THS AP Chemistry
Experiment: Determination of the Empirical Formula of Silver Oxide
Experiment Overview
In this experiment, the percent composition and empirical formula of silver oxide
will be determined. Silver oxide decomposes to silver metal and oxygen when
strongly heated. Heating silver oxide causes the oxygen to be driven off, leaving
only the silver metal behind. According to the law of conservation of mass, the
total mass of the products of a chemical reaction must equal the mass of the
reactants. In the case of the decomposition of silver oxide, the following equation
must be true:
Mass of silver oxide = mass of silver metal + mass of oxygen
If both the initial mass of silver oxide and the final mass of the silver metal are
measured, the decrease in mass must correspond to the mass of oxygen that
combined with silver. The percent composition and empirical formula of silver
oxide can then be calculated, based on combining the ratios of silver and oxygen
in the reaction.
Objective
To determine the percent composition and the empirical formula of silver oxide
Pre-Lab Questions
A piece of iron with a mass of 85.65 g was burned in air. The mass of the iron
oxide produced was 118.37 g.
1. Use the molar mass of iron to convert the mass of iron used to moles.
2. According to the law of conservation of mass, what is the mass of oxygen
that reacted with the iron?
3. Calculate the number of moles of oxygen in the product.
4. Determine the empirical formula of the iron oxide.
Equipment & Chemicals:
▫ silver oxide samples, 0.5 g
▫ crucible and lid
▫ crucible tongs
▫ Bunsen burner & hose
▫ tripod stand
Safety:
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AP Chemistry Lab #1
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pipestem triangle
ceramic fiber pad
wash bottle with distilled H2O
watch glass
balance, milligram (0.001-g)
THS AP Chemistry
Silver oxide is slightly toxic and is a fire risk when in contact with organic material
or ammonia. Handle the crucible and its lid only with tongs. Do not touch the
crucible with your hands. There is a significant burn hazard associated with
handling a hot crucible – remember that a hot crucible looks exactly like a cold
one. Always keep your face at arm’s length from the crucible. Wear goggles and
your lab coat. Wash hands thoroughly with soap and water before leaving the lab.
Procedure
1. Set up a Bunsen burner. Use the tripod stand with a clay pipestem triangle.
Place the empty crucible in the clay triangle. Light the burner and brush the
bottom of the crucible with the burner flame for about one minute. Turn off
the Bunsen burner and allow the crucible to cool.
2. Using tongs to handle the crucible, measure the mass of a clean, empty
crucible and its lid to the nearest 0.001 g. Record the mass in the data
table.
3. Add approximately 0.5 grams of silver oxide to the crucible. Measure the
combined mass of the crucible, crucible lid, and silver oxide to the nearest
0.001 g. Record.
4. Place the crucible with its lid on the clay triangle. Light the Bunsen burner
again and slowly heat the crucible by brushing the bottom the crucible with
the burner flame for 2-3 minutes. Place the burner under the crucible and
gently heat the crucible for an additional 10 minutes.
5. After 10 minutes, adjust the burner to maximize the flame temperature. Heat
the crucible with the most intense part of this flame for 15 minutes.
CAUTION: Do not inhale the smoke! Do not lean over the crucible. Keep
the crucible at arm’s length at all times.
6. After 10 minutes, turn off the gas source and remove the burner.
7. Using tongs remove the lid and place it on the ceramic fiber pad. With the
tongs, remove the crucible from the clay triangle and place it on the ceramic
fiber pad.
8. Allow the crucible and its contents to cool completely on the bench top for
at least 10 minutes.
9. Make note of the number of the balance you are using. Use the same
balance throughout the experiment.
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AP Chemistry Lab #1
THS AP Chemistry
10. Measure the combined mass of the crucible, lid and silver meal product.
Record the mass in the data table.
11. Dump the contents of the crucible onto a watch glass. Note the
appearance and consistency of the product. Is any silver oxide still
present? Record all observations in your lab book.
12. Dump the entire content of the crucible into the waste container located in
the hood. Carefully clean the crucible and lid.
13. Repeat for the experiment for trial two.
Data Tables
Balance Number: _________
Trial #1
Trial #2
Mass of crucible and lid (g)
Mass of crucible, lid and silver oxide (g)
Mass of crucible, lid and silver metal (g)
Analysis
Show all your calculations in your lab book. Write the question or label
the entry.
Box each of your answers.
Skip at least one line between entries.
Enter the answers to each calculation in your calculations table.
1.
a. Calculate the mass of silver oxide.
b. Calculate the mass of the silver metal product.
c. Use the law of conservation of mass to calculate the mass of
oxygen that combined with the silver.
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THS AP Chemistry
2.
a. What is the percent composition of silver in silver oxide?
b. What is the percent composition of oxygen in silver oxide?
3. Use the molar mass of silver and oxygen to calculate the number of
moles of each product.
4. Calculate the ratio between the number of moles of silver and the
number of moles of oxygen in the product. What is the empirical
formula of silver oxide?
5. Write the correct empirical formula for silver oxide using the oxidation
numbers for silver and oxygen.
6. Write a balanced chemical equation for the decomposition of silver
oxide to form silver metals and oxygen using the correct empirical
formula for silver oxide.
7. Calculate the theoretical yield of silver metal in this experiment.
8. Determine the percent yield of silver metal.
9. Discuss sources of error in this experiment that might account for a
percent yield lower or higher than 100%. Be specific.
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AP Chemistry Lab #1
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Calculations Table
Trial 1
mass of silver oxide (g)
mass of silver metal (g)
mass of oxygen (g)
% composition of silver
% composition of oxygen
moles oxygen (mol)
moles silver (mol)
mole ratio Ag:O
empirical formula (AgxOy)
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Trial 2