Experiment #2: A Review of Basic Laboratory Techniques
In addition to the safety rules operating in a laboratory, many of the techniques used have their own dangers. This experiment will allow you to review the proper techniques for the use of some common equipment while at the same reviewing the appropriate safety procedures. You are asked in this lab to separate a mixture of sand and salt. The masses of the separated components will then be compared with the mass of the sand/salt mixture.
Objectives:
         To review basic laboratory techniques.
         To review safety procedures associated with certain equipment.
         To perform a simple quantitative experiment.
 
Apparatus: Safety goggles, Bunsen burner, electronic balance, ring stands, ring clamps, thermometer clamp, wire gauze, pipe-clay triangle, beaker tongs, ceramic tile, crucible tongs, filter funnel, filter paper, 250 mL beakers, evaporating dish, glass rod, thermometer, wash bottle, test tube, test tube holder, 100 mL graduated cylinder, 10 mL graduated cylinder
 
Materials: sand/salt mixture
 
Procedures:
1.   Prepare the following data table in your notebook:
      Mass of 250 mL beaker + sand/salt mixture                   =
      Mass of empty 250 mL beaker                                        =
      Mass of sand and salt                                                       =
      Volume of water added                                                     =
      Temperature reached                                                        =
      Mass of evaporating dish + dry sand                               =
      Mass of evaporating dish                                                 =
      Mass of dry sand                                                               =
      Volume of filtrate                                                               =
      Volume of filtrate transferred to test tube                       =
       Mass of test tube + dry salt                                            =
       Mass of empty test tube                                                  =
       Mass of dry salt                                                               =
       Mass of salt in all of the filtrate                                      =
       Total mass of sand after drying + salt in filtrate            =
       Original mass of sand + salt                                            =
       Mass lost or gained                                                         =
 
2.   Choose a clean, dry 250 mL beaker.   Find it's mass on the balance and record this in your data table. (Use the best precision that the balance offers).
 
3.   Place about 20 grams of the sand and salt mixture in the beaker. Find the mass of the beaker and sand/salt mixture on the balance and record it in the data table.
 
4.   Using a 100 mL graduated cylinder, measure out 100 mL of water. Remember to read the volume from the bottom of the meniscus. Record this volume in your data table.   Pour this water into your sand and salt mixture.
 
5.    Assemble the equipment on the ceramic tile hot plate to heat this mixture. You will require the ceramic tile hot plate, retort stand, two rings, wire gauze, thermometer , thermometer clamp and the beaker with the sand/salt/water mixture.  The upper ring should be placed to hold the beaker in place so that it does not slip off the wire gauze.
 
6.   Light the Bunsen burner as follows:
      i) Put on your safety goggles. Ensure that your hair and all your clothing is well away from the burner.
     ii) Check the immediate area for flammable liquids or any other flammable substances.
    iii)  Adjust the air control of the burner so that it is almost closed.
    iv)  Turn the gas valve at the base clockwise until its off. Then open it counterclockwise 1 to 2 turns.
     v)  Hold the sparker over the top of the burner and open the gas cock to the halfway point. Squeeze the sparker to generate a ignition source.
    vi)  If the burner is still unlit after 5 seconds, turn off the gas supply and wait for 20 seconds before attempting to light it again.
   vii)  Once the burner is lit, adjust the air and gas controls to obtain a blue flame of the size required.
 
7.   Place the burner under the beaker to be heated. Stir the contents with the glass rod, being careful not the damage the bulb of the thermometer. Continue warming the mixture until the temperature reaches about 80oC.  While the beaker is warming, set up the filtering apparatus.  The filter paper should be folded in half, and in half again, then opened up as a cone.  Insert the cone into the filter and dampen it with the wash bottle.
 
8.   When the contents of the beaker have reached about 80oC, turn off the gas and read the thermometer as accurately as possible. Record the temperature in your data table.  Remove the thermometer carefully and place it on the table so that it won't roll off.  Remove the beaker from the retort stand setup with the beaker tongs as it will still be hot. Pout the contents of the beaker into the filter paper cone. Pour slowly, so that the liquid does not rise above the level of the filter paper.
 
9.   When the last of the liquid has been transferred to the filter funnel, use a wash bottle to rinse any remaining sand into the funnel.
 
10.  While the funnel is still dripping, determine the mass of a clean dry evaporating dish. Record the mass in your data table.
 
11. When the funnel has stopped dripping, carefully use the glass rod to scrape the residue (sand) off the filter paper into the evaporating dish.  Try not to get any paper mixed in with the sand.
 
12.  Assemble the retort stand with an iron ring, pipe clay triangle and an evaporating dish.   Heat the sand to dryness.  When the sand is try, turn off the burner.  Remove the dish with crucible tongs and place it on the ceramic tile to cool.
 
13.  While the evaporating dish is cooling, measure the volume of the filtrate (the liquid that came through the filter paper) in a 100 mL graduated cylinder.  Record the volume in your data table.  Do not throw the filtrate away as it will be required in a later step of this procedure.
 
14.  Determine the mass of a clean, dry test tube. Record the mass in your data table.
 
15.  Determine the mass of the cool evaporating dish plus sand.  Record it in your data table.  Calculate the mass of sand. Enter the result in your data table.
 
16.  Measure out, as accurately as possible, 3 mL of the filtrate in a 10 mL graduated cylinder.  Transfer this to the weighed test tube. Record the volume in your data table.
 
17.   Relight the Bunsen burner.  Holding the test tube in a test tube holder, heat the contents to dryness.  When heating a test tube, ensure that the mouth of the test tube is not pointing at yourself or anyone else.  Do not heat the bottom of a test tube.  If the some of the contents shoot out of the end, wash out the test tube and repeat steps 16 and 17.
 
18.  When the contents of the test tube are dry, turn off the burner and allow the test tube to cool. Determine the mass of the test tube and its contents and record this in your data table.  Calculate the mass of the dry salt.  Enter this into your data table.
 
19.  Calculate what fraction of the filtrate you heated in the test tube.  Now calculate how much salt was in the total filtrate.  Enter the answer in your data table.
 
20.   Add the mass of sand, recovered after heating in the evaporating dish, to the total mass of salt in the filtrate.  Enter the answer in your data table.   Compare this answer with the original amount of the mixture that you used.  It should be the same!  Enter any discrepancy into your data table.
 
21.   Dispose of the sand by placing it in the container provided by the teacher.  Do not pour sand down the sink!  Wash all glassware, and return all pieces of equipment to their correct storage locations.
 
Questions
1.   You should not heat a beaker with a Bunsen burner that has a yellow flame.  Why not?
 
2.   Why did you use the glass rod the way you did in filtering the mixture?
 
3.   Why did you use wire gauze when heating the beaker, but a pipe clay triangle when heating the evaporating dish?
 
4.   What are the main differences between the two types of tongs that you used?  How do these differences account for their more efficient use?
 
5.  What safety procedures are taken when a mercury thermometer is accidentally broken?
 
6.  Describe briefly why the final mass of sand and salt was not exactly the same as the mass at the beginning of the experiment.