In this chapter we will discuss several of the common experimental techniques, which we will utilize for carrying out experiments in this chemistry Laboratory course and as well describe the apparatus required for various experiments, additionally to the general laboratory apparatus by which we are already familiar. Safety in the laboratory and preparation of a laboratory notebook are very significant aspects of any laboratory course.
Laboratory Regulations and Safety:
Chemistry laboratories are potentially dangerous place since they have inflammable liquids, poisonous chemicals and fragile glass wares. Wherever high - pressure cylinders of gases are utilized, they as well pose a potential danger. Safety in laboratory is significant not only to you, but to other students and staff as well in the laboratory. Hence, proper precautions must be taken and safe experimental procedure must be given while working in a chemistry laboratory.
Several significant common safety precautions are following below. Any special precautions or safety measures, if needed, are given in the particular experiments. We should read all such carefully and follow them faithfully.
Table: List of hazardous chemicals and their effects.
Salts of Ag, Sb, Ti. V, C2O42-, F, MnO4, H2S
SO2, NO2,Cl2, Br2, 12, HNO3, H,SO4, HF
HClO3, HClO4 and their salts
Most of these are very dangerous but only if swallowed. AgNO3 causes caustic burns. Almost as poisonous as HCN. Exposure dulls the sense of smell.
All are dangerous as well as unpleasant. When concentrated, all cause rapid destruction of the skin; HF is especially dangerous.
Most of these are narcotics, causing mental confusion
Toxic vapours causing dizziness and in suspected to be a cancer agent.
Very highly inflammable
Burns the skin
The most common accidents in the chemistry laboratory are cuts from broken glassware. If we contain a cut, wash the wound well through cold water instantly. If bleeding is severe pertain pressure straight on the wound to stop the bleeding and then proceed to the health clinic.
Burns usually caused via hot equipment can be treated as the cuts are treated, that is, wash the burnt part by cold water for various time and often apply pure honey to it. Chemicals very frequently cause burns as well.
A small fire in the beaker, caused via the vapours of an inflammable liquid, can be extinguished through covering it by a watch glass. If the clothes catch fire, one should lie on the floor and wrapping a blanket around the body can smother the fire into extinguishing.
If one occurs to swallow a poisonous chemical, plenty of water should be specified if the person is conscious. For a corrosive poison, calcium hydroxide solution (lime water) should be given as soon as possible. An antidote should be following only in the case of non- corrosive poisons.
Sometimes a faulty technique during the experiment can guide to an explosion. We should work by extremely oxidizing or explosive chemicals only under strict supervision.
Chemical spill in the eyes:
Flush eye(s) with large amounts of cold water. Then bathe the eyes with 5% boric acids if the accident involved a base or 50% sodium bicarbonate if the accident involved an acid.
Acids like HNO3 , H2SO4,NaHCO3 ,HCl
Alkalines e.g., NaOH , KOH etc.
Wash with NaHCO3 or 2M ammonium carbonate (leaves no residue on clothes), and then apply vasline or a soothing cream.
Wash with 1M acetic acid. Then apply vasline or a soothing cream.
Wash with 2M ammonia , keep the affected part dipped in NaHSO3 till bromine is washed off, and then apply vasline.
Wash with ethanol and then hospital treatment
Apply ethanol on a cotton wool pad.
Laboratory note book:
One of the significant traits of a scientist is the habit of keeping good record of the work that has been done. The record should reflect all the planning that has gone in also as the observations at different stages of the experiment. A chemist must noticed things as whether there was a color change whenever the reactants were mixed or a reagent was added to the solution; whether a precipitate was shaped or a gas evolved; whether the reaction was exothermic, and record them. Such observations might appear insignificant but experiences contain proved it helpful in correct interpretation of an experimental consequence. While preparing a laboratory notebook, the given significant features might be kept in mind.
The laboratory notebook is a complete log of all operations, dates times, and information must be entered regularly. A superior format will be:
1. Title of experiment Date
2. Aim of the experiment
3. Brief outline of experimental procedure
6. Calculations if necessary
Laboratory Apparatus and Operations:
We will discover at the next page of this learn chapter for this course, sketches and diagram, of common general laboratory apparatus we will encounter in the chemistry laboratory. We will be making utilize of them frequently. Make sure we familiarize us by each of them in your locker. Wet chemical analysis and preparatory chemistry require the use of some other apparatus and laboratory operations with which you should become familiar. It is presumed that you are already familiar with common laboratory apparatus and glassware such as the test tubes, boiling tubes, beakers, burners, test tube stand, conical flasks, watch glasses, funnels, glass tubes, china dishes, pipettes, burettes, funnel stand, tripod stand, burette stand etc. In this division at proper places we will familiarize by several more glassware and apparatus that will be employed in diverse experiments in this course. Heating, evaporation, precipitation, digestion, filtration, drying and ignition, cooling, weighing are some of the important laboratory operations, which we will perform during our study of chemistry as part of us programme. Let us learn such operations and several of the apparatus needed for them in several details.
Heating is one of the general operations that we frequently perform in a chemistry laboratory. We resort to heating for a variety of reasons. Heating amplifies the solubility of most substances. It as well increases the rate of chemical reactions. We have to heat substance to dry them. In gravimetric analysis, the precipitate is sometimes heated to a high temperature to convert it into a compound of constant composition.
3. Clamp holder
4. Clip (Mohr's chip or rubber clip)
5. Crucible and crucible cover
6. Crucible tongs
8. Evaporating dish
9. File, triangular
10. Filter stand or rack
11. Flask, conical
12. Flask, flat bottom
13. Flask, round bottom
14. Funnel (filter)
15. Funnel (Separatory)
16. Iron stand and rings
17. Measuring cylinder
18. Medicine dropper
19. Mortar and pestle
21. Test - tube
22. Test - tube brush
23. Test - tube holder
24. Test - tube rack
27. Tripod or tripod stand
28. Wash bottle (plastic)
29. Watch glass
30. Wire gauze
Fig: Common laboratory apparatus.
In all the chemistry laboratory courses, we will utilize the following heating devices:
The Bunsen burner is an extensively used heating device in an inorganic chemistry laboratory. It is utilized to get moderately high temperature of up 600°c. The maximum temperature is attained via adjusting the regulator so as to admit rather more air than is needed to make a non- luminous flame.
Boiling water bath are for heating solutions up to 100 °c, for evaporation of liquids to decrease their volumes and for digestion of precipitates. The simplest form of a water bath is a beaker in that water is boiled. The vessel to be heated is kept on the rim of the beaker. Copper of Aluminum water bath as shown in fig are commercially available. Such have a copper or aluminum bowl fitted via a series of metallic rings to adjust the size of the opening. This allows heating of vessels of diverse sizes. The bath is partly filled through water and heated on a burner or electrically.
Electric ovens or drying ovens are extremely convenient heating devices. They contain a temperature range from room temperature to about 300°c. The temperature can be thermostatically controlled to within +1-2°c. They are chiefly for drying solids or precipitates and glasswares at comparatively low controlled temperature.
Electrically heated muffle furnaces are utilized to ignite sample to high temperature either to burn organic matter prior to inorganic analysis or to convert precipitates to a weighable form in gravimetric analysis. Temperature of up to 1200°c can be attained through muffle furnaces.
During experiments, we might be asked to reduce the volume of a solution. Sometimes we might have to evaporate a solution to dryness. Both such operations can be conveniently carried out in a porcelain-evaporating dish. Rapid evaporation can be achieved via heating the dish having the solution directly on wire gauze.
If corrosive fumes may evolve during evaporation, the process must be carried out in a fume hood. Whenever evaporating to dryness, in order to avoid bumping and spattering, we should remove the dish from the burner whilst there is still liquid left. The heat capacity of the hot dish is sufficient to complete the operation without further heating. We might as well accomplish the reduction in volume of a solution via direct heating in a small beaker over wire gauze or via heating in a boiling tube held in a holder over a naked flame. But while evaporating in a boiling tube, care must be taken that the liquid doesn't bump violently.
Precipitation is one of the most significant operations, which we are extremely frequently needed to perform in wet chemical analysis. Precipitation is a process in which ions present in solution is converted into an insoluble compound termed precipitate through the addition of another compound termed precipitant or precipitating reagent. Precipitation is generally carried out in test tube (in qualitative analysis) or in beakers (in quantitative analysis).
The solution of precipitant is added gradually via means of a dropper, pipette or burette and through efficient stirring. The solution of the precipitant is added down the side of the precipitating vessel via avoiding splashing. Only a moderate excess of the precipitant should be added.
A very huge excess precipitant might sometimes lead to dissolution or contamination of the precipitate. After the precipitate has settled, a few drops of the precipitate should constantly added be to ensure complete precipitation.
In gravimetric analysis, to ensure complete precipitation and to build all particles of filterable size, the precipitate is digested before filtration. Digestion as well helps in reducing the amount of absorbed impurities. In several cases settling the beaker aside and leaving the precipitate in contact via the mother liquor at room temperature for 12-24 hours carry out digestion.
In others terms, wherever a higher temperature is permissible, digestion is generally effected via heating for 15-20 minutes near the boiling point of the solvent. The beaker is kept covered through a watch glass through its convex surface downward.
Filtration is the procedure of separation of a solid (crystals or precipitate) from the liquid (mother liquor). Filtration is a extremely significant and generally utilized operation in chemistry laboratory. Filtration can be carried out either under atmospheric pressure (ordinary filtration) or under decreased pressure (suction filtration). Filters for filtering precipitate are of diverse kinds. We will discuss here 3 types of them:
Filter paper is frequently utilized to filter precipitates in qualitative analysis. In several gravimetric estimation, the precipitate is ignited at thigh temperature to convert it to a well -defined compound of recognized composition. For instance, Fe3+ is precipitated as hydrated iron oxide, Fe2O3, xH2O and ignited Fe2O3 before weighing. When a precipitate is to be ignited, it should be collected in an ash less filter paper, which leaves little residue on ignition. Filter paper is suitable when the precipitate is not easily reduced through the action of carbon of the paper on ignition.
Filter paper for quantitative analysis is made of diverse degrees of porosity. The filter paper utilized must be of such porosity as to retain the smallest particles of precipitate and yet permit rapid filtration. Filter papers of 3 grades are usually made, one for very fine particles these BaSO4, a second for average precipitates such as AgCl, which contain medium - sized particles, and a third for gelatinous precipitates such as Fe 2O3, xH2 O.
Proper folding and fitting of the filter paper in the funnel can amplify the rate of filtration. A properly folded filter paper is demonstrated in fig the circle of filter paper is folded exactly in half. This is folded again in quarters in such a way that the vertices of the 2 quarters don't coincide, but are displaced about 3mm at the corners. The outside corner of the paper is the torn off and the paper located in a glass funnel in such a way that three layers of filter paper are on one side a single layer on the other.
To seal the paper into funnel, the paper is moistened and the upper part pressed gently against the walls of the funnel by fingers. The upper edge of the filter paper should be about 1 cm from the upper rim of the glass funnel. The filter should never be more than about two- thirds full of the solution. After the filter paper is seated in the funnel, the liquid enclosing suspended precipitate is poured down a glass rod into the funnel as illustrated in fig. Care must be taken in transferring of the precipitate to avoid losses.
The particles adhering to the beaker or rod are eliminated via scrubbing the through walls by moistened rubber porcelain. Wash the remainder of the loosened precipitate from the beaker and from the porcelain into the funnel. After the precipitate is transferred to the filter, it is washed through 5 or 6 more portions of wash liquid. Add the liquid around the top edge of the filter paper to wash the precipitate down into the funnel. Each portion should be permitted to drain before adding the next one. Common filtration is commonly a slow operation. It can be speeded up via utilize of suction filtration. If the filtration doesn't need to be ignited, it most conveniently collected in a sintered glass crucible (fig) via suction filtration. This crucible has a porous disk that allows the liquid to pass through, but retain solid particles. Suction can be applied via means of a water pump. Water pump sucks out air, reducing the pressure inside the filtration flask and therefore speeding up the rate of filtration. Whenever a huge quantity of precipitate or any other solid is to be filtered, a Buchner funnel, which is revealed in fig., is employed.
The Bucher funnel consists of a porcelain funnel in that a perforated plate is incorporated. A filter paper circle, cut correct to size covers the perforated plate. The Bucher funnel is fitted into the filter flask via means of a cork. The filter paper is wetted through water and suction put on before pouring in the solution to be filtered.
Drying and Ignition of Precipitates:
In gravimetric analysis after a precipitate has been filtered and washed, it must be brought to a steady composition before final weighing is concluded. Drying or ignition of the precipitate achieves this. Whether a precipitate should be dried ignited based upon the nature of the precipitate and upon the type of filtering medium used. Precipitates such as BaSO4, PbCrO4, AgCl, nickel dimethylglyoximate become dry and acquire a constant weight on heating up to 250 °C. The precipitates of such kind can be conveniently filtered in a sintered glass crucible and dried in an electric oven. Here we would like to point out that the precipitates of the above kind can as well be filtered in ash less gravimetric filter paper and then ignited to a constant weight. But ignition requires a higher temperature of up to 1200°C. Thus, it is more convenient to filter them in a sintered glass crucible and dry in an electric drying oven. On the other hand, gelatinous precipitates these as those of Fe2O3.xH2O and Al (OH)3 clog the pores of the sintered filter crucible and therefore, are filtered through an ash less filter paper. They as well have a variable composition and should be ignited to convert them into a form of steady composition (such as Fe2O3 or Al2O3) suitable for weighing. Calcium is often precipitated as the oxalate, CaC2O4, which is not weighed as such but is decomposed by ignition to CaO and then weighed.
Place a silica crucible on a clay pipe triangle kept on a tripod stand (fig). Heat the crucible powerfully for half an hour on a Bunsen burner flame. Take away the burner and permit the crucible to cool in air for 2 - 3 minutes. Then place the crucible in desiccators by the help of a pair of tongs (fig). Let the crucible to accomplish the room temperature and then weigh it. Repeat the procedure of heating, cooling and weighing till the weight of the crucible becomes steady.
Detach carefully the well drained filter paper having the precipitates from the funnel. Fold the filter paper into a packet so as to entirely enclose the precipitate. Situate the packet into the weighed silica crucible supported on a clay pipe triangle and tripod stand. Tilt the crucible
slightly and partially cover by the lid. Place a small flame under the crucible so that the filter paper and the precipitate become dry. Then amplify the flame slightly so as to slowly carbonize the paper. Don't permit the paper to burn, as this might cause a mechanical loss of the precipitate. If the paper catches fire, put off the fire by covering the crucible through the lid by the help of a pair of tongs.
Whenever the paper has entirely carbonized, enhance the size of burner flame until the bottom of the crucible is heated to redness. Maintain heating strongly until the carbon residue is burnt away. Cool the crucible in a dessicator and then weigh. Repeat the procedure of heating, cooling and weighing till the weight of the crucible by the precipitate become steady.
After the crucible and the precipitate have been dried in an electric-drying oven or heated strongly on a burner flame, they should be cooled to room temperature before weighing. Cooling is done in a desiccator as given in fig.
A desiccator is an airtight container that encloses a drying agent or desiccant these as anhydrous calcium chloride, silica and so on. the desiccant absorbs moisture and keeps the air dry in the desiccators. The desiccant has to be transformed from time to time as it becomes spent after absorbing moisture. The interface between the lid and the body of the desiccators is lubricant to build an airtight seal. The correct method to open desiccators is to slide the lid sideways until it can be eliminated. Whenever pacing the lid on the table, the greased surface should be kept upwards. Volumetric Tools and Techniques such tools and techniques generally encountered during volumetric analyses.
Volumetric flasks are flat bottom flasks with long necks designed to contain definite stated volumes of liquid. They are available in sizes ranging from 5cm' to 5dm'. Of these, the most usually utilized in volumetric analysis is the 250cm3 capacity flask.
Most of such flasks have round fit stoppers. A volumetric flask invariably has a calibration mark on its neck indicating the level to that the liquid must be added to attain the volume indicated as the capacity of the flask. Therefore, volumetric flasks are utilized mostly for the preparation of standard solutions of a definite volume.
A brief process of filling the volumetric flask can be stated here. The material whose solution is to be prepared is weighed into a weighing container say a weighing bottle, watch glass etc. the material is then put inside a small beaker of capacity between 50cm 3 and 100cm3 and dissolved with a small volume of distilled water.
The weighing material is itself rinsed with a small amount of water onto the beaker. More water is added to ensure the material is totally rinsed away from the weighing bottle. The beaker is allowed to cool to room temperature if it appears the body of the beaker is getting warm or hot. The cooled solution is then poured into the volumetric flask of definite volume and capacity through the use of a funnel placed on the mouth of the volumetric flask.. The beaker is rinsed with small volumes of water and the rinsing added to the flask.
The funnel is next rinsed via squirting water onto it from a wash bottle into the volumetric flask. After this is done, the funnel is taking away from the mouth of the flask. Water is now added to the volumetric flask from the wash bottle up to its neck but not to the mark. The flask is stoppered and shaken scrupulously. It is permitted to settle and after that, water from the wash bottle is added to finally make it to the mark.
Pipettes are employing for transferring liquids or solutions from one container to another container. They are of 2 kinds. The commonest and the one we most likely will employ is the transfer pipette. This is a long tube with a short cylindrical bulb at the middle. They have varying capacities between 1 cm3 to 50cm3. Of these the most commonly used for quantitative analysis are the 10, 20 and 25cm 3 capacity pipettes.
The 2nd type of pipette is the graduated or measuring pipette. This is a straight, uniform bore that is graduated along its length. It is utilized for delivering liquids of definite volume which are generally not up to the round figure value of 10, 20 cm3. If volumes greater than 20cm3 are required to he delivered, a burette will likely be the equipment to be used. A pipette is employed to transfer liquids as follows. The transfer pipette which must have been washed through soap and rinsed with water is seen to be clean and dry. It is now rinsed by the solution to he put into it about 2 times. The pipette is now situated in the hulk of the solution to be put into it about 2 times. The pipette is now placed in the bulk to be transferred through its tip well dipped inside the liquid and approximately touching the bottom of the container enclosing the solution to be transferred. The liquid is sucked up to a level just above the calibration mark on the stem of the pipette. The top of the pipette is then closed by the tip of the fore finger while the pipette is being withdrawn from the liquid. Whilst using our finger tip and holding the pipette upright, we liberate the finger pressure to allow the solution to run out until the lower part of the meniscus falls on the mark. If there is any drop of the liquid hanging from the tip of the pipette, the tip of the pipette is made to just touch the bottom surface of the container containing the liquid. Don't off blow the remaining solution at the tip of the pipette.
Fig: How to transfer liquid with a pipette to a flask
A burette is a long glass tube fitted with a tap or stopcock through which the liquid enclosed in it is delivered via a small opening at one end. It is designed to measure acutely the volume of liquid delivered during a titration. The commonest one has capacity of 50cm3 though there are other capacities and are all graduated at 1cm3 and 0.1cm3 correspondingly. The burette readings can be reported to two decimal places. This regular practice is to read the lower part of the meniscus of a liquid in the burette. This part of reading the burette is frequently found to be inappropriate via several students as a consequence of errors due to light. So a card or a strip of paper is situated as the other side of the student such that the top of the strip is level by the bottom edge of the meniscus. For extremely colored solutions these as that from potassium permanganate, the top of the meniscus is read instead as light is not likely to affect our sight during reading of the burette. A burette is utilized as follows. After ensuring that the burette is washed clean and dry, it is then rinsed 2 times by distilled water and permitted to drain via opening the tab or the stopcock. Lubricate the stopcock or tap through grease so as to prevent leakage. Now pour in the liquid generally through the utilize of a funnel situated on top of the mouth of the burette pass the mark on the graduate burette. Then remove the funnel instantly. Now run the burette via opening the tap or stopcock so that the liquid runs out during the opening at the end of the burette thereby entirely filling up the burette from the tip to the zero mark. A note of advice on the way the burette is run during titration. Whenever running liquid out of the burette, utilize our left hand to open the tap and our right hand to hold the flask at similar swirling time as the titration proceeds.
The conical flask.
The conical flasks are utilized in volumetric analysis as a container in that the reactants meet and the product is formed. The most conventional size for volumetric work is the 250cm3 conical flask.
Common laboratory reagents
We will be using a number of reagents and chemical throughout our experiments. There are laboratory assistants to help you to get reagents. Most of such chemicals are kept in the reagent shelves and are properly labelled. The bench shelves contain generally liquid reagents, that consists of hydrochloric, sulphuric and nitric acids. In addition such, other solutions as silver nitrate, ammonium hydroxide, sodium hydroxide, barium chloride, and so on, might as well be kept there. We have to be very suspicious while using all such, especially, the acids. Mishandling any chemicals might consequence in injury. We should thoroughly read the section 3.0 in the unit before starting your experiment. Thus tells you about safety measures in the laboratory. The solid reagents are kept on a ordinary table. We should utilize a spatula and take only the needed amount of the compounds from the bottle or the pack. Don't misuse any chemical. The liquid should be taken through the help of droppers. Our laboratory demonstrator will give the special chemicals and solutions needed for any experiment at the time of performing the experiment.
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