Basic Laboratory Techniques

Working of Bunsen Burner

Materials Required

Real Lab Procedure

  • Connect the gas-inlet of the bunsen burner to the gas tap through a rubber tube.
  • Turn on the Bunsen burner and light it using a spark lighter.
  • Ensure the air holes at the bottom of the burner are completely opened.
  • The gas will mix with more air and the flame will burn much hotter producing a blue flame called the non-luminous flame.
  • Close the air hole by rotating the air adjusting disc.
  • Now the gas will only mix with ambient air and this reduced mixing produces an incomplete reaction producing a cooler, but brighter, luminous yellow flame.

Precautions

  • Remove all the flammable and combustible material from the lab bench or work area when the Bunsen burner is to be used.
  • Tie-back long hair, dangling jewelry, or loose clothing.
  • Replace all hoses found to have defect before using.
  • Use a spark lighter with extended nozzle to ignite the burner.
  • Adjust the flame by turning the air adjusting disc to regulate air flow and to produce an appropriate flame for the experiment.
  • Do not leave open flames unattended and never leave the laboratory while the burner is on.
  • Shut off gas when its use is complete and ensure that the main gas valve is off before leaving the lab.

Cutting a Glass Tube or Rod

Materials Required

Real Lab Procedure

  • Place the glass tube on a bench or flat surface and without applying too much pressure, hold it firmly.
  • Using the triangular file make a single deep scratch on the glass tube by placing the file perpendicular to the tube and pushing it down and across the tube.  Do not saw!  By placing the triangular file perpendicular to the tube, you ensure that the scratch made is a straight one.
  • You've got a scratch on the glass tube and that is all it needs to break it.   Now, place both your thumbs directly behind the scratch and applying gentle pressure and using a quick motion bend the tube towards you.  It just breaks.  
  • You may find that the broken edges of the tube is not smooth and can cause bruises.  This can be made smooth by rotating the broken edges over a flame for 2 - 3 minutes and then allowing it to cool.

Precautions

  • Make a single deep scratch at the desired length with one stroke of file.
  • To avoid injury, hold the glass tube with the help of a thick piece of cloth.
  • Do not heat the end for long time. It may seal the end or make it narrow.

Bending a Glass Tube

Materials Required:

Real Lab Procedure

  • Hold both ends of the glass tube by hand and introduce it lengthwise into the luminous flame of the burner. 
  • Don't keep it in a fixed position over the flame; instead roll the glass tubing with the fingers to evenly heat it.
  • You'll feel the area of the glass being heated becoming soft and delicate.  When this happens apply gentle pressure so that it bends by itself. When the desired angle is formed, remove the tubing from the flame.
  • Place the bent limb on the glazed tile and press it gently to make it coplanar. Then allow the tubing to cool. 

Precautions

  • Select the tube of sufficient length to keep your hands safe from heat. Do not try to bend very small glass tubes of length less than 20 cm.
  • While heating, the glass tube should be rotated in order to ensure uniform heating.
  • Never bend the glass tubing by force. Doing so can break the tubing.

Drawing Out a Glass Jet from a Delivery Tube

Materials Required

Real Lab Procedure

  • Holding the delivery tube with both hands, place it lengthwise in the flame.
  • Keep rotating the tube in the flame as this ensures uniform heating.  Continue to heat it until it softens.
  • Now remove the tubing from the flame and gently pull both ends of the tube. What happens is that  the middle portion becomes narrow as a capillary.  Do this till the thickness is about 2 mm.
  • Now cool and cut the narrow portion that has been obtained using  them the triangular file.  We have now two jets.
  • The broken edges of the jets that are not smooth can be rounded by rotating over the flame for 2 - 3 minutes and then allowing them to cool. 

Precautions

  • While drawing a jet, pull apart the two ends of the red-hot tube slowly so that it becomes thin uniformly.
  • Do not heat the ends too long, as it may seal the ends or make them too narrow.

The Wash Bottle

Material Required

Real Lab Procedure

  • Take the  500 ml flat-bottom flask and fill it with water.
  • Fit  the flask with an appropriate cork that has two bores.
  • Pass the two bent tubes, one bent at an angle of 120o and the second at 60o through the bores. The angles are slanted in such a way that the bent portions of the tubes lie in a straight line.
  • The upper portion of the 120o angled tube in held in the mouth whereas a jet is fitted to the tube angled at 60o.
  • On blowing air through the mouth, water comes out from the other tube through the jet.

Precautions

  • The edges of the tubes must be rounded off.
  • The longer arm of the tube bent at 60o should be only very slightly above the bottom of the flask so that it can be used even when it contains only a small amount of water.
  • All connections must be air tight.

Boring a cork

Materials Required

Real Lab Procedure

Softening the cork

A cork gets harder over time and trying to bore a cork that has hardened results in formation of cracks.  We need to wet the cork in water to soften it.  Once the cork becomes flexible, press it in a cork presser that is a mechanical device.  Alternatively, we can wrap the wet cork in a piece of paper and place it under our shoes and press it.  We now have a softened cork.  

Boring the cork

  • Place the cork on a table or a flat surface with its narrow end facing up.  
  • To ensure we get a straight hole, mark the position of the borer on both the sides of the cork. 
  • If the cork taken is a rubber one, we can apply some glycerine on the borer.  The reason we do this is glycerine acts as lubricant on the hard rubber cork.  
  • Now hold the cork tightly with the left hand and applying force, start the boring process using a twisting motion.  Make sure the borer remains vertical throughout.  
  • When half of the cork has been bored, take the borer out and reverse the cork. Start boring from the reversed side till a hole is obtained. 
  • We can now remove the borer.

Fitting a glass tube in the bore

  • We'll now fit the glass tube into the hole bored in the cork.
  • Dip the end of the cork through which the tube is going to be inserted in water.  Do the same with the end of the tube to be used.  This ensures easy insertion of the tube into the cork.
  • Hold the cork in one hand and the tube in the other hand. 
  • Hold the tube close to the wet end and insert the tube into the bored hole of the cork using a rotatory motion. 

Precautions

  • Select bores of diameter slightly smaller in size than that of the tube to be inserted in the hole.
  • Make a mark on both sides of the cork.
  • To obtain a smooth hole, drill half the hole from one side and other half from other side of the cork.
  • Since the rubber is hard, the end of the tube to be inserted is usually dipped in caustic soda solution or glycerine before fitting it in the hole.

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