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Elizabeth Gardner

Mrs. Shafer

AP Chemistry Pd. 3

8 September 2010

AP Chemistry Laboratory #1

Objective:

The objective of this lab is to find the empirical formula of silver oxide.

Data:

Measurements

Trial #1                  Trial #2                  Trial #3
Mass of crucible and      45.5370                   21.5892                   22.1983
lid, g
Mass of crucible, lid,    46.0410                   22.0730                   22.7105
and silver oxide, g
Mass of crucible, lid,    46.0018                   22.0399                   22.6731
and silver metal, g
Appearance of             Dry, hard, white with     White colored,            Light gray/white,
product                   silvery glimmer           plastered to crucible     sandy texture

Data Results

Silver Oxide              Silver                    Oxygen
Mass (g)                  .504                      .4648                     .0392
Percent Composition       100%                      92.22%                    7.78%
Moles                                               4.309                     1.2

Ratio & Empirical Formula:

Ag:O2      3.5:1 = 7:2

AgxOy   Ag + O2       becomes          Ag7O4   Ag + O2
Gardner 2

Questions:

1.     To find the mass of silver oxide and the mass of the silver metal product, the law of

conservation of mass must be used to calculate the mass of oxygen that combined with silver.

First, take the mass of the crucible, lid, and silver oxide which was previously measured, and

subtract the mass of the empty crucible and lid.

46.0410 g (crucible, lid, and silver oxide)
- 45.5370 g (crucible and lid)
0.46480g (silver oxide)

Then find the mass of the silver metal product by subtracting the mass of the empty

crucible and lid from the mass of the reacted silver product with the crucible and lid.

46.0018g (crucible, lid, and silver product)
- 45.5370 g (crucible and lid)
0.4648 g (silver product)

The law of conservation of mass states that mass that goes into a reaction must be equally

present in the product. Using this concept, the mass of oxygen in the silver oxide can be found

by taking the previously calculated mass of the silver oxide reactant and subtracting the mass of

the silver product.

.504 g (silver oxide)
- .4648g (silver product)
.0392g (oxygen in silver oxide)

2.     The percent composition of silver and oxygen in silver oxide is found by separately

taking the mass of the silver and oxygen and dividing it by the mass of the silver oxide. To

convert the products into a percentage, simply multiply by 100.

silver
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3.        In order to find the moles of the silver and oxygen gas produced by the reaction, the

amount of oxygen and silver used in the reaction must converted into molar mass through

dimensional analysis.

-                                                 -

4.        Finding the ratio between the number of moles of silver and the number of moles of

oxygen is imperative to finding the empirical formula of silver oxide. To find this ratio, the

moles of oxygen and silver must be divided by the element with the smallest amount of moles in

the reaction, which in this case is oxygen.

-                                     -

-                                         -

Therefore, Ag:O     1.75:1 = 7:2

After acquiring the ratio of silver to oxygen, it is simple to apply this ratio to an empirical

formula.

AgxOy      Ag + O2        becomes       Ag7O4      Ag + O2

5.        The above reaction is not balanced. Both sides of the reaction must have the same

amount of silver and oxygen in order for it to be balanced. Because there are 7 silver on the

reactant side, a coefficient of 7 must be added to the product side of the reaction as well. The

oxygen is also imbalanced, as there are 4 oxygen on the reactant side but only 2 on the product

side. The imbalance of oxygen can be corrected by adding a coefficient of 2 to the product side

of the reaction. This balances the equation, as both sides include 7 silver and 4 oxygen.

Ag7O4       7Ag + 2O2

6.        The theoretical yield of a product in a chemical reaction reveals the mass of the product

that could be obtained if 100% of the reaction was converted. In this case, the periodic table

must be consulted to find the theoretical empirical formula for silver oxide. Because silver
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typically has a charge of 1 and oxygen has a charge of -2, the theoretical empirical formula is

Ag2O. When the molar mass of Ag2O is found, it needs to be converted from the original .504

grams used at the beginning of the experiment into grams silver through the process of

dimensional analysis.

7.       The percent yield is used to find the amount of product formed compared to the amount

of product that theoretically could have been obtained. The equation for percent yield is listed

below.

% yield=

8.       Because the percent yield calculated is less than 100%, flaws in the experiment are

exposed. The fact that the percent yield was lower than 100% proves that not enough of the

mass of the product was present in the experiment. This may have been due to the fact that

during the experiment, the silver oxide was being weighed in separate beaker while the crucible

was being heated. When the lead scientist momentarily departed from the laboratory for a

restroom break, the two assistant scientists forgot to reweigh the crucible when the silver oxide

was transferred from the beaker to the crucible, assuming all .504g of silver oxide were

attempt to compensate for the potential loss of silver oxide (the weight of the empty beaker was

subtracted from the weight of the beaker with some iron oxide remains inside, and then added to

the weight of the crucible, lid, and iron oxide). Despite these additional calculations, the entire

procedure had potential for small errors.
Gardner 5

Another possible point of error occurred during the calibration of the scales and the

measuring process. After much weighing had taken place, it became apparent that about five

other scientists were leaning on the table that the scale sat upon and their movements were

affecting some of the measurements. Once this became apparent it was put to a stop, but it was

almost entirely too late at that point in the experiment. The table vibrations could have caused

the silver oxide to be measured at .5 grams but the true mass may have been less. If this was the

case, the amount oxygen in the silver oxide would have been miscalculated because it was

derived directly from the mass of the silver oxide. The mass of the silver oxide would have been

less and thus the silver composing it would have been calculated as less.

Yet another possibility is that not all of the silver oxide got an opportunity to react.

When the final product was examined with a stirring stick, it had a white, shimmery appearance.

The product did not seem extremely silvery until it was broken up into smaller pieces. Because

the silver oxide was not stirred and the flame was hitting only one spot throughout the majority

of the experiment, it is possible that the top layer of the silver oxide was neglected, not getting an

opportunity to fully evaporate and therefore leaving the reaction unfinished. This may have

skewed the ensuing calculations, causing the products of the reaction to be less than the projected

results indicated by the theoretical yield.

Any of these causes or even causes outside of those discussed would have affected the

outcomes of the calculations later performed. These errors would decrease the amount of

product in the reaction, decreasing the numerator in the percent yield equation, leading to a

decreased total percent yield.
Gardner 6

Conclusion:

The objective of this lab was to initiate a reaction of silver oxide to ultimately calculate

its empirical formula. The possible points of error that were previously discussed may have

caused miscalculations in the determination of even the simplest calculations. If there was less

silver oxide in the crucible before the reaction began due to a measurement problem, all of the

questions would have been solved assuming there was less silver oxide than there actually was.

It would have made an impact as stated above in the question.

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