Essay/Term paper: The sequence of chemical reactions

Essay, term paper, research paper:  Chemistry

The Sequence of Chemical Reactions


Drew Selfridge
Dave Allen, Lab partner
Instructor
Yang February 11, 1997

INTRODUCTION This experiment was to recover the most amount of copper after it
is subjected to a sequence of reactions. The copper is originally in solid
form, but the reactions will turn it into free Cu+2 ions floating in solution.
The ions will then be regrouped to form solid copper once again. During this
process, however, some of the Cu+2 ions may be lost. The copper will subjected
to changes in pH and heat. These steps were responsible for the breakdown and
reconstruction of the copper. The percent of copper retrieved will reflect the
skill with which the reactions were administered.

EXPERIMENTAL On an analytical balance, measure the mass of the copper while in
the vial. Remove approximately 0.35 g into a 250 mL beaker. check the balance
and record the mass of the remaining mixture in the vial. In the laboratory
hood, dissolve the copper with ~ 3 mL of nitric acid. Allow the beaker to
remain under the hood until the fumes cease. The remaining solution should be
blue. Bring the beaker back to the lab station and add ~ 10 mL of distilled
water. Stir the mixture, all the while adding ~ 8 mL of 6M of NaOH to the
beaker. Check with litmus paper to ensure that it is slightly basic. Fill the
beaker with up to 100 mL mark with distilled water. Heat the solution and allow
it to boil for 5 minutes. Prepare a squirt bottle with hot water. Filter the
solution and rinse the beaker with the hot water. Rinse the filter cake with
hot distilled water. Transfer the filter paper into a clean beaker. Add ~ 10
mL of 3M sulfuric acid to the beaker in order to dissolve the filtrate. Remove
and rinse the filter paper. Now add ~ 0.35 g of zinc powder to the solution and
stir until the solution becomes clear. Dissolve the excess zinc with more
sulfuric acid. Decant the liquid with a stirring rod, retaining only the copper.
Rinse the copper with distilled water and steam dry. Weigh the mass.

DATA/RESULTS initial mass of copper (g) 0.319 final mass of
copper (g) 0.305 % recovery = (final mass/initial mass) x 100
95.6

OBSERVATIONS -between steps 1 through 4 the solution is blue. -between steps 5
through 8 the solution is dark brown. -between steps 9 through 12 the solution
is blue-green. -between steps 13 through 16 the Zinc turns red as the blue color
slowly leaves the solution.

CALCULATIONS % Recovery = (final mass / initial mass) x 100 % Recovery = (0.305
- 0.319) x 100 % Recovery = 95.6%

CONCLUSION (a) The overall yield of the reaction was 95.6%. There may have
been copper lost in transfer from beaker to beaker or stuck to the stirring rod
while the copper was in the ionic state. The solid copper may have been lost in
the filter paper or in the decanting of the liquid. The majority of the copper
lost was probably lost when the copper was transferred from beaker to beaker or
during the recanting of the liquid. The filter paper and stirring rod probably
account for a small fraction of the copper lost.
(b) The class average for the experiment was 96.11%. Based on this
average our results were very precise to 0.5% The hypothesis would be that 100%
of copper could be recovered there for our results were also accurate to 4.39%.
(c) The hypothesis was supported by the experimental results because
two groups recovered 100%. (d) Our results were less then the class average.
This explained by possilbe loss of copper when transferring between different
stages of the experiment. (e) Buring of the copper during the drying stage
would be a systematic error that would result in a class average greater than
100% yield of copper.