|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.|
| To review basic laboratory
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
|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
|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
|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
|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
|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
|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
|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.