Chemistry Name: Percent Yield/Limiting Reactants Worksheet Period:
F. Problem-Solving Complete the following problems Show all your work Point values
for each problem are given. Partial credit will be awarded.
1. The explosive, TNT, is composed of 37.0% carbon, 2.20% hydrogen, 18.5% nitrogen, and 42.3% oxygen. (5 points)
a. Determine the empirical formula for TNT.
2. What mass of barium chloride (BaCl2) is needed to react completely with 46.8 g of sodium phosphate according to the given equation. (4 points)
3 BaCl2 + 2 Na3PO4 → Ba3(PO4)2 + 6 NaCl
3. When octane (C8H18) is burned in oxygen, carbon dioxide and water are produced. If 320 g of octane are burned and 392 g of water are recovered, what is the percent yield of the experiment? (5 points)
4. Determine the percent composition of sucrose (C12H22O11). (3 points)
5. What mass of lead(II) iodide will be produced when 16.4 g of lead(II) nitrate is added to 28.5 g of potassium iodide? What is the limiting reactant? (5 points)
Stoichiometry Unit Test
Name _____________________ Date_______________________TOTAL SCORE: ANSWER KEY Period_____________________
Directions: Place your name, the date, and the period in the upper right hand corner. This test is worth a total of 100 points. Read all of the directions carefully for each section of the test. Calculators may be used. Use the periodic table on the wall for reference when needed. Scrap paper will be provided and will be collected with your test.
A. Multiple Choice (20 points): Select the best answer to each question. Please print your
answer using capital letters only.
B 1. Which of the following has the greatest mass? A. 4.2 mol of carbon
B. 8.34 x 1024 atoms of lead
C. 9500 formula units of calcium carbonate (CaCO3) D. 12.6 g aluminum nitrate (Al2(NO3)2)
A 2. The mass of one mole of lithium hydroxide (LiOH) is: A. 24 g
B. 31 g C. 25 g D. 47 g
A 3. Percent yield is the quantity of product actually produced compared with the quantity:
A. of product expected. B. of the limiting reactant. C. usually produced on average. D. of the reactant in excess.
D 4. The equation for the synthesis of ammonia is: N2 + 3 H2 → 2 NH3. How may moles of H2 are needed to produce 6 mol NH3?
A. 4 B. 6 C. 8 D. 9
A 5. If 16.4 g Na2CrO4 are combined with 26.2 g AgNO3 in a double replace- ment reaction, what will be the limiting reactant?
A. Na2CrO4 B. AgNO3 C. NaNO3 D. Ag2CrO4
C 6. The empirical formula and molecular formula for a compound: A. are the same
B. are different
C. can be the same or different
C 7. The percent composition of Mg in Mg(OH)2 is: A. 58.3 %
B. 61.4 % C. 41.7 % D. 24.8 %
C 8. In 60.0 g of N2O there are: A. 3.61 x 1025 atoms B. 1.00 x 1023 molecules C. 8.21 x 1023 molecules D. 2.77 x 1025 formula units
A 9. The coefficients in a balanced chemical equation represent ratios of all of the following except:
A. mass B. moles C. volumes D. particles
B 10. The empirical formula for a compound that contains 36 g carbon, 8 g oxygen, and 6 g hydrogen is:
A. C4H6O B. C6H12O C. C9H2O4 D. C6H12O6
B. Fill in the Blank (20 points): Write the correct answer in the space provided.
1. One mole of gas occupies _22.4 L________ at STP.
2. The amount of product recovered from a chemical reaction is the __actual_______ yield. 3. One mole of calcium carbonate contains ___6.02 x 1023 ________ particles.
4. The molar mass of HCl is ___36.5 g/mol______.
5. When 3 moles of calcium chlorate are decomposed in the reaction Ca(ClO3)2 → CaCl2 + 3 O2, ___9____ moles of oxygen gas are produced.
6. When 5.0 g of aluminum combine with 3.0 g of sulfur to produce aluminum sulfide (Al2S3), the limiting reactant is _sulfur__________.
7. While a molecule is the smallest representation of a molecular compound, a formula unit is the smallest representation of a(n) __ionic_______ compound.
8. All stoichiometry problems are based upon the __molar______ ratios that exist between the substances in a reaction.
9. _Stoichiometry_____________ is the study of the quantitative, or measurable, relationships that exist in chemical formulas and chemical reactions.
10. In the reaction of H2SO4 with NaOH, the molar ratio of H2SO4 to NaOH is _1:2_____.
C. Matching (16 points): Match the descriptions below with the correct answer from the
list of words on the right. Print, and use capital letters only. No words will be used twice.
H 1. percent by mass of each element in a compound A. molar volume
F 2. mass in grams of one mole of a substance B. atomic mass
B 3. mass of an atom expressed relative to the mass of C. Avogadro’s
one carbon-12 atom number
E 4. sum of the atomic masses of all the atoms in a compound D. expected yield
C 5. the number of particles in a mole is known as this E. formula mass
D 6. the amount of product that should be produced in a F. molar mass chemical reaction
7. the volume occupied by one mole of gas at STP is G. limiting
A known as reactant
G 8. determines the quantity of products in a chemical reaction H. percent composition
D. Short Answer. Answer each question below as completely as possible. Point values are
given for each question. Partial credit will be given.
7. List the 3 main types of stoichiometric problems. (3 points) a. mass - mass
b. mass - volume
c. volume - volume
8. What is the difference between an empirical formula and a molecular formula? (3 points)
An empirical formula gives the simplest whole number ratio of atoms of elements in a compound. A molecular formula gives the actual number of atoms of elements in a compound.
9. List the 4 steps involved in solving a stoichiometric problem. (4 points) a. Write a balanced chemical equation.
b. Convert given information to moles.
c. Determine molar ratio between given and unknown.
d. Convert moles of unknown to units you are seeking.
10. Cite two examples of how stoichiometry is important in everyday life. (2 points) a. Look for specific examples of safety, economics, public policy decisions, consumer decisions
b.
11. Moles allow for easy conversion among these three quantities. (3 points) a. mass
b. particles
12. Name the two acids used in the titration lab. (2 points) a. HCl
b. H2SO4
E. Essay. (5 points) Answer the following question as completely as possible. Partial
credit will be given.
Briefly describe how titration techniques can be used to determine molar ratios in a chemical reaction.
If you use solutions of equal concentration, one substance can be added to another until an indicator turns color, indicating the reaction is complete. The volume of each solution used can be measured and calculated as a ratio. This ratio gives you the molar ratio of the chemical reaction.
F. Problem-Solving. Complete the following problems. Show all your work. Point values
for each problem are given. Partial credit will be awarded.
1. The explosive, TNT, is composed of 37.0% carbon, 2.20% hydrogen, 18.5% nitrogen, and 42.3% oxygen. (5 points)
a. Determine the empirical formula for TNT.
C 37.0 g = 3.08 mol /1.32 = 2.33 x3 = 7 H 2.2 g = 2.18 mol /1.32 = 1.66 x3 = 5 N 18.5 g = 1.32 mol /1.32 = 1.00 x3 = 3 O 42.3 g = 2.64 mol /1.32 = 2.00 x3 = 6
C7H5N3O6 or C7H5(NO2)3
b. The molar mass for TNT is 227 g/mol. What is the molecular formula for TNT?
Formula weight of C7H5(NO2)3 = 227 g/mol. Therefore the molecular formula is
2. What mass of barium chloride (BaCl2) is needed to react completely with 46.8 g of sodium phosphate according to the given equation. (4 points)
3 BaCl2 + 2 Na3PO4 → Ba3(PO4)2 + 6 NaCl
molecular weight of Na3PO4 = 164.0 g/mol.
molecular weight of BaCl2 = 208.2 g/mol.
46.8 g/ 164 g/mol = 0.285 moles Na3PO4
molar ratio = 2/3 = 0.285/x x = 0.428 moles BaCl2
0.428 moles BaCl2 x 208.2 g/mol = 89.0 g BaCl2
3. When octane (C8H18) is burned in oxygen, carbon dioxide and water are produced. If 320 g of octane are burned and 392 g of water are recovered, what is the percent yield of the experiment? (5 points)
C8H18 + 25 O2 → 16 CO2 + 18 H2O
Molecular weight of octane = 114 g/mol
320 g octane / 114 g/mol octane = 2.8 mol octane molar ratio = 2 / 18 = 2.8 / x x = 25.3 mol H2O
25.3 mol H2O x 18.0 g/mol = 454.7 g H2O = expected yield
4. Determine the percent composition of sucrose (C12H22O11). (3 points)
molecular weight of sucrose = 342 g/mol
C 12.0 g/mol x 12 = 144 /342 42.1% H 1.0 g/mol x 22 = 22 /342 6.4% O 16.0 g/mol x 11 = 176 /342 51.5%
5. What mass of lead(II) iodide will be produced when 16.4 g of lead(II) nitrate is added to 28.5 g of potassium iodide? What is the limiting reactant? (5 points)
Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3
(16.4 g Pb(NO3)2 x 331 g Pb(NO3)2 / mol) x (1 mol PbI2 / 1 mol Pb(NO3)2 ) x
(461 g PbI2 / mol PbI2 )
= 22.8 g PbI2 limiting reactant
28.5 g KI x(1 mol KI / 166 g KI) x (1 mol PbI2 / 2 mol KI) x 461 g PbI2 / mol PbI2