Archer G11
Partner: Joon
16 August 2011
Determination of the Empirical Formula of Silver Oxide
Purpose – The purpose of this lab is to find the empirical formula for silver oxide. The empirical formula
can be found by decomposing silver oxide using heat, massing the silver that is left and then using
stoichiometry to determine the empirical formula. It would be helpful to know the empirical formula
since the empirical formula can be converted to molecular formula using molar mass. It allows chemists
to identify an unknown substance so they can predict the properties of the compound.
Hypothesis – I think that silver oxide will turn into Silver metal and Oxygen gas thus the color will turn
from black to silver since oxygen will gain enough energy to overcome the bond with the silver thus
forming Oxygen gas and float off.
Materials:
Materials
Silver Oxide (Ag2O)
Crucible and lid
Tongs
Ring stand and clamp
Wire gauze with ceramic
Clay pipestem triangle
Bunsen Burner
Spatula
Timer
0.0001-g precision balance
Trial 1
0.502 g
Trial 2
Trial 3
0.502 g
0.502 g
3 crucibles
2 tongs
3 ring stands and clamps
3 gauzes
3 triangles
3 burners
1 spatula
3 timers
1 balance
Procedure
1.) Put a clay pipestem triangle on the ring stand and clamp
2.) Put a crucible and lid on the triangle
3.) Adjust the height of the clamp so that the crucible is a little higher than the Bunsen burner
4.) Light the Bunsen burner
5.) Brush the fire against the bottom of the crucible for a minute
6.) Turn off the burner
7.) Wait for it too cool down
8.) Use a tong to move the crucible and lid to the electronic balance
9.) Measure the mass of the crucible and lid to the nearest 3 decimal places
10.) Add about 0.5g of silver oxide to the crucible
11.) Place the crucible and lid on the triangle so that there is a small opening
12.) Light the Bunsen burner
13.) Brush the fire against the bottom of the crucible for 2-3 minutes
14.) Place the Bunsen burner under then crucible and heat it for 10 minutes
15.) Maximize the flame temperature
Archer G11
16.) Wait 10 more minutes
17.) Turn off the Bunsen burner
18.) Use tongs to remove the crucible and lid from the triangle and place it on a wire gauze with
ceramic
19.) Slightly cover the crucible with the lid
20.) Wait 10 minutes for the crucible to cool down
21.) Measure the mass of the crucible, lid and silver metal product that is in it
22.) Throw the silver metal in the trash bin
23.) Repeat the experiment 2 more times
Results: The substance in the crucible turned from black pebbles to a white powder. Under the powder
was silver metal that melted and stuck to the bottom of the crucible. The bottom of the crucible turned
black temporarily before turning back to white. A gas was emitted that did not have a pleasant smell.
Trial 1 Empirical Formula Table
Mass in grams
Moles (moles)
Empirical Formula
Crucible + lid
Crucible + lid +
silver oxide
Crucuble + lid +
silver metal
Silver oxide
45.748
-
-
Percent
Composition in
silver oxide (%)
-
46.250
-
-
-
46.223
-
-
-
-
-
Silver
Oxygen
0.467
0.035
Ag2O
93.10
6.90
Silver
Oxygen
0.475
0.027
Ag5O2
94.40
5.60
Substance
2.166 × 10-3
Theoretical
4.332 × 10-3
2.166 × 10-3
Actual
4.403 × 10-3
1.688 × 10-3
Percent Yield
101.71%
77.14%
0.502
Silver
Oxygen
Trial 2 Empirical Formula Table
Substance
Crucible + lid
Crucible + lid +
silver oxide
Crucuble + lid +
silver metal
Silver oxide
Mass in grams
Moles (moles)
Empirical Formula
42.530
-
-
Percent
Composition in
silver oxide (%)
-
43.032
-
-
-
42.999
-
-
-
0.502
2.166 × 10-3
Theoretical
-
-
Archer G11
Silver
Oxygen
0.467
0.035
Silver
Oxygen
0.469
0.033
4.332 × 10-3
2.166 × 10-3
Actual
4.348 × 10-3
2.063 × 10-3
Percent Yield
100.43%
94.29%
Silver
Oxygen
Ag2O
93.10
6.90
Ag2O
93.10
6.90
Trial 3 Empirical Formula Table
Mass in grams
Moles (moles)
Empirical Formula
Crucible + lid
Crucible + lid +
silver oxide
Crucuble + lid +
silver metal
Silver oxide
44.166
-
-
Percent
Composition in
silver oxide (%)
-
44.671
-
-
-
44.635
-
-
-
0.502
-
-
Silver
Oxygen
0.470
0.035
Ag2O
93.10
6.90
Silver
Oxygen
0.469
0.036
2.166 × 10-3
Theoretical
4.358 × 10-3
2.179 × 10-3
Actual
4.348 × 10-3
2.250 × 10-3
Percent Yield
Ag2O
93.10
6.90
Substance
Silver
Oxygen
99.79%
102.86%
2Ag2O (s) ---> 4Ag (s) + O2 (g)
Analysis:
Mass of silver oxide = (mass of crucible + lid + silver oxide) – (mass of crucible + lid)
Trial 1: 46.250 – 45.748 = 0.502 g
Trial 2: 43.032 – 42.530 = 0.502 g
Trial 3: 44.671 – 44.166 = 0.505 g
Mass of silver = (mass of crucible + lid + silver metal) – (mass of crucible + lid)
Mass of silver equals mass of crucible, lid and silver metal minus the mass of crucible and lid.
Trial 1: 46.223 - 45.748 = 0.475 g Ag
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Trial 2: 42.999 - 42.530 = 0.469 g Ag
Trial 3: 44.635 - 44.166 = 0.469 g Ag
Mass of oxygen = (mass of crucible + lid + silver oxide) – (mass of crucible + lid + silver metal)
Mass of oxygen equals mass of crucible, lid and silver oxide minus the mass of crucible, lid and silver
metal.
Trial 1: 46.250 - 46.223 = 0.027 g O2
Trial 2: 43.032 - 42.999 = 0.033 g O2
Trial 3: 44.671 - 44.635 = 0.036 g O2
Mass  Moles = (mass in grams) / (molar mass of the compound)
Turn mass to mole by dividing the mass with the molar mass of the element or compound.
Trial 1: 0.502 / 231.739 = 2.166 × 10-3 moles Ag2O
Trial 1: 0.475 / 107.87 = 4.403 × 10-3 moles Ag
Trial 1: 0.027 / 15.999 = 1.688 × 10-3 moles O
Trial 2: 0.502 / 231.739 = 2.166 × 10-3 moles Ag2O
Trial 2: 0.469 / 107.87 = 4.348 × 10-3 moles Ag
Trial 2: 0.033 / 31.998 = 2.063 × 10-3 moles O
Trial 3: 0.505 / 231.739 = 2.179 × 10-3 moles Ag2O
Trial 3: 0.469 / 107.87 = 4.348 × 10-3 moles Ag
Trial 3: 0.036 / 31.998 = 2.250 × 10-3 moles O
Theoretical yield in mole = (moles of silver oxide) × (mole ratio)
Theoretical yield in mole equals to the moles of silver oxide times by the mole ratio
Trial 1: (2.166 × 10-3) × (4 / 2) = 4.332 × 10-3 moles Ag
Trial 1: (2.166 × 10-3) × (1 / 2) = 1.083 × 10-3 moles O2 = 2.166 × 10-3 moles O
Trial 2: (2.166 × 10-3) × (4 / 2) = 4.332 × 10-3 moles Ag
Trial 2: (2.166 × 10-3) × (1 / 2) = 1.083 × 10-3 moles O2 = 2.166 × 10-3 moles O
Trial 3: (2.179 × 10-3) × (4 / 2) = 4.358 × 10-3 moles Ag
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Trial 3: (2.179 × 10-3) × (1 / 2) = 1.090 × 10-3 moles O2 = 2.179 × 10-3 moles O
Theoretical yield in grams = (theoretical yield in mole) × (molar mass of the compound)
Theoretical yield in grams equals theoretical yield in mole times the molar mass of the compound
Trial 1: (4.332 × 10-3) × 107.87 = 0.467 g Ag
Trial 1: (1.083 × 10-3) × 31.998 = 0.035 g O2
Trial 2: (4.332 × 10-3) × 107.87 = 0.467 g Ag
Trial 2: (1.083 × 10-3) × 31.998 = 0.035 g O2
Trial 3: (4.358 × 10-3) × 107.87 = 0.470 g Ag
Trial 3: (1.090 × 10-3) × 31.998 = 0.035 g O2
Finding empirical formula ratio = (moles) / (moles of the smallest number)
Empirical formula is found by dividing all the moles with the moles of smallest number (this will turn the
moles of the smallest number into 1)
Trial 1: (4.403 × 10-3) / (1.688 × 10-3) = 2.6 moles Ag
Trial 1: (1.688 × 10-3) / (1.688 × 10-3) = 1 moles O --> Ag2.6O --> Ag5O2
Trial 2: (4.348 × 10-3) / (2.063 × 10-3) = 2.1 moles Ag
Trial 2: (2.063 × 10-3) / (2.063 × 10-3) = 1 moles O --> Ag2.1O --> Ag2O
Trial 3: (4.348 × 10-3) / (2.250 × 10-3) = 1.9 moles Ag
Trial 3: (2.250 × 10-3) / (2.250 × 10-3) = 1 moles O --> Ag1.9O --> Ag2O
Percent Yield = (actual yield in grams) / (theoretical yield in grams)
Trial 1: 0.475 / 0.467 = 101.71% Ag
Trial 1: 0.027 / 0.035 = 77.14% O
Trial 2: 0.469 / 0.467 = 100.43% Ag
Trial 2: 0.033 / 0.035 = 94.29% O
Trial 3: 0.469 / 0.470 = 99.79% Ag
Trial 3: 0.036 / 0.035 = 102.86% O
Archer G11
The hypothesis isn’t quite correct. However, it isn’t wrong either. By the process of heating, some
oxygen molecules really did turn into oxygen gas and float off. The substances in the crucible are mostly
white powder rather than the silver solid. This proves that some sort of reaction had happened although
the result isn’t what the hypothesis suggested it to be. The oxygen was harder to remove than what had
been initially predicted thus the substance didn’t turn completely into silver metal. The substance
turned into white powder most likely because it had some oxygen removed, but not all so it’s a mixture
of silver metal and silver oxide molecules.
Conclusion: The hypothesis is correct but not fully correct. It could be improve to a better one. The
hypothesis doesn’t fully work because the oxygen molecules are quite hard to remove. Some of the
oxygen molecules are still bonded in the substance, causing the product to obtain a white color instead
of a silver solid. As shown in the first trial, there’s most likely some errors causing the empirical formula
to be Ag5O2 instead of Ag2O. There are many possible reasons for this error. The most likely reason for
this error was that the flame wasn’t intense enough and so not all oxygen was removed from the
compound. Because of that, the mass of oxygen was included in the mass of silver thus the mass of
silver measured was higher than it should’ve been. The results of the other trial aren’t perfect, either.
There could’ve been many errors to the experiment causing the results to be slightly mistaken. The
errors could’ve been human errors such as touching the crucible after heating it. The oil from the hands
could’ve added to the mass of the crucible causing it to weigh heavier than it should’ve been. Also, the
flames might not have been intense enough which is why the oxygen doesn’t get completely removed.
The oil from the hands could be prevent by carefully using the tongs to move the crucible and patiently
wait for the crucible to completely cool down. As for the flame intensity, in the future, more than one
Bunsen burner could be use to help intensifying the flame, giving oxygen enough energy to completely
detach from the silver and form oxygen gas.
Archer G11