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How To... Lab Safety Techniques

—by Anne Wallingford

Remember! Always wear gloves, safety goggles, and an apron or lab coat when working in the lab.

Having the proper safety equipment is a must! Safety is of the utmost importance in any lab setting. There may be volatile chemicals that could be spilled or hazardous odors that could be harmful to you and others in the lab. Having the proper safety equipment is a must have! There are procedures that must be followed for accidents and it is important to know those as well. Emergency contact numbers should be posted where everyone in the lab has easy access to them. The equipment you are using may be expensive, which is why there are banks and financial institutions that help to fund labs and cover expenses. Keep in mind that Fisher Investments or any other firm could help with monetary needs but your life and personal safety are most important while working in a lab. With that in mind use these tips and instructions to help ensure safety in a laboratory setting.

How to:
Insert Glass Tube | Use Filter Paper | Use Lamps | Use Burners | Heat Liquids | Evaporate Flammable Liquids | Evaporate Non-flammable Liquids | Test for Odors | Ignite a Crucible | Use Pipets | Read a Graduate Cylinder | Use a Buret | Use a Centrifuge

Inserting Glass Tubing into a Stopper
If force is used when inserting glass tubing, funnel stems, or thermometers into stoppers, the glass will break. A hand cut by shattered tubing could require stitches, and permanent nerve damage has also happened in these types of accidents.

To safely insert glass tubing into stoppers,,,

  1. Moisten both the glass tubing and the stopper with glycerol.
  2. Wrap a cloth towel around your hand.
  3. Hold the tube 2-3 cm. (1"-1.5") from the end to be inserted. Twist and push the moistened tubing into the moistened stopper.
  4. Use distilled water to rinse away any excess glycerol.

Gravity Filtering Using Filter Paper Filter Paper

  1. Follow the diagram to fold a piece of filter paper.
  2. Wear gloves.
  3. Place the folded filter paper into a funnel.
  4. While holding the funnel over a waste container, moisten the filter paper and funnel with your solvent. (You can use an empty beaker for your waste container.)
  5. Press the moistened filter paper against the moistened funnel. This will seal the edges.
  6. Hold the funnel against the inner wall of your receiving container.
Slowly pour your solvent into the funnel, keeping the funnel stem filled with filtrate. (This creates suction and speeds up the filtering process.) Never fill the funnel more than 2/3 full. Hint: A buret clamp fastened to a ring stand will hold the funnel in place while you pour.

Vacuum Filtering Using Filter Paper

  1. Place a sheet of filter paper flat down in a Buchner funnel. (A Buchner funnel is a flat-bottomed funnel with a perforated surface.)
  2. Wear gloves.
  3. Attach one end of an aspirator to a filter flask. Attach the other end of the aspirator to the water faucet.
  4. While holding the funnel over a waste container, moisten the filter paper with solvent. (You can use an empty beaker for your waste container.)
  5. Open the faucet valve completely to create suction.
  6. Place the funnel's stem against the inner wall of a filter flask; this reduces splashing. Hint: Funnel adaptors designed for Buchner funnels will hold the funnel in position.
  7. Gently transfer the solvent and precipitate to the filter paper. Using fluid from a wash bottle, rinse the precipitate.
  8. When suctioning is finished, disconnect the hose from the filter flask, THEN turn off the faucet.
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Alcohol Lamps
Alcohol lamps do not get as hot as gas burners, but are suitable for use when gas burner connections are not possible.

A low-form alcohol lamp has a lowered center of gravity and is less likely to tip over than is a taller, narrow lamp.

Because the flame of an alcohol lamp is almost invisible, adding a small amount (10 grams per liter) of sodium chloride to the burner fuel (ethyl alcohol) will produce a visible flame. Or you can purchase an ethyl alcohol burner fuel that already has an additive.

Make sure the room is well ventilated when using alcohol lamps.

Gas & Electric Burners
Labs will usually have one of three types of gas: artificial gas, natural gas (methane), or cylinder (propane) gas. There are different types of burners for each type of gas.

Although Bunsen burners are traditional in many labs, Tirrill burners have a lower center of gravity and offer separate controls for temperature and flame height.

Pressurized canisters of butane gas come with burner attachments and are suitable for short-term use.

Burner assemblies can be added to 14 oz. propane tanks for a portable demonstration unit.

Burner connector tubing will connect a Bunsen or Tirrill burner to your gas line. Do NOT use standard red rubber tubing! Burner connector tubing is insulated, has corrugated ends to hold nipples firmly in place, and is available in different lengths.

Electric burners combine the safety of electricity with the efficiency of a gas heat source. Radiant heat is concentrated at the top of the burner, yet the unit remains cool enough to hold.

Heating Liquids in a Test Tube

  1. Fill the test tube no more than 1/3 full.
  2. Using a Stoddard clamp, hold the test tube over the flame, rotating the tube in small circles in and out of the flame. Heat the top of the liquid, not the bottom of the test tube.
         Never point the test tube at anyone, including yourself!
  3. Remove the test tube from the heat before the liquid boils over.

Heating Liquids in a Flask

  1. Attach a support ring sized to fit your beaker to a ring stand.
  2. Place wire gauze across the support ring.
  3. Position the support ring with the gauze over the burner, but do not yet light the flame.
  4. Place either boiling chips or a glass stirring rod into the beaker and transfer your fluid into the beaker. Do not fill the beaker more than half way.
  5. Set the fluid-filled beaker on the wire gauze.
  6. Fasten the beaker to the ring stand with either a larger support ring or a clamp.
  7. Light the burner.
  8. Use a clean glass rod to adjust either the boiling chips or stirring rod directly over the flame. (This will control the sudden formation of a superheated liquid over the flame's tip.)
  9. When heating is finished, extinguish the flame. Do not touch the beaker until it has cooled!
NOTE: If using a beaker to create a hot water bath, place a test tube filled no more than ¼ full into the beaker of water. This method is used if you have a small quantity of a solution that needs to be kept at a constant temperature for a period of time. Proceed as above.

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Evaporating a Non-flammable Liquid

  1. Work inside a fume hood.
  2. Fasten a support ring to a ring stand. Place wire gauze over the support ring.
  3. Pour a small amount of your liquid into an evaporating dish.
  4. Place the evaporating dish on the gauze over a low flame.
  5. Once the material has evaporated, use tongs to move the evaporating dish to wire gauze for cooling.
Evaporating Non-flammables

Evaporating a Flammable Liquid

  1. Work inside a fume hood.
  2. Do NOT use an open flame! Place wire gauze on the heating surface of a hot plate. (A solid surface hot plate offers the greatest safety.)
  3. Insert a glass stirring rod into a glass beaker and fill the beaker 2/3 full with water. Maintain the water level in this beaker during the heating process. (See diagram below.)
  4. Clamp the beaker to a ring stand, or use a support ring to hold the beaker in place.
  5. Pour a small amount of the flammable liquid into the evaporating dish.
  6. Place the evaporating dish on top of the beaker.
  7. Once the material has evaporated, use tongs to move the evaporating dish to wire gauze for cooling.
  8. Remove the beaker from the heat source. Place the hot beaker on wire gauze for cooling.
Evaporating Flammables

Testing for Odors
Use your hand to fan vapors towards your nose. Never hold your face directly over vapors!

Igniting a Crucible

  1. Attach a support ring to a ring stand. Place a clay triangle over the support ring.
  2. Place your substance in a porcelain crucible and balance the crucible on the clay triangle.
  3. Heat over a flame; use crucible tongs to turn the crucible for even heating.
  4. Once the crucible glows red, do not touch it. Extinguish the flame. Let the crucible sit until it's at room temperature.
  5. If the contents of the crucible are to be ignited without air, use crucible tongs to place the crucible cover on the crucible before igniting.
  6. For complete combustion, place the substance in the crucible and balance the crucible on the triangle. Use the tongs to slightly tilt the crucible. Adjust the crucible cover so it covers 2/3 of the crucible. Ignite.
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Using Pipets
Caution: Glass pipets break easily. When not in use, pipets should be stored in pipet stands, baskets, or flat holders. Pipet jars can be used for soaking used pipets, and pipet washers make clean-up time faster and easier.

Never use mouth suction to fill a pipet!

  1. Wash the pipet with a glass detergent such as Alconox and rinse with tap water. Then rinse with either deionized or distilled water.
         Continue rinsing until no moisture droplets remain on the inner walls.
  2. Fasten a pipet pump or pipet filler bulb to the open end of the pipet.
  3. Insert the tip of the pipet into the reagent being transferred. Use suction from the pipet pump or bulb to draw up 2-3 ml. of solution. Never use mouth suction to fill a pipet!
  4. Using the pipet pump or bulb to control air pressure, remove the pipet from the reagent. Hold the pipet over a waste container. (A beaker can be used as a waste container.)
  5. Gently tip the pipet so the inner walls of the pipet are washed with the solution. Release the contents into the waste container.
  6. Again insert the pipet tip well below the surface of the reagent. Use suction to draw the liquid into the pipet. This time, the liquid should be 2-3 cm above the fill mark.
  7. Using the pipet pump or bulb to control air pressure, remove the pipet from the reagent.
  8. While holding the pipet over the waste container, release the pump/bulb and drain the pipet to the fill mark. Remove the last drops by touching the pipet to the wall of the waste container.
  9. While controlling the flow with the pipet pump/bulb, deliver the reagent to the receiving container. Keep the pipet's tip above the contents and against the container's inner wall. (This will prevent splashing.)
Do not blow or shake the last bit of reagent from the pipet's tip! The pipet has been calibrated to allow for this.

Reading a Graduate Cylinder
Note: To obtain an accurate measurement of a liquid, always read the volume at the bottom of the meniscus.

  1. Lower your eye to the level of the liquid. Read the volume at the bottom of the meniscus.
  2. If it is a light-colored or clear liquid in the graduate cylinder, hold a piece of black paper behind the cylinder. Use white paper if the liquid is dark.
Hint: Cylinders marked "graduated to contain" measure volume as a result. Cylinders marked "graduated to deliver" measure volume when the liquid is meant to be poured after measuring.

Graduated cylinder

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Using a Buret
In a titration, a solution flows from a buret into another solution until a chemical reaction is complete. Common titrations involve acid and alkali indicators.

  1. Use a glassware detergent, such as Alconox, to wash the buret. Rinse first with tap water, then with distilled or deionized water. Continue to rinse until no moisture droplets remain on the buret's inner wall.
  2. Use a buret clamp to fasten the buret to a ring stand.
  3. Grease the buret's stopcock with high volume grease, or use Teflon TFE stopcocks. (The latter are ideal because they do not become 'locked' after use.)
         Note: Frozen stopcocks are the result of improper buret cleaning. One way to try and free a stopcock is to soak the plugged tip in carbonated soda. The gas bubbles may loosen the joint. Replace the soda when the bubbles stop.
          If this doesn't work, you can try holding the plugged tip in a low burner flame. When the barrel's warm, try to turn the stopcock. Be sure to wear heat-resistant gloves and safety goggles if you try this, because when forced, burets can shatter.
          If neither of these methods works for unfreezing a stopcock, the stopcock has fused to the buret and the buret will need to be replaced.
  4. After greasing, close the stopcock.
  5. Use either a buret funnel or a buret filling kit to pour your solution into the buret. Fill to just above the 0 (zero) mark.
         Note: Unlike cylinders or pipets, burets are graduated from the top down because they fill from the top.
  6. Place a waste container underneath the buret. (An empty beaker can be used as a waste container.) Open the stopcock just enough to bring the fluid to the zero mark. The meniscus will be just below the top graduation.
          If you are right-handed, operate the stopcock with your left hand, wrapping your hand around the buret. Reverse this if you are left-handed.
  7. Wait 30 seconds while the liquid drains from the wall of the buret. Record your volume.
  8. Place a receiving flask with your solution underneath the buret. Place a colored paper underneath your flask. Use white if the anticipated color change is dark, use black if the anticipated color change is white or clear.
  9. Open the stopcock. Let the solution (titrant) in the buret continue to flow until you near the endpoint. (The endpoint is the point where color changes slow.) As you near the endpoint, control the flow with the stopcock. When a single drop makes a color change that lasts 30 seconds, close the stopcock.
          Swirl the flask gently during the titration.
  10. After closing the stopcock, wait another 30 seconds for the solution to drain from the buret's wall. Record the final volume.
  11. Remove your flask. Place a waste container under the buret. Drain the buret, then rinse and wash it.
Remember! Failure to clean the buret is the main cause of frozen stopcocks!

Using a Centrifuge
A centrifuge compacts a precipitate at the bottom of a centrifuge tube, making it easy to decant any liquids. The process takes 20-45 seconds.

Centrifuges come with constant an adjustable speed controls, and in 4-tube and 6-tube models. A good centrifuge should have suction-cup feet, low vibration, and tube shields.

Because the low speed of a centrifuge may be 1000 rpm and the high speed 5000 rpm, the apparatus should have an automatic power interruption if the lid is opened during operation.

  1. Fill the centrifuge tubes. Liquid should not be more than 1 cm from the top of the tube.
  2. Fill the tubes with an equal amount of solvent.
  3. Label the tubes.
  4. To keep the spinning centrifuge balanced, always used an even number of tubes placed opposite each other.
  5. If only one tube will contain a precipitate, fill the second tube with an equal amount of solvent. Be sure to label the tubes!

© 2004 Anne Wallingford. All rights reserved.

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How to:
Insert Glass Tube | Use Filter Paper | Use Lamps | Use Burners | Heat Liquids | Evaporate Flammable Liquids | Evaporate Non-flammable Liquids | Test for Odors | Ignite a Crucible | Use Pipets | Read a Graduate Cylinder | Use a Buret | Use a Centrifuge

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102009 Wednesday, May 09, 2012