Chemistry, Inorganic. 1. Jeffery, G. H. II. Vogel, Arthur Israel. Vogel's textbook .. Vogel's Textbook of Quantitative Inorganic Analysis and to prepare this. Vogel's Qualitative Inorganic ronaldweinland.info - Ebook download as PDF File .pdf), First published under the title A Text-book of Qualitative Chemical Analysis. Vogel's - Textbook of Quantitative Chemical Analysis (5th Edition; Longmann) - Free Vogel, Arthur - Qualitative INORGANIC Analysis - (5th ed - ).pdf.
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Vogel's Macro and semimicro qualitative inorganic analysis. First-3d ed. published under title: A text-book of qualitative chemical analysis; 4th ed. published. Vogel's Qualitative Inorganic Analysis 5th ed. Pages · · Vogel's - Textbook of quantitative chemical analysis (5th Edition. Pages·· View: PDF | PDF w/ Links. Related Content. Related Content: A Textbook of Quantitative Inorganic Analysis—Theory and Practice (Vogel, Arthur I.) Journal of .
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The resulting spectrum. The train of prisms gives an angular dispersion of about 11 between the red and the blue ends of the spectrum.. The instrument can be mounted on a special stand. This prism turns the beam of light so that it falls on the face of the end prism of the train of five prisms and is reflected into the observer's eye..
The loop is heated in the Bunsen flame until it is red hot and then quickly dipped into powdered borax. It is the author's experience that the loop method is far more satisfactory. The wavelengths of the brightest lines. According to their procedure. As already stated. Borax bead tests a platinum wire. The spectra of the various elements are shown diagrammatically in Fig. These tests will be described under Section 2. The adhering solid is held in the hottest part of the flame.
If the resolution of the spectroscope is small. Tests for certain metals can be carried out conveniently on solutions using flame atomic emission spectrometry F AES or flame atomic absorption spectrometry FAAS. The danger of the bead falling off is reduced by holding the wire horizontally. Borax bead test 5. The free end of the platinum wire is coiled into a small loop through which an ordinary match will barely pass.
They are then heated in the lower oxidizing flame. The bead and adhering substance are first heated in the lower reducing flame. It is important to employ a minute amount of substance as otherwise the bead will become dark and opaque in the subsequent heating.
After each test. Some authors assume that the metal metaborate combines with sodium metaborate to give complex borates of the type Na2[Cu B02 4]. The coloured borax beads are due to the formation of coloured borates. The colourless.
Fe B02h and Fe B02h are formed in the reducing and oxidizing flames respectively. Carry out borax bead tests with salts of these metals and compare results with those given in Chapter 3. Thus a blue phosphate bead is obtained with cobalt salts: In certain circumstances the borax-bead test is inconclusive.
Thus with copper salts in the oxidizing flame. Phosphate or microcosmic salt bead tests the bead is produced similarly to the borax bead except that microcosmic salt. Microcosmic salt bead test 6. In the reducing flame i. The borax bead also provides an excellent method for cleaning a platinum wire. In general. They accordingly adhere better to the platinum wire loop. Yellow when hot. Colourless when hot.
This reaction is employed for the detection of silicates: Green when cold.. When a silicate is strongly heated in the bead. Grey when cold. Pale yellow when hot. The following general notes on basic laboratory operations should be carefully studied. Conical or Erlenmeyer flasks these should be of It is useful to remember that 10 ml of liquid fills a test-tube of this size to a depth of about 5.
If this is moistened. Beakers those of Clock glasses of the appropriate size should be provided. Smaller test-tubes are sometimes used for special tests. Test-tubes the best size for general use is 15 x 2 cm with 25 ml total capacity. For evaporations and chemical reactions which are likely to become vigorous. Equipment 1. A test-tube brush should be available for cleaning the tubes. Sodium carbonate bead tests the sodium carbonate bead is prepared by fusing a small quantity of sodium carbonate on a platinum wire loop in the Bunsen flame.
The various colours of the phosphate beads are collected in Table 2. The rods should be about 20 em long for use with test-tubes and em long for work with basins and small beakers.
Wet reactions on macro scale 2. Such reactions lead to: The introduction of a funnel. For heating moderate volumes of liquids a somewhat larger tube. The majority of reactions in qualitative analysis are carried out in solution. A rod pointed at one end.
Open glass tubes must not be used as stirring rods. Stirring rods a length of glass rod. This is usually best detected by filtering a little of the mixture and testing the filtrate with the reagent. These flasks cannot be heated. A rubber bulb may be attached to the short tube. A stirring rod of polythene polyethylene with a thin fan-shaped paddle on each end is available commercially and functions as a satisfactory 'policeman' at laboratory temperature: It is recommended that the wash bottle be kept ready for use filled with hot water as it is usual to wash precipitates with hot water.
When set aside the walls flatten out again and air is sucked into the bottle through the tube. Hydrogen sulphide gas is highly poisonous.
Wash bottle this may consist of a ml flat-bottomed flask. The pressure pushes the liquid out through the tube. Precipitation when excess of a reagent is to be used in the formation of a precipitate. Precipitation 6. A rubber-tipped glass rod or 'policeman' is employed for removing any solid from the sides of glass vessels. Precipitation with hydrogen sulphide operations with hydrogen sulphide are of such importance in qualitative inorganic analysis that they merit detailed discussion.
The flow rate can easily be regulated by changing the pressure exerted by the hand. When studying the reactions of ions the concentrations of the reagents are known and it is possible to judge the required volume of the reagent by quick mental calculation. As the air bubbles through the liquid. In most cases. It should always be borne in mind that a large excess of the precipitating agent may lead to the formation of complex ions and consequent partial solution of the precipitate.
Polyethylene wash bottles Fig. Insulating cloth should be wound round the neck of the flask in order to protect the hand. The efficiency of the method is low. One method. Hydrogen sulphide must be handled in a fume cupboard with good ventilation.
Passage of the gas is continued 3 Stopcock D is optional. C is a stopcock which controls the flow of gas from the generator. With the gas flowing. B is a wash bottle containing water and serves to remove any hydrochloric acid spray that might be carried over from the Kipp's apparatus in the gas stream. The most satisfactory procedure the 'pressure' method is best described with the aid of Fig. The conical flask is connected to the wash bottle by a short length of rubber tubing.
The stopper is first loosened in the neck of the flask and the gas stream turned on C first. Fortunately its unpleasant smell repels people from breathing in dangerous amounts. The solution is contained in a small conical flask A. The 'bubbling' method is not recommended and should not be used for macro analysis.
In order to ensure that all the air has been expelled. A precipitate may be washed by decantation. Complete precipitation should be tested for by separating the precipitate by filtration. Filtration Washing 8. The size of the filter paper is controlled by the quantity of precipitate and not by the volume of the solution.
The best method is to add a little filter paper pulp macerated filter paper to the solution and then to filter in the normal manner. Filter paper pulp increases the speed of filtration by retaining part of the precipitate and thus preventing the clogging of the pores of the filter paper.
Such a reagent can most conveniently be used in teaching laboratories or classroom demonstrations when studying the reactions of ions. The delivery tube must be thoroughly cleaned after each precipitation. When a precipitate tends to pass through the filter paper. Occasionally a test-tube replaces the conical flask. This procedure is unnecessary for 4 It must be borne in mind that the gas may contain a small proportion of hydrogen due to the iron usually present in the commercial iron II sulphide.
For a quantitative precipitation of sulphides e. The upper edge of the filter paper should be about 1 cm from the upper rim of the glass funnel.
This can most easily be prepared in the bottle B of the apparatus shown in Fig. Filtration and washing the purpose of filtration is. The advantages of the 'pressure' method are: I a large surface of the liquid is presented to the gas and 2 it prevents the escape of large amounts of unused gas.
The same device can be put together with glass joints. Displacement of the gas in the flask by loosening the stopper when the bubbling has diminished considerably will ensure complete precipitation.
Gelatinous precipitates. A moderately fine-textured filter paper is generally employed. It should never be more than about twothirds full of the solution. Liquids containing precipitates should be heated before filtration except in special cases. The side arm of the flask is connected by means of thick-walled rubber tubing 'pressure' tubing to another flask. When only a small quantity of the precipitate is available.
A filter flask of ml capacity is fitted with a two-holed rubber bung. This is best done by directing a stream of water from a wash bottle first around the upper rim of the filter and following this down in a spiral towards the precipitate in the apex.
If the amount of precipitate is small. This is most readily done by pouring the solvent. To surmount the difficulty. Other test papers are employed similarly. The speed of filtration depends inter alia upon the length of the water column. Removal of precipitate from the filter 9. The lower end of the tube or of the funnel should touch the side of the vessel in which the filtrate is being collected in order to avoid splashing.
In the second. Removal of the precipitate from the filter if the precipitate is bulky. Upon applying suction to the filter paper fitted into the funnel in the usual way. If it is desired to maintain a small volume of the liquid. It is frequently necessary to dissolve a precipitate completely. The completion of washing. Aids to filtration the simplest device is to use a funnel with a long stem.
For this purpose either a Whatman filter cone No. In the first. If the solution is to be tested for acidity or alkalinity. A more convenient method. They may be filtered through a small pad of glass wool placed in the apex of a glass funnel. The most rapid evaporation is achieved by heating the dish directly on a wire gauze. Both types of support are folded with the filter paper to form the normal type of cone Fig. Filtration with suction can be achieved by components with glass joints.
The Jena 'slit sieve' funnel. Evaporation the analytical procedure may specify evaporation to a smaller volume or evaporation to dryness. The Buchner funnel is fitted into the filter flask by means of a cork. After the filter paper has been supported in the funnel. When filtration is complete. For many purposes a water bath a beaker half-filled with water maintained at the boiling point is quite suitable will Evaporation Fig.
For a large quantity of precipitate. Two thicknesses of well-fitting filter paper cover the plate. When the volume of liquid is small. Filtration is carried out under reduced pressure exactly as with a Buchner funnel. Strongly acidic or alkaline solutions cannot be filtered through ordinary filter paper. This consists of a porcelain funnel in which a perforated plate is incorporated. Both operations can be conveniently carried out in a porcelain evaporating dish or casserole.
Should corrosive fumes be evolved during the evaporation. A useful anti-bumping device. It consists -. When evaporating to dryness. The reduction in volume of a solution may also be accomplished by direct heating in a small beaker over a wire gauze or by heating in a wide test-tube 'boiling-tube'. Other apparatus. Great care must be taken not to char the filter paper. Drying of precipitates partial drying. A test-tube brush should be used to clean test-tubes and other glass apparatus.
If this is not the case. Some working hints a Always work in a tidy. The device must not be used in solutions that contain a precipitate. If a reagent bottle is empty. Test-tubes may be inverted in the test-tube stand and allowed to drain. It should be extinguished when no longer required. The cleaning agent is highly corrosive! Remember a tidy bench is indicative of a methodical mind.
Reagents should always be added portion-wise. They should be returned to their correct places upon the shelves immediately after use. A safer but slower method is to place the funnel and filter paper. Glass apparatus which appears to be particularly dirty or greasy is cleaned by soaking in chromosulphuric acid concentrated sulphuric acid containing about g of potassium dichromate per litre.
A few minutes should be devoted at the end of the day's work to 'cleaning up'. More complete drying is obtained by placing the funnel containing the filter paper in a 'drying cone' a hollow tinned-iron cone or cylinder. Neither strong acids nor strong alkalis should be thrown into the sink.
All glassware should be put away clean. Avoid using unnecessary excess of reagents. The funnel is thus exposed to a current of hot air. The size of the Bunsen flame should be no larger than is absolutely necessary. A string duster is useful to wipe up liquids split upon the bench. Drying precipitates All glass and porcelain apparatus must be scrupulously clean. Cleaning of apparatus the importance of using clean apparatus cannot be too strongly stressed.
The writing up of experiments should not be postponed until after one has left the laboratory. It is a good plan to cover these with filter paper to prevent the entrance of dust.
A handle may be formed. Since volumes of the order of 1 ml are dealt with. Solids corks. These can readily be made by cutting 2 mm diameter glass rod into 12 cm lengths. On no account may they be thrown into the sink.
Stirring rods solutions do not mix readily in semimicro test-tubes and centrifuge tubes. Apart from inaccuracies which may thus creep in. Various sizes are available. Stirring 2.
Test-tubes and centrifuge tubes small Pyrex test-tubes usually 75 x lOmm. When a precipitate is to be separated by centrifuging. Particular care must be directed to having both the apparatus and the work bench scrupulously clean.
In washing a precipitate with water or other liquid. Semimicro operations 2. Test-tubes 1. For rapid concentration of a solution by means of a free flame. The various operations occupy less time and the consumption of chemicals and glassware is reduced considerably.
The sharp edges are fire-polished by heating momentarily in a flame. Droppers for handling liquids in semimicro analysis. Dropper b will be referred to as a capillary dropper. The former one finds application in 30 or 60 ml reagent bottles and may therefore be called a reagent dropper. Hold the dropper vertically over a clean dry 5 ml measuring cylinder. Introduce some distilled water into the clean dropper by dipping the capillary end into some distilled water in a beaker and compressing and then releasing the rubber teat or bulb..
Before use the droppers must be calibrated. Two varieties are shown in Fig. Droppers 3. The bottles a and b cannot be used for concentrated acids and other corrosive liquids because of their action upon the stoppers.
Attach a small label to the upper part of the dropper giving the number of drops per m!. The simplest containers for these corrosive liquids are 30 or 60 ml dropping bottles with glass stopper containing a groove the so-called 'TK bottle'. The dropper should deliver between 30 and 40 drops per m!. A list of such reagents is given in Table 2. A dropping bottle of 30 ml capacity with an interchangeable glass cap Fig.
It must be remembered that the volume of the drop delivered by a dropper pipette depends upon the density. The standard commercial form of medicine dropper. Calculate the volume of a single drop.. If the dropper delivers 20 drops of distilled water. These dropping bottles Fig. Repeat the calibration until two results are obtained which do not differ by more than 2 drops. Reagent bottles and reagents a semimicro reagent bottle may be easily constructed by inserting a reagent dropper through a cork or rubber stopper that fits a 30 or 60 ml bottle.
For the study of reactions it is best to divide reagents into two groups. This dropper is somewhat more robust than that shown in Fig. Those reagents which are most frequently used should be kept by each worker separately. Count the number of drops until the meniscus reaches the 2 ml mark. The other reagents. When using these side shelf reagents. Under no circumstances should the capillary end of the dropper be dipped into any foreign solution.
SM Acetic acid. In practice. The tube and its contents. Centrifuge 5. Sulphuric acid. Ammonia solution. This operation centrifugation replaces filtration in macro analysis. IM M Hydrochloric acid. The centrifuge the separation of a precipitate from a supernatant liquid is carried out with the aid of a centrifuge. If accidental contact should be made. Nitric acid. This is an apparatus for the separation of two substances of different density by the application of centrifugal force which may be several times that of gravity.
O i l here Fig. When using a centrifuge.. An inexpensive constant speed. A small 2-tube hand centrifuge with protecting bowl and cover Fig. The advantages of centrifugation are: The buckets can either 'swing out' to the horizontal position or.
The central spindle should be provided with a locking screw or nut: The hand-driven centrifuge is inexpensive and is satisfactory in most cases. In the latter case. These are: Several types of centrifuge are available for semimicro analysis. Spilling may corrode the buckets and produce an unbalanced head. Maintain the maximum speed for seconds.
The centrifuge tube is held at an angle in the left hand. As the pressure is very slowly released the liquid rises in the dropper and the latter is lowered further into the liquid Most semimicro centrifuges will accommodate both semimicro test-tubes 75 x 10 mm and centrifuge tubes up to 5 ml capacity. A little practice will enable one to judge the exact time required to pack the precipitate tightly at the bottom of the tube.
To remove the supernatant liquid. Surface tension effects prevent surface particles from settling readily. Agitate the surface with a stirring rod if necessary.
An unusual sound may be due to the breaking of a tube. It is of the utmost importance to avoid strains or vibrations as these may result in stirring up the mixture and may damage the apparatus. The advantages of the latter include easier removal of the mother liquor with a dropper. Fix the cover in place. Do not attempt to retard the speed of the centrifuge with the hand.
If a suspicious sound is heard. It is best to wash the precipitate at least twice. The solution in the dropper should be perfectly clear. Semimicro operations Washing the precipitates it is essential to wash all precipitates in order to remove the small amount of solution present in the precipitate. The wash liquid is a solvent which does not dissolve the precipitate but dilutes the quantity of mother liquor adhering to it.
Washing 6. Great care should be taken as the capillary approaches the bottom of the centrifuge tube that its tip does not touch the precipitate. In difficult cases. The wash liquid is usually water. Transferring of precipitates in some cases precipitates can be transferred from semimicro test-tubes with a small spatula two convenient types in nickel or monel metal are shown in Fig..
The supernatant liquid is removed by a capillary dropper. A small conical flask 25 or 50 m! For those who prefer wash bottles.
This operation is usually difficult Wash bottles 7. Wash bottles for most work in semimicro analysis a 30 or 60ml glass stoppered bottle is a suitable container for distilled water.
The 'bumping' or spattering of hot solutions may often be dangerous and lead to serious burns if the solution contains strong acids or bases. The latter heating operation requires very careful manipulation and should not be attempted by beginners. Similar remarks apply to semimicro test-tubes. It is a good plan to wind a thin rubber band about 5 mm from the top of Fig.
Heating of solutions solutions in semimicro centrifuge tubes cannot be heated over a free flame owing to the serious danger of 'bumping' and consequent loss of part or all of the liquid in such narrow tubes. On the whole it is better to resort to safer methods of heating.
Heating solutions Water bath 9. The simplest procedure is to employ a small water bath. The mouth of the test-tube must be pointed away from others nearby. The danger of 'bumping' may be considerably reduced by employing the antibumping device shown in Fig. The test-tube may be washed by holding it in an almost vertical upside down position with its mouth over the receptacle and directing a fine stream of solution or water from a capillary dropper onto the sides of the test-tube.
If the precipitate in a test-tube is to be treated with a reagent in an evaporating dish or crucible. This may consist of a ml Pyrex beaker. A more elaborate arrangement which will.
Useful holders. The apparatus is constructed of monel metal. This rack will accommodate four centrifuge tubes and four semimicro test-tubes. I Fig. Evaporations where rapid concentration of a liquid is required or where volatile gases must be expelled rapidly.. The dimensions of a rack of smaller size are given in Fig. Dissolving of precipitates the reagent is added and the suspension is warmed.
Some precipitates may undergo an ageing process when set aside for longer times e. If corrosive fumes are evolved. Precipitations with hydrogen sulphide various automatic generators of the Kipp type are marketed.
This can result in an increased resistance against the reagent used for dissolution. In many cases the flame may be removed whilst a little liquid remains. Owing to the highly poisonous and very obnoxious character of hydrogen sulphide. It is advisable to arrange the timetable of work with these precipitates in such a way that dissolution can be attempted soon after precipitation. If only partial solution occurs. This may be placed in an air bath consisting of a 30 ml nickel crucible and supported thereon by a ring Fig.
In later chapters. A little practice is required in order to achieve regular boiling by intermittent heating with a flame and also to avoid 'bumping' and spattering.
Evaporation to dryness may also be accomplished by direct intermittent heating with a micro burner of a crucible supported on a nichrome or silica triangle or of a semimicro beaker supported on a wire gauze. A short length of wide-bore rubber tubing is fitted over the mouth of a semimicro test-tube with about I cm protruding over the upper edge.
Suitable devices for this purpose are shown in Fig. Precipitation may be carried out in a centrifuge tube. The Quickfit version of c can be put together 7 For a 3 ml centrifuge tube or a 4 ml test-tube. Apparatus b is employed when the test reagent is a liquid. The chemical reaction is started in the test-tube and a 'filter tube' containing a tightly-packed plug of cotton wool is inserted through the rubber collar.
A wash bottle containing water should always be attached to the generator in order to remove acid spray compare Fig. The tap in the gas generator is then turned off.
The delivery tube is drawn out to a thick-walled capillary mm in diameter and carries at the upper end a small rubber stopper which fits the semi micro test-tube? The smaller size is satisfactory for most purposes. In those cases where spray is likely to affect the test paper. Identification of gases many anions e. An alternative apparatus for liquid reagents is shown in c: The perfectly clean delivery tube is connected to the source of hydrogen sulphide as in Fig.
It is possible to use allglass apparatus if available. If the liquid must be warmed. The simplest form a consists of a semimicro test-tube with the accompanying 'filter tube.
The tube dipping into the liquid in the wash bottle should preferably be a heavy-walled capillary.: The rubber bulb is inserted into C. The sample under test is placed in B. They will meet all normal requirements for testing gases evolved in reactions in qualitative analysis. When the amounts of evolved gas are likely to be small. Cleaning of apparatus Cleaning of apparatus it is essential to keep all apparatus scrupulously clean if trustworthy results are to be obtained.
The apparatus is then rinsed several times with tap water. The apparatus may be warmed by placing it in a hot water bath. Special brushes Fig. All apparatus must be thoroughly cleaned with chromosulphuric acid concentrated sulphuric acid containing about g of potassium dichromate per litre or with a brush and cleaning powder.
The double bulb ensures that all the evolved gas reacts. A drop or two of the liquid reagent is introduced into the absorption tube. The approximate dimensions of the essential part of the apparatus are given in a. All the above apparatus. The tubes may be allowed to drain in a special stand or else they At the end of the laboratory period.
Larger apparatus may be allowed to drain on a clean linen towel or glass cloth. Droppers are best cleaned by first removing the rubber bulbs or teats and allowing distilled water to run through the tubes. When clean. Spot plates. Never place them on the bench. Do not return the solid reagent to the stock bottle. Try to estimate your requirements and pour out only the amount necessary.
This task can often be done while waiting for a solution to evaporate or for a precipitate to dissolve while being heated on a water bath.
All apparatus should have been cleaned during the previous laboratory period.
The liquid reagents recommended are given in Section 2. At the end of each laboratory period. Semimicro apparatus the apparatus suggested for each workbench is listed below. Rinse the droppers several times with distilled water after use. I When in difficulty.
Each item of apparatus should have a definite place so that it can be found readily when required. Never return the reagent to the bottle. Serious errors leading to a considerable loss of time and. Pour a little of the reagent e. Return each reagent bottle to its proper place immediately after use. Examine the label on the bottle before adding the reagent. Pour or shake a little of the solid on to a clean. Some practical hints a Upon commencing work. Similar remarks apply to the use of TK dropper bottles.
Do not allow the dropper tip to touch anything outside the reagent bottle. The smaller 4 ml test-tubes will generally suffice: Griffin form. It must be pointed out that whilst the weight of the sample for analysis has been reduced. Chemical Microscopy in G. Some of the modifications. Feigl and their collaborators must be mentioned in this connection.
There is no sharp line of demarcation between semimicro and micro analysis and much of the technique described for the former can. No attempt will be made to deal with operations centred round the microscope magnification up to as the specialized technique is outside the scope of this volume. Thus whereas in macro analysis the weights and volumes for analysis are 0.
Micro analysis is sometimes termed milligram analysis to indicate the order of weight of the sample employed. Gutzeit and. Svehla Ed. Keune and H. Microanalytical operations 2. A special technique must be used for handling such small quantities of materials. Spot analysis has been developed as a result of the researches of numerous chemists: The supernatant liquid may be removed either by a capillary dropper Fig. Centrifuge tubes are conveniently supported in a rack consisting of a wooden block provided with 6 to 12 holes.
After centrifuging. It seems that the greatest potential for progress lies in the use of the common macro procedures or simple modifications of them to carry out preliminary separations followed by the utilization of spot tests after the group or other separation has been effected.
Micro centrifuge tubes Fig. Solutions are separated from precipitates by centrifuging. Adaptors are provided inside the buckets baskets in order to accommodate micro centrifuge tubes with narrow open ends. Hence the following pages will contain an account of the methods which can be used for performing macro operations on a micro scale and also a discussion of the technique of spot analysis.
The latter consists of a thin glass tube internal diameter about 2 mm: Two types of centrifuge tubes are shown: Semimicro centrifuges Section 2.
The correct method of transferring the liquid to the Precipitations are usually carried out in micro centrifuge tubes. Incomplete schemes of qualitative inorganic analysis have been proposed which are based largely upon spot tests: The pipette is removed and the liquid blown or drained out into a clean dry centrifuge tube.
Another useful method of transferring the centrifugate to. The small hole A in the side of the tube permits perfect control of the vacuum. Only gentle suction is applied and the opening A is closed with the finger. The siphon is made of thermometer capillary and is attached to the capillary pipette by means of a short length of rubber tubing of I mm bore.
As the liquid rises in the pipette. A To pump Fig. The centrifuge cone is held in the right hand and the capillary pipette is pushed slowly towards the precipitate so that the point of the capillary remains just below the surface of the liquid.
For the washing of precipitates the wash solution is added directly to the precipitate in the centrifuge tube and stirred thoroughly either by a platinum wire or by means of a micro stirrer.
The mixture is then centrifuged. The heating of solutions in centrifuge tubes is best carried out by supporting them in a suitable stand compare Figs. It may be necessary to repeat this operation two or three times to ensure complete washing. When higher temperatures are required. Most of the operations are usually so designed that it is only necessary to transfer solutions. If the precipitate is gelatinous. The transfer of precipitates is comparatively rare in micro qualitative analysis.
Wire triangle r. Micro beakers may be heated by means of the device shown in Fig.. Micro beaker or crucible fNickel crucible Fig.
The centrifuge tube must be of type a Fig. Rubber stopper Clamp f. Dropper pipettes are cleaned by repeatedly filling and emptying them with distilled water. Micro centrifuge tubes are cleaned with a feather.
After suction has commenced and the liquid removed. They are then filled with distilled water and emptied by suction as in Fig. The experimental details will be evident by reference to Fig..
The stoppered flask. A transfer capillary pipette is cleaned by blowing a stream of water through it. The flow of the hydrogen sulphide must be commenced before introducing the point of the capillary into the centrifuge cone. Such a fine capillary delivers a stream of very small bubbles of gas. The delivery tube may be prepared by drawing out part of a length of glass tubing of 6mm diameter to a capillary of l-2mm bore and cm long.
If this is not done. The point of saturation of the solution is indicated by an increase in the size of the bubbles. The identification of gases obtained in the reactions for anions may be conducted in an Erlenmeyer or conical flask of 5 to 10 ml capacity. The passage of hydrogen sulphide into a solution in a micro centrifuge tube is carried out by leading the gas through a fine capillary tube in order not to blow the solution out of the tube.
A plug of pure cotton wool is inserted into the wide part of the tubing. A small strip of impregnated test paper is placed on the loop of the pin. The complete arrangement is illustrated in Fig. An improved apparatus consists of a Rubber stopper Fig. Preliminary preparation II All glass apparatus must be of borosilicate e. Pyrex glass. The actual 'spotting' is the fundamental operation in spot test analysis.
The technique of spot tests is fully described in Section 2. In these chemical tests manipulation with drops macro. The following micro apparatus ll will be found useful: An all-glass apparatus is also available. Spot reactions may be carried out by any of the following processes: Confirmatory tests for ions may be carried out either on drop reaction paper or upon a spot plate.
If the evolved gas is to be passed through a liquid reagent. Spot test analysis 2. Polyethylene micro pipettes with elastic bulb on the top are also suitable. Micro burettes sometimes find application for the delivery of drops.
Before dealing with the apparatus required for spot test reactions. Throughout this book. A number of loops are made by bending platinum wire of suitable thickness.
Pipettes which are used frequently may be supported horizontally on a stand constructed of thin glass rod. A useful glass pipette. Operations in spot test analysis Fig.
The preparation may involve some of the operations of macro analysis on a diminished scale see Section 2. For these two terms to be comparable. It must be pointed out that new smooth platinum wire allows liquids to drop off too readily. An account of the latter forms the subject matter of the present section.
They are kept in Pyrex test-tubes fitted with corks or rubber stoppers and labelled with particulars of the size of drop delivered. A liberal supply of glass tubes and pipettes should always be kept at hand.
Very small and even-sized drops can be obtained by means of platinum wire loops. After use. The removal and addition of drops of test and reagent solutions is most simply carried out by using glass tubing. The concentration limit is the greatest dilution in which the test gives positive results. The limit of identification is the smallest amount recognizable. They may be stored in a beaker about 10 cm high with the constricted end downwards and resting upon a pad of pure cotton wool.
The capillary dropper Fig. Where light-coloured or colourless precipitates or turbidities are formed. It is advisable.
The last-named is heated over a micro burner. Traces of turbidity and of colour are also readily distinguished in micro test-tubes 50 x 8 mm or in micro centrifuge tubes. The wire holder is arranged to fit over a small beaker. Glassware and porcelain crucibles are best cleaned by immersion in a chromic acid-sulphuric acid mixture or in a mixture of concentrated sulphuric acid and hydrogen peroxide. Transparent spot plates of glass are also available. It must be emphasized that all glass and porcelain apparatus.
The commercial spot plates are made from glazed porcelain or plastic and usually contain 6 to 12 depressions of equal size that hold 0. The liquid in a micro centrifuge tube or in a test-tube may be warmed in a special stand immersed in a water bath see Figs. Gas reactions are carried out in special apparatus. The latter is constructed of thin aluminium or nickel wire. This is usually best detected by filtering a little of the mixture and testing the filtrate with the reagent; if no further precipitation occurs, a sufficient excess of the reagent has been added.
It should always be borne in mind that a large excess of the precipitating agent may lead to the formation of complex ions and consequent partial solution of the precipitate; furthermore, an unnecessary excess of the reagent is wasteful and may lead to complications at a subsequent stage of the analysis.
When studying the reactions of ions the concentrations of the reagents are known and it is possible to judge the required volume of the reagent by quick mental calculation. Precipitation with hydrogen sulphide operations with hydrogen sulphide are of such importance in qualitative inorganic analysis that they merit detailed discussion. Hydrogen sulphide gas is highly poisonous, its lethal dose How to use H 2 S safely and sparingly 16 Wet reactions on macro scale 2.
Fortunately its unpleasant smell repels people from breathing in dangerous amounts. Hydrogen sulphide must be handled in a fume cupboard with good ventilation.
One method, which is sometimes employed, consists of passing a stream of gas in the form of bubbles through the solution contained in an open beaker, test-tube, or conical flask; this procedure is sometimes termed the 'bubbling' method. The efficiency of the method is low, particularly in acid solution; absorption of the gas takes place at the surface of the bubbles and, since the gas is absorbed slowly, most of it escapes into the air of the fume chamber and is wasted.
The 'bubbling' method is not recommended and should not be used for macro analysis. The most satisfactory procedure the 'pressure' method is best described with the aid of Fig. The solution is contained in a small conical flask A, which is provided with a stopper and lead-in tube; B is a wash bottle containing water and serves to remove any hydrochloric acid spray that might be carried over from the Kipp's apparatus in the gas stream; C is a stopcock which controls the flow of gas from the generator, whilst stopcock D provides an additional control 3 for the gas flow.
The conical flask is connected to the wash bottle by a short length of rubber tubing. The stopper is first loosened in the neck of the flask and the gas stream turned on C first, followed by D so as to displace most of the air in the flask: this will take not more than about 30 seconds.
With the gas flowing, the stopper is inserted tightly and the flask is gently shaken with a rotary motion; splashing of the liquid on to the hydrogen sulphide delivery tube should be avoided. In order to ensure that all the air has been expelled, it is advisable to loosen the stopper in A again to sweep out the gas and then to stopper the flask tightly.
Passage of the gas is continued 3 Stopcock D is optional; it prevents diffusion of air into the wash bottle and thus ensures an almost immediate supply of hydrogen sulphide.
Complete precipitation should be tested for by separating the precipitate by filtration, and repeating the procedure with the filtrate until the hydrogen sulphide produces no further precipitate. Occasionally a test-tube replaces the conical flask; it is shown with the stopper in b. The delivery tube must be thoroughly cleaned after each precipitation. The same device can be put together with glass joints. The advantages of the 'pressure' method are: I a large surface of the liquid is presented to the gas and 2 it prevents the escape of large amounts of unused gas.
Alternatively, a saturated aqueous solution of hydrogen sulphide can be used as a reagent. This can most easily be prepared in the bottle B of the apparatus shown in Fig. Such a reagent can most conveniently be used in teaching laboratories or classroom demonstrations when studying the reactions of ions. For a quantitative precipitation of sulphides e. Filtration Washing 8. Filtration and washing the purpose of filtration is, of course, to separate the mother liquor and excess of reagent from the precipitate.
A moderately fine-textured filter paper is generally employed. The size of the filter paper is controlled by the quantity of precipitate and not by the volume of the solution. The upper edge of the filter paper should be about 1 cm from the upper rim of the glass funnel. It should never be more than about twothirds full of the solution. Liquids containing precipitates should be heated before filtration except in special cases, for example that of lead chloride which is markedly more soluble in hot than cold water.
Gelatinous precipitates, which usually clog the pores of the filter paper and thus considerably reduce the rate of filtration, may be filtered through fluted filter paper or through a pad of filter papers resting on the plate of a Buchner funnel Fig.
The best method is to add a little filter paper pulp macerated filter paper to the solution and then to filter in the normal manner.
Filter paper pulp increases the speed of filtration by retaining part of the precipitate and thus preventing the clogging of the pores of the filter paper. When a precipitate tends to pass through the filter paper, it is often a good plan to add an ammonium salt, such as ammonium chloride or nitrate, to the solution; this will help to prevent the formation of colloidal solutions.
A precipitate may be washed by decantation, as much as possible being retained in the vessel during the first two or three washings, and the precipitate then transferred to the filter paper. This procedure is unnecessary for 4 It must be borne in mind that the gas may contain a small proportion of hydrogen due to the iron usually present in the commercial iron II sulphide.
Displacement of the gas in the flask by loosening the stopper when the bubbling has diminished considerably will ensure complete precipitation. This is best done by directing a stream of water from a wash bottle first around the upper rim of the filter and following this down in a spiral towards the precipitate in the apex; the filter is filled about one-half to two-thirds full at each washing.
The completion of washing, i. If the solution is to be tested for acidity or alkalinity, a drop of the thoroughly stirred solution, removed upon the end of a glass rod, is placed in contact with a small strip of 'neutral' litmus paper or of 'wide range' or 'universal' test paper on a watch glass.
Other test papers are employed similarly. Removal of precipitate from the filter 9. Removal of the precipitate from the filter if the precipitate is bulky, sufficient amounts for examination can be removed with the aid of a small nickel or stainless steel spatula.
If the amount of precipitate is small, one of two methods may be employed. In the first, a small hole is pierced in the base of the filter paper with a pointed glass rod and the precipitate washed into a test-tube or a small beaker with a stream of water from the wash bottle. In the second, the filter paper is removed from the funnel, opened out on a clock glass, and scraped with a spatula.
It is frequently necessary to dissolve a precipitate completely. This is most readily done by pouring the solvent, preferably whilst hot, onto the filter and repeating the process, if necessary, until all the precipitate has passed into solution.
If it is desired to maintain a small volume of the liquid, the filtrate may be poured repeatedly through the filter until all the precipitate has passed into solution. When only a small quantity of the precipitate is available, the filter paper and precipitate may be heated with the solvent and filtered.
Aids to filtration the simplest device is to use a funnel with a long stem, or better to attach a narrow-bored glass tube, about 45 cm long and bent as shown in Fig. The lower end of the tube or of the funnel should touch the side of the vessel in which the filtrate is being collected in order to avoid splashing. The speed of filtration depends inter alia upon the length of the water column.
A filter flask of ml capacity is fitted with a two-holed rubber bung; a long glass tube is passed through one hole and a short glass tube, carrying a glass stopcock at its upper end, through the other hole.