Jess Sproul
Chapter 2 Notes
Chapter 2
Chemicals and Apparatus:
Putting the Tools to Work
2A:Selecting and Handling
Reagents and Other Chemicals
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Select the best grade chemical
available at all times.
Replace cap to every container
immediately after use of chemical.
Never set a stopper on a desktop.
Never return excess reagent to a
bottle.
Never insert a spatula, spoon, knife,
or other instrument into a solid
reagent container.
Keep the reagent shelf and lab
balance neat and clean.
Observe local regulations regarding
disposal or surplus chemicals.
2B: Cleaning and Marking
Laboratory Ware
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Mark separate trials individually with
pencil, wax pencil, or other marking
ink.
Clean glassware thoroughly with hot
detergent solution, rinsed with tap
water, and then rinsed with deionized
water.
Don’t clean interior of glassware with
paper towel as it is a waste of time and
could potential contamination.
2C: Evaporating Liquids
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Evaporation is a good way to
decrease the volume of a volatile
solution.
It is also a good way to eliminate
unwanted species, such chloride and
the nitrate ion.
2D: Measuring Mass
There are different types of balances:
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Semimicroanalytical Balance: maximum load of 10-30 grams;
precision of ±0.01 mg
Microanalytical Balance: capacity of 1-3 grams; precision of
±0.001 mg.
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Follow these instructions when using a balance:
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Center the load.
Protect balance from corrosion.
Observe special precautions for weighing liquids.
Consult instructor if balance needs adjustment.
Keep balance and its case extremely clean.
Always allow a heated object to return to room
temperature before weighing.
Use tongs or gloves to prevent the contamination of a
dried sample by the uptake of moisture.
2D-5 Sources of Error in Weighing
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Errors in weighing should fall well within the limits of
the experimental error due to the analytical operations.
If, for example, an error of 0.001 g. were made in
weighing out a gram sample of fireclay containing
0.25% Of MgO, the resulting error in the determination
of the magnesia could be no greater than 0.1% of its
value, which is negligibly small. A 1 mg. error, however,
made in weighing the 0.0069 g. Of Mg2P207 would
involve an error of over 14% in the magnesia value,
and this would be intolerable.
(http://humboldt.edu/~scimus/Instruments/AnalWgtSmith/AnalWgt.htm)
2E:The Equipment and Manipulations
Associated with Weighing
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Mass can change with the absorption of moisture
from the atmosphere.
Samples are brought to constant mass by a cycle
that involves heating at an appropriate temp.,
cooled, and then weighed.
Constant mass provides some assurance that
physical or chemical process that occurred during
heating are complete.
2F: The Equipment and Manipulations
for Filtration and Ignition
Crucibles are used as either containers or
filtering devices that allow the supernatant
to pass through while retaining the
precipitate.
 Sometimes, filter paper is used and it must
be burned off. If this is the case, be sure
to handle the heated crucible with care.
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2G: Measuring Volume
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Volume is measured with pipets, burets, and
volumetric flasks.
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Pipets are used for moving specific volumes of liquid
from minute amounts to volumes of 25 mL and possibly
more.
Burets are used for adding small amounts of liquid to a
given container at controllable intervals.
Volumetric flasks are used for measuring and creating
standard solutions.
2H: Calibrating Volumetric Ware
Calibrating a Volumetric Pipet
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Weigh the dry, empty pipet to nearest milligram, then add
liquid and weigh again. Use density to determine the actual
volume of the liquid.
Calibrating a Buret
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Weigh an empty 125-mL flask, then fill a buret to the 0.00
mL mark. Empty the buret into the flask and use density to
determine the true volume.
Calibrating a Volumetric Flask
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Weigh the clean, dry flask to the nearest milligram. Fill to
mark with water and reweigh. Calculate true volume using
density.
2I: The Laboratory Notebook
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Record all data and observations
directly in lab notebook.
Supply each entry with a heading
or label.
Date each page.
Never erase or remove any entry.
Never remove a page from
notebook.
2K: Safety in the Laboratory
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Learn location of eye fountain, fire blanket, shower, and fire
extinguisher.
Wear eye protection at all times.
Don’t touch chemicals bare-handed.
Never perform unauthorized experiment.
Never work alone.
Never eat or drink in lab.
Always use a bulb to draw liquid into pipet.
Wear adequate foot covering.
Be careful with heated objects.
Always fire-polish ends of freshly cut glass. Never force glass
tubing through hole of a stopper.
Use fume hoods when evolving harmful gases.
Notify instructor of injuries.
Dispose of solutions and chemicals as instructed.