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Dakota State University Page 81 of 232 Experiment 4: Synthesis of a Compound General Chemistry I and II Lab Manual Percent Yield: Dakota State University Page 82 of 232 Experiment 4: Synthesis of a Compound General Chemistry I and II Lab Manual Pre-Lab Questions:
1. How are we dealing with excess fumes in this experiment?
2. What is necessary for the ad hoc fume hoods to work? Here, I mean what must you do, not
what it is hooked up to.
3. What is the concentration of potassium hydroxide? Dakota State University Page 83 of 232 Experiment 4: Synthesis of a Compound General Chemistry I and II Lab Manual Post-Lab Questions:
1. Excluding human or calculation errors, how is it possible to have a percent yield greater than
2. What are the steps where your product could be lost and why? Dakota State University Page 84 of 232 Experiment 5: Empirical Formula General Chemistry I and II Lab Manual Experiment 5: Empirical Formula
Purpose: To determine the empirical formula of a hydrate
Purr: Phrase uttered by happy cats everywhere. Background:
See “Basic Laboratory Procedures”: Bunsen burner, balance
In the previous experiment, we made a hydrated compound. These compounds are
excellent for demonstrating the principles of how mass can be used to determine empirical
formula, because, provided the salt is stable enough, all you have to do is heat them up to drive
off the water. The weight difference, then, between the hydrate and the anhydrous salt is the
mass of the water. In essence, this is all we are really doing in today’s experiment.
VERY carefully, clean a crucible with a little bit of concentrated nitric acid. If all of the
stains do not come out, don’t worry about it; after a nitric acid cleaning, nothing will come out
anyway. Follow that by washing and drying the crucible.
Place the crucible on an iron ring attached to a ring stand using a clay triangle. Place the
lid on it slightly ajar. Heat the crucible to remove the water from it, gently at first, then with a
strong heat until the bottom of the crucible glows red hot. Remove the heat, using crucible
tongs, put the lid fully on the crucible, and allow it to cool. Avoid touching the crucible because
moisture from your fingers will affect your results. By putting your hand near, but not ON the
crucible, you should tell if it is still hot or not.
When the crucible seems to no longer be hot, use crucible tongs to bring the crucible and
lid over to the balance. Obtain the mass of the empty crucible and lid. Return the crucible to the
clay triangle, and repeat the drying step. If the difference in the mass of the crucible and lid is
greater than 0.02 g between the two dryings, repeat the drying step one more time; otherwise,
proceed to the next step.
Still using tongs, take the crucible dried to a constant mass to the solid hydrate provided
for you. Put enough of the hydrate into the crucible to fill it perhaps 1/3 to ¼ full. Still using the
tongs, get the mass of the crucible, lid and hydrated salt.
To dry the h...
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