) of 10 g CuSO4.5H2O and bubble SO2 through the mixture. CuCl precipitates. Filter out the precipitate and wash
it with a solution of SO2 in water and then with concentrated acetic acid.
CuCl – white crystals, insoluble in water, on air turns to green alkali copper chloride

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Publication Date: 06-13-2010

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