PROBLEMS ON PERCENT COMPOSITION,
EMPIRICAL FORMULA, AND MOLECULAR
FORMULA
1. Calculate the formula or molecular mass for the following substances:
Potassium sulfate
sulfur dioxide
Calcium hydroxide
2. Calculate the molar masses for the following substances:
Potassium nitrate
Magnesium sulfate
Dinitrogen pentoxide
3. Calculate the mass in grams of .38 mol sodium sulfite
4. Calculate the number of moles in 35.4 grams lithium carbonate
5. Calculate the number of atoms in 777.46 g of Li
6. Number of molecules in 43 g of ammonia
7. Number of F.U. in 105.2 grams of magnesium sulfate
8. Number of SO4-2 ions in 14.3 grams of chromium (III) sulfate
9. Calculate the number of liters of methane gas in 2.20 moles at STP
10. Determine the percent by mass of sodium in sodium sulfate.
11. Calculate the percent by mass of metal in chromium (II) chloride
12. Chlorine trifluoride is a colorless, reactive gas that is used in nuclear fuel reprocessing.
What is the percentage composition of each element in chlorine trifluoride?
13. Ammonium nitrate is used as a nitrogen fertilizer and in explosive mixtures. What is the
mass percentage of each element in this compound?
14. Liquid ammonia (100% ammonia) and pure ammonium nitrate are used as fertilizers due
to their nitrogen content. Both sell for approximately $200 per ton. Based on the
nitrogen content, which would be a better buy?
15. Phosphorous oxychloride is the starting compound for manufacturing substances used as
flame retardants for plastics. An 8.53 mg sample contains 1.72 mg of phosphorous.
What is the mass percentage of phosphorous in this compound?
16. Ethyl mercaptan is an odorous substance added to natural gas to make leaks easily
detectable. A sample of ethyl mercaptan weighing 3.17 g contains 1.46 g of sulfur.
What mass percentage of this substance is sulfur?
17. Determine the empirical formula for each of the following compounds:
48% zinc and 52% chlorine
62.6% Pb, 8.4% N, and 29% O
19% tin and 81% iodine
44.9% K, 18.4% S, and 36.7% O
18. Determine the empirical formula for each of these compounds from the experimental
data:
1.99 grams of aluminum combines with 1.76 grams oxygen
2.95 grams of sodium combines with 2.05 grams sulfur
19. Determine the molecular formula for each of the following compounds from the
experimental data:
80.0% carbon, 20% hydrogen, and a molecular mass of 30.0 amu
92.3% carbon, 7.7% hydrogen, and a molecular mass of 26 amu
37.5% carbon, 6.3% hydrogen, 55.8% chlorine, and a molecular mass of 127.0 amu
20. Nicotine, a compound isolated from tobacco leaves, is found on analysis to have: 74.0%
carbon, 8.7% hydrogen, and 17.3% nitrogen. The molecular mass is found to be 162
amu. Calculate the molecular formula for nicotine.
21. Sulfadiazine, a sulfur drug used in the treatment of bacterial infections, is found on
analysis: 48.0% carbon, 4.0% hydrogen, 22.4% nitrogen, 12.8% sulfur, and 12.8%
oxygen. The molecular mass was found to be 250 amu. Calculate the molecular
formula for this drug.
22. The characteristic odor of pineapple is due to an ester known as ethyl butanoate. It
contains C, H, and O. Combustion of 2.78 g of this compound produced 6.32 g of CO2
and 2.58 g of H2O. What is the empirical formula of this compound?
23. Nicotine, the addicting drug in tobacco, is composed of C, H, and N. It has a molecular
mass of 160 amu. A 5.250 g sample of nicotine was combusted, producing 14.232 g of
carbon dioxide and 4.083 g of water. What is the molecular formula for nicotine?
24. A 13.736-gram sample of capsaicin, the compound that gives the hot taste to chili
peppers, was analyzed. It has a molecular mass of 305.4 amu. It contained 9.72 grams
of carbon, 1.225 grams of hydrogen, and .631 grams of nitrogen. The rest was oxygen.
What is the molecular formula for capsaicin?
25. Aspartame, otherwise known as the artificial sweetener Nutrasweet, has a molecular
mass of 294 amu. It contains 57.14% carbon, 6.12% hydrogen, 9.52% nitrogen, and
27.2% oxygen. What is its molecular formula?
26. The taste of sour milk is lactic acid. What is the molecular formula for lactic acid if the
percent composition is 40.00% C, 6.71% H, 53.29% O, and the approximate molar mass
is 90 g/mol?
27. Halothane is a popular inhalation anesthetic. It contains 12.15% carbon, 28.86%
fluorine, .506% hydrogen, 40.5% bromine, and 17.97% chlorine. What is the empirical
formula for this substance?
28. A 5.325-gram sample of methyl benzoate, a compound used in the manufacture of
perfumes, is found to contain 3.758 g carbon, .316 g hydrogen, and 1.251 grams of
oxygen. What is the empirical formula for this substance?
29. Vanillin, the dominant flavoring in vanilla, contains three elements: hydrogen, carbon,
and oxygen. When 1.05 grams of this substance is completely combusted, 2.43 grams of
carbon dioxide and .50 grams of water are produced. What is the empirical formula for
vanillin?
30. Ethylene glycol is used in automobile antifreeze and in the production of polyester. The
name glycol stems from the sweet taste of this poisonous compound. Combustion of
6.38 g of this compound gives 9.06 g of CO2 and 5.58 g of H2O. The compound only
contains C, H, and O. What are the mass percentages of the elements in ethylene glycol?
Using these percentages, calculate the empirical formula for this compound.
31. A rocket fuel used in the space shuttle was analyzed. It was found to contain 30.45%
nitrogen, and 69.55% oxygen. What is the empirical formula for this compound? If the
molecular mass of the compound is 92.02 amu, then what is its molecular formula?
32. Sorbitol is used in sugar free gums as a sweetener. After analysis, a sample of sorbitol
contained 3.96 g of carbon, .769 g of hydrogen, and 5.28 g of oxygen. What is its
empirical formula? If the molecular mass is 182 amu, then what is the molecular
formula of sorbitol?
33. Neurotransmitters are important chemicals in the brain that assist in the firing of
neurons. Norephinephrine is a neurotransmitter that is released in the body when the
body is threatened or depressed. It contains 56.8 percent carbon, 6.5 percent hydrogen,
28.4 percent oxygen, and 8.3 percent nitrogen. It has a molecular mass of 169 amu.
What is its molecular formula?
34. Tooth enamel, or hydroxyapatite, is an essential part of the tooth structure. Its
composition is 39.8% calcium, 18.5% phosphorous, 41.43% oxygen, and .2% hydrogen.
What is the empirical formula? It has a molecular mass of 1004 amu. What is the
molecular formula of this compound?
35. A compound found deep within the heart of the Amazon jungle is isolated from a rare
tropical flower root. After analysis, the compound is found to have anti-cancer qualities.
Scientists are hoping to synthesize it in the laboratory. After decomposition, it is
discovered that it contains 2.1 g of carbon, .374 g of hydrogen, 1.775 g of chlorine, .7 g
of nitrogen, .8 g of oxygen, and .7725 g of phosphorous. What is its empirical formula?
It has a molecular mass of 261 amu. What is its molecular formula?
36. The fat stored in the hump of a camel is a source of both energy and water. The fat
consists entirely of tristearin, a typical animal fat. If the camel combusts 4.45 grams of
tristearin during metabolism for energy, and 12.5076 grams of carbon dioxide are
produced, and 4.9852 grams of water are produced, what is the empirical formula for
tristearin, which contains only carbon, hydrogen, and oxygen? If the molecular mass of
tristearin is 890 amu, then what is the molecular formula for tristearin?
37. Permethrin was widely used to control lice and other insects, but has been banned by the
EPA recently due to its carcinogenic properties. A company suspected of producing it
was investigated. A 12.95 gram suspected sample was taken from the company and
analyzed using combustion analysis. 32.065 grams of CO2 and 11.485 g of H2O were
produced. What is the empirical formula for the unknown chemical found at the
company? If the molecular mass of permethrin is 213.29 amu, is the sample found at
the company permethrin? How do you know? Assume it contains only C, H, and
O.
38. Trioxane is an important fuel source that is used to make camping and military fuel bars.
It is also used to dissolve formaldehyde for shipping. It contains only C, H, and O.
17.471 g of trioxane is burned in an apparatus, and 10.477 g H2O and 25.612 g CO2 are
formed. What is the empirical formula for this compound? If the molecular mass of
trioxane is found to be 90.079 amu, then what is its molecular formula?
39. The koala bear dines exclusively on eucalyptus leaves. Its digestive system detoxifies
the eucalyptus oil, which is a poison to other animals. Eucalyptus oil is primarily a
substance called eucalyptol, which contains 77.87% carbon, 11.72% H, and the
remainder oxygen. What is the empirical formula of this substance? A mass
spectrum of this compound showed a peak at 154 amu. What is the molecular formula
for the substance?
EASY STOICHIOMETRY PROBLEMS!
ASSUME STP FOR ALL GASES UNLESS OTHERWISE DESIGNATED!
1. Carbon dioxide can be commercially prepared by heating chalk, or calcium carbonate.
How many moles of carbon dioxide can be produced when 3.05 moles of calcium
carbonate are heated?
2. Tungsten metal is reacted with carbon to produce tungsten carbide, an extremely hard
compound used to make drills and saw blades. How many moles of tungsten carbide
will be produced if 1.25 moles of tungsten are reacted with plenty of carbon?
3. Propane (C3H8) is used in BBQ grills because of the intense heat produced when it
burns. How many moles of carbon dioxide are produced when 2.25 moles of propane
are burned with plenty of oxygen?
4. Aluminum hydroxide, a popular antacid, is made when aluminum oxide is reacted with
water. How many moles of aluminum oxide will be needed to produce .64 moles of
aluminum hydroxide, if there is plenty of water?
5. Methanol (CH3OH) is used as a fuel additive, to get gasoline to burn cleaner. It is
produced by reacting carbon monoxide with hydrogen gas. How many moles of
methanol can be created when 4.60 moles of hydrogen gas are reacted with plenty of
carbon monoxide?
6. Silver chloride is used to produce photographic paper. It is made by reacting aqueous
silver nitrate with aqueous aluminum chloride. How many moles of silver nitrate will be
needed to produce .90 moles of silver chloride, if there is plenty of aluminum chloride?
7. Sodium chlorate is used to produce yellow fireworks. Heating sodium chlorate creates
oxygen and sodium chloride. How many moles of sodium chlorate are needed to
produce 5.70 moles of oxygen?
8. Glucose (C6H12O6) is burned in the human body for energy. Carbon dioxide and water
are produced as waste products. How many moles of oxygen are needed to combust
3.12 moles of glucose?
9.
Group 1 metals are explosive when they come into contact with water. If 20.0 grams of
potassium were to explode with excess water, how many moles of hydrogen would be
produced?
10. Potassium chlorate is the prime ingredient in most Chinese fireworks. If I have 25
grams of potassium chlorate, how many moles of oxygen can I produce?
11. Acetic acid, found in apple cider and apple butter, can cause explosions when heated in
aluminum pans. If 250 mL of a 4 M solution of acetic acid were used with plenty of
aluminum, then how many moles of hydrogen gas would be produced?
12. Kidney stones can form in the human body if too much soda is consumed. Phosphoric
acid can react with calcium nitrate to form a painful solid. How many moles of
phosphoric acid are needed to react with 85 grams of calcium nitrate?
13. Iron (III) hydroxide is used to remove poisonous arsenic from drinking water. How
many grams of sodium hydroxide are needed to react with excess iron (III) chloride to
produce 2.80 moles of iron (III) hydroxide?
14. Aluminum wiring can be a fire hazard because it can oxidize, or combine with oxygen.
How many grams of aluminum are needed to react with 3.00 moles of oxygen?
15. Acids can be extremely dangerous when stored next to metals, because they can give off
hydrogen gas when reacted with metals. Zinc reacts violently with hydrochloric acid to
produce hydrogen gas and zinc chloride. How many moles of zinc chloride are
produced when 750.0 mL of a 3.000M solution of hydrochloric acid are reacted with
plenty of zinc?
16. Copper metal can be produced commercially through a single replacement reaction of
aluminum metal and copper (II) chloride. How many grams of aluminum are required to
react with 10.05 moles of copper (II) chloride?
17. Sulfur dioxide gas, a form of smog, is formed when sulfur burns with oxygen from the
air. How many liters of sulfur dioxide gas would be released at STP if we burned 2.50
moles of sulfur with plenty of oxygen?
18. Bombardier beetles inject boiling hydrogen peroxide, or H2O2, into their victims. It then
decomposes into hydrogen and oxygen gas. How many molecules of oxygen can be
produced if 4.10 moles of hydrogen peroxide are decomposed?
19. Hydrogen gas is produced for rocket fuel by taking methane, or CH4, and reacting it with
steam. The other product is carbon dioxide. How many liters of hydrogen gas can be
produced if 45.5 grams of methane are reacted with plenty of steam?
20. Hydrochloric acid, which is widely used for cleaning and disinfecting, is made when
hydrogen gas reacts with chlorine gas. How many liters of chlorine gas are needed to
react with 35.5 liters of hydrogen gas?
21. Lead (II) sulfide is used in making infrared detectors for security systems. How many
grams of lead (II) sulfide can be created when 120.5 grams of lead (II) nitrate are reacted
with plenty of sodium sulfide solution?
22. Silver metal is used to plate mirrors. It can be precipitated out of solution by adding zinc
metal to silver nitrate solution. How many grams of silver metal can be precipitated out
of solution, if 120.5 grams of zinc are used with plenty of silver nitrate? How many
grams of silver nitrate will be needed?
23. Antacids react with the hydrochloric acid in your stomach in order to neutralize the acid.
How many grams of hydrochloric acid can be neutralized by a 25.0 gram tablet of
calcium hydroxide? How many grams of water will be produced?
24. Lithium hydroxide is used in the Space Shuttle and in submarines to remove carbon
dioxide gas out of the air. It forms lithium carbonate and water as a result. If an air
filter contains 135.5 grams of lithium hydroxide, how many liters of carbon dioxide can
be removed at STP? How many grams of water will be produced?
25. Air bags in cars have been designed to inflate when solid sodium azide, or NaN3,
decomposes to make sodium metal and nitrogen gas. How many liters of nitrogen gas
are produced at STP when 345.0 grams of sodium azide are decomposed? How many
grams of sodium metal are produced?
26. Baking soda is sodium bicarbonate, or NaHCO3. It can be used to neutralize any acid, so
it is ideal for cleaning up acid spills. If 120.0 grams of sodium bicarbonate are reacted
with 500.0 mL of 2.00M hydrochloric acid, how many liters of carbon dioxide will be
produced at STP? Which reactant is your limiting reactant? Water and sodium
chloride are also produced!
27. Barium sulfate is used in barium shakes, which an individual drinks before having XRays taken. It highlights areas of the intestines and stomach, to look for cancerous
growths. If 250.0 mL of 1.0M barium nitrate is added to 500.0 mL of 2.0M sodium
sulfate, how many grams of barium sulfate will be produced? Which reactant is your
limiting reactant?
28. Cigarette lighters use butane, or C4H10, as their fuel. If 120.0 grams of butane burn with
only 55.0 liters of oxygen gas at STP, how many liters of carbon dioxide are produced?
Which reactant is your limiting reactant?
29. Strontium carbonate is used to color signal flares, used for emergencies on the highway.
How many grams of strontium carbonate can be made when 2.00 L of a 1.00M solution
of strontium chloride is added to 3.00L of a 3.00M solution of sodium carbonate?
Which reactant is your limiting reactant?
30. How many liters of oxygen could be theoretically made if 35.5 grams of potassium
chlorate are decomposed in a firework? If 6.5 liters was actually made, what is your
percent yield?
31. How many liters of hydrogen can be made at STP if 55.0 grams of aluminum react with
750 mL of a 3.00M solution of hydrochloric acid? Which reactant is your limiting
reactant?
TOUGHER PROBLEMS WITH STOICHIOMETRY!
ASSUME STP FOR ALL GASES UNLESS OTHERWISE DESIGNATED!
1. If 25.0 grams of hydrogen react with 25.0 grams of oxygen, which reactant will run out
first? What mass of water will be produced? What is your excess reactant?
2. If 25.0 grams of barium nitrate are placed in a 100.0 ml of 2.00 M sodium sulfate, what
mass of precipitate will form?
3. 460.0 mL of a 3.00M solution of nitrous acid is added to 45.0 grams of powdered
aluminum hydroxide. How many grams of water can be produced?
4. If 214 liters of oxygen were created at STP, how many grams of nickelous chlorate were
decomposed?
5. 34.5 grams of a non-metal oxide were created from phosphorous acid decomposing.
How many grams of the other product are also produced? Phosphorous acid is used as a
flame retardant in clothing.
6. How many liters of gas can be generated from 105.5 grams of lithium sulfite, used as a
photographic paper preservative, reacting with excess chloric acid?
7. Calcium oxide reacts with water in the production of concrete. How many grams of
calcium oxide reacted with excess water if 120.5 grams of product formed?
8. Ammonium chloride is used in the manufacture of circuit boards. If 745 mL of a 4.00M
solution of ammonium chloride is reacted with 85.5 grams of lithium hydroxide, how
many liters of gas are generated at STP?
9. Hydrofluoric acid cannot be stored in glass bottles because the acid attacks compounds
called silicates in the glass. For example, sodium silicate reacts with the acid in the
following way:
Na2SiO3(s) + 8HF(aq) ------------> H2SiF6(aq) + 2NaF(aq) + 3H2O(l)
How many moles of acid are required to chemically eat away .500 mol of sodium
silicate?
How many grams of sodium fluoride form if only .500 mol of HF were to react this
way?
How many grams of sodium silicate can be reacted if only 10.5 grams of HF react?
10. What mass of a salt would be produced when 2.00 L of a 4.00M solution of phosphoric
acid react with 690.0 mL of a 1.50M solution of aluminum hydroxide?
11. How many grams of barium reacted with excess hydroiodic acid, if 65.5 liters of gas
were liberated at STP?
12. How many grams of sodium oxide would be required to form 320. grams of base, if the
other reactant is in excess?
13. What mass of water is produced from the decomposition of 126 grams of nitrous acid?
14. What mass of product will be produced when 40.0 g of diphosphorus pentoxide are
mixed with 40.0 g of ferrous oxide?
15. If 200.0 liters of carbon dioxide at STP react with excess water to form carbonic acid,
and if all the carbon dioxide is consumed, how many molecules of water will be
consumed?
16. What mass of aluminum chlorate will be required to produce 255 liters of oxygen at
STP?
17. What mass of silver iodide can be precipitated from 70 mL of a 4M solution of
magnesium iodide and 59.5 grams of silver nitrate?
18. 78.0 grams of potassium are mixed with 44.8 liters of chlorine at STP. What is the
limiting reactant? What mass of product is created?
19. How many grams of a non-metal oxide would be required to neutralize 500.0 mL of a
4.00M solution of lithium hydroxide if water and lithium perfluorate were produced?
20. If 345 grams of plumbic nitrate is heated in a flare, then how many liters of gas are
released if the reaction is done at STP?
21. If 135 grams of dichlorine pentoxide are reacted with 75.0 grams of calcium oxide, what
is your limiting reactant? How many grams of product can be made?
22. What mass of a non-metal oxide would be required to react with 350.0 mL of a 6.00M
solution of barium hydroxide, if water is produced along with barium phosphate?
23. What mass of lithium perchlorate and water are produced when excess lithium
hydroxide solution is reacted with 255 grams of a non-metal oxide?
24. If 374 grams of diiodine trioxide powder reacts with 440.0 mL of a 5.00M solution of
sodium hydroxide, what mass of each product can be produced?
25. If 4.55 grams of potassium periodate in solution and water are manufactured, how many
grams of a non-metal oxide did you start with, assuming the non-metal oxide was
reacted with excess potassium hydroxide solution?
ULTIMATE STOICHIOMETRY PROBLEMS WITH NON-STANDARD GASES
1. 50.0 grams of ammonium chloride powder are mixed with 125 grams of solid barium
hydroxide. What volume of gas would you expect to collect at 1.20 atm, and at 40.0 oC?
2. If you want to collect 20.0 ml of oxygen at 25.0 oC and 95.0 Kpa, what mass of lithium
chlorate would be necessary to decompose?
3. What pressure of carbon dioxide in psi would be needed to produce 150.0 grams of sodium
carbonate in a 4.50 liter bottle at 20.0 oC, if you were using excess aqueous sodium hydroxide?
4. How many milliliters of hydrogen gas can be produced if 55.0 mL of 4.00M nitric acid is
reacted with excess zinc at 105 kPa on a 30.0 oC day?
5. How many liters of oxygen are needed to combust with propane to make 20.0 liters of carbon
dioxide in a gas grill, when the temperature outside is 28.0 oC and the pressure is 770.0 mm Hg?
Assume the gas is at these conditions when collected.
6. What volume of gas can be produced in a lab where P is 16.0 psi and T is 25.0 degrees
Celsius if you collect it from the reaction of 50.0 g ammonium sulfate powder with 50.0 g
aluminum hydroxide powder?
7. You want to make 40.0 ml of gas from decomposing some aluminum carbonate. The
temperature of the lab is 23.0 degrees Celsius and the pressure is 790.0 torr. If you collect the
gas that is released, what mass of reactant is necessary?
8. 100.0 grams of sodium sulfite are mixed with 200.0 mL of 3.00 M phosphoric acid at 780.0
mm Hg and 25.0 oC, and the resulting gas is collected, answer the following questions.
a. Which reactant is limiting?
b. How many moles of gas are formed?
c. What volume of gas could be collected?
9. What mass of zinc would need to react with excess hydrochloric acid in order to produce
25.0 ml of hydrogen gas collected at 25.0 oC and 105 kPa?
10. How many liters of chlorine gas at 25.0 oC and 0.950 atm can be produced by the reaction
of 185 g of MnO2 and 1200.0 mL of a 3.00M solution of HCl?
MnO2(s) + 4HCl(aq) -> MnCl2(aq) + 2H2O(l) + Cl2(g)
11. What volume of oxygen gas at 320.0 K and 680.0 torr will react with 5.00 L of NO gas at
the same temperature and pressure?
2 NO + O2(g) -> 2NO2(g)
12. 750.0 mL of a 4.00 M solution of bromic acid are reacted with 850.0 grams of nicklic
carbonate. What volume of gas would you expect to collect at 18.0 psi and 40.0 oC?
13. How many grams of each reactant are required to produce 5.70 liters of ammonia gas at 104
kPa and 305 K, if aqueous barium bromide and water are also produced?
14. How many grams of arsenic acid are required to produce 45,000 ml of CO2 gas at 2400 mm
Hg and 200.00C, if you have excess sodium carbonate?
15. How many grams of an acid would be required to react with 14.5 liters of ammonia at 55.0
degrees C and 1100.0 Torr, if ammonium chlorate is the only product?
16. How many liters of a non-metal oxide gas are required to react with 25.5 grams of solid
zinc hydroxide, if zinc sulfate and water are being produced? The reaction occurs at 45.0
degrees C and 119 kPa pressure.
17. 155 grams of sodium hydroxide pellets can be neutralized by now many liters of sulfur
dioxide gas at 82.00C and 995 mm Hg?
18. If 254 liters of carbon dioxide present in a container, then how many grams of stannic
hydroxide can react with the gas if the reaction is done at 34.0 psi and 13.0 degrees C?