COMMON LABORATORY OPERATIONS AND TECHNIQUESA. BUNSEN BURNER1. Lighting the Burnera. Examine the parts of the Bunsen burner. Make a sketch of the burner, label and statethe function of its parts.b. Attach the rubber tubing from the burner to the gas outlet on the lab bench. Bring thelighted match or striker up 4-5 cm above the barrel while turning on the gas valve.c. Adjust the gas supply so as to have a flame of not more than 8 cm high. Close the airholes of the burner and observe the appearance of the flame.______________________________________________________________________Hold the porcelain dish on this flame for a moment. What is deposited on the porcelaindish? _________________________________________________________________d. Open the air holes until the flame is pale blue and has two or more distinct cones. Aslight buzzing or roaring sound is characteristic of the hottest flame from the burner. Toomuch air may blow the flame out. Adjust the air intake until the roaring stops. What is theeffect on the flame upon opening of the air holes? _____________________ Does thistype of flame have the same effect on the porcelain dish? Why?______________________________________________________________________Spray powdered charcoal on the flame and note its effect. ____________________________________________________________________________________________What makes the flame luminous? __________________________________________e. When the best adjustment is reached, three distinct cones are visible. Always use thiskind of flame unless directed otherwise.f. Extinguish the flame when it is not being used, by turning off the gas valve at the outlet.2. Determining the Flame Temperaturesa. Wet a piece of cardboard and hold it vertically through the center of the flame, with thelower end of the cardboard resting against the top of the burner.b. Remove the cardboard as soon as it shows a tendency to char. From the scorchedportions note the relative temperature of the different parts of the flame.c. Draw a sketch of the flame to illustrate the different regions.B. GLASS MANIPULATION1. Cuttinga. Place the glass tubing flat on the table. At a desired point make a single scratch with asharp triangular file.b. Grasp the glass tubing with both hands and place the thumbs one cm beside thescratch. Position the thumbs such that they are opposite the scratch.c. Break the glass tubing by applying a gentle pressure. If it does not yield to gentlepressure, make a deeper scratch.d. The edges of the cut glass tubing are sharp and should be polished by rotating it at thenon-luminous portion of the burner’s flame. This is to prevent the sharp edges of theglass from cutting the corks and rubber tubing as well as your fingers.2. Bendinga. Take a piece of glass tubing about 30 cm long and hold it lengthwise over the flame.b. To bend the glass tubing properly, it must be heated uniformly over a distance of 5 to 8cm. This can be done using a flame spreader.c. Roll the tube back and forth until it has become quite soft.d. When it has become sufficiently soft, (i.e., the glass tubing begins to take a pink colorand sag gently) take it out of the flame.e. Bend quickly to the desired shape and hold until it hardens. Try to get a good idea of theangle before you begin to work so that you may work rapidly and secure the desired

bend at once.f. Make one right angle and one 30O bent glass tubing.NOTE: Reheating and rebending produce unsightly and often frail apparatus.3. Drawing Outa. Roll the tube over the flame until it softens. The tube must be constantly rotated, toprevent the softened portion from sagging.b. Quickly remove it from the flame, and while holding it in a vertical position, gently pull theends apart until the bore is of the desired size.c. Cut to the desired nozzle size and fire polish the tip.4. Boring corks and rubber stoppersa. Select a cork such that its size will fit into the mouth of the flask or test tube.b. Soften by rolling it between the tabletop and the palm of your hand. Select a sharp corkborer one size smaller than the tube that will be inserted.c. Place the cork on the desk and cut half through it with the borer under gentle pressurethen reverse the cork and bore through from the other end.d. Smoothen the walls of the cork with a round file.e. If the hole bored is too small, enlarge it by carefully filing with a round file. Only smalladjustment should be made in this way.f. Rubber stoppers are bored in the same manner as mentioned. Select a very sharp borerone size larger than the hole to be made, and wet it with glycerin. Proceed as in boringthe cork, but do not apply too much pressure.5. Inserting a glass tubing through a cork/rubber stopperNOTE: This operation is the most common cause of accidents in the laboratory.a. Wet the cork and the glass tubing with water.b. Place your hand on the tubing 2-3 cm away from the stopper. Protect your hand with atowel.c. Simultaneously twist and push the tubing slowly and carefully through the hole.C. CLEANING OF GLASSWAREa. Clean all glassware with a soap or detergent solution. Use brush if appropriate.b. Once the glassware is thoroughly cleaned, rinse several times with tap water and thenonce or twice with distilled water.c. Roll each rinse around the entire inner surface of the glass wall for a complete rinse.Discard each rinse through the delivery point of the vessel (e.g., beaker spout).d. Invert the clean glassware on a clean paper towel or rubber mat to dry. Do not dry heavyglassware (graduated cylinders, volumetric flasks, bottles), or for that matter anyglassware over direct flame.e. The glassware is clean if, following the final rinse, no water droplets adhere to the cleanpart of the glassware.f. If you must use a piece of glassware while it is still wet, rinse it with the solution to beused in the manner described in step 5c.D. TRANSFERRING OF LIQUIDS/SOLUTIONSa. When the liquid or solution is to be transferred from a reagent bottle, remove the glassstopper and hold it between the fingers of the hand used to grasp the reagent bottle.Never lay the glass stopper on the laboratory bench; impurities may be picked up andthus contaminate the liquid when the stopper is returned.b. To transfer a liquid from one vessel to another, hold a stirring rod against the lip of thevessel containing the liquid and pour the liquid down the stirring rod, which, in turn,should touch the inner wall of the receiving vessel. Return the glass stopper to thereagent bottle.c. Do not transfer more liquid than is needed for the experiment; do not return any excess

liquid or unused liquid to the original reagent bottle.E. MEASURING VOLUME OF LIQUID/SOLUTIONSa. The eye should always be level with the meniscus when you are making a reading.b. For measurements of clear or transparent liquids/solutions, the volume is read using thelower meniscus. For colored liquids/solutions, the upper meniscus is used.F. HEATING A LIQUID/SOLUTION IN A TEST TUBENOTE: Never fix the position of the flame at the base of the test tube and never point the testtube to anyone. The contents may be ejected violently if the test tube is not heated properly.a. The test tube should be less than one third full. Hold the test tube with a test tube holderat an angle of about 45º with the cool flame. A cool flame is a nonluminous flamesupplied with a reduced amount of fuel.b. Move the test tube circularly in and out of the flame, heating from top to bottom.G. PRECIPITATIONa. Place 2 mL of sodium chloride solution in a test tube and slowly add 2 mL of silvernitrate solution. Write the balanced chemical equation for this reaction.______________________________________________________________________NOTE: Be careful in handling silver nitrate solution. This solution may leave dark stains onthe skin, clothes or bench top.b. The solid formed is the precipitate and in this case, the slightly soluble silver chloride.Allow the precipitate to settle.c. Add a few drops of silver nitrate solution. Continue addition until no precipitation isobserved. Divide the mixture into two portions and keep these for procedure 8.H. SEPARATING A LIQUID FROM A SOLID1. Filtration1. Preparation of the filter paper to be used for gravity filtration:i. Cut a circle out of a 5” x 5” piece of filter paper. Fold the trimmed filter paper in exacthalves and fold it again crosswise into two.ii. Make a small tear in one corner. This tear seals the paper against the inflow of airto the underside of the filter paper.iii. Open the folded paper so as to form a cone with one paper thick on one side andthree paper thick (with the torn corner) on the other.iv. Place it in a funnel. Moisten it with a little water and press it against the top wall ofthe funnel to form a seal. The filter paper must always be smaller than the funnel.v. Support the funnel with a clamp or a funnel rack.b. Transfer the precipitate formed from the previous activity by carefully pouring themixture, with the aid of a glass rod, into the filter paper. The liquid that passes throughthe liquid is called the filtrate.c. The tip of the funnel should touch the wall of the receiving beaker to reduce anysplashing of the filtrate.d. Fill the bowl of the funnel until it is less than two-thirds full.e. Always keep the funnel stem full with the filtrate; the weight of the filtrate creates a slightsuction on the filter in the funnel, thus this hastens the filtration process.f. Set aside both precipitate and filtrate for the next two activities.2. Decantationa. Shake out the precipitate retained in the filter paper into a beaker with 10 mL of water.b. Allow the solid to settle at the bottom of the vessel for several minutes.c. Transfer the liquid (called supernatant) into another container with the aid of a cleanstirring rod.d. Do this slowly so as not to disturb the solid. Is this method applicable for the separationof all solid-liquid mixtures? Why? ___________________________________________e. Rinse the precipitate with water and decant again.

f. Which of the two separation methods (i.e., decantation or filtration) is better in isolatingprecipitate? Why? _______________________________________________________3. Evaporationa. Pour the filtrate obtained from filtration into the evaporating dish. Place the evaporatingdish on the wire gauze supported on an iron ring clamped to an iron stand. Heat the dishusing a cool flame.b. Continue heating until the crystals begin to appear. Cover the dish with a watch glassand allow the contents to cool. The solid remaining after evaporation is called theresidue. What is the residue made of? _______________________________________I. WEIGHINGa. Weigh 0.5 g of sand. Weighing may be done on platform balance or on an analyticalbalance. Rough weighing (to the nearest half gram), is to be made on the platformbalance. Analytical balance is used for more accurate mass measurements.b. The character of the substance will often determine the nature of the container where itis to be weighed. Use a weighing paper, a watch glass, a beaker, or some container tomeasure the mass of the chemicals.c. Do not place the chemicals directly on the balance pan. If in doubt as to the container,ask your instructor.J. TECHNIQUE IN HANDLING CHEMICALSa. A reagent is a substance which has a definite composition and a set of specificproperties. The strong solutions are marked “concentrated” and the weak solutions,“dilute”. Some examples of the reagents are:Sulfuric acid H2SO4 Ammonia NH3

Hydrochloric Acid HCl Sodium hydroxide NaOHAcetic acid CH3COOH Calcium hydroxide Ca(OH)2

b. Before getting the desired amount, read the label twice to be sure it is the correctchemical. Transfer the desired amount into the receiving container. Once removed,these should never be returned.c. Don’t take out more than what is needed to minimize wastes. Do not return excesschemicals to the reagent bottle. In pouring reagents from bottles, don’t place thestopper on the table but hold it between your fingers.d. Never touch, taste or smell chemicals unless specifically directed to do so.