Common Laboratory Operations and Techniques

• Cutting a Glass Tubing


  Place the glass tubing along the edge of the table and with the use of a triangular file, scratch the tubing at the point where it is to be cut. Do this in one direction only until a deep grove is made. Then hold the tubing with both hands and with the mark away from you, break the glass tubing. Make sure that both hands are close together on the side of the tubing
• Fire Polishing Sharp Glass Edges


  Hold the cut end of the tubing over a Bunsen burner flame. Then rotate the tubing slowly until the glass starts to melt. (Do not touch the heated portion with your bare hands.)
• Bending a Glass Tubing


  Place a fish tail on top of the barrel of the Bunsen burner to spread

  out the non-luminous flame. Then heat the glass tubing at the

  desired point, rotating it slowly until it becomes soft. Remove the

  tubing from the flame end and bend.
• Handling of Reagents: Solid Reagents

  For reagent bottles with a screw cap, remove the cap and place it on the table, bottom up. Solid reagents should always be scooped out the bottle with a clean and dry spatula. Use paper strip when transferring reagents into a narrow-mouthed container. To obtain powdered samples from a wide-mounted container easily, tilt the reagent bottle and then slowly rotate it. Never put back any solid into the reagent bottle since this may contaminate the reagent.
• Liquid Reagents


  For a reagent bottle with glass stopper which cannot stand by itself, remove the stopper by pulling it out with the index and middle finger, palm facing upward. While the stopper is still between the two fingers, pick up the bottle and pour the liquid from the side opposite the table, otherwise the left on the lip may run down the side of the bottle and damage the label.
• Measuring the Volume of a Liquid


  The apparatus commonly used for measuring the volume of a liquid is the graduated cylinder. The burette, pipette, volumetric flask, and medicine dropper can also be used. When measuring the volume of a liquid with a graduated cylinder, place the cylinder on a flat surface and read at eye level the lower meniscus for liquids which wet glass like water and the upper meniscus for liquids which wet glass like mercury.
• Heating of Chemicals


  Heating Liquids in a Beaker or in an Evaporating Dish

  When heating liquids in a beaker or in an evaporating dish, place the beaker or dish on a wire gauze supported in an iron ring attached to an iron ring stand or on a tripod. The wire gauze is used to produce uniform heating of the vessel and to prevent the vessel from cracking.
• Heating Liquids in a Test tube


  When heating liquids in a test tube, use a test tube holder. The test tube is held in a slanting position at about 45o with the open end away from the persons working around you.
• Heating Solids in a Test Tube


  When heating solids in a test tube clamp the test tube in an iron stand at about 45o. The flame is applied slowly, moving it back and forth.
• Heating Solids in a Porcelain Crucible

  Solids may be heated into high temperature in a porcelain crucible which is supported by a clay triangle over an iron ring or tripod. The crucible is carefully placed on the clay triangle either in an upright or slanting position.
• Decantation


  Is the process of separating a heavy and readily settling solid from a liquid. The supernatant liquid is poured off (without disturbing the solid) down the side of the receiver through a stirring rod placed against the lip of the receiver.
• Filtration


  A method of separating a finely divided solid from a liquid in which it is suspended is called filtration. A filter paper is used to hold the solid while the liquid filters through the pores of the filter paper. The liquid that passes through is called the filtrate while the solid that remains in the paper is the residue.
• Evaporation


  Is the conversion of liquid to vapor state by exposure to air or by breathing. In evaporation by heating, the liquid is placed in an evaporating dish set on wire gauze supported by an iron ring is attached to an iron stand. Use a low flame when the contents of the evaporating dish are almost dry.
• Measuring Mass


  First, clean the pan of the balance and check if the pointer is at zero. In weighting chemicals, place the material on a weighed container, never directly on the pan for this might corrode the metal pan. Move the rider carrier until the object balances with the rider carrier. The mass of the object is indicated by the rider of the balance. After weighing, set all rider carriers to zero.